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EESA09 Lecture#3

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Environmental Science
Tanzina Mohsin

Midlatitude Cyclones Hurricanes in the Great Lakes -Effects of Great lakes hurricanes: a lot of rainfall -2006-07 no hurricanes in Great Lakes Snow Storm in 2011 Youtube Clip -This hurricane: Gulf Low from Gulf of Mexico Air masses are major components of mid-latitude cycles -cT, cP, mP, mT -Winds not intense like hurricanes -under certain circumstances snow storms can be very disastrous -Midlatitude cyclones can act as a precursor to thunderstorms or tornadoes How can we link this to Large Scale flow? cP – mostly Northern Canada mP- from Maritimes (over ocean – some part of pac and atlantic) cT and mT - tropical air masses – gulf of mexico – mid western US Fronts -are small components of midlatitude cyclones, the whole system, when you put together the fronts you have the whole system -there are 4 types of fronts; are usually at the division between the air masses 1. Stationary 2. Warm 3. Cold 4. Occluded Mechanism: polar front theory – Midlatitude Cyclone -starts with disturbance at stationary front -cP = NE - cold -mT – SW - warm -when air masses move and create battleground, that stationary front becomes unstable – associated with an horizontal wind shear (horizontal gradient of wind direction and can be unstable)– Step #1 -Step #2 – cold front and warm front pushing against each other, wind direction in a low pressure system is counter-clockwise. Under certain conditions, along the polar front, the cP and mT are pushing against each other; this is the pivot point – and it’s the lowest local pressure -Step #2 – major precipitation front along cold front. Fully developed wave (12-24 hours) -centre pressure continues to drop -warm sector formed between two fronts -Step #4 – now cold front catches up with warm front, and warm sector is squished. -Step #5 – Occlusion occursd as cold front catches up with warm front. – Comma shaped cloud – typical shape of mid-latitude cyclone. Most intense part of storm. -Step #6 – storm dissipates after occlusion; source of energy (mT air) has been cut off, i.e. no more latent heating Try to distinguish among the storms -hurricane vs. midlatitude cyclones -hurricanes form in the ocean with tropical latitude. -Mi
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