Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Atmospheric Motion Pressure Gradient Force- The difference in atmospheric pressure will cause air to move from high pressure to low pressure. This is something like water flowing down hill or seeking its own level. Coriolis Force- This is a deflection of the wind caused by the spinning earth. The deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The result is that air moving out of a high pressure cell or into a low pressure cell will develop a rotation. Gravity- The principal effect of gravity can be seen in cold air drainage. As the earth’s surface cools at night, cold air will flow down hill. Thus the valleys are always cooler than the hillsides above them. Friction - Friction is only important for air in contact with the earth’s surface in the planetary boundary layer (PBL). This is about 1 km thick. The principal effects are in rough terrain, forests, and downtown urban canyons. As the air rises it cools and so slows down. Air pushed away by rising column Convection cell Hot air expands becomes less dense and rises Hot Cool air sinks. As it hits the ground it spread out. To the left to replace the rising air Cold Hadley Cell Circulation and the Trade Winds Prevailing Wind Belts of Earth. The earth is encircled by several broad prevailing wind belts, which are separated by narrower regions of either subsidence or ascent. The direction and location of these wind belts are determined by solar radiation and the rotation of the earth. The three primary circulation cells are known as the: Hadley cell; Ferrel cell; and Polar cell. On or near the equator, where average solar radiation is greatest, air is warmed at the surface and rises. This creates a band of low air pressure, centered on the equator known as the intertropical convergence zone (ITCZ). The Intertropical Convergence Zone draws in surface air from the subtropics. When this subtropical air reaches the equator, it rises into the upper atmosphere because of convergence and convection. It attains a maximum vertical altitude of about 14 kilometers (top of the troposphere), and then begins flowing horizontally to the North and South Poles. This rising air comprises one segment of a circulation pattern called the Hadley Cell (see diagram below). The Hadley cell eventually returns air to the surface of the earth, near 30 deg N and S. The descending portion of the Hadley Cell produces a band of high air pressure at these latitudes called the subtropical high. From this zone, the surface air travels in two directions. Winds are generated between the subtropical high and the equatorial band of low pressure (ITCZ), as air moves from high surface pressure toward low surface pressure. These winds are deflected from east to west as they travel toward the equator by the coriolis force, and are called the Trade Winds or the Tropical Easterlies. The other portion of the surface air moves towards the poles from the subtropical high zone. This air is also deflected by the Coriolis force, producing the Westerlies. Jet streams and Rossby waves Jet streams are fast flowing, narrow air currents found at the tropopause, the transition between the troposphere (where temperature decreases with height) and the stratosphere (where temperature increases with height) They are located at 10-15 kilometers above the surface of the Earth. They form near boundaries of adjacent air masses with significant differences in temperature, such as the polar region and the warmer air to the south. The path of the jet typically has a meandering shape, and these meanders are one manifestation of Rossby waves. Rossby waves propagate westward with respect to the flow in which they are embedded, which translates to a slower eastward migration across the globe than smaller scale short wave troughs. The major jet streams are westerly winds (flowing west to east) in the Northern Hemisphere. During the summer, easterly jets can form in tropical regions, typically in a region where dry air encounters more humid air at high altitudes. Low level jets can form wherever low level winds are squeezed. Questions 1. 2. 3. 4. 5. 6. 7. 8. 9. what is Coriolis Force How Gravity affect atmospheric motion How does Friction affect atmospheric motion How does Gravity Pressure affect atmospheric motion Explain Jet streams How does the three cell model work Draw the three cell model What are trade winds Explain Rossby waves Exam questions (a) What are jet streams? (b) Examine the factors influencing the global pattern of surface and upper air circulation. a) Outline the main causes of air movement. (b) Discuss the application and limitations of the tri-cellular model.