• If t or cools (andmo to form an airma

• Fai• Wh they bring us

hea• Air••••• Po y blow out their

reg

Lecture 6. Air Masses

he same air stays over a region for many days, it warms istens or dries) into balance with the underlying surface ss.rly uniform air masses may extend 1000’s km across.en air masses blow over us from their formation region,t waves and cold snaps. mass types (and formation regions):Continental polar (AK, Canada, winter)Maritime polar (N Pacific)Maritime tropical (Gulf of Mexico, Hawaii)Continental tropical (SW deserts, summer)lar and tropical air masses are rapidly modified after theions of origin and don’t make it to Seattle in pure form.

ses

• Sto ld airmasses,the erature changes.

3

Mid-latitude Weather: Battle of the Air Mas

rms and fronts form near contrasts between warm and con blow these airmasses around to make day-to-day temp

TWB, p. 2

• Pol are emittinginfr , so they cool.

• In t ures are coldestat t

• The

TWB, p. 22

Formation of Polar Airmasses

ar airmasses form in winter, because the ground and air ared radiation, but there is little sunlight to heat them uphese airmasses, air cools as it gently sinks, and temperathe ground (an ‘inversion’). cold dense air spreads southward like pancake batter.

TWB, p. 24

Formation of Tropical Airmasses

• Helowtionlenprolen

(EOM)

er

Daytime Heating

at goes from ground toest inch of air by conduc-, mixed upward by turbu-

t convection. Windmotes enhanced turbu-ce, mixing.

Conduction

Convection

Warm Cool

s

• GrocieRadcol

• Wiwe

(EOM)

Nighttime Radiation Temperature Inversion

und radiates more effi-ntly, cools faster than air.iative cooling fastest on

d, clear night.nd, turbulence mixes air,akens inversion.

The c atic winds.

Thermal Belts on Hillsides

old air currents blowing down hillsides are called katab

• If a eat or mix it up.

• If a s aroundora

ine

EOM 3.6

Protecting the Orange Crop Against Frost

ir is subfreezing only near ground (radiation inversion), h

ir is subfreezing above tree-tops too, spray water (freezenges, releasing latent heat and insulating them.

Wind MachOrchard heater

EOM 3.5

• Liqfreeexpliqu

• Bimbenmeoth

• Eleterwitpla

• Rad hter = hotter).Use

EOM 3.14

EOM 3.16

Thermometers

uid thermometer - liquid with lowzing point (e. g. mercury) in bulbands with temperature, forcing someid up the narrow bore.

etallic thermograph - stripds when heated since onetal expands faster than theer.ctrical resistance thermome-- based on resistance changeh temperature; used on air-nes.iometers - based on brightness of emitted radiation (brigd on satellites.

Bimetallic