GEOG 111 1st Edition Lecture 26 Outline of Last Lecture I The Circumpolar Vortex review II Wave Cyclones a Example Outline of Current Lecture I The Circumpolar Vortex review II Snow a Significance b Formation c Atmospheric patterns Current Lecture I Snow complex aggregations of ice crystals that develop in cold clouds in connection with the Bergeron process a Significance i Substantial part of the global land surface ii Snow changes the climate iii Natural hazards 1 Avalanches 2 Killer flooding 3 Southeastern not used to snowfall chaos b Formation i Cold air moisture ii Snow particle type varies by temperature and moisture iii Deformation of crystals 1 In the cloud environment 2 On the ground iv Total snow accumulation depends on 1 Snowfall rate duration a The heaviest snowfall events display long durations and or high snowfall rates 2 Wetness of the snow a Typical 1 10 ratio of snow to melted precipitation E g 1 snow to 1 rain b Dry snow 20 1 c Wet 5 1 These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute 3 Antecedent temperature of surface this relates to conditions during prior day e g solar insolation and surface characteristics e g specific heat and albedo v Ingredients for a perfect snowstorm 1 Air that s cold enough near the surface a Strong anticyclone to the north helps as it provides a replenishing supply of cold dry air b Not that melting snowflakes evaporating rain droplets or sublimating snowflakes can cool down the air significantly c Dry air and high precipitation rates are helpful 2 Slow moving wave cyclone that moves south of the area 3 A relative absence of warm advection aloft i e no warm nose 4 Frontal surface higher above surface surface front farther to the south vi Example March 1993 Super storm 1 Over 30 inches in NC 2 Cyclone progresses to the North c Atmospheric patterns i Low pressure center at surface rotating counterclockwise further away from warm front colder the air is 1 Heavy snowstorm is when cyclone is in the South ii Vertical temperature profile 1 Column below freezing ideal 2 Isothermal profile close to freezing more realistic a When it snows up high it s frozen but melts as it falls b Snow melts into rain which causes enough cooling to bring the near surface air to freezing iii Northwest flow snowfall 1 Occurs as 50 of mountain snowfall events 2 Low level moisture scavenged from lakes and forced upward along mountains by orographic lifting 3 Occurs after a cyclone
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