Air Pressure Astronomy/Meteorology Chapter 19 Air Pressure Astronomy/Meteorology

Understanding Air Pressure 19.1 Air Pressure Defined Pressure exerted by the weight of the air above Exerted in all direction http://www.youtube.com/watch?v=vGulvutZJpg - 6 minutes Measuring Air Pressure Barometer – device used to measure air pressure Bar= pressure Metron = measuring instrument Pressure increases  pushes mercury up unit = millibar Air pressure at sea level is 1013.2 mbars

Factors Affecting Wind 19.1 Air moves from high pressure to low pressure Wind result of differences in air pressure Differences in air pressure b/c of unequal heating (temp) Solar radiation source of wind Air doesn’t move in straight lines b/c Pressure differences Coriolis Effect Friction

Pressure Difference 19.1 Great difference = greater wind Isobars – lines on a map that connect places of equal air pressure Pressure gradient – spacing between lines Close: steep pressure gradient = high winds Widely spaced: weak pressure gradient = light wind http://www.youtube.com/watch?v=hKGQJEp-Pys 2 minutes Driving force of wind High to low

Coriolis Effect 19.1 Describes how Earth’s rotation affects moving objects Northern Hemisphere = deflected to the right Southern Hemisphere = deflected to the left Only Affects wind direction Strong winds equals strong deflection Strongest at poles Basically nonexistent at equator http://www.youtube.com/watch?v=mcPs_OdQOYU 2 minutes

Friction 19.1 Affects wind speed and direction Only affects a few km from Earth’s surface Jet streams = fast moving rivers of air that travel between 120 – 240 km/hr from east to west

Pressure and Centers and Winds 19.2 Highs and Lows Cyclones – centers of Low Pressure Pressure decreases from the outer isobars towards center Northern Hemi: counterclockwise Low = Left Southern Hemi: clockwise Anticyclones – centers of High Pressure Pressure increases from outer to inner Northern Hemi: clockwise Southern Hemi: counterclockwise

Pressure and Centers and Winds 19.2 Weather and Air Pressure Rising air = clouds and precipitation Surface Convergence = Cyclonic (low) Sinking air = clear skies Surface Divergence = Anticyclone (high)

Pressure and Centers and Winds 19.2 Weather Forecasting Low-pressure centers – can produce bad weather Lows move W to E Predicting is difficult

Global Winds = Non-Rotating Earth Model 19.2

Global Winds = Rotating Earth Model 19.2

Regional Wind Systems 19.3 Local Winds – small-scale winds Caused by either topographic effects or variation in surface (land and water) Land and Sea Breezes Land heats and cools faster than water

Valley and Mountain Breezes Air on slopes of mountains heated more during the day than the valley floor Slope air = less dense  glides up slope to generate a valley breeze Air cools quickly at night = more dense = sinks into valley

How Wind is Measured 19.3 Wind Direction Wind Speed Prevailing Wind – wind consistently blows more often from one direction US = westerlies move from west to east Wind Speed Anemometer – measure wind speed

El Nino and La Nina El Nino = irregular intervals of 3 to 7 years of warm countercurrents that replace normal cold offshore waters Affects Ecuador and Peru La Nina= temperature in eastern Pacific are colder than average

Normal Conditions El Nino Conditions

http://www.youtube.com/watch?v=SR5VPAqVQBw 3 minutes http://www.youtube.com/watch?v=fN_NmCpry38 4 min 30 sec http://www.youtube.com/watch?v=mHpZhKUldBg 3 min 15 sec