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Chapter 11.docx

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University of Calgary
GOPH 375

Chapter 11: Severe Weather not responsible for 298-304? Maybe  Global warming potential: ability of each gas to trap heat  Tipping point: when small changes produce a large effect  30 years of weather makes climate  Hydrological cycles are not the cause of the ice age because the cycles determine climate but have nothing to do with ice ages. Cycles happen all the time, ice ages only happens for periods of time. At one point in time we were not in an ice age and h cycles still existed  Drill through polar caps in mars, compare to earths, to see how sun effects climate variation  El Nino – climate variation. Usually trade winds push warm water to the west side of the Pacific Ocean (tropics/rain/jungle), leaving cold water on the east side (deserts). Every few years surface currents and winds reverse producing heavy rain in deserts o Fig 11.8 lasts 6-18 months as low latitude (tropical) conditions o Largest was 1997-98: drought, fires, cyclone, flooding, snow, tornadoes. Broke up some hurricanes, warmer winter, increased crop productivity, less fatalities o Most destructive was 1982-83 o Caused St. Lawrence River Valley ice storm 1998 (2 most costly natural disaster in Canada)  Southern Oscillation : when low pressure air is replaced by high pressure  Teleconnections: weather changes in one area trigger changes around the world. o Fig 11.11 circulations from SA, Indonesia. When it switches there’s a change in water temperature that effects weather all over o Happens every few years, global circuit takes about 4 years to move around the earth  La Nina: when cooler waters move into the equatorial pacific ocean. Trade winds, and other wind systems change their paths o Heavy rain, drought, hurricanes, fires,  La Nada: Pacific Ocean is neutral (not excessively warm or cold), thus weather is hard to predict  Pacific decadal oscillation: 2 periods at mid latitude positions of the Pacific Ocean. Warm/cool phases  Fig 11.12/Fig 11.14  Climate is changing, simulations can predict how temperature extremes will evolve, but not precipitation or storms Drought and Famine  Drought: 50% less rainfall for 3 months (growing period)  Drought doesn’t mean desert, just temporary shortage of water that life needs to adjust to  Famine is the slowest natural disaster  1930’s dust bowl – drought caused famine. Drought caused by ridge of high pressure with clockwise flow resulting in dry, hot descending air  Drought is most expensive natural disaster in a cumulative sense Heat waves  No damage to things, but more people die than other natural disasters. Opposite of ice storms  Die from heat exhaustion - kill because the nights are hot as well as days – respite (no rest aka relief)  Table 11.5 Fig 11.17  Highways buckled, warped bridges, sidewalks cracked  Mostly elderly/infants people that die  Humidity makes temperature feel hotter  Heat disorders, silent killers  July 1995 Chicago: death by hyperthermia, mostly elderly, people who lived on the top floor of buildings, limited access to AC. 1930s wave people slept on rooftops/beaches, 1995 death toll was higher because people were afraid of violence and locked themselves in their rooms  2003 Europe: 35,000 died. More city deaths because buildings/streets absorb heat during the day and release it at night thus no night relief for people  Heat wave 1956  Heat wave frequency is increasing because climate is getting warmer (greenhouse) , to be more deadly as most people live in cities now Cyclones  Mid latitude cyclones are air masses rotating counter-clockwise about a low pressure core  Thunderstorms radius is smaller than a cyclone, but wind speed and momentum is higher than a cyclone  Inside cyclonic thunderstorm could be a tornado  Cyclones linked to jet stream troughs  Nor’ easters: large scale cyclones created by potent storms in Atlantic Canada and Northeastern US . more frequent than hurricanes, cause major snowstorms o Weather bomb = rapidly intensifying, unpredictable snowstorm. low pressure o Witches of November = November is windy over great lakes, warm lakes accelerate cyclones  NA east coast “white hurricane” 1993: massive snowfall Nova Scotia/Atlantic Ocean. Blizzard + hurricane caused by jet stream trough colliding with 3 air masses in Florida Thunderstorms  Caused by severe convection “unstable air”  Unstable because of water vapor content. Happens in the summer, not so much winter because cold air in the winter doesn’t hold a lot of water vapor  Lapse rate: rate of cooling with height , greater than 6-10 degrees C/km atmosphere is unstable  A thunder cloud begins with a continuous updraft of warm moist air which condenses, and pulls in cold/dry air when it falls  Storm stops when drown drafts drag in so much cool/dry air that it chokes off the upward draft that fuel the storm  Warm and humid air is best for thunderstorms, condensation also fuelled by release of latent heat absorbed during evaporation  Vertical transfer of heat called convection  If air is humid enough and rises, you get positive feedback mechanism caused by water vapor condensing to a liquid (and freezing to a solid) o Positive Feedback CIRCLE: water condenses releases heat, which cause more convection, which causes more water to condense. This cycle will continue until it runs out of vapor or it cools down enough  Thunderstorm is a “runaway convection”  Thundersnow: winter thunderstorms, warm air rides above cold air and becomes destabilized  Windsor Ontario has most thunderstorms in Canada; a warning is issued when: wind >90km/hr, hail >2cm, rain >50mm in an hour or 75 mm in 3 hours  Thunderstorms produce dangerous effects o Intense rain/flash floods  Flash floods cause a lot of damage when they run into water.
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