Atmospheric Circulation And Weather Systems

The air pressure decreases by 1mb for every 10 m increase in height. Since, 1000m/10m=100 units, hence, the pressure at 1000m will be 1000-100=900mb.

Other options are hence, incorrect.

As shown in the figure,

A is correct. ITCZ is located near the equator, where the trade winds from the hemispheres meet.

B is incorrect. The Tropic of Cancer is dominated by Subtropical Highs.

C is incorrect. Tropic of Capricorn is also dominated by Sub-Tropical Highs.

D is incorrect. Arctic circle is dominated by Polar Vortex.

The direction of wind is influenced by the Coriolis force, caused by the rotation of earth on its axis. This force deflects the winds towards the right in northern hemisphere, which leads to anti-clockwise circulation around a low-pressure zone.

All other options are incorrect.

Air masses are formed when the air above huge homogeneous areas acquires the characteristics of the area. This leads to the air having little horizontal variations in form. Accordingly,

C is correct, as it is a cold, large and homogeneous mass of land.

A is incorrect, as the size of the forested areas are not large enough to create air-mass

B is incorrect, as Himalayas do not constitute a homogeneous platform.

D is incorrect due to regional variations across the Deccan Plateau.

(i) The unit used to measure air pressure is BAR. More commonly, mb or milli-bar is used to report the figures.

The pressure on weather maps is reported at sea level due to the gravitational effects. At sea level, the air is denser and exerts higher pressure.

(ii) The winds in the northern hemisphere are characterised as north-easterlies because:

• North: The wind follows the pressure gradient. It originates in STH and flows towards the equator.(N->S)

• Easterlies: Due to the rotation effect of Earth (Coriolis Force), the winds get deflected to the right in the Northern Hemisphere. Hence, they seem to originate in the east and flow westwards.

(iii) In a situation where isobars are parallel to each other and are generally straight, the inwards pressure gradient force is balanced out by outwards Coriolis force. Consequently, the winds flow parallel to the isobaric lines. This is known as geotropic winds.

(iv) Land and Sea breeze constitute the local wind systems in coastal areas. This is produced by differential heating of land and sea. As land heats and cools faster than the sea, there is a reversal of direction of the breeze from day to night. During the day, sea breeze blows towards land and at night, the land breeze blows towards sea.

(i) The speed and direction of the winds is influenced primarily by 3 factors:

• Pressure Gradient Force: the Pressure gradient forces are stronger in areas where the difference in pressure from one isobar to another is higher, this exerts and inward force along high pressure areas and outward force along low pressure areas. It influences the

• Frictional Forces: The frictional forces affect the velocity of wind. These forces are strongest along the surface and decrease with increasing elevation, as the air at the surface is denser and more prone to viscous effects. About 3km above sea level, the effect of friction is negligible.

• Coriolis Force: The rotation of the earth around its axis exerts a force on the winds. It acts perpendicular to the isobars, and deflects the wind towards right in northern Hemisphere, and towards left in Southern Hemisphere.

(ii)

The possible reasons for the formation of high pressure belts over 30 degree latitudes on both sides are:

• The convective currents along the equator, caused by high insolation, give rise to a low pressure area along the ITCZ. The air from this region rises upwards, and moves towards the poles. Hence, there is an accumulation of air along the 30 degree latitudes. This air sinks down and creates STH. This sinking is caused by the cooling of air.

(iii) Tropical Cyclones originate over the tropical seas and oceans because they meet all the conditions necessary for their development:

• Large surface areas and temperatures over 27 degrees

• Influence of Coriolis Force

• Minimal variations in vertical wind speed.

• Presence of weak low pressure area.

• Upper divergence above sea level system.

Also, the supply of moisture from the sea strengthens the storm continuously.

Torrential rains and high velocity winds are found along the “EYE-WALL” of the storm. This is so because the central area or the eye is the area of subsiding warm air, and the winds circulate around this area, causing torrential rain. There are outward emanating clouds and rain bands, which extend up to 600-1200 km from the eye.

TV REPORTS

NEWSPAPER REPORTS

This satellite image shows the cloudiness over the Peninsula on 29^th June, 2019.

The clouds extend from north-east to south-west direction, indicating the south-west monsoons that prevail over the subcontinent during June-July.

TV forecasts are generally real-time forecasts, which talk about impending cyclones, hurricanes and wind-storms- they warn people regarding these disasters and ask them to evacuate their houses. This happens alongside marked predictions, which is similar to the role played by newspapers.

I compared the forecasts on online platforms with the true weather conditions. There was a high degree of accuracy in the forecast, with greater accuracy in predicting rainfall than measuring temperatures. With advanced satellite technologies, it is easier to predict the incoming winds, and consequently we can detect the precipitation figures with greater precision.