WindsWinds

What makes the wind blow?

• uneven heating of the atmosphere

• warm air rises (forming low pressure)

• cool air sinks (high pressure) to replace the warm air

• movement from high to low pressure is what generates wind

• steep pressure gradient=high winds

• lower pressure gradient=slower wind

The Coriolis Effect

• The deflective effect of the earth's rotation on all free-moving objects, including the atmosphere and oceans.

Gaspard-Gustave de Coriolis, 1835

coriolis effectcoriolis effect

A plane flying from Anchorage, Alaska directly toward Miami, Florida would miss its target due to the Coriolis effect. The target location where the plane was headed when it took off has moved with Earth's rotation, so the plane would end up to the right of its original target.

coriolis (n.hemisphere)

coriolis demo

Coriolis Effect(Southern Hemisphere)

Coriolis Effect(Southern Hemisphere)

A plane flying from Tierra del Fuego, Argentina directly toward Rio de Janeiro, Argentina would miss its target due to the Coriolis effect. The target location where the plane was headed when it took off has moved with Earth's rotation, so the plane would end up to the left of its original target.

In reality, pilots take the Coriolis effect into account so they do not miss their targets

coriolis (s. hemisphere)

coriolis demo

Surface Winds• Winds between pressure zones are named for the

direction that they come from:

• Three main wind systems:

• trade winds: blow from 30˚ towards the equator; warm and steady in both direction and speed; provided regular trade routes for sailing ships

• Prevailing westerlies: blow from 30˚ to 60˚; change direction and speed frequently; speed increases with latitude & is faster over ocean than land

• Polar easterlies: blow from poles towards 60˚; cold and stormy

Wind Belts

view wind belts animation

global IR imagery

High Altitude Winds

• Jet Stream: narrow stream of air in the upper troposphere which moves eastward at high speed-usually in middle latitudes

• height range: 6,000-12,000 meters, speed: 150-300 knots

• dips account for cold polar air in US during winter

• related to strong thunderstorms in spring & summer

• used by planes to assist with eastbound flights

Daily winds

• during day, land heats faster than water, and generates a sea breeze: cool breeze blowing from the ocean to replace the rising warm air from land

• at night, land cools faster than water and generates a land breeze (opposite of above)

land and sea breezes

Monsoons

• seasonal change in wind direction

• in summer (from water to land)

• in winter (from land to water)

• are similar to effects of land vs sea breezes but on a much grander scale

• most famous from over India, SE Asia & Indian Ocean-winds turn completely around between winter and summer

Air MassesAir Massesair mass: huge section of the lower troposphere that has the same kind of weather throughout

air that stays in one area for a long time takes on the weather of that area

Originate in parts of the world where winds are light (polar and subtropical high pressure belts)

interaction of air masses is what causes weather events (storms, etc)

kinds of air masseskinds of air massesair masses are named for their source regions

maritime tropical (mT): warm & humid from tropical seas

continental tropical (cT): hot & dry from tropical land areas

maritime polar (mP): cold & humid from cold ocean waters

continental polar (cP): cold and dry from land areas in high latitudes

continental arctic (cA): cold and dry from ice covered Arctic

weather in an air massweather in an air massweather of a given place will resemble the weather of the region where the air mass originated

examples:

cP in Florida during summer=cool spell

cT in NJ during summer=very hot & dry

the faster an air mass moves, the more dramatic change in weather

Skies in an air massSkies in an air massconditions depend on temperature of surface versus temp of air mass

if ground surface is colder:

bottom layer is stable, inversions form, smog, condensation, light rain, poor visibility

if ground surface is warmer:

bottom layer is unstable, convection forms cumulus clouds, good visibility; dry air=fair, humid air=showers

What is a Front?What is a Front?

front: the boundary between any two air masses

an approaching front means a change in temperature and humidity

greater change in air masses=greater change in weather

will usually bring precipitation (warm air is forced to rise along the frontal wedge)

kind of frontskind of frontsFour types of fronts:

1. cold: cold air is advancing and displacing warmer air up a steep slope

2. warm: warm air is pushing ahead and displacing cold air over a more gentle slope

3. stationary: neither air mass is being displaced

4. occluded: when a cold front overtakes a warm front

cold frontcold front

warm frontwarm front

view cold/warm front animation

Stationary frontStationary front

occluded frontoccluded front

front symbolsfront symbols

surface mapssurface maps

last Sunday’s forecast

last Sunday’s forecast