Lecture 3: ATMOSPHERE (Outline)
| Basic Structures and Dynamics | |
| General Circulation in the Troposphere | |
| General Circulation in the Stratosphere |
Thermal Energy to Kinetic Energy
Balance of Force in the Horizontal
How Does Coriolis Force Affect Wind Motion?
Frictional Effect on Surface Flow
Single-Cell Model:
Explains Why There are Tropical Easterlies
Breakdown of the Single Cell è Three-Cell Model
Atmospheric Circulation: Zonal-mean Views
Thermally Direct/Indirect Cells
| Thermally Direct Cells (Hadley and Polar Cells) | |
| Both cells have their rising branches over warm temperature zones and sinking braches over the cold temperature zone. Both cells directly convert thermal energy to kinetic energy. | |
| Thermally Indirect Cell (Ferrel Cell) | |
| This cell rises over cold temperature zone and sinks over warm temperature zone. The cell is not driven by thermal forcing but driven by eddy (weather systems) forcing. |
Is the Three-Cell Model Realistic?
| Yes and No! | |
| (Due to sea-land contrast and topography) | |
| Yes: the three-cell model explains reasonably well the surface wind distribution in the atmosphere. | |
| No: the three-cell model can not explain the circulation pattern in the upper troposphere. (planetary wave motions are important here.) |
Global Distribution of Deserts
Upper Tropospheric Circulation
Subtropical and Polar Jet Streams
| ¶U/¶z µ ¶T/¶y | |
| The vertical shear of zonal wind is related to the latitudinal gradient of temperature. | |
| Jet streams usually are formed above baroclinic zone (such as the polar front). |
Jet Streams Near the Western US
Walker Circulation and Ocean Temperature
Monsoon: Another Sea/Land-Related Circulation of the Atmosphere
Stratosphere: Circulation and Temperature
Climate Variations in Stratosphere
| Sudden Warming: in Northern Pole | |
| Ozone Hole: in Southern Pole |
| Every other year or so the normal winter pattern of a cold polar stratosphere with a westerly vortex is interrupted in the middle winter. | |
| The polar vortex can completely disappear for a period of a few weeks. | |
| During the sudden warming period, the stratospheric temperatures can rise as much as 40°K in a few days! |
| Planetary-scale waves propagating from the troposphere (produced by big mountains) into the stratosphere. | |
| Those waves interact with the polar vortex to break down the polar vortex. | |
| There are no big mountains in the Southern Hemisphere to produce planetary-scale waves. | |
| No sudden warming in the southern polar vortex. |