Presentation on theme: "Chapter 10. General Circulation of the Atmosphere General refers to the average air flow, actual winds will vary considerably. Average conditions help."— Presentation transcript:
General Circulation of the Atmosphere General refers to the average air flow, actual winds will vary considerably. Average conditions help identify driving forces. The basic cause of the general circulation is unequal heating of the Earths surface Warm air is transferred from the Tropics to the Poles Cool air is transferred from the Poles to the Tropics
General Circulation of the Atmosphere Single Cell Model Assume 1. uniform water surface 2. Sun always directly overhead the Equator 3. Earth does not rotate Result: huge thermally direct convection cell rising at equator and sinking at poles(Hadley) Three Cell Model Allow earth to spin = three cells (Hadley, Ferrell, Polar) Alternating belts of pressure starting with L at Equator (L H L H) (Eq, Sub Trop, Sub Polar, Polar) Alternating belts of wind with NE just North of Equator
General Circulation of the Atmosphere Average Surface Wind and Pressure: The Real World Semi-permanent high and lows Northern vs. Southern Hemisphere Major features shift seasonally with the high sun North in July South in December
General Circulation of the Atmosphere General Circulation and Precipitation Patterns Rain where air rises (low pressure) Less rain where air sinks (high pressure) Average Wind Flow and Pressure Patterns Aloft North-South temperature and pressure gradient at high altitudes creates West-East winds, particularly at mid to high latitudes.
Jet Streams kt winds at 10-15km, thousands of km long, several 100 km wide and a few km thick (polar and subtropical) Observations: Dishpan Experiment Illustrates waves, with trough and ridge, develops in a rotating pan with heat on the exterior and cold at the center.
Jet Streams Polar and Subtropical Jet Established by steep temperature and pressure gradients between circulation cells. Between tropical-mid-latitude cell (subtropical) and mid-latitude-polar cell (polar) Gradients greatest at polar jet Topic: Momentum Low-latitudes: atmosphere gains momentum High-latitudes: atmosphere losses momentum Conservation of Momentum
Jet Streams Other Jet Streams Tropical easterly jet stream Low-level jet (nocturnal) Polar night jet streams