AOS 100/101 Spring 201t8 HOMEWORK #6 (Due Fri. April 20) Please provide concise,

Question

AOS 100/101 Spring 201t8 HOMEWORK #6 (Due Fri. April 20) Please provide concise, grammatically correct, neatly written answers to the following questions. All questions can be answered in, at most, a few sentences. Don't forget to write your name on the paper!!! NAME: 1)A nearly continuous line of thunderstorms rings the globe near the equator. This feature is known as the Inter-Tropical Convergence Zone (ITCZ). The thunderstorms are fed by low-level inflow toward the equator from both hemispheres and they exhaust upper-level outflow toward the poles in both hemispheres as shown in Fig. 1a below. Explain why, in the face of the Earth's rotation, this circulation produces low-level winds from the east and upper-level winds from the west as shown in Fig. 1b (10 pts) Outflow Outflow 200 hPa H - Inflow 0 LInflow hPa 30 N 30e s Upper-level westerly winds 30 N Lower-level easterly winds Lower-level easterly winds 30os Upper- level westerly winds FIG. 1

Explanation / Answer

1. Along the belt of Intertropical Tropical Convergence Zone, the warm moist air masses move towards the equator under the influence of the Coriolis force. An apparent force arising due to the rotation of the Earth turns the winds towards the right in the Northern Hemisphere and towards the left in the Southern Hemisphere. The low-level winds thus move towards the west. The air masses then converge and rise vertically. They do so under the influence of Coriolis force which forces the air to move towards the east. So the upper-level winds are westerly.

2. The effect of thermal wind is important when the vertical variation of geostrophic wind is considered. At lower latitudes, such as in New Orleans, the surface temperature is higher than in higher latitudes, e.g. Minnesota. This causes a horizontal temperature gradient and a resulting vertical wind shear. Along the 500 mb isobar, the geostrophic wind is at a higher altitude over New Orleans due to vertical expansion of air mass. The velocity of geostrophic wind moving parallel to 500 mb isobar decreases as the height of 500 mb level moves down due to the influence of subsidence in a high-pressure zone. Thus, 500 mb geostrophic wind is larger at LA than MN.

3. The geostrophic wind should be blowing northeasterly over Madison, but the isobars are unevenly spaced and there is an influence of centrifugal force. So, the velocity of the geostrophic wind reduces and the wind actually becomes gradient wind blowing at a speed less than geostrophic wind. While walking towards Southwest, the low pressure should be towards the left, according to the Buys Ballot's Law. Thus, your path is to the right of the geostrophic wind direction.   

4. Since pressure gradient force in the 1 km layer is constant, it will not be balanced by the combined effects of Coriolis force and frictional forces. With increasing height, the friction would decrease, and the Coriolis force would dominate resulting in the counter-clockwise motion of the rising air.

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