43 terms

Chapter 19

Air Pressure
Pressure exerted by weight of air. Exerted in all directions, pressure pushing down balances pressure pushing up
Standard Sea Level Pressure
1013.2 millibars
Device used to measure air pressure
Aneroid Barometer
Small, flexible metal box called aneroid cell (capsule)
Air flows in areas of high pressure to low pressure
3 Factors Combining to control wind
Pressure difference, Coriolis effect, and friction
Pressure Gradient
Amount of pressure change occurring over a given distance
Closely spaced isobars
Indicate steep pressure and high winds
Widely spaced isobars
Indicated weak pressure gradient and light winds
Coriolis Effect
How Earth's rotation effects moving objects. In Northern Hemisphere, objects deflected at right of path of motion. Southern Hemisphere deflected at left. All air deflected at right angle. It influences wind direction, strongest at poles, strongest wind= greater deflection of Coriolis effect
Slows air movement, which changes wind direction
Jet streams
Fast moving "rivers" of air that occur above friction layer. Move in east-to-west direction
Centers of low pressure. Air rises in center
Centers of high pressure. Air subsides (sinks) at center
Cyclonic vs. Anticyclonic winds
Pressure gradient, friction, Coriolis effect applied to pressure center in Northern Hemisphere, winds blow inwards and counterclockwise around a low pressure. Southern Hemisphere opposite. Both Hemispheres friction causes inward or outward in cyclone or anticyclone
Fair Weather associated with anticyclone (high pressure)
Descending air, clear weather, dry conditions
Low pressure (cyclone) system in US moves from West to East
Produce bad weather, paths are unpredictable, takes a week to cross country
Weather and Air Pressure
Rising air= cloud formation and precipitation
Weather Forecasting
Weather reports emphasize locations and possible paths of cyclones and anticyclones, low pressure produce bad weather at any season
Non-rotating Earth
Air at equator would rise and move toward poles
Horizontal convergence
Net inward movement of air causes area occupied by air mass to shrink
Horizontal divergence
Net outward movement of air causes area occupied by air mass to increase
Subtropical High
Dry, sinking near equator
Polar high
Dry, sinking near poles
Equatoria low
Wet, rising air near equator
Subpolar low
Wet, rising air near poles
Trade winds
2 belts of wind blowing constantly from east to west on north and south sides of subtropical highs from equator
Dominant west-to-east motion- characterized regions on poleward side of subtropical highs
Polar eateries
Blow polar high to sub polar low. Not constant
Polar front
Stormy frontal zone separating cold air masses of polar origin from warm air masses of tropical origin
Influence of continents
Only truly continuous pressure belts is sub polar low in South Hemisphere (no land masses to disrupt flow)
Seasonal reversal of wind direction associated with large continents, especially Asia. In winter, wind blows from land to sea ( seasonal high-pressure system) In summer, wind blows from sea to land (seasonal low pressure= rainy)
Local winds
Caused by topographic effects or variations in surface composition-land and water
Land and sea Breezes
In sumer mountains, land surface is heated more intensely during daylight hours than water
Sea breeze
Originates in day and flows towards land. Most intense in mid-afternoon
Land breeze
Originates in evening and flows towards water
Valley and Mountain Breezes
Warm air moves up mountain during day, cool air moves down during night
Prevailing wind
Wind that blows more often in one direction than another
Wind vanes
Indicate wind direction and 0˚=N, 90˚=E, 180˚=S, 270˚=W
Instrument that measures wind speed
El nino
Name given to periodic warming in central and eastern Pacific. Cold water is replaced with warm equatorial water. Major el nino can cause extreme weather
La nina
In eastern Pacific. Colder temp's than average
Nina and Nino
Weather patterns can affect fish industry, climate, and farming industry