Geography Class 21 o 35

Geography Class 21

INTRODUCTION (5:12 PM)

Overview & doubts related to the previous class.

INSOLATION, HEAT BUDGET, AND ALBEDO (5:22 PM)

The amount of incoming solar radiation is called insolation.

The amount of insolation received by the Earth is 2 billionth of solar energy.

The amount of insolation received on the surface= 1.92 calories per cm2 per minute called the Solar Constant.

The incoming solar radiation is shorter in wavelength.

This radiation is absorbed by the Earth's surface and is reemitted as long-wavelength Terrestrial Radiation.

GREEN HOUSE EFFECT (5:48 PM)

The atmosphere is transparent to incoming solar radiation and opaque to outgoing terrestrial radiation.

The warming of the Earth's atmosphere and its surface by the absorption of terrestrial radiation by some of the gases is called the Green House effect.

The gases responsible are called Green House Gases, for example, CO2, CH4, N2O, HFCs (Hydro-fluro carbon), PFCs (Per-fluro carbon), SF6 (Sulphur hexafluoride), Water vapor, etc. 

The Earth's surface absorbs incoming solar radiation and emits terrestrial radiation hence it acts as a source of heat for the atmosphere.

Therefore, temperature decreases with height at the rate of 6.5 degrees celsius per km which is called the Normal Lapse Rate.

HEAT TRANSFER (5:56 PM)

Methods of heat transfer:

Radiation 

It involves the transfer of heat in the form of radiant energy.

The incoming solar energy is in the form of electromagnetic radiation.

Conduction 

It involves the transfer of heat through molecular activity at the zone of contact.

It occurs at the zone of contact between the troposphere and the Earth's surface.

Convection

Transfer of heat by vertical movement of the mass of air. 

For Example, the convection of air along the equator.

Advection

Transfer of heat by horizontal movement of mass.

For Example, planetary winds and ocean currents.

FACTORS AFFECTING INSOLATION (6:16 PM)

Transparency of the atmosphere

Cloud cover, dust particles, water vapor, etc. reduces the transparency of the atmosphere and reduces insolation received at the surface.

Latitude

Latitude of a place decides the angle of incidence of insolation which affects insolation received per unit area of the surface.

For Example, in tropical regions insolation falls vertically and is concentrated in a small area. Along temperate and polar regions angle of incidence is oblique and insolation is distributed over a larger area.

Length of the day

Longer the day, the more the insolation received at the surface. The length of the day depends on the season.

HEAT BUDGET (6:29 PM)

On the global scale the Earth must reradiate as much heat back to space as it receives from the sun.

This is necessary in order to maintain a uniform temperature on the Earth.

The gains and losses in heat by way of incoming solar radiation and outgoing terrestrial radiation are called Heat Budget.
 

Doubts related to heat budget (7:15 PM)

ALBEDO (7:24 PM)

Albeo is the ratio between the reflected amount of solar radiation and the incoming solar radiation by the Earth as a whole.

It is also called as Reflection Coefficient.

The average albedo of the Earth = 35%.

TEMPERATURE (7:42 PM)

The degree of hotness or coldness of a surface is called temperature.

Factors affecting Temperature:

Insolation

Insolation in turn depends upon the transparency of the atmosphere, latitude, and length of the day.

Even though the sun's rays are vertical along the equator throughout the year, the equator will not have maximum temperature due to cloud cover.

Albedo

Surface with higher albedo reflects back more insolation resulting in less absorption of heat causing lower temperature.

Nature of the surface

Earth behaves differently depending upon the specific heat of the surface.

The land surface with lower specific heat, heats up more rapidly and intensely than the water surface.

Also, the land cools rapidly.

Distance from the sea or continentality

The locations that are in the interior of the continent experience a higher range of temperatures than coastal locations.

For Example, Delhi experiences hotter summers and colder winters than Mumbai.

Distribution of continents

Northern Hemisphere with more proportion of land than oceans experience a higher range of temperature than the Southern Hemisphere with more water surface.

Altitude

Temperature decreases with an increase in altitude.

Winds

Air in motion is called Winds.

They transport temperatures prevailing in one area to another. 

For Example, planetary winds. 

Ocean currents

Ocean currents are like rivers inside the oceans.

They transport warm water from the tropics to polar regions and vice versa helping in the global distribution of temperatures.

TOPIC FOR THE NEXT CLASS: DISTRIBUTION OF TEMPERATURE ACROSS THE GLOBE

Geography Class 22

Revision of the previous class (05:10 PM) 

Temperature and Factors affecting the temperature (05:18 PM) 

Terms related to the temperature

Temperature is the degree of Hotness or coldness.

The thermometer is used to measure the temperature

Diurnal range of temperature: Difference between daily max and daily minimum.

Mean Daily Temperature: Sum of 24 hours of temperature/24

Mean monthly temperature: It is the sum of a daily temperature of a month divided by the number of days in a Month

Annual Range of temperature: Highest-Lowest Mean monthly temperature.

The highest recorded temperature is 58 degrees in Al Azizia (Libya) 

But as per WMO, it is 56.8 in Death Valley (USA California) 

Lowest temperature: Vostok station, Antarctic (-88 degrees) 

Distribution of Temperature

Variation in temperature, Is not uniform along the latitude at the different places due to a number of factors, and when we connect these lines of uniform temperature along the latitude is known as Isotherm. 

Across the earth, Isotherms shift north and south with the apparent movement of the sun.

The Isotherms move northward between January to July and they shift south between July to January.

The shifting of Isotherms is more in the Northern hemisphere than in the southern hemisphere.

This indicates higher seasonal variations in the northern hemisphere.

This is due to the presence of a vast landmass in the Northern Hemisphere.

Moving from land to oceans, Isotherms bents along a particular latitude.

Isotherms bents polewards in January over the oceans.

Isotherm bent Equatorward in July over the oceans.

Near the Equator Annual range of temperature is very less, The Range of temperature increases from the Equator up to higher latitudes, This Range is more in the Northern hemisphere.

Temperature Inversion (05:57 PM) 

The average rate of decrease in temperature up in the altitude is called as Normal lapse rate 

Under certain special conditions, Reversal of the Normal lapse rate occurs so that temperature increases with altitude. This phenomenon is called temperature inversion.

The Zone of temperature change in the atmosphere is called a temperature inversion zone.

Types of temperature inversion

a)Radiation inversion

The conditions that favour radiation inversion are:

Long winter nights

Calm and windless conditions 

Clear and cloudless sky.

In these conditions, the land surface radiates heat more rapidly during the night, This loss of Radiation by the land surface causes the land to cool down and the air just above the surface also cools.

This colder air is overlaid by warmer upper air which has absorbed heat from radiation loss.

Therefore temperature increases with increases in altitude creating a temperature inversion 

b) Air drainage type of inversion(06:35 PM) 

The mountains and hilltops experience rapid fall in temperature during the night.

The valley sides remain warmer due to radiation exchange between the valleys.

The cooler and denser air from the hilltops sinks to the valley floor due to Gravity.

After some time the warmer air rests over the cooler air resulting in a Temperature inversion.

c) Advection inversion 

It is produced when a thick layer of warm air passes over the cold water's surface or snow-covered surface creating temperature inversion.

d) Frontal inversion

It is caused due to frontal convergence of air masses.

Along the Fronts, the warmer air is forced upward from the ground by the undercutting of cold air which leads to temperature inversion where warm air is lying above the cold air.

Significance of temperature inversion (06:52 PM) 

Temperature inversion prevents convection by creating stability in the lower atmosphere and hence prevents precipitation.

The temperature inversion conditions with cold air near the surface are suitable for fog formation.

It also reduces wind activity and prevents the distribution of pollutants causing bad air quality, For Example: Around Delhi, during winters the pollutants are trapped for a longer duration creating bad air quality.

In urban areas during winter fog mixes up with smoke resulting in the formation of Smog which is a thick layer and reduces air quality.

The formation of Fog reduces visibility and disrupts the Transportation network.

Air Drainage type of inversion decides the pattern of settlements in Mountainous regions, Mountain slopes are preferred over valley floors or hilltops.

Agriculture in hilly areas is impacted by Air drainage inversion.

Example: Fruit orchards of Uttrakhand and Himachal, Coffee plantation of Brazilavoid valley floors 

Pressure (07:26 PM) 

Pressure is the force experienced per unit area.

Atmospheric pressure is the pressure exerted by the Earth's atmosphere.

The average atmospheric pressure near sea level is equal to 1013milibars.

Pressure is measured using barometers.

Factors that cause variation in pressure

a)Temperature: When Air is heated it expands and the outward pressure of molecules is spread over a larger area therefore the pressure of air decreases.

When Air is cooled it contracts to cause an increase in pressure 

b)Altitude: The pressure experienced by Air at ground level is higher than that of Air at higher altitudes.

When Air Rises due to convection its volume increases and pressure decreases.

When air sinks due to subsidence its volume decreases and pressure increases.

c)Rotation: The rotation of Earth causes air at the poles to be thrown away towards the Equator.

If we consider the effect of only rotation air piling up around the Equator produces a belt of high pressure and along poles a belt of low pressure.

Formation of pressure Belts (07:53 PM)

The Belt of low pressure experienced along the Equator region is known as the Equatorial low

And the Zone of High pressure at the poles is known as Polar High.

Air Rises at the Equator and moves upward till tropopause and from there separates in two directions i.e two poles.

At 30 degrees (North and South) it sinks down due to the air being dense now as it is now occupying a smaller area so the pressure increases, so the region is Sub Tropical High.

From 30 degrees Air then divides into 2 directions again, One moving towards the equator and another moving towards the poles.

The air near the polar region is always subsiding in nature, Because there is no convection, There is a High-pressure belt so air never vertically rises,

Air near the polar region gets thrown due to the rotation of the earth and starts to move away from the poles, which earlier was occupying a smaller area now due to getting thrown away occupies a larger area and at a 60-degree belt has the low-pressure belt. (Temperate low)

And this air coming from the poles meet the air from the Sub tropics, This convergence causes convection and rises vertically upward and upon reaching the troposphere again divides into two one moving pole side and another towards the subtropics.

And again meeting the subtropics air at the upper atmospheric level descends at 30 degrees.

This all results in the formation of Atmospheric cells. 

Between o to 30 degree=Headley cell

Between 30 to 60 degree= Ferrel cell.

Between 60 to 90 degree=Polar cell

Planetary winds flow along the surface.

0 to 30 degree =Trade winds

30-60 degree= westerlies

60-90 degree=polar Easterlies

 

The Topic for the next class: Winds-Planetary, Local and Seasonal winds.

 

 

Geography Class 23

Last class revision(5.10 PM).

Development of pressure belts(5.19 PM):

Air rising at the equator due to high temperature causes expansion and therefore the development of a low-pressure belt at the equator.

This connecting air at the equator spreads out as it reaches the top of the troposphere and moves toward the poles.

This air as it converges towards the polar region its density increases and begins to sink which is subsiding, leading to a high-pressure belt at 30 degrees N and S.

Some of the high-pressure air moves toward the equator and some toward the pole.

The air moving towards the equator replaces the air rising there completing a cell.

Low temperatures at the poles, resulting in a contraction of air and the development of high pressure.

Air blowing away from poles spread out to larger space and pressure falls leading to a low-pressure belt along 60% north and south.

Some of the air from the sub-tropical high-pressure belts moving toward the pole reaches 60 degrees north and south and converges with air from the poles leading to convection along 60 degrees north and south.

The rising air 60 degrees north and south spread out at the edge of the troposphere, a part of it moves towards the equator and the rest towards the poles.

Distribution of pressure across the world(5.41 PM):

The distribution of pressure across the earth can be studied using isobars.

Isobars are the lines joining places with equal pressure.

With the apparent movement of the sun between the tropics, the pressure belts shift north and south.

Pressure in January:

The equatorial low-pressure belt extends into the southern hemisphere.

The sub-tropical high-pressure belt of the southern hemisphere is found only over the oceans.

The low temperature in the northern hemisphere produces a continuous high-pressure system, linking it with the high-pressure cells of Siberia and North America.

Pressure in July:

Equatorial low-pressure belts extend too much into the northern hemisphere due to intense heating in India and Tibet.

Sub-tropical high-pressure belt in the northern hemisphere is not continuous and exists only over oceans as weak high-pressure cells.

In the southern hemisphere, a continuous belt of high pressure is formed.

Winds(6.10 PM):

The wind is air in motion.

Forces affecting the motion of wind:

Pressure grading force:

The rate of change of pressure concerning distance is called a pressure gradient.

The pressure differential in the atmosphere causes the movement of air from high pressure to low pressure.

The force causing this movement is called the pressure gradient force.

Pressure gradient force acts in a direction perpendicular to isobars.

Pressure gradient forces increase with the increase in the rate of change of pressure.

That is pressure gradient force is more when isobars are placed closely.

Frictional force:

Any moving object moving near land experiences a frictional force in the direction opposite to that of its movement.

It is maximum near the surface than at higher altitudes.

It is maximum over the continents than oceans.

Coriolis force:

It is a fictional force produced due to the rotation of the earth

It is the combined effects of various forces and factors such as centrifugal force, angular velocity, and variation in speed of rotation at different latitudes.

It causes any moving object to defect towards the right in the northern hemisphere and the left in the southern hemisphere.

The degree of Coriolis force depends on the speed of the moving body, the latitude at which the body is moving, speed of rotation of the earth.

Geostrophic winds(7.17 PM):

At some latitude where the isobar is straight and there is no friction, the pressure gradient force is balanced by Coriolis force and the result wind flows n a parallel direction of isobars. This is called geostrophic winds.

Geostrophic winds along low-pressure and high-pressure cells result in the formation of cyclonic and anticyclonic circulations.

 

Pressure system	Pressure condition at the center	The pattern of winds in the north Hampshire	The pattern of winds in the South Hampshire
Cyclone	Low	Anticlockwise	clockwise
Anti-cyclone	High	clockwise	Anticlockwise

Planetary winds(7.37 PM):

These are the winds blowing throughout the year and are found across the entire planet.

Trade winds/Easterlies:

They blow from subtropical high to equatorial low.

In German trade means Track as they blow in the same direction, throughout the year.

Trade winds are dry and stable in the area of origin.

Moving toward the equator picks up moisture and causes precipitation along the eastern margins.

Reaching the western margins, as they are devoid of moisture the offshore trade winds will not result in precipitation causing desert formation.

In addition to this nearness to the sub-tropical high-pressure belt and pressure belt and presence of cold ocean current creates dry conditions, eg Sahara desert, Kalahari deserts, etc.

The topic of the next class: Planetary winds to continue.

 

 

Geography Class 24

Revision of the previous class (05:07 PM) 

Westerlies (05:21 PM)

They blow from Subtropical high to temperate low in both hemispheres.

The vast landmass in Northern Hemisphere obstructs the Westerlies whereas, in the Southern hemisphere, they blow strongly and consistently due to the huge water expanse.

Therefore they are called as Roaring forties, Furious fifties, and shrieking sixties in the southern hemisphere.

Polar Easterlies

It blows from a polar high-pressure belt to a temperate low-pressure belt.

They are extremely cold, stable, and dry.

And they blow for long distances and affect the climate.

Zones of Planetary winds (05:30 PM)

 

Inter-Tropical Convergence Zone(ITCZ)

Convergence of Trade winds from both the sides of tropics.

It is centred on the Equator.

5 degree North and south of the Equator normally during Equinox, But shift as well North and southwards.

This zone experiences low-pressure, calm, and windless conditions therefore it is called as the Zone of Doldrums. 

Summers: ITCZ Shift toward North of the Equator.

Winter: ITCZ shift toward the south of the Equator.

Humidity will be greater due to Convection.

Horse Latitude (05:41 PM)

 

30 Degree North and South.

It is a Zone of Sub tropical high-pressure belt near 30 degrees North and south.

Due to vertically descending belts, This is the region of light and calm winds.

Tri-cellular Meridional circulation 

The Surface winds blow from High to Low-pressure belts but in the upper atmosphere, the direction of air circulation is opposite to surface winds.

This together with convection and subsidence along low-pressure and High-pressure belts result in three cellular circulations along each meridian called Tri cellular meridional circulation.

The three cells are the Headley cell, the Ferrel cell, and the Polar cell.

Seasonal winds (06:00 PM)

They are not flowing Throughout the year

And do not cover the entire planet

The seasonal differences in Temperature and pressure cause the movement of Air and subsequent winds blowing in particular seasons are called Seasonal winds.

Example: South West Monsoon.

Local winds

They are a regular phenomenon

Differences in the heating and cooling of the Earth's surfaces and the cycles that develop daily or annually create several common winds called local winds.

Land and sea breeze

The land gets heated up more quickly than the adjacent sea during day time.

Low pressure is developed over the Land and High pressure over the sea.

This causes the circulation of relatively cool air from the sea to adjacent land called sea breeze.

Rapid loss of Heat from the land causes a reversal of daytime pressure conditions due to High pressure on land and low pressure over oceans.

Winds blowing from land to sea cause Land breezes.

Fishermen along coastal regions use land and sea breeze for fishing activity.

Mountain and valley breeze

During Day time mountains' slope heats up rapidly compared to the valley.

This results in the air from the valley moving up along the slopes called as valley breeze or Anabatic winds.

At night the temperature difference between Mountain slopes and valleys is reversed causing winds to blow from mountain to valley causing Mountain breeze which is also called Katabatic winds.

Tips and tricks to outline the world physical  Map (06:47 PM)

Local winds of the world in Map (07:28 PM) 

Hot winds: 

Chinook: Western North America along the Rockies mountain from the mountain towards the plains in a west-to-east direction 

Significance: Also called a snow eater when the entire Rockies area, Prairies land is covered with snow where wheat is grown in winter so snow melts which is helpful for wheat cultivation during winter.

Fohn: Along the Alps in Europe which flow south to North direction.

Significance: It helps in the melting of snow in Germany, similar to chinook.

Harmattan: The region is Nigeria and flows from Northeast to southwest, from land to sea.

Significance: Harmattan is dry winds that cut moisture when flowing from the Humid region of Africa, This is the reason it is also called Doctor winds.

Haboob: Hot winds of Sudan which have no specific direction

Sirrocco: Winds from Sahara to the Mediterranean region and then crossed the Mediterranean sea reaches Europe, hits the mountain, and causes orographic Rain. Also called Blood Rain as the winds from the Sahara come along with the Red Dust of the Sahara.

Khamsin: Sirocco is known as Khamsin in Egypt, and Gibli in Libya, All the characteristics same as Sirocco.

Berg: In South Africa, East to West From Land to the ocean.

Samoon: In Iran, and Iraq, No specific direction, Also called poison winds.

Loo: North India, Direction west to East.

Karaburan: Mongolia and Northern China, Direction: Northeast to the southwest.

Brickfielder: In Southern Australia, Direction: North to south 

Cold winds (07:49 PM) 

Blizzard: North America, particularly in USA and Canada.Direction from North to south.

Blizzard in Siberia is called Burran.

Norte/Northe: Direction North to South, Region USA, and Mexico respectively.

Pamperos: In Argentina, South to North

Mistral: Region France, Direction North to south.

Levant: Southern Spain, Direction East to west.

Bora: Along the coast of the Adriatic sea from North East to Southwest direction.

 

The topic for the next class: Humidity, Continuation of Climatology.

 

Geography Class 25

Revision of the previous class (05:12 PM) 

Humidity, Evaporation, and Condensation (05:20 PM)

The amount of water Vapour in the atmosphere is called Humidity, It helps in energy balance on the surface of Earth through Evaporation and Condensation.

Humidity is the index of the atmosphere's potential for Yielding precipitation.

Measurement of Humidity in the atmosphere

3 ways:

Specific humidity

It is the ratio of the weight of water vapor in grams to the weight of air in kgs expressed as grams/kg of Air.

It indicates the actual amount of Moisture present in the air.

Here amount of water vapor remains the same, It is not showing the effect of temperature.

b)Absolute humidity

It is the ratio of the weight of water vapor in grams to the volume of air in a meter cube

Expressed as grams per meter cube of air

Measures humidity in grams/m3 i.e 100 gms/m3

It decreases with the expansion of air and increases with the contraction 

c)Relative humidity

Measures Humidity in percentage 

It is the ratio between the amount of water vapor present in the air to the maximum amount of water vapor it can hold at a given temperature.

Relative humidity seen just with temperature.

If the temperature is increased the maximum capacity increases and relative humidity decreases.

If the temperature is decreased maximum capacity decreases Relative humidity increases.

Air is said to be saturated when Relative humidity reaches 100%.

Evaporation (05:58 PM) 

The conversion of liquid water into water vapor is called Evaporation

3 important factors

Higher the temperature, the Higher the rate of evaporation.

Humidity: Higher the humidity, the Lower the rate of evaporation.Due to the saturation of Air.

Wind speed: Higher the wind speed, the Higher the rate of evaporation as Air movement provides a constant supply of fresh air.

Distribution

Highest in 30 degrees 

Lowest in the polar region.

Condensation (06:07 PM)

The process of conversion of water vapor into liquid water is called as condensation.

It is the reversal of evaporation.

The temperature at which condensation takes place is called a dew point.

If condensation happens below zero degree celsius it is called a frost point.

Condensation forms

Dew

It is the moisture deposited in the form of liquid water droplets on land surfaces.

The conditions favorable for the formation of dew are long winter nights, Calm air, and cloudless sky.

 

Frost

It is a thin layer of ice on a solid surface.

It is formed when the temperature of the surface is below the freezing point and the water droplets are falling on such a cold surface.

 

Rime

The deposition of needle-like white opaque icy crystals on the surfaces with temperature below zero degrees Celcius.

It occurs when supercooled water droplets in the air come in contact with the surface below the freezing point.

 

Fog (07:05 PM)

It is produced near the surface when the temperature of the air drops suddenly.

The visibility will be less than 1 km.

The condition required for the formation of fog is the same as the condition of temperature inversion

Following conditions favor fog formation commonly

Long winter night, Calm air, and cloudless sky.

Types of Fog:

Radiation fog, Valley fog, Frontal fog, Advection fog

Mist

It consists of small droplets of water suspended in the air.

It is similar to fog but with a lower density of water vapor.

Visibility in Mist is between 1-2 km.

 

Haze

It is caused by smoke and dust particles with humidity.

It is generally observed in Urban areas.

Visibility in Haze is up to 2 km.

Clouds and precipitation (07:13 PM)

Stability condition

It is the condition when air resists vertical movement and remains in its original position.

Stability is when the air is cooled at its base or when air subsides along high-pressure belts.

Pressure is unlikely in this condition.

Instability condition

It is a condition where air does not resist vertical movement and leads to cloud formation and precipitation. 

Instability occurs along the regions of High temperature and low pressure.

Types of Clouds (07:26 PM) 

Cirrus

Cirrus means Thin, High altitude, and feathery appearance

White in color and indicates fair weather.

Ciro stratus

Layered and High altitude with a milky appearance.

Stratus

Stratus means layered.

Alto

Alto means middle altitude.

cumulus

Cumulus clouds have a cotton wool-like appearance with dome-shaped cauliflower top

Also called globular masses

Nimbus

Nimbus means Rain bearing

Alto Cumulus

Globular masses of clouds with a cotton wool-like appearance at middle altitude.

Altostratus

A layer of clouds in sheets along the middle altitude.

Stratus

A low uniform layer of cloud near the ground level produces light drizzle. 

 

Cumulonimbus clouds

Overgrown cumulus clouds are very dark heavy and dense with an anvil top.

It causes heavy rainfall with thunder and lightning.

 

The Topic for the next class: Precipitation, Type of Rainfall.

 

Geography Class 26

Revision of the previous class (05:13 PM) 

Precipitation (05:28 PM)

Precipitation requires the following three condition

a)Upliftment mechanism: To cause moist air to rise

b)Saturation and cooling of air below the due point

c)Presence of Hygroscopic nuclei such as dust particles around which water droplets can accumulate.

Types of precipitation

a)Convectional Rainfall

It occurs in the region of intense heating near the ground surface.

Heating causes air to expand and rise resulting in the upliftment.

They are often accompanied by thunderstorms and lightning due to the formation of cumulonimbus clouds.

They are experienced throughout the year in equatorial regions and in summers in tropical regions.

 

b)Orographic Rainfall

When warm and moist air is forced to rise across mountain slopes it cools down causing precipitation along the windward side.

However, on the leeward side, the descending air will not cause precipitation creating a rain shadow region, for example, The Western Ghats of India.

 

c)Frontal Rainfall

It occurs along frontal zones due to the convergence of different types of air masses.

The warm air mass rises above the cold air mass causing precipitation.

Frontal precipitation is common along the temperate region.

 

Distribution of precipitation

Along the Equatorial region, the highest precipitation is experienced above 200 cm per annum.

It is due to the convectional Rainfall

Along subtropical regions around 30 degrees minimum rainfall experienced 25 cms per annum.

The Mid-latitude regions between 30 to 40 degrees of North and south experience uniform and moderate precipitation due to the frontal rainfall.

Due to the presence of moist maritime air mass oceans receive more precipitation than the continents.

Coastal regions receive higher precipitation than the interior.

Thunderstorm and Lightning (05:49 PM) 

Due to intense heating and strong vertical convection, Cumulonimbus clouds are formed.

The Raindrops in these clouds move up and down due to strong air currents creating electric charges which accumulate on opposite sides of clouds.

When both types of charges have attracted a flash of light is produced due to the exchange of charges called lightning.

Lightening causes Vaccum in the cloud due to the Rapid expansion of air.

It is filled by the surrounding cold air producing claps of Thunder.

Cloud Burst (06:10 PM)

IMD defines cloud burst as Rainfall over 10cm per hour concentrated in a small area of a few km.

Formation of cloud burst

High temperature and higher humidity favour strong and rapid convection.

Steep topography along the mountainous region causes a huge buildup of clouds without precipitation due to the funnelling effect.

The Rapid convection prevents the Raindrops to fall down.

Once the cloud becomes too heavy for the air to hold on it drops together in quick succession resulting in a cloud burst.

In India, cloud bursts can be observed along the Himalayas, Rajasthan desert, and monsoon coasts.

Tornado (06:36 PM)

 

A violently rotating column of air extends from the ground to the base of a Thunderstorm.

It appears like a funnel descending from a cloud.

The wind speed goes up to 400 km per hour.

It is formed with changes in wind speed and direction creating a horizontal spinning effect within a storm cell.

This effect is tipped vertically by rising air moving up through the thunderclouds.

A water spout is a whirling column of air and water mist developed over water bodies.

Jet streams (07:11 PM)

WMO defines jet streams as a strong narrow current concentrated along a quasi-horizontal axis in the upper troposphere or lower stratosphere characterized by strong vertical and lateral wind shear.

Featuring one or more velocity maxima.

Characteristics:

They are thousands of km in length and 100 km in width.

Normally blows from west to east.

winds are faster during winter.

The entire system follows the sun.

It follows the Zig Zag path in the form of Rosby waves.

Causes

Jet streams are generated due to the temperature difference between the two regions that is Tropical and Temperate, Temperate and polar, etc.

The difference in pressure gradient with altitude above cold and warm air mass causes strong movements of winds.

The larger the temperature difference, the stronger the winds.

Types of Jet streams (07:49 PM)

 

a)Polar front jet streams.

They are formed where the polar and Ferrel cells meet.

They are irregular and discontinuous.

They blow from west to East.

b)Subtropical westerly jetstream

Associated with temperature gradient between Headley and Ferrel cell.

It is more regular and strong, It blows from west to east.

Tropical Easterly Jet stream

Forms over India and Africa only in summer due to the intense heating of the Tibetan plateau.

The direction is east to west.

d)Polar Night jet stream

Formed over the polar region above the troposphere during winters.

They are associated with the formation of the ozone hole.

The direction is from west to east.

e)Local jet stream

They are formed due to local thermal and dynamic conditions.

Example: Somali jet streams

Significance of the Jet streams

The jet stream is responsible for cyclonic and anticyclonic conditions along the surface.

Upper divergence in jetstreams causes lower convergence and upper convergence causes lower divergence.

It changes the weather condition along the surface by suppressing or increasing precipitation.

It is used in Aircraft navigation.

The polar night jetstreams are responsible for Ozone depletion.

The jet streams help in the transportation of pollutants into the upper troposphere from urban regions and help in clearing fog and smog during winter.

It helps in the formation of temperate cyclones and intensifies them.

The monsoon in south Asia is controlled and affected by subtropical westerly, Tropical easterly, and Somali jet streams.

The sub-tropical westerly jet streams help in bringing western disturbance causing precipitations during winters in the Northwest region.

The interactions of jet streams with la Nina conditions cause the formation of a heat dome over North America.

Meandering of Jetstreams near polar regions during winters results in the outbreak of polar vortex causing freezing conditions along lower latitudes.

The topic for the next class is: Polar vortex, Continuation of climatology 

 

Geography Class 27

Revision of the previous class  in a detailed way (05:05 PM)

Polar Vortex (05:30 PM)

Polar Vortex is a large area of low pressure and cold air surrounding the Earth's pole.

The term Vortex refers to the counter-clockwise flow of air which keeps the cold polar air locked inside.

The polar winter night jetstreams keep this region covered with strong winds.

Occasionally when the vortex weakens due to the weakening of jetstreams the vortex expands and sends the cold air southwards along with jetstreams.

This brings down the temperature in southern Regions to colder levels of below zero degree Celsius.

Air masses (05:47 PM)

It is the extensive portion of the atmosphere.

Whose physical properties such as temperature pressure and Humidity are homogeneous horizontally and vertically for hundreds of km.

The temperature of the source area shall remain uniform horizontally with a very gradual change in the vertical direction.

The humidity conditions should also be uniform with the least variability.

The surface area shall remain homogenous for a few hundred km.

The Regions with light divergent winds, High-pressure belts, and anticyclonic circulations are more favorable for the formation of air masses due to stable conditions.

Types of Air masses

Classified based on different factors such as:

Source area:Continental(c) formed over the continents and Maritime(m) formed over oceans 

Temperature: Warm and Cold air mass

Pressure: Stable(s) and Unstable air mass(u)

Latitude:Arctic air mass(a) and Antarctic air mass(aa) Polar air mass(P) Tropical air mass(T0 Equatorial air mass(E)

a and aa is continental

P & T is continental and maritime respectively.

E is maritime.

Significance of Air mass (06:16 PM)

Air masses Transport heat from one region to another and help in the global distribution of temperature.

When Air mass moves away from its source area it changes the temperature and pressure conditions of the destination regions.

Maritime air masses bring More moisture toward the continental region increasing its humidity and causing precipitation higher precipitation along the coastal regions due to the influence of Maritime air masses.

The dry Continental air masses along the subtropical regions help in maintaining the aridity conditions.

The cold air mass formed over Siberia and Canada affects the surrounding region for long-distance causing cold conditions.

The maritime air mass of the Indian ocean plays an important role in precipitation over India during Monsoon.

The interaction of warm and cold air masses in temperate regions leads to the formation of fronts and temperate cyclones.

The maritime tropical and equatorial air masses in the Atlantic and Indian oceans help in the development of Tropical cyclones.

Temperate Cyclones (06:56 PM)

Front

A narrow zone of transition dividing two air masses of differing temperature and humidity conditions is called the front.

They are usually formed in Mid latitude or temperate regions.

The process of formation of fronts is called frontogenesis

The process of decay of fronts is called as

Types of Fronts (07:07 PM)

Stationary front

It is a front where the surface position of a front is not changing and the two air masses are unable to push each other.

When a stationary front is disturbed it results in a warm front or cold front.

Cold front

It is the boundary between warm and cold air mass where the cold air mass is advancing and undercutting the warm air mass.

It results in a steeper gradient along the front leading to rapid upliftment of warm air and the formation of cumulonimbus clouds.

It results in heavy rainfall over the smaller regions.

C) Warm front

It is the boundary between warm and cold air mass where the warm air mass is advancing and overriding the cold air mass.

The gradient of the front is gradual resulting in strato nimbus clouds.

It causes moderate rainfall over a larger area.

Occluded Front (07:39 PM)

It is the later stage of front formation where the air in the warm sector is no longer at the ground surface due to the meeting of a warm and cold front.

It is a compound zone with both warm and cold front characteristics.

The occluded front gradually results in frontolysis.

It is the later stage of front formation where the air in the warm sector is no longer at the ground surface due to the meeting of a warm and cold front.

It is a compound zone with both warm and cold front characteristics.

The occluded front gradually results in frontolysis.

Formation of Temperate Cyclones (07:45 PM)

6 Stages

Stage 1:Convergence of two air masses with different characteristics. Air masses move parallel to each other and a stationary front is formed.

Stage 2: Warm and cold air masses penetrate into the territory of each other forming a wave-like the front.

Stage3: With warm and cold fronts starting to move towards each other, The warm sector is wedged between the cold sector.

Stage 4: The warm sector is narrowed in extent due to the advance of a cold front.

Stage 5: The occlusion starts with warm air rising completely above the cold air and the cold front completely overtaking the warm front.

Stage 6: The warm sector completely disappears, the occluded front is eliminated and the cyclones die out.

Temperate cyclones are also called Mid-latitude cyclones or extratropical cyclones or wave cyclones.

They are more prominent in the regions between 35-65 degrees North and south.

Role of Jet streams in Temperate Cyclones

Jet streams Being Quasi horizontal in nature results in upper divergence in some locations and upper divergence causes surface convergence which helps in bringing together the warm and cold air masses and the subsequent formation of fronts.

The topic for the next class: Tropical cyclones

 

Geography Class 28

Revision of the previous class and Doubts are taken (05:12 PM)

Tropical cyclones (05:40 PM)

A Tropical cyclone is a low-pressure high velocity wind system originating within the tropics over the oceans.

Names in different regions:

Indian Ocean	Cyclone
Atlantic ocean	Hurricane.
South china sea	Typhoon
Japan	Taifu
Philippines-	Bagui
Australia	Willy Willy

Stages in Tropical cyclone (05:58 PM)

7 stages of Tropical Cyclones

a)Temperature: Above 27-degree celsius over the ocean to ensure sufficient evaporation 

b)Depth of warm water: The 27-degree Celcius temperature should extend up to 60-70 meters in depth.

c)The humidity of Air: High Humidity of 50-60 % near the surface.

d)Minimum vertical wind shear: So that Humid and warm air is not swept away.

e)Coriolis force: It causes wind deflection therefore cyclones are developed only between 5 degrees North to 25 degrees North or 5 Degree south to 25 degrees south.

f)Pre Existing Low-pressure conditions: These get intensified to form Cyclones.

g)Upper Air divergence: Causing convergence near the surface.

In the above, the First 5 are the necessary condition.

Formation

A strong Convection results in the build-up of huge cumulonimbus clouds 

The Release of Latent heat provides more energy to the system supporting further strong Convection.

When the wind starts to descend along the sides the entire system is stabilized.

The Lateral winds near to the surface start to Rotate around the Low-pressure centre due to the Coriolis force.

After some time some of the dense air rising near the centre starts to descend resulting in the formation of an eye.

Once a cyclone is formed it moves under the influence of planetary winds and deflects toward the northwest direction.

When a cyclone makes landfall or enters the waters of higher latitude, It dissipates and comes to an end.

Structure of the Cyclone (07:18 PM)

Eye: It is the centre of the storm about 5-50 km in diameter with a clear sky, Calm conditions, Lowest pressure, and Highest temperature.

Eye wall: A wall of thick cumulonimbus clouds with 10-20 Km of width. It has the strongest wind in the cyclone. Thunderstorm occurs in this region due to intense convection.

Spiral bands: AKA rain bands or feeder bands extend for 100 km and lead to Galaxy like appearance.

Annular Zone: A Zone of suppressed cloudiness, High temperature, and low humidity.

Outer convective bands: At the edge of the main cloud mass with instability and convection

Naming System of Cyclones (07:25 PM)

In 2004, 8 countries of the Northern Indian Ocean agreed to have a common naming system for Cyclones. Each of the countries arranged them in alphabetical order.

And it was submitted in a set of 8 names.

The Regional Specialized Meteorological centre of WMO located in New Delhi maintains the list arranged in sequential order and assigns the names when the wind speed crosses 62km/hr.

The suggested names shall be neutral politically, Religiously, and Culturally as well as concerning Gender.

It should be easy to pronounce.

All the names in the earlier matrix, Expired in 2019, and a new matrix suggested by 13 countries was agreed upon effective from 2020.

Recurvature of the cyclones (07:46 PM)

When the Air currents in the local atmosphere push the air from the poles towards the Equator and interfere with Cyclone formation the Cyclone which is about to diminish gets more wind and deflects right or eastward under the influence of westerlies this phenomenon is known as Recurvature of the cyclones.

Recurvature is very difficult to predict, for example, Cyclone Ockhi of 2018.

Cyclones in the Indian Ocean (07:52 PM)

The number of Cyclones in the Bay of Bengal is more than in the Arabian sea in a Ratio of 4:1

Reasons:

Strong Wind shear in the Arabian sea

Temperature is higher in the  Bay of Bengal because more rivers enter the Arabian sea.

Colour-coded warning of IMD for Cyclones (07:57 PM)

It is used by IMD to signify the intensity of the situation and the warning associated with it

Four colours are used:

Green-No warning

Yellow-Be aware

Orange-Be prepared.

Red-Take Action

The objective is to alert people of Hazardous weather and prepare them for handling disaster situations.

It is Universal and issued during floods and heavier Rainfall for cyclones it is represented through a matrix.

Difference between Tropical and Temperate cyclones (08:01 PM)

You Can Refer to a chart Drawn in the class

The topic for the next class: Climatic Regions 

 

 

Geography Class 29

Climatic regions: (5:25:57 PM):

0 to 10 degree:-Hot and a wet equatorial type of climate.

10 to 30 degree:-Hot zone includes desert, savanna climate, and Monsoon type of climates.

30 to 45 degrees- Meditterean, steppe, and China type of climate.

45 to 60 degrees-Coll temperate zone Includes British, Siberian, and Laurentian types of climate.

66 1/2 degrees and above-Arctic zone.

Hot and wet equatorial climate:(6:04:41 PM):

Temperature is always high throughout the year.

Precipitation happens through convection.

The daily maximum temperature is 30 degrees and the daily minimum is 20 degrees.

The diurnal range of temperature is more than the annual range and both are very less.

Humidity levels are high.

No marked differences between the seasons.

Precipitation above 250 cm through conventional rainfall.

Life is rich here.>> Vegetation is evergreen in nature.

Evergreen rainforests exist here.

Vegetation shows the layered arrangement of trees.

Sunlight is the limiting factor.

The diversity of flora and fauna is very high.

Regions- Amazon basin, Parts of Colombia, Ecuador, Congo Basin, Indonesia, Malaysia, Singapore, Papua New Guinea.

Monsoon type of Climate:(6:25:10 PM):

Hot zone eastern Margin.

Seasonal reversal of winds.

Precipitation is concentrated during the monsoon period.

One or more months of the dry season.

Vegetation is a deciduous type.

Trees shed leaves during winter.

Regions- South Asia including India, Pakistan, Bangladesh, Indo-China, Eastern Africa, and Northern Australia.

Within the monsoon type, onshore trade winds cause precipitation from both directions throughout the year called a tropical marine climate.

Examples- Central America, SE Brazil, etc.

Sudan type of climate:

Hot zone continental type of climate.

Grasslands in tropical regions.

Precipitation is lesser in the eastern margin and more than in the western margin.

Rainfall in summer due to convection.

The definite dry season during winters.

The average annual rainfall is 70 cm.

Scattered drought-resistant trees.

Regions- Sudan region, Savanna region to the south of the equator in Africa, South America-Llanos, and Campos and North Australia.

Desert Type of climate:(7:10:00 PM):

Hot zone western climate.

Formed by 3 conditions;

-Nearness to the subtropical high-pressure belt.

-Offshore trade winds.

-the presence of cold ocean currents.

Precipitation is very less with less than 25 cm per annum.

High Diurnal range of temperature.

Vegetation is xerophytic in nature.

Eg- Cactus, dates, etc.

Regions-Sahara desert, Mohave desert, Arizona desert, Atacama desert, Namib desert, Kalahari desert, Victoria desert, Gibson desert.

Medditerean type of climate:

Aso called warm temperate western margin.

In summers ITCZ shifts northwards bringing offshore trade winds with no precipitation.

In winters ITCZ shifts southwards bringing onshore westerlies and causing good rainfall.

In winter they are also under the influence of temperate cyclones causing rainfall.

It is known for its characteristic dry summers and wet winters.

Summers are not very hot.

Vegetation is drought-resistant, deep-rooted short bushes.

Examples-Grapes, are olives, oranges, and other citrus fruits.

Regions- California, Central Chile, Southwestern part of South Africa, Southwest, and Southern Australia.

Steppe type of climate:(7:34:40 PM):

Warm temperate continental type.

Precipitation is higher than in tropical grasslands due to the influence of temperate cyclones during winters.

During summers the precipitation is through convection resulting in moderate rainfall throughout the year.

The grass is short and green.

Soil is very fertile.

They are known for large-scale commercial agriculture and animal rearing.

Regions-Steppes of Central Asia, Prairies in North America, Pampas in South America, Velds in south Africa, Downs in Australia, etc.

China Type of Climate:

warm temperate eastern margin.

Precipitation is throughout the year.

In summer, they are affected by tropical cyclones and in winter they are under the influence of temperate cyclones.

Summers>> Not too hot, Winters>> Not too cold.

Vegetation is dense and luxurious.

Deciduous and evergreen species.

Regoins>> Southeastern USA, SE Brazil, South Eastern China, SE South Africa, SE Australia.

Laurentian type of climate:

Cool temperate eastern margin.

Temperature ranges between 20 degrees in summers to below zero degrees in winters.

Rainfall> throughout the year but more in summers.

Under the influence of temperate cyclones.

Vegetation- Upto 50 degrees N and S is deciduous and broad-leaved and beyond that it is coniferous.

Regions-Eastern Canada, NE USA, Northern China, Korea, and Japan, SE Argentina.

Next class-Continuation of the climatic regions.

 

Geography Class 30

Brief Discussion of Previous Class (5:09 PM)

Siberian Type (5:15 PM)

This is also called cool temperate continental

Summers are hotter, and winters are extremely cold and dry.

This results in anti-cyclonic circulations.

The rainfall is through the convection in summer, and through the snowfall in winter

Vegetation is coniferous and is in the single largest stretch of vegetation on the earth.

It is low in biodiversity but high in economic value.

It is the only climate that is exclusively present in the northern hemisphere.

Regions: Siberia, Russia, Poland, Scandinavia, Canada, Alaska

British Climate(5:30 PM)

Cool Temperate Western Margin

They are under the influence of Offshore westerlies, throughout the year.

This causes precipitation which is moderate throughout the year.

They are under the influence of warm ocean currents, which keep their ports ice-free even during winter.

It is known for its characteristic mild winter and cool summer.

Vegetation is a mixed type, i.e. mixture of broad-leaf and coniferous.

Regions: United Kingdom, Norway, the western coast of Western Europe, Western Canada, Southern Chile, New Zealand, and Tasmania.

Polar type of Climate (5:40 PM)

It is also known as the Tundra type of Climate.

It is covered with ice throughout the year.

During summers when the snow melts, vegetation grows stunted, like mosses, sedges, and lichens.

The rest of the region is covered with permafrost.

Regions: Any region beyond the Arctic and Antarctic circles.

Koeppen Classification

Oceanography (6:03 PM)

Ocean bottom Topography

Ocean temperature

Salinity

Ocean Deposits

Coral reefs

Oceanic Currents and Circulations

El Nino and related phenomena

Tides

Ocean Bottom Topography (6:24 PM)

Continental shelf

These are submerged shallow portions of the continental crust with depths between 150-200 m

It is rich in sunlight, oxygen, and nutrients, which favours the growth of plankton.

The width of the continental shelf is dependent upon the slope of the adjacent land.

It is wider along the coastal plain, and narrow along the mountainous coast.

The continental shelf is rich in biodiversity and is known for its rich fishing grounds.

Continental Slope

It is the boundary between continents and oceans, formed by the outer edge of the continents.

They are much steeper than the continental shelf

Continental Rise

It is the base of the continental slope, with a lower slope.

It continues into abyssal plains.

Submarine Canyon (6:54 PM)

These are the canyons, formed along the continental shelf and slope, because of the turbidity currents of the river, entering the ocean.

Abyssal Plain

They are also called Oceanic basins

They are tectonically inactive oceanic floors, with relatively smooth surfaces.

The average depth varies between 3000-6000m

Seamounts

These are isolated volcanic features and volcanic mountains formed due to volcanic activities, along hotspots and subduction zones.

Volcanic Islands, Island Arc, Archipelago

These are formed due to volcanic activities along the subduction zones and hotspots.

(* Formation has been covered in Plate tectonics)

Guyots

While seamounts are sharply pointed, guyots are flat-topped hills, with summits below the water level.

Mid-Oceanic Ridges

They are formed along Ocean-Ocean divergent plate boundaries.

Trenches

They are formed along the Ocean-Ocean convergence and Ocean-continental convergence plate boundaries.

Temperature (7:17 PM)

Differences concerning the Atmosphere

The water heats up slowly and cools down slowly.

The sunlight penetrates only upto 200m 

The albedo of the open ocean is low compared to land.

The temperature distribution through mixing is slower.

Factors

Latitudes

In Lower latitudes, higher insolation results in higher temperatures.

Along, higher latitudes, lower insolation, and lower intensity cause lower temperatures.

Winds

Winds help in the distribution of temperature across the globe.

For Example, in the regions where westerlies are active, water temperature remains higher, than in the region of polar easterlies.

Ocean currents

They help in heat balance, between the equatorial and polar regions.

Warm ocean currents increase the temperature, and cold Ocean current decreases it.

Role of Landmass

The seas which are surrounded will have higher water temperatures, than open ocean waters.

Vertical distribution

The first layer is called Epilimnion (up to 200m)

The second layer is called Thermocline (or Metalimnion) (200-1000m)

The third layer is called Hypolimnion (beyond 1000m)

Epilimnion:

It extends up to 200m in depth.

The average temperature is between 20-25 degrees celsius.

It is a zone of constant sunlight and mixing due to winds.

It is a zone of uniform temperature.

It is the zone of Life

Thermocline:

It is the twilight zone, because of the very low amount of sunlight.

The temperature decreases rapidly with depth.

Hypolimnion:

It is a zone of uniform and very cold temperatures.

The average temperature is nearly 4 degrees Celsius

It is because seawater attains maximum density at 4 degrees Celsius.

It is also known as a dark zone.

Horizontal Distribution

The surface temperature lies between 20-25 degrees Celsius in tropical regions and decreases gradually towards the polar region.

The three distinctive layers are visible along tropical regions.

However, along polar regions, there will be a single uniform layer of cold temperature.

Salinity (7:50 PM)

Salinity is the number of grams of dissolved salts in a thousand grams of seawater.

It is measured as parts per thousand (ppt).

The average salinity of Earth's ocean is 35 ppt.

Sources of salinity

Sources of addition

Sediments brought by rivers, which get dissolved over a long period of life.

Volcanic eruptions along the oceanic floor

Evaporation in Ocean

The salinity of oceans always remains constant.

The factors increasing salinity are balanced by the factors decreasing salinity.

Sources reducing salinity

Addition of river water

Rainfall

Ice melting

precipitation of salts along the oceanic floors.

Dissolved salts in Sea Water (Decreasing Order): Chlorine, sodium, sulfate, magnesium, Calcium

The Topic for the Next class: Oceanography (continued)

 

Geography Class 31

Revision of the previous class (05:11 PM) 

Factors influencing salinity (05:23 PM)

a)Temperature: The higher temperature will result in Higher salinity

b)Wind speed: Higher wind speed causes a higher rate of evaporation resulting in higher salinity.

c)Ocean Currents: Help distribute salinity from one region to another.

Regions for Higher salinity

Also, Refer World map as drawn in the class.

Sub-Tropical Regions: Due to the Higher rate of Evaporation. Examples: Mediterranean sea, Red sea, Persian Gulf, and Sub-tropical regions of the Atlantic and Pacific oceans.

Regions with below-average salinity: North sea, Baltic sea, Berring sea, Arctic Ocean, Southern Ocean

Regions with Exceptionally High salinity: Lake van, Dead sea, and Great salt lake.

Oceanic Deposits (05:37 PM)

Terrigenous Deposit: Deposits are derived from the land and found in oceans which is why also known as Lithigeneous. Example: Sand, Gravel, Mud, silt.

Biogeneous Deposits: Shells, Corals, Ooze(These are the deposits derived from calcareous and silicious shells and skeletal remains of marine microorganisms. Biogeneous deposits are also called organic deposits.

Hydrogenous Deposits: Example: Salt, Polymetallic nodules.

Cosmogenous Deposits: Meteorites debris.

Coral Reefs (05:47 PM)

Coral Reefs are masses of limestone and dolomite accumulated by a lime-secreting organism called coral polyps.

They are developed due to the symbiotic relationship between coral polyps and zooxanthellae algae.

The coral reef provides habitat to nearly 31 phyla of Animals leading to Rich biodiversity, Therefore they are also called rainforests of oceans.

Conditions

a)Temperature: 20 degrees celsius, Not beyond 30 degrees North and south latitude.

b)Depth: Maximum depth between 200-250 feet below sea level.

c)Sediment-free water: Therefore coral reefs are not found near deltas.

d)Salinity: Average of 35 parts per thousand.

e)A platform on which the corals can build reefs i.e Continental shelves.

Corals are not found in the western margins of the continents due to cold ocean currents.

Distribution (06:15 PM) 

Atlantic Ocean: Around the Caribbean sea, Mexico, and the surrounding regions.

Indian Ocean: Red sea, Persian gulf, western and Northern Indian ocean, A&N islands, Lakshwadeep, Gulf of Mannar, Gulf of Kutchh, Maharashtra Coast, and Goa Karnataka coast.

Southeast Asia and Pacific: Covering Coral Triangle from Indonesia, Malaysia, Philippines, and Australia(Great Barrier Reef), The islands of the pacific ocean.

Types of Coral Reefs (06:24 PM) 

Fringing Reefs

 

A narrow and discontinuous patch of coral reef located near the coast. Example coral reef of the Caribbean sea.

Barrier Reef 

 

A wide and continuous coral reef located far from the coast and is separated by a lagoon, Example: Great Barrier Reef.

Atoll Reef

 

A circular Coral reef developed around a sea mount or Gyot or island. Ex: Lakshwadeep, Maldives, and islands of the pacific ocean.

Coral Bleaching (06:34 PM)

Corals receive their colouration from zooxanthellae.

Coral Bleaching refers to the loss of colour of corals due to the stress-induced expulsion of symbiotic algae.

The reasons behind coral bleaching are:

Changes in water temperature, salinity, Increased sedimentation, Increased pollution, and Ocean acidification.Increased incidence of cyclones, Storms, and Elnino.

Examples of Coral Bleaching: Between 2014 to 2017, Due to El Nino the Great Barrier Reef was bleached by nearly 50%.

In 1997-98 the Northern Indian ocean lost the majority of coral reefs.

Oceanic circulation (07:18 PM)

Surface/Ocean Current 

An ocean current is the general movement of the ocean's surface water in a definite direction over long distances.

Types of ocean currents:

a)Warm Ocean current: Moves from Equator to pole

b)Cold ocean current: Moves from poles to the Equator.

Factors affecting ocean currents

Winds: The steady blowing of winds drag the surface water in its direction and brings about the surface flow and sets the water currents in motion.

The shape of the Coastline and Topography: Modify the ocean currents' direction.

Differences in temperature, salinity, and density: Cause the water to move and reduce variations such differences guide the movement of ocean currents.

Coriolis force: It causes ocean currents to deflect right in the Northern hemisphere and left in the southern hemisphere.

Ocean Currents of the world (07:45 PM)

 

Currents of the Atlantic Ocean

Under Trade winds influence 

a)North Equatorial current

South Equatorial current 

c)Counter Equatorial current which goes along the Equator in the west-to-east direction.

d)Florida current: Anteles +Gulf current, Along the coast of Florida.

e)Gulf stream: Towards the Northeast direction, USA coast.

f)North Atlantic Drift: Gulf stream takes a total right turn once it crosses Newfoundland under the influence of westerlies and Coriolis force.

g)Norweigian current: Along the coast of Norway

h)The canary current: A cold current, Along the canary islands, flowing southwards.

Two cold ocean currents Labrador and the East Greenland current. Labrador joint Gulf stream and East Greenland joins North Atlantic Drift.

Seaweed in the Gyre grows which is known as sargasso that is what the sea is known as Sargasso sea.

The Topic for the next class: El Nino

 

 

Geography Class 32

Brief Discussion on the Previous Class (5:13 PM)

Currents of the South Atlantic Ocean (5:22 PM)

South equatorial current, which moves along Brazil forms the Brazilian current. It is a warm current. 

The Brazilian current gets deflected towards the left in the southern hemisphere (Due to Coriolis force) and joins the West Wind Drift.

West Wind Drift is a cold current, which circulates the continent of Antarctica. (It flows under the influence of Westerlies).

The Brazilian current once when comes under the influence of West wind drift is called South Atlantic Drift.

Near the coast of Africa, it turns upward and is known as Cold Benguela Current.

Benguela current is responsible for the formation of the Namib and Kalahari Deserts.

Cold Benguela current joins the South Equatorial current.

Falkland Current flows along the eastern coast of the South American continent.

Gyre is formed in the South Atlantic Ocean, 

Currents of the Pacific Ocean (5:34 PM)

North Equatorial current gets divided by the archipelago and turns rightward. This current is known as Warm Kuroshio Current (along the coast of Japan).

It is a warm current moving along the coast of the Philippines and Japan.

The North Pacific Current is an ocean current that flows west-to-east between 30 and 50 degrees north in the Pacific Ocean.

It gets divided near the North American Continent.

One branch moves upward and is known as Warm Alaskan Current.

Another branch moves southward and is known as the cold California Current.

Cold California Current joins the North Equatorial Current. therefore a gyre is formed here.

Near Sakhalin Island, there are two cold currents- Oyashio Current and Okhotsk Current.

Southern Pacific Ocean

The southern equatorial current moves down and is called Warm East Australian Current.

Coming down, it joins West wind drift and is known as Cold South Pacific Drift.

Then it flows along the coast of the South American continent and is known as the cold Humboldt Current.

Then, finally, it joins the South Equatorial current.

Indian Ocean currents (5:48 PM)

Southern Indian Ocean

There is a Southern equatorial current.

It gets divided into two currents by Madagascar: Mozambique current and Madagascar Current

Mozambique and Madagascar combine to form the Agulhas current.

It flows along with West Wind Drift and then, moves along the western coast of Australia. It is then known as Western Australian Current.

Western Australian Current then, merges with the Southern Equatorial current.

Northern Indian Ocean

Here, the wind reversal takes place. Also, there is huge dominance of land in the Northern Indian Ocean.

Winters

We have North Equatorial Current, South Equatorial current, and Counter equatorial current during the winter.

North equatorial current flows westward, above the equator.

Counter equatorial current flows in between the North and South Equatorial Currents.

The Northeast monsoon drives the water of the Bay of Bengal and Arabian sea to circulate in an anti-clockwise direction as the Northeast monsoon drift.

Summers

The entire water of the Northern Indian Ocean comes under the influence of the Southwest Monsoon.

This produces a clockwise flow of the southwest monsoon drift.

During this time, there are no north equatorial currents and counter equatorial currents.

Significance of Ocean Currents (6:25 PM)

The continuous movement of water from east to west in the tropical region causes cold water upwelling, along the eastern parts of oceans.

This causes a drop in the temperature

Accumulation of warm waters along the western parts of the ocean in tropical regions, leads to a rise in water temperature.

The western parts of the Ocean within the tropical regions, experience favourable conditions for the formation of cyclones.

The cold ocean currents along the western coast in sub-tropical regions, suppress precipitation through the desiccation effect.

It contributes to the formation of deserts. For example, the Kalahari desert and Namib desert due to the Benguela current, the Atacama desert due to the Humboldt current, etc.

Warm and Cold ocean currents merge near the temperate regions to create favourable conditions for the development of large-scale fishing banks. 

For Example Grand Bank (near Newfoundland Island due to the merging of labrador current with the gulf stream)

The off-shore winds along the western margins of the continent, in tropical and sub-tropical regions push the surface water away.

This causes the cold water from the bottom to rise upwards to the surface.

This brings cold and nutrient-rich water to the surface through upwelling. 

The reasons for upwelling support large-scale fishing growth. For example, the Humboldt current along the coast of Peru and chile.

Ocean Currents help in the global distribution of temperature and salinity.

the warm ocean currents in the temperate region along the western coast of continents, result in mild winters and keep the port ice-free.

For example, North Atlantic Drift along Britain.

Ocean currents can be used in navigation, to find directions in the open oceans.

The merging of Warm and Cold Ocean currents results in fog formation, which may obstruct ocean navigation.

Upwelling and downwelling (7:17 PM)

Downwelling

The on-shore winds pile up the water near the coast, causing the sinking of water below the surface layer.

Downwelling is more active where warm and cold ocean currents meet.

Upwelling

The off-shore winds push the surface water away and cause the cold water from the bottom to rise from the surface.

Upwelling is more active in the regions of cold ocean currents.

In Polar regions, ice formation leaves the water saltier and denser causing it to sink.

Thermohaline Circulation (7:21 PM) 

The deep ocean currents are driven by differences in the water density, which is controlled by the temperature and salinity and is called thermohaline circulation.

The circulation begins near polar regions, of the downwelling where ice formation leaves the water saltier and denser leading to the sinking.

This underwater current moves in a single and continuous belt across the different oceans.

They are connected to surface water currents in the regions of upwelling.

They are also called Great Ocean Conveyor belts.

Atlantic Meridional Overturning Circulation (7:46 PM)

AMOC is a part of the thermohaline circulation, in the Atlantic ocean.

The recent report of the IPCC, talks about the weakening of AMOC, due to global warming.

Factors responsible for the weakening 

The temperature difference between the tropical and polar regions is decreasing due to the warming of the arctic region.

This weakens the north Atlantic drift.

The excessive addition of freshwater due to increased melting of ice in polar regions.

This reduces downwelling as the freshwater is less dense.

Impacts

Western European countries will experience harsh winters and frozen ports.

Western parts of Oceans in the tropical regions, will experience a rise in sea levels.

Increased occurrence of cyclones in tropical waters.

Disturbance of fishing zones.

Disturbance of marine ecosystem.

Water Mass (7:53 PM)

It is a body of water with uniform characteristics of temperature and salinity.

They are three types:

surface water mass- For example, Antarctic Surface Water mass

Intermediate water mass: For example Sub tropical Intermediate water mass of the Atlantic Ocean.

Deepwater mass: For example, North Atlantic Deep Water Mass

water mass helps in the generation and maintenance of thermohaline circulation.

they result in upwelling and downwelling.

The movement of water mass helps distribute temperature, salinity, and oxygen.

The uniformity of conditions, within water mass, supports plankton and coral growth.

The Topic for the next Class: El Nino and the related phenomena

 

Geography Class 33

Discussions on the last Class (5:10 PM)

Walker circulation (5:39 PM)

Along the western coast of South America, the ITCZ is usually above the equator throughout the year, this results in strong trade winds.

The offshore trade winds push the water, away from the coast, causing cold water upwelling, along the eastern pacific in addition to existing cold ocean currents.

This reduces the water temperature and the air above this cold water is dry and stabilized, and Convection is suppressed.

Water flows westward as southeast trade winds blow toward the western pacific region.

This water gets heated up and rises through convection causing cloud formation and precipitation along the western pacific.

The rising air flows eastward, in the upper troposphere, and descends along the eastern pacific completing the cell.

This results in high pressure and low temperature, in the eastern pacific ocean.

And high temperature and low pressure in the western pacific region.

This results in the convective cell, known as walker circulation.

In normal conditions, the eastern pacific coast experiences, drought, and the western pacific experiences good rainfall.

El Nino (6:07 PM)

Once in 3-7 years in October-November, the ITCZ moves too much south to the equator.

This results in the weakening of trade winds and disruption of upwelling.

The warm tropical surface waters, earlier flowing towards the west, flow back eastwards, causing a further reduction in the upwelling.

This results in warm surface water on the coast, of central and South America, which is called as El-Nino.

The appearance of El Nino causes the air pressure to drop over the eastern pacific coast and rise over the western pacific.

This see-saw variation, of air pressure, is called El Nino southern oscillation (ENSO)

El Nino causes heavy precipitation along the eastern pacific and drought conditions along the western pacific.

After one or two years the enhanced Hadley circulation strengthens the trade winds and increases the upwelling, bringing back the normal condition

Impacts of El NINO

The disturbance of the walker circulation causes the disturbance in global weather patterns and the convective cycles are also disturbed in other oceans.

It causes drought and dry conditions in India and Australia.

It negatively impacts Indian Monsoon, causing delays in monsoon, a decrease in precipitation as well as an increase in the number of breaks in monsoon.

It causes heavy precipitation along the coastal deserts of Peru and Chile.

The dry condition in India and Australia triggers forest fires and bushfires.

the warm water along the eastern pacific along Peru and chile coast inhibits the growth of plankton and algae and suppresses upwelling devastating the marine ecosystem, and killing fish on large scale.

It results in a catastrophic impact on the fishing and fertilizer industry.

the decomposition of fish releases hydrogen sulfide, causing dark waters and making it toxic.

El Nino years cause mass coral bleaching due to disturbance of the stable conditions and higher temperature.

It results in severe dust storms in India and Australia.

During El NINO, high-pressure conditions in the Caribbean Sea, Western Pacific, and Bay of Bengal suppress the cyclone formation.

The strongest recorded El Nino was in 1982-83, 1997-98, and 2014-16, 2018-19.

La Nina (6:27 PM)

El Nino is usually followed by La Nina.

It is the intensified high pressure, and cold temperature along the eastern pacific and lower low pressure and higher high temperature along the western pacific.

This causes very heavy precipitation, in India and Australia, resulting in floods.

The La Nina Years, 2020-21, 21-22, 22-23. This is called Triple Dip. (La Nina consecutively in three years)

El Nino Modoki (7:21 PM)

Modoki means similar but different.

While El Nino is characterized by strong warming in the eastern pacific ocean, El Nino Modoki results in warming in the central pacific with cooling in the eastern and western pacific oceans.

It creates a two-cell Walker circulation over the tropical pacific region, with precipitation in the central part and dry conditions in the eastern and western parts.

While El Nino results in diminished hurricanes in the Caribbean sea, El Nino Modoki results in increased hurricanes.

During this time, the number of cyclones is more in the Arabian sea, than in the Bay of Bengal

Madden Julian oscillation (MJO) (7:39 PM)

Unlike ENSO which is stationary, MJO is an eastward moving disturbance of clouds, rainfall, winds, and pressure that traverses the planet in the tropics and returns to its initial starting point in 30-60 days on average.

MJO has two parts, the convective part with enhanced rainfall and the subsiding part with suppressed rainfall.

MJO can influence the timing and strength of monsoons, as well as tropical cyclones.

MJO can increase or decrease the impact of El Nino on India.

Indian Ocean Dipole (IOD) (7:44 PM)

The difference in sea-surface temperature between the Western Arabian sea and the eastern Indian Ocean, near Indonesia and Australia is called as Indian Ocean Dipole.

Similar to MJO, it is a coupled ocean and atmospheric phenomenon.

Positive IOD

Warm sea surface in the western part compared to the east.

Less rainfall in Indonesia and Australia.

It is good for Indian Monsoon.

Reduces the impact of El Nino on India.

Arabian sea experiences a higher number of cyclones than the Bay of Bengal.

Negative IOD

Warm sea surface along the eastern part than the western part.

More rainfall in Indonesia and Australia.

Negatively impacts the Indian Monsoon.

Increases the effect of El Nino on India.

The topics for the Next Class: Heat Domes, Biogeography

 

 

Geography Class 34

Discussion on the last class (5:12 PM)

Heat Dome (5:36 PM)

The phenomena of heat dome that occurred in Canada and the USA in 2021.

It occurs when the atmosphere traps hot air like a lid 

It is due to when the combined effect of La Nina and weakened Jet streams.

La Nina results in strong subsidence of hot air, along the eastern pacific.

Jet streams when weakened start to meander in their path.

This weakened Jet stream, meandering too much allows the hot air from the tropical region to reach the higher latitude and traps the hot air descending due to La Nina too.

This results in higher than normal temperatures causing the heat dome.

Tides (6:03 PM)

The regular rise and fall of water levels in the world's oceans resulting from gravitational attraction by the moon and the sun is called Tides.

The combined gravitational pull of the Sun and Moon pulls the oceanic water in a bulge.

The centrifugal force due to the earth's revolution pulls another bulge, in the opposite direction.

The bulges in one direction create low water in another.

As the earth rotates, the position of high and low waters change across the surface.

Factors Affecting Tides

Gravitation pull of Sun and Moon

Relative position of the Sun and Moon

Centrifugal force of earth's revolution.

Uneven distribution of Water

Ocean Bottom topography

Types of Tides

Spring tide

These are very high, high tide, and very low tides.

They are experienced when the sun, earth, and moon are in a straight position.

This is called syzygy

The conjunction is when the earth, moon, and sun are in E-M-S

Opposition is when alignment is M-E-S

Neap tide

These are smaller high tides and smaller low tides.

A neap tide is when the sun and moon are in a perpendicular direction.

The position is called Quadrature.

The tides which are observed twice a day are called semi-diurnal tides

Those which are observed once a day are called Diurnal tides.

Significance of Tides

Tidal power generation

It helps in navigation for the tidal ports.

It helps in fishing activities. 

Helps in maintaining higher biodiversity along the tidal range.

Helps in the natural cleansing of the coasts.

It restricts the delta formation, as it doesn't allow the sediments to accumulate.

At other places it causes coastal erosion.

Maritime Zones (6:42 PM)

Baseline

It is the average line where the land ends and the ocean begins.

Internal Waters

It includes all the water bodies along the landward side of the baseline.

Territorial Sea

It is 12 nm from the baseline.

A country exercises sovereign jurisdiction on the bottom, surface, and air. However, innocent passage is allowed with restrictions.

Contiguous Zone

It is up to 24 nm from the baseline.

Sovereign jurisdiction over the bottom and surface but not in the air.

Exclusive Economic Zone

up to 200 nm from the baseline.

A country can exploit the resources on the ocean floor.

It extends beyond 200 nm if the continental shelf crosses it.

It will be allowed till the edge of the continental shelf.

High seas

International waters come under International Seabed Authority.

Biogeography (7:12 PM)

It is the study of the soil in relation to vegetation.

Soil

The loose surface material consists of inorganic and organic matter and is the source of water and nutrients for the vegetation.

True soil is characterized by distinct horizons and the capacity to support vegetation.

Horizon

Horizon is a distinguishable layer in the soil that has certain chemicals and a distinct colour.

Regolith

The layer of unconsolidated materials is derived from weathering of the parent rock.

Soil Profile

It is the vertical arrangement of the horizons down to the parent rock material.

Soil Formation (7:45 PM)

Soil depends on five major factors: Parent rock, climate, organism, relief, and time.

Parent Rock Material

It decides the texture, colour, and basic mineral composition of the soil.

For Example Quartzite rocks, result in a sandy texture.

However, the role of the parent rock decreases with time.

Climate

It is the most dominant factor which affects the soil directly, by controlling weathering, percolation, and other processes.

It results in the development of different horizons.

Organisms

Plant roots, burrowing animals, and microorganisms help in loosening up the soil and better air and nutrient circulation.

Relief

It determines the thickness of the soil.

Time

It controls the other factors and determines the maturity of soil.

Soil Formation Processes

Transformational Process

The change of soil constituents from one form to another through breakdown, weathering, decay, etc.

Translocational Process

It involves the movement of soil constituents from one horizon to another within the soil profile.

Eluviation: The downward transport process through which the minerals are removed from the top layer

Illuviation:  It is the reverse of eluviation, in which matter accumulates in the lower horizon.

Leaching: the percolating water removes humus and the soluble bases from the upper horizon and deposits them in the lower horizon through the process of leaching.

Leaching is more active in humid regions.

The Topic for the next class: Soil (continued), Mapping, and Indian Geography.

 

Geography Class 35

A brief discussion on the previous class (5:10 PM)

Laterization (5:34 PM)

It is active in hot and wet equatorial regions.

Heavy leaching removes silica and other minerals, except for iron and aluminium, which accumulate at the surface, forming a hard crust.

This process is called Laterization.

It results in laterite soil.

It is slightly acidic.

Podzolization(5:42 PM)

It occurs in temperate regions and mountainous regions.

The decomposition of coniferous litter releases organic acids.

During precipitation, the water mixing through these organic acids creates a strongly acidic solution that removes iron, aluminium, organic matter, and other minerals except silica.

This leaves the top layer acidic.

It results in podzol soil.

Calcification (5:55 PM)

It occurs in regions where evaporation exceeds precipitation.

Water rises through capillary action in the soil.

It causes the deposition of calcium carbonate in the top layer

It is more active in temperate grasslands.

It results in the black earth

Salinization

It involves the accumulation of highly soluble sodium and magnesium salts, in the topsoil.

It is due to excessive evaporation, and very less precipitation.

It is active in arid and semi-arid regions

It is also common in the regions of flood irrigation.

Gleisation

It occurs in water-logged conditions.

The colour of topsoil changes due to the reduction reactions.

It involves the accumulation of organic matter in the upper layers of the soil.

It is common in coastal regions along lagoons and deltas.

Distribution of Soils (6:04 PM)

Two types of soil- Pedocal and Pedalfers

Pedocal

Net upward movement of water

evaporation exceeds precipitation

Types are Prairie soil, chernozem soil, chestnut soil, Desert soil

Pedalfer

Net downward movement

Precipitation exceeds evaporation

Types are Laterite soil, red soil, Podzol soil

USDA Classification

 

Entisol	Fresh Alluvium
Inceptisol	Old alluvial, volcanic soil
Spodosol	Podzol soil
Alfisol	Leached Soil with Al and Fe
Ultisol	Leached Soil
Oxisol	The top layer is weathered with rich Al and Fe
Vertisol	Black Soil
Histosal	Peaty Soil rich in Organic Matter
Mollisol	Prairie Soil
Aridisol	Desert Soil

Mapping (6:18 PM)

Europe

Seas: Mediterranean Sea, Adriatic Sea, Black sea, Caspian sea

Mountains: Ural mountains, Alps mountain, Caucasus mountain, Mt Elbrus

Countries: Vatican City

Cities: Istanbul, Rome

North America:

Sea:  Californian bay, Gulf of Mexico, Bering sea

Mountains: Rocky Mountains, Appalachian mountains, Mt Denali

Places: Death Valley

Latin America: Except for Greenland, Canada, and USA, all other countries in the North and South American continent.

South America

Places: Drake Passage, Valdes Peninsula, Angel falls

Mountains: Andes Mountains, Mt Aconcagua, Ojas del salado

Rivers: Amazon, Lake Orninoco

Oceania (7:18 PM)

Countries: Australia, New Zealand

Island groups are divided into Micronesia, Melanesia, and Polynesia

Micronesia includes Caroline Island, Kiribati, etc

Melanesia includes New Guinea, Fiji, etc

Polynesia includes Hawai, New Zealand, Tonga island, Easter Island

Places: Great Dividing Range, Great Barrier Reef, Mt Wilhelm, Southern Alps

Antarctica

Antarctic treaty System, 1961 held that Antarctica can be used only for peaceful experiments.

The base stations of India in Antarctica are Dakshin Gangotri, Maithri, and Bharati.

India (7:38 PM)

We have both land and maritime neighbours.

Land Neighbours are Pakistan, Afghanistan, China, Nepal, Bhutan, Bangladesh, and Myanmar.

Afghanistan shares a border with India along Wakhan Corridor.

Countries arranged in order of length of the border with India: Bangladesh(4000 km)> China(3500 km)>Pakistan(3300 km)>Myanmar(1700 km)>Nepal(1650 km)>Bhutan(700 km)>Afghanistan(100 km)

Countries with maritime boundaries: Bangladesh, Pakistan, Myanmar, Sri Lanka, Maldives, Indonesia, Thailand

Union territories of India: Andaman and Nicobar islands, The Government of NCT of Delhi, Ladakh, Puducherry, Lakshadweep, Jammu and Kashmir, Chandigarh, and Dadra and Nagar Haveli and Daman and Diu.

The highest peak in India is K2 and the Second highest peak is Kanchenjunga

The lowest point in India is in Kuttanad (Kerala)

The topic for the next class: Physical geography of India