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# Bay Area Earth Science Institute BAESI - PowerPoint PPT Presentation

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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Presentation Transcript

Pressure

San Jose State University,

January 24, 2004

http://www.met.sjsu.edu/baesi/

Weather and Climate

Q: What causes the weather to change?

We must analyse the predominant forces in the atmosphere, namely:

gravity

rotation of the earth

friction

Principle forces

Weather and Climate

• Measured in millibars (mb) or inches of mercury

• Surface Pressure:

Sea level pressure:

1012 mb or

29.9 in of mercury

Weather and Climate

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

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

Weather and Climate

Weather and Climate

• 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

• 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

Northern

Hemisphere

Weather and Climate