What is Air Pressure The pressure exerted by

What is Air Pressure? © The pressure exerted by the weight of air above © Measured in millibars (mb) or Mercury (Hg) for weather maps © Shown as Isobars on the maps

Wind • Air flows from areas of high pressure (H) to areas of lower pressure (L).

Global Winds • Trade winds – Two belts of winds that blow almost constantly from east to west • Westerlies – Dominate west to east motion of the atmosphere (Jet Stream occurs here) • Polar easterlies – Winds that blow east to west • Polar front – Interaction of warm and cool air masses produces a stormy belt

How do we get pressure differences on Earth? © The unequal heating of earth’s surface by the sun

Isobars • Closely spaced isobars: indicate a steep pressure gradient and high winds. • Widely spaced isobars: indicate a weak pressure gradient and light winds.

Measuring Wind • Direction – Labeled by the direction from which they blow – Ex: winds blowing from the Southeast. – Tool: Wind Vane

Wind Speed – Anemometer • Measures how fast wind is blowing

Jet Streams © Jet streams are fast-moving rivers of air © Speed: 120 and 240 kilometers per hour © Direction: West-to -east direction.

Air Masses

Air masses are classified based on their and amount of

Air masses get their characteristics based on

The abbreviations c, m, T, P, and A. For each letter, describe its property: Word c continental m maritime T Tropical P Polar A Arctic Means dry moist warm cold very cold

warm and moist cold and dry

http: //www. classzone. com/books/earth_science/terc/content/visualizations/es 2001 page 01. cfm? chapter_no=20

c. P air mass m. T air mass dry, cool air warm, moist air High Pressure Area Low Pressure Center

A front is two air masses with different properties.

There are four types of fronts. § Cold Fronts. § Warm Fronts. § Stationary Fronts. § Occluded Fronts.

Cold Fronts • Cold air is dense, sinks, moves under warm air. • Can cause snow to form

Cold Front

Cold Front http: //www. free-online-private-pilot-ground-school. com/images/cold-front. gif

Warm Fronts § A moving warm air mass collides with a slowly moving cold air mass. § Can cause rain if humidity is high

Warm Front

Warm Front http: //www. free-online-private-pilot-ground-school. com/images/warm-front. gif

Stationary Fronts § When warm and cold fronts meet “head on” § Can cause rain, snow, fog, or clouds.

Occluded Fronts § Cold air catches up to Warm Air § Can cause cloudy, rainy, or snowy weather.

Occluded Front http: //www. physicalgeography. net/fundamentals/7 r. html

Occluded Front http: //www. free-online-private-pilot-ground-school. com/images/occluded-front. gif

Interpreting Weather Maps

Weather Station Models

• ff = Wind Speed dd= Wind Direction P= Pressure N= Cloud Cover TT = Temperature ww = Present Weather Td = Dew Point

Practice Interpreting These

You Should Be Able To Interpret This

What Do You See?

Project Storm Website • http: //www. uni. edu/storm/

Review Questions • • • What is Air Pressure and what Units is it in? What is an Isobar? Where do different air pressures come from? What are the 4 fronts? What things do you look for when interpreting a weather map?