Major hot deserts in northern hemisphere are located between 20-30 degree north and on the western side of the continents. Why?

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 INDEX-

1. Narration
2. Causing Factors
3. Answer Structure
4. Question
5. Ideal Answer

Narration- 

           

In the first stage-

1. If we go to the study of heat balance over the earth we find that -
2. due to the Geoid shape of the earth we have a latitude heat imbalance over Earth 
3. where up to 35 to 40 degrees north and South latitude earth has a heat surplus zone, and 
4. beyond that is having a deficient zone.

In the second stage 

1. if we study the relationship between temperature and pressure 
2. we know that high temperature forms a low air pressure zone, which simply means the vertical air currents are higher 
3. resulted in the expansion of the year causing lower per unit weight of air.

Against it -

1. whenever we have comparatively a lower temperature the reverse happens and we have a higher pressure zone.

Now-

1. overheat surplus zone in the middle of it, 5 Degrees N/S of the equator, we have an equatorial low-pressure belt, and 
2. at the margin of this heat surplus zone we have a subtropical high pressure belt.

   

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Now if we study the definition of wind- 

1. we came to know the horizontal movement of air 
2. from the high pressure to the low pressure, 
3. within a definite direction, is known as wind.

It simply means -

1. from the subtropical high-pressure belts we have wind movement from the equatorial low-pressure belt.

Now go to study the rotation movement of Earth-

          

1. we know due to the Earth's rotation 
2. we have day and night on the earth second 
3. it causes equal distribution of heat over Earth, but, 
4. in the context of our answer  the most important factors that cause the Coriolis force effect over the Earth 
5. that means during horizontal movement over the earth's surface 
6. we have deflection in moving direction due to different rotational speeds over the Earth 
7. which is caused by the geoid shape of the earth.

So,-

1. when the wind moves from the subtropical high-pressure belt towards the equatorial low-pressure belt 
2. due to the Coriolis force effect 
3. there is a deflection in the wind direction, and 
4. as a result of that we have the tropical easterly wind movement, 
5. also known as the trade winds or doldrums.

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Now, go for the Atlas mapping study so we will be finding that- 

1. every continent is surrounded by the ocean water body 
2. that means when the wind makes its entry it enters from the eastern margin of the continent in the tropical zone.
3. during this movement wind has friction over the Ocean surface and 
4. we are aware of the fact there is a "temperature gradient" over the Ocean surface and terrestrial land surface 
5. in which the ocean surface maintains a lower temperature means higher pressure, and 
6. because the wind movement is from high pressure towards low pressure, so 
7. finally these Easterly winds move from the ocean surface towards the continent's eastern margin.

Entry from the eastern margin means-

       

1. the eastern margin receives a high amount of precipitation, and 
2. in the gradual advancement the amount of precipitation gradually decreases, 
3. so, by the moment wind reaches the Western margin of the continent it is having a significant slash in the amount of precipitation.

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Now look closely at the ocean current movements in your atlas and you will find-

         

1. the cold ocean current movement is on the Western margin of the continent, 
2. so continents have cold ocean currents on the Western margin means continents' west coast maintains a lower temperature which means high pressure which results in the contraction of air, and 
3. sinking air current means no condensation process.

In combination dry wind movement over to the Western margins and high pressure over the Western coast cause very low precipitation.

     

In the definition of the desert-

     "the single point definition is the area which receives the annual precipitation less than 25 CM would simply be declared as desert."

1. In subpolar and the polar region the precipitation is in the form of snowfall which means the land is dry, and 
2. In the sub-tropical region, in the belt of 20-30 Degrees N/S altitudes, the rain form precipitation is less than 25 cm 
3. again the land is dry and this type of dry land is known as desert.

So,-

1. in the context of the above explanation 
2. this question is a physical geography question 
3. which is very straightforward in its nature 
4. simply asking why we have the hot desert on the Western margin of the continent between 20 to 30° latitude.

Now in the last terms-

1. why between 20 to 30° North and South attitude?? 
2. because over this latitude position, we have the formation of high-pressure belt 
3. simply means the air is not expanding, but, against it actually contracting 
4. so it is a downward air movement that subsides or sinks with dry conditions over these latitudes.

So, with the combination of all these factors we have the warm tropical desert between 20 to 30 degrees north and South latitude over the Western margin of the continent.

 

Note-

       And how the presence of these deserts have what affects the given region's weather (मौसम) we will discuss in coming blogs.

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Answer Structure-

1. Definition
2. Diagram
3. body- With the explanation of three combined factors
4. Reasons explained in conclusion

Question-

        Major hot deserts in the northern hemisphere are located between 20-30 degrees north and on the western side of the continents. Why?

Ideal Answer- 

The formation of the subtropical hot desert is a combination of three (03) factors –

     

1. one latitudinal heat imbalance, 
2. second the Easterly wind movement over continents, and 
3. third emergence of cold ocean current on the West coast of continents.

       

We know due to latitude the heat imbalance on 20 - 30 degree North and South latitudes formation of high pressure belt means less amount of rainfall precipitation. 

In conjunction with this,-

1. Easterly movement causes higher rainfall on the east margin causing the presence of rainforests, 
2. then moderate in the middle so the presence of savannah types grassland and, 
3. in last,  on the Western margin the lesser precipitation.
4. Along with it, the presence of a cold ocean current on the Western coast causes the formation of high pressure again resulting in less condensation and less precipitation.

The definition of desert says, "area receiving annual rainfall precipitation less than 25 CM", in the context of that above mention 03 factors cause, on the Western margin of continent, annual precipitation less than 25 cm so presence of warm subtropical hot desert on the west margin between 20 to 30 degree North latitude of continent.

Thanks.