EVAT 554 OCEAN-ATMOSPHERE DYNAMICS

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Presentation transcript:

EVAT 554 OCEAN-ATMOSPHERE DYNAMICS LECTURE 9 LARGE-SCALE ATMOSPHERIC CIRCULATION (CONT) (Reference: Peixoto & Oort, Chapter 3,7)

HADLEY CELL CIRCULATION THERMALLY-DRIVEN CIRCULATION Approximate circulation as steady, linear, two-dimensional (meridional-vertical plane) HADLEY CELL CIRCULATION Pole Equator THERMALLY-DIRECT CIRCULATION FOR AN IDEALIZED NON-ROTATING EARTH

WHAT ABOUT EXTRATROPICS? THERMALLY-DRIVEN CIRCULATION Approximate circulation as steady, linear, two-dimensional (meridional-vertical plane) WHAT ABOUT EXTRATROPICS? Pole Equator THERMALLY-DIRECT CIRCULATION FOR AN IDEALIZED NON-ROTATING EARTH

THERMALLY-DIRECT CIRCULATION Descending Air High Pressure Ascending Air Low THERMALLY-DIRECT CIRCULATION COLD WARM Descending Air High Pressure Ascending Air Low THERMALLY INDIRECT CIRCULATION WARM COLD

MERIDIONAL CIRCULATION PATTERNS HADLEY CELLS ARE THERMALLY DIRECT CIRCULATIONS… As are the (weak) polar cells 30 60 N S Latitude High Low Surface Pressure Systems ‘FERREL CELLS’ ARE THERMALLY-INDIRECT CIRCULATIONS

HORIZONTAL ATMOSPHERIC CIRCULATION Cloud and Precipitation Occur in Areas of Surface Convergence and Rising Motion

GLOBAL ATMOSPHERIC CIRCULATION January July There are important seasonal changes in the semi-permanent features of the surface atmospheric circulation ITCZ migrates with Sun, but lags it...

GLOBAL ATMOSPHERIC CIRCULATION January July There are corresponding seasonal changes in the upper air (e.g. 500 mb) circulation

GLOBAL ATMOSPHERIC CIRCULATION Surface Pressure Systems Vertical Atmospheric Circulation 30 60 N S Latitude Low High Low High Low Surface Pressure Systems Zonally-averaged ps

GLOBAL ATMOSPHERIC CIRCULATION Surface Pressure Systems Westerly 30 60 N S Easterly Surface Wind Systems Surface Pressure Systems Zonally-averaged ps

GLOBAL ATMOSPHERIC CIRCULATION east-west component of wind at surface consistent with Geostrophic Balance  (westerlies)  (easterlies) L’Hopital’s rule Why should there be any easterlies here??

GLOBAL ATMOSPHERIC CIRCULATION Geostrophic Balance Hydrostatic Balance Combine these THERMAL WIND

THERMAL WIND THERMAL WIND

MERIDIONAL-VERTICAL CIRCULATION Continuity Steady state Streamfunction