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Lecture 6

Lecture 6 Notes.docx

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Environmental Science
Course Code
Tanzina Mohsin

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Lecture 6 Polar lows Primer What are Polar Lows?  Cyclones forming over the open sea in polar regions  Have several hundred kilometers in diameter  Last a day or two  Sometimes called “Arctic hurricanes” due to well defined “eye”  Winds must be gale force ( > 50 kph)  Not as strong as hurricanes How do they form?  Continental cold arctic air (cP or cA) moves over open sea water (relatively warm)  Heat source (sensible and latent) of the open sea fuels the storm  In many ways similar to hurricanes o Sea surface temperatures as energy source o Eye formation o Warm core o Dissipate over land o Open sea  Arctic air mass  cloud formation (due to latent heat) Polar lows formation and duration  Polar lows form quickly reaching maximum intensity within 12 to 24 hours  Dissipate quickly  Most last less than 12 hours o Only a few last more than 24 hours in EC study Where do they form?  Polar regions over open sea – relative warmth is energy source  Northern Hemisphere o Atlantic Ocean o Pacific Ocean o Canadian Seas  Limited by sea ice conditions – open water a necessary condition Polar Lows: Canadian Waters  Most polar lows occur in the Labrador Sea  Hudson Bay and Baffin Bay are limited by annual sea ice cycle – polar lows occur in the fall until sea ice forms Seasonal Distribution of Polar Lows  Winter peak o Cold, continental air and open water are necessary conditions  Relative minimum in February o Reduced open water o Strong high pressure over Arctic Polar lows: Atlantic Ocean  Observed polar lows 1999-2003  Clustering off coast of Norway resulting from persistent open water in this area  Tail end of North Atlantic Current  Similar to Canadian polar lows  Enhanced reduction in February events Polar Lows: Pacific Ocean  Gulf of Alaska  Warm coastal current flow northward along BC/Alaska coast Polar Lows: Pacific Ocean distribution  Wintertime peaks  Relative minimum in January Polar Lows and “The Day After Tomorrow”  Hurricane–like snowstorms over Canada, Scotland and Siberia  How can you compare polar lows and hurricanes? o Strength o Latitude o Duration Firestorms  What are firestorms? o Self-sustaining storm (convective cell) that forms from an intense fire o Can form pyrocumulus clouds  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 draws in more oxygen for combustion and more detritus for burning 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 orangish “cloudlike” appearance is not a cloud buy 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  Okanagan Mountain Park Fire (2003)  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 Dust Storms  What are they? o In arid regions of the Earth, the wind can generate clouds of dust called dust storms. Dust is loose surface material or volcanic emission mainly composed of soil particles, particularly silicon dioxide (SiO2). Soil particles are organized in three general categories: clay, silt, a
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