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Bay Area Earth Science Institute (BAESI). Pressure San Jose State University, January 24, 2004 http://www.met.sjsu.edu/baesi/. *. Q: What drives the weather in the atmosphere? Q: What causes the weather to change? We must analyse the predominant forces in the atmosphere, namely:
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Bay Area Earth Science Institute (BAESI) Pressure San Jose State University, January 24, 2004 http://www.met.sjsu.edu/baesi/ Weather and Climate
Q: What drives the weather in the atmosphere? Q: What causes the weather to change? We must analyse the predominant forces in the atmosphere, namely: pressure and pressure gradients, gravity rotation of the earth friction Principle forces Weather and Climate
Pressure • Measured in millibars (mb) or inches of mercury • Surface Pressure: Sea level pressure: 1012 mb or 29.9 in of mercury Weather and Climate
Temperature change Density change Formally, the equation of state describes this relationship: p=RT p-Pressure (Pa) - density (g m-3) R - Gas Constant (287 J K-1 kg-1) T - Temperature (K) What causes pressure to change? Weather and Climate
Determines the direction and speed of winds Can help explain general circulation of atmosphere. General guidelines: High pressure: clear skies/fine weather Low pressure: cloudy skies/changeable weather Why is this? Pressure Differences Weather and Climate
Pressure Gradient Force Weather and Climate
Coriolis Force Weather and Climate
The rotation of the Earth • Rockets, migrating birds, and large scale weather systems are all deflected due to the rotation of the Earth. • The Earth’s rotation causes • Rotational movement that deflects the winds. • The Coriolis Force is the name of this rotational force that deflects motion. Weather and Climate
Coriolis Force • Affects direction, not speed of object • Maximum at the poles • Zero at the equator Always acts to the right of the motion in Northern Hemisphere. Always acts to the left of the motion in the Southern Hemisphere. Weather and Climate
Geostrophic Wind Northern Hemisphere Weather and Climate