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University of Toronto Scarborough
Environmental Science
Tanzina Mohsin

Wind – Lecture 6: Other Storms Polar Lows: - Cyclones forming over the open sea in polar regions (usually cold – but need warm temp. to be heated to fuel the storm) - Several hundred km in diameter - Lasts a day or two - Sometimes called “Arctic Hurricanes” due to well defined “eye” - Winds must be gale force (>17m/s)  the winds are not so strong and that’s why the storm is generally short lived How do they form? o Continental cold arctic air (cP or cA) moves over open sea water (relatively warm)  The cold air mass over the land mass of the arctic zone, it moves over to the ocean and the ocean water surface temp. is much higher  therefore, huge substantial difference in temperature that causes the change in phase!!!!  Heat source (sensible and latent) of the open sea fuels the storm o In many ways similar to hurricanes:  Sea surface temperatures (SSTs) as energy source  Eye formation  Warm core  Dissipate over land o Differences between hurricanes (tropical storms) and polar lows?  The latitude of formation • Hurricanes occur in tropical regions • Polar lows occur in polar regions Polar Formation and Duration: o Polar lows form quickly reaching maximum intensity within 12 to 24 hours o Dissipate quickly o Most last less than 24 hours  48/61 storms were less than 24 hours in a Environmental Canada study Where do they form? o Polar regions over open sea – relative warmth is energy source o Northern hemisphere  Atlantic ocean, Pacific ocean, Canadian seas o Limited by sea ice conditions – open water is a necessary condition Polar Lows: Canadian Waters: o Most polar lows occur in Labrador Sea o Hudson Bay and Baffin Bay are limited by annual sea ice cycle – polar lows occur in the fall until the sea ice forms Seasonal Distribution: o Winter Peak  Cold, continental air and open water are necessary conditions • Cold arctic air is only found in the winter time in polar regions • You don’t want sea ice but open water o Relative minimum in February  Reduced open water  Strong high pressure overArctic Polar Lows: Atlantic Ocean: o Observed polar lows 1999-2003 o Clustering off coast of Norway resulting from persistent open water in this area o Tail end of North Atlantic Current  The current is not letting sea ice to form, therefore it is warmer, and you have open water; therefore, there are relatively more polar lows occurring where currents are o Similar to Canadian polar lows o Enhanced reduction in February events Polar Lows: Pacific Ocean o Gulf of Alaska o Warm coastal current flow northward along BC/Alaska coast o Distribution:  Wintertime peaks  Relative minimum in January Polar Lows and “The Day After Tomorrow”: o Were the killer storms of the DayAfter Tomorrow enhanced polar lows?  Hurricane-like snowstorms over Canada, Scotland and Siberia Firestorms: - Self-sustaining storm (convective cell) that forms from an intense fire o Once the storm arises, it is very hard to put out this fire because it is self-sustaining - Can form pyrocumulus cloud o White or grey, not orange-ish (the orange-ish colour is from the ashes of the storm) How do they form? o Initial trigger is a localized fire  Lightning/forest fire  Bomb  Chemical explosion  Nuclear explosion o Updraft forms due to heating of surface air (chimney effect) o Surface convergence (winds) which results draws in more oxygen for combustion and more detritus for burning  Oxygen is getting burned but there is wind within that fire, so wind is carrying more oxygen and is fueling the fire  Anything that is flammable, the wind is attracting all those flammable things • Everything other than water can burn and therefore the fire is getting the two types of fuel which is oxygen and flammable things and therefore, the storm is self-sustaining  this is why it is so hard to control or put our fire storms o Winds can be gale or hurricane strength o ***Latent heat is not a major fuel source for these storms*** o Radiant heat from fire can spontaneously cause other fires in the vicinity o The orange-ish “cloudlike” appearance is not a cloud but formed from ash o Clouds however can form (pyrocumulus) above the fire storm  Formed due to condensation of moisture in the updraft  Firestorm ash provides cloud condensation nuclei for cloud droplets to form on Where do they form? o Not limited geographically as are other storms o Trigger and fuel are the requirements o Tends to occur in dryer areas (more susceptible to forest fires) “Firestorm” – the Movie: o 1998 movie “firestorm” o Firefighter (male) saves ornithologist (female) Dust Storms or Sand Storms: - In arid regions wind can cause dust or sand storms - Same characteristics (both sand or dust storms), except with dust storms, the particles are smaller o Dust is usually formed from silicon dio
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