• Mi• Me• Syn• Glo

Lecture 10. Local Circulations

Scales of Air Motioncroscale (air circulation less than 5 km across)soscale (5-500 km)optic Scale (500-3000 km)bal Scale (3000 km or more)

(EOM)

Tied n blowing infrom• Mi

• Me

• Syn

Local circulations

with local temperature contrasts or mountains, rather tha elsewhere.croscale (less than 5 km)ConvectionClear-air turbulencesoscale (5-500 km)Mountain wavesLand/Sea and Mountain/Valley breezesoptic/Global Scale (larger than 500 km)Monsoons

• The• If a day or more, it

wil geostrophic bal-anc

• Ho n a few hours orless tward, but PGFrem ure.

Coriolis Force and Local Circulations

Coriolis force bends all winds to right (NH).n air parcel experiences roughly the same PGF for half al blow roughly along the isobars at a speed that achievese, with CF equal and opposite to PGF.wever, air parcels move through many local circulations i. During this time, the Coriolis force bends the wind righains dominant; air mainly blows from high to low press

• He e and cold air tosin

• Thi a side.

• If t le on top of theupd

Convection

ating of surface forces hot, less dense (buoyant) air to risk.s takes place in eddies (whirls) a few hundred meters on

he convection extends high enough, clouds may be visibrafts

The t ghts is often dueto wi

EOM, p. 169

Clear Air Turbulence

urbulence we sometimes feel as bumpiness on aircraft flind shear, or rapid change of winds with height.

ind shear

EOM, p. 169

If lower layer cloudy, can see cloud billows due to w

• Can Boulder, CO)• Oft

Mountain Waves

produce strong winds in lee of mtns. (up to 150 mph inen visible as ‘lee wave clouds’ at the wave crests.

Lee Wave Clouds

(EOM)

Cold• Wh

buivat(Anlan

• A cpol ountain range

umbia valleys.• Co g as it descends.• Str gaps (100 mph

win• Co but remains

col

Strong Downslope Winds, dry winds occur:en a cold air masslds over an ele-ed plateau.tarctic and Green-

d icecaps)old continentalar airmass spills over the crest of and through gaps in a mYugoslavian Bora, French Mistral.Cold, dry easterly winds down Fraser, Snoqualmie, Col

ld dense air spills down the mountain slopes, acceleratinong downslope winds, especially in valleys downwind ofds in Enumclaw).

ld is reduced by compressional warming as air descends,der than mild marine air.

• ChE oFoeSan

• Strmoforair old and dense.

• Airdes

• Latcanper

Warm downslope winds

inook (‘snoweaters’) -f Rockieshn - N of Alpsta Ana Winds - LA

ong winds produce auntain wave whichces mild mountaintopdown the lee side of the mountain even though it is not c is compressionally warmed as itcends, producing a warm dry wind.ent heating due to upslope precipitation help raise mountaintop and lee-side tem-atures.

EOM 7.9