ATOMOSPERIC PRESSURE, WIND & CIRCULATION

. INTRODUCTION

Important because:

• pressure patterns drive wind patterns which in turn drive oceanic circulation patterns

  • atmospheric & oceanic circulation: major mechanisms for transferring heat energy around earth

  • impacts temperature patterns

• pressure & circulation patterns impact precipitation patterns

Global Wind Speed Patterns

Learning Outcomes

By the end of this unit you should be able to:

• describe the impact of pressure, density, and Coriolis on surface winds, and illustrate the horizontal and vertical wind flow patterns in cyclones and anticyclones;

• diagram global pressure and wind patterns and describe the seasonal shift in global pressure and wind;

• distinguish land breezes from sea breezes, and winter monsoon winds from summer monsoon winds, and explain when and why they occur;

• diagram the large scale ocean circulation patterns in the northern and southern Atlantic and Pacific oceans and relate oceanic circulation patterns to atmospheric circulation patterns.

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. DENSITY AND PRESSURE

Atmospheric pressure

• force exerted by the atmosphere on a surface

• measured in millibars or hectopascals (1 mb = 1 hPa); isobars

• pressure differences cause wind to blow

  • wind direction: wind blows from high to low pressure

  • wind speed: the steeper the pressure gradient, the faster the wind speed

• determined by density

Density

• number of molecules per some volume of space

• air temperature impacts density & thus pressure

  • differences in temperature create differences in pressure

  • warm air less dense than cold air at the same altitude

  • warm air rises; cold air sinks

• altitude impacts density & thus pressure

  • as altitude increases, density decreases

  • air at higher altitudes always less dense than air at lower altitudes regardless of temperature

• vertical air flow impacts density & thus pressure

  • rising air always associated with low pressure regardless of temperature

  • sinking air always associated with high pressure regardless of temperature

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. CORIOLIS

• deflection due to rotation of earth

• deflection to right in northern hemisphere when looking down the pressure gradient

• deflection to left in southern hemisphere when looking down the pressure gradient

• magnitude of deflection greatest at poles, least at equator.

  GLOBAL PRESSURE AND WIND PATTERNS

  

  Intertropical Convergence Zone (~0-10^o)

  • winds blow into low pressure regions

  • Trade winds

  Subtropical high pressure cells (~20-40^o)

  • winds blow out of high pressure cells

  • Trade Winds toward Equator

  • Westerlies toward Poles

  Subpolar low & Polar front (~40-70^o)

  • winds blow into low pressure region

  • Westerlies

  • Polar Easterlies

  Polar high

  • winds blow out of high pressure cells

  • Polar Easterlies

  
  

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  . LOCAL AND REGIONAL WINDS

  Land and sea breezes

  Sea breeze

  Land breeze

  Monsoon winds in Southeast Asia  

  Winter monsoon

  Summer monsoon

  
   

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  . OCEANIC CIRCULATION PATTERNS   

  
  

  • East coasts: warm ocean currents

  • West coasts: cold ocean currents