Que-Ans: [5 Marks Each]

Question 15 Marks

Factors affecting the atmospheric pressure Explain in details.

Answer

The factors affecting atmospheric pressure are as follows:

$1.$ Altitude:

Air is prevalent up to many kilometers in the atmosphere from the surface of the earth.

Due to gravitation force of the earth, every upper layers exerts pressure on the lower layer.

So, the air at the lower strata remains compressed and dense while it is thin in the upper layers.

Higher the place the air will be thinner.

The thin air is lighter and exerts less pressure.

The air pressure decreases @ $1\ cm$ or $13.32\ mb$ for every $165$ metres.

Everest in Himalayas is $8848$ metres high.

The air there is very thin so the pressure there decreases by about $54\ cm$ or $320\ mb.$

Air Pressure at different altitude according to Chrichfield:

Altitude $($Metres$)$	Air Pressure $($In Millibars$)$
Sea Level	$1013$
$1000$	$899$
$3000$	$710$
$5000$	$540$
$10000$	$265$

$2.$ Temperature:

Air expands due to heat and occupies more space.
So the pressure decreases.
Air contracts due to cold and occupies less space.
Such air becomes heavy so the air pressure becomes high.
Due to the difference in temperature, the day time pressure is less while the pressure is more during night time.
The pressure is less over landmass during summer and is high during winter.
Similarly, the temperature in equatorial region is high so the pressure is low,while the polar regions feel more pressure due to very low temperature.
Thus, the atmospheric pressure depends on the temperature of respective places.

$3.$ Humidity:

Water vapour is lighter than the air.
So, if the humidity increases lower will be the air pressure.
When the humidity in the air decreases its pressure increases.
During rainy season, there is more humidity in the air so the pressure is low.
The air over the oceans contains more humidity.
As a result the air pressure remains low over oceans compared to landmass.
The air over equatorial region is more humid so the low air pressure develops over there.

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Question 25 Marks

Draw a figure showing pressure belts and describe Equatorial low pressure belt.

Answer

Due to the effect of the factors that change the air pressure, the earth experiences light or heavy pressure on different regions of the surface.
Such air pressures are known as pressure centers if they are limited to a certain region or area of the earth's surface.
The light and heavy pressures of air formed on the earth's surface are in the form of pressure centers in its early stages.
Then, when favorable conditions prevail, they extend east-west.
Air pressure belts are formed.
Thus, pressure belts are centers arranged in almost the same latitudinal boundary and with uniform pressure.
In the latitudinal east-west belt there are more high pressure regions. It is called heavy pressure belt.
In the east-west belt there are more light pressure regions.
This is called a low pressure belt or a low pressure belt.
This type of strap will be clear from the figure.

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Question 35 Marks

Explain illustratively the Sea and Land Breezes.

Answer

$1.$ Sea Breeze:

Land areas heat up faster than oceans during the day.
This creates light pressure on land and heavy pressure on oceans.
To make up for the light pressure on the land areas, the wind blows from the oceans to the land areas during the day, which is called ocean waves.

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Question 45 Marks

What is meant by wind $?$ State the types of wind and give information about Monsoon winds.

Answer

Wind is the wind that moves in the direction of the horizon.
The types of wind are as follows.

$(1)$ Permanent winds
$(1)$ Easterly winds $(2)$ westerly winds $(3)$ polar winds.
$(2)$ Seasonal winds
$(1)$ Summer seasonal winds $(2)$ Winter seasonal winds $(3)$ Local winds.

Sea and land waves $(2)$ Mountain and valley waves $(3)$ Chinook and Foen $(4)$ Lu and Norvester $(5)$ Mistral and Bora $(6)$ Sirocco and Hermeton
Seasonal winds: The direction of winds in some regions of the earth's surface has changed with the seasons.
Thus, winds that change direction according to the seasons are called seasonal winds.
India, Pakistan, Bangladesh, Myanmar, Sri Lanka, China, Korea, Japan, Taiwan etc. are the major countries experiencing seasonal winds.
Apart from this, northern Australia, Madagascar, Nigeria, Ghana, and the southern part of the US are also slightly affected by the monsoon.
Seasonal winds can be divided into two parts.

$1.$ Summer-Monsoon Wind:-

In summer, a low pressure develops over the north-western landmass due to high temperature.
Over the water mass of Arabian Sea and Bay of Bengal, low temperature results in the development of high pressure.
Under these circumstances, the Easterlies Trade Winds from the south of equator serge ahead towards forth to maintain the pressure equilibrium.
After crossing equator these winds change their direction and become South-West monsoon winds.
These are known as Summer Monsoon Winds.
As these winds happen to blow over vast water mass they contain abundant moisture and so give heavy rains near coastal area.
Heavy rainfall occurs on the windward side of the mountains which obstruct these winds, e.g. due to Western

Ghats, Malabar’s on the western coast gets more than $200\ cm$ rainfall.

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Question 55 Marks

What is wind? Give information about permanent winds by stating the types of winds.

Answer

Wind is the wind that moves in the direction of the horizon.
The types of wind are as follows.

$(1)$ Permanent winds.
$(1)$ East winds $(2)$ Westerly winds $(3)$ Polar winds.
$(2)$ Seasonal winds.
$(1)$ Summer seasonal winds $(2)$ Winter seasonal winds $(3)$ Local winds.
Sea and land waves $(2)$ Mountain and valley waves $(3)$ Chinook and Foen $(4)$ Heat and Norvester $(5)$ Mistral and Bora $(6)$ Sirocco and Hermeton.
$1.$ Permanent winds:

This wind is known as permanent wind as it blows continuously from one direction for many months.
These winds cover many large areas of the earth, moving from the high pressure belt to the light pressure belt.
It is also called planetary wind.
There are three types of winds.

$(1)$ East winds:

These winds are blow in the tropics from the equatorial high pressure belt to the equatorial low pressure belt in both the hemispheres.
The east wind is constantly blowing in one direction at a steady speed.
These winds blow from the east with a slight twist due to the rotational speed of the earth.
Hence these winds are called east winds.
These winds have been used for sea trade in the past as they are moving at a steady pace. Hence they are known as “commercial winds”.
According to Feral's law, the wind blows to its right in the northern hemisphere. It is seen coming from the northeast corner.
That is why he calls it "northeast commercial winds".
In the Southern Hemisphere, it is known as a fiery trade wind because it blows from the angle of fire.
As these winds get warmer towards warmer regions, they increase their moisture storage capacity, but decrease their rainfall capacity.

$(2)$ Westerly winds:

These winds are in both hemispheres from the equatorial high pressure belt to the polar low pressure belt in the temperate zone regions.
These winds blow from southwest in the northern hemisphere, north-east and northwest in the southern hemisphere to the south-east.
So in the northern hemisphere it is called southwest westerly wind and in the southern hemisphere it is called northwest westerly wind.
It is called "counter-trade wind" as the direction of westerly winds is opposite to the direction of commercial winds.
The winds blow from the warmer regions to the colder regions and bring perennial rains to the western regions of Europe, Canada, Chile, etc. on the west coast of the continents.

$(3)$ Polar winds:

These winds are y in both hemispheres from polar high pressure belt to polar low grid belt.
Thus the wind from the poles is known as the polar wind.
Polar winds blow from northeast to southwest in the northern hemisphere and from northeast to southwest in the southern hemisphere.
These winds coming from the poles are extremely cold.
As a result, the cold wave recedes in the regions through which it passes.
The ability to retain moisture in these cold winds is not special so these winds do not give rain.
Cyclonic and counter-cyclonic conditions are created when cold winds from the poles converge with warm winds relative to the temperate zone.

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Question 65 Marks

Winter Monsoon Winds $($North$-$East Monsoon Winds$):$

Answer

Some Asiatic landmass cools faster in winter.
So high pressure pockets develop here.
At this time the nearer water mass is a little warmer, so low pressure pockets develop there.
As a result, winds blow from landmass towards oceans.
These winds blow over South and South-Asian countries from north-east direction, so these are called North-East Monsoon Winds.
As these winds blow over from landmass, they contain less moisture and do not give much rain.

When some of their branches pass over the ocean, they hold moisture.

December January, the North-East Monsoon winds shower most of the annual rains over Coromandel

Coast on the eastern sea coast of India and to northern parts of Sri Lanka.

Rains caused by these monsoonal winds is irregular and uncertain.
The rainy season starts earlier sometimes and ends also earlier.
It starts late sometimes but ends earlier.
Sometimes these monsoon winds cause very heavy rains or occasionally cause droughts.
That is why the farmers of this region believe in fate.
In India, monsoon winds are responsible for uncertainty of rainfall.

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