5) a: With reference to the thermal wind relationship and basic properties of th

Question

5) a: With reference to the thermal wind relationship and basic properties of the Earth's radiation budget, explain why the mean tropospheric vertical wind shear is westerly on Earth. B: using a simple illustration, explain why the direction of this vertical shear is the same in both the Northern and Southern Hemispheres. 5) a: With reference to the thermal wind relationship and basic properties of the Earth's radiation budget, explain why the mean tropospheric vertical wind shear is westerly on Earth. B: using a simple illustration, explain why the direction of this vertical shear is the same in both the Northern and Southern Hemispheres. B: using a simple illustration, explain why the direction of this vertical shear is the same in both the Northern and Southern Hemispheres.

Explanation / Answer

Strong westerly winds blow in the upper troposphere and lower stratosphere of the midlatitudes. The thermal wind tells the jet stream is strongest in the upper half of the troposphere, which is the atmospheric layer extending from the surface of the planet up to a height of 15 km.Vertical wind shear is the second critical factor in the determination of thunderstorm type and potential storm severity. Vertical shear, or the change of winds with height, interacts dynamically with thunderstorms to enhance vertical draft strengths.There are connections between pole-to-equator energy transport and the relative angular momentum of the trophosphere.As angular momentum is being continously transferred between earth and atmosphere in the region of tropical surface easterlies,the relative angular momentum of the atmosphere increases with rate of overtuning of the tropical hadley cells.The westerly that are formed by this circulation are in the high trophosphere over the subtropics and mid latitudes.The strengthened westerly winds also increase the strength of vertical wind shear over these latitudes.Atmosphere creates a thermodynamic balance between vertical wind shear and the horizontal temperature gradient.Excess solar radiation and convective overtuning combine to provide energy that warm the tropics,a radiation deficit tends to cool the trophosphere.The thermodynamic balance is relevant to the poleward energy tranport and hence the trophospheric vertical wind shear is westerly on earth.

b.  The circulation of wind in the atmosphere is driven by the rotation of the earth and the incoming energy from the sun. Wind circulates in each hemisphere in three distinct cells which help transport energy and heat from the equator to the poles. The winds are driven by the energy from the sun at the surface as warm air rises and colder air sinks.Because of the curvature of the earth, the most direct rays of the sun strike the earth in the vicinity of the equator resulting in the greatest concentration of heat, the largest possible amount of radiation, and the maximum heating of the atmosphere in this area of the earth. At the same time, the sun's rays strike the earth at the poles at a very oblique angle, resulting in a much lower concentration of heat and much less radiation so that there is, in fact, very little heating of the atmosphere over the poles and consequently very cold temperatures.

Warm air rises until it reaches a certain height at which it starts to spill over into surrounding areas. At the poles, the cold dense air sinks. Air from the upper levels of the atmosphere flows in on top of it increasing the weight and creating an area of high pressure at the poles.The air that rises at the equator does not flow directly to the poles. Due to the rotation of the earth, there is a build up of air at about 30° north latitude. (The same phenomenon occurs in the Southern Hemisphere). Some of the air sinks, causing a belt of high-pressure at this latitude.hence the direction of this vertical shear is same in both the northern and southern hemispheres.

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