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EESA09 #6.doc

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University of Toronto Scarborough
Environmental Science
Tanzina Mohsin

EESA09Lecture 6Polar LowsWhat are Polar LowsPolar lowspoleward of the polar front the division between cold polar air and warm tropical air storms can formSometimes due to similarieties to hurricanes they have been called hurricanes or Arctic hurricanesHow do they FormCold arctic air forms over sea ice or continental land surface moves over to much warmer ocean water substantial change in surface properties is the Arctic frontConteinental cold artic air cP or cA moves over open sea water relatively warmContrast in temperature between the air mass and ocean surface is largeoPolar ocean is coldonly a few degrees above freezingoOcean waters can be 20 to 40C warmed than Artic air massAir mass receives substantial heating from the ocean surface belowmajor driver of stormoInduces vertical motion by convection followed by surface convergence and a CCW vortexOcean provides moisture to air masscumulous clouds form as air risesAir diverges at surface cirrus clouds form giving characteristic hurricanelike appearanceoProvides secondary source of energy to the stormlatent heatMost polar lows extend to the tropopause roughly 8 km above the surface in polar regionsCan achieve low pressures of 980 mb typical of hurricanes and strong MLCWinds can be gale force exceed 62 kmhProduce heavy frozen precipitation such as hail and snowThe core is warm relative to its surroundings like a hurricanebut not like a MLCPolar lows fully develop within 24 hours and dissipate within a couple of days unlike a tropical cycloneThey move quickly compared to other storms often exceeding 50 kmhWhen move over land dissipate as cut off from sensible heat flux from oceanWhere do they FormSmaller than both MLC and tropical storms 2001000 km in diameter
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