In the News: more record highs – fewer lows http://dotearth.blogs.nytimes.com/2009/11/12/warmingtrend-seen-in-temperature-records/?ref=science 1 In the News: SNOW!!! Snotel: Bracket cr. 13” Sacajawea Sacaja ea 12” Lick cr. 11” Bridger 15” Bozeman 24” 24 2 In the News: new all-time records! 3 http://cateye.msu.montana.edu/ Summary of October’s Weather NOWData, Observed Weather, Preliminary gy Data: http://www.weather.gov/climate/index.php?wfo=tfx Climatology Average Temp = 40.2 °F, - 3.1 °F below normal Precipitation = 0.98 in - 0.13 less than normal 23 days with min min. temperature < 32 °F F 6 clear days 15 partly tl cloudy l d d days 10 cloudy days Total HDD (base 65) = 757, 83 above normal Total HDD since July 1 = 945, -230 less than normal Total CDD (base 65) = 0, 0 less than normal Total CDD since Jan 1 = 339, 80 above normal 4 Midlatitude Cyclones a. Why do we care about midlatitude cyclones? l ? b. Polar front theory c Life cycle of a c. midlatitude cyclone l 5 http://upload.wikimedia.org/wikipedia/commons/2/2c/Feb242007_blizzard.gif a. Why midlatitude cyclones? Midlatitude cyclones: Low pressure center characterized by the presence of frontal boundaries; travel great distances and affect large areas 6 http://upload.wikimedia.org/wikipedia/commons/3/35/Extratropical_formation_areas.jpg a. Why midlatitude cyclones? Midlatitude cyclones: 7 Textbook Figure 10-1. a. Why midlatitude cyclones? Midlatitude cyclones: Look at latest: http://www.hpc.ncep.noaa.gov/basicwx/day07loop html 7loop.html 8 http://upload.wikimedia.org/wikipedia/commons/3/35/Extratropical_formation_areas.jpg Midlatitude Cyclones ERTH 303 17 Nov., Nov 2009 a. Polar front theory b. Life cycle of a midlatitude cyclone c. Upper troposphere and s surface rface processes d. Upper-level pp flow and large-scale weather e Conveyor Belt model e. 9 a. Polar Front theory Polar Front Theory: Vilhem Bjerknes, Bergen Norway, early 20th century Described formation, growth, and dissipation of midlatitude cyclones Vilhemn Bjerknes, 1862-1951. Norwegian Geophysicist who developed Polar Front Theory Theory. http://media-2.web.britannica.com/eb-media/95/65195-004-2ED1EBA5.jpg http://upload.wikimedia.org/wikipedia/en/0/01/Vilhelmbjerknes.jpg 10 a. Polar Front theory 11 c. Life cycle of a midlatitude cyclone Cyclogenesis 12 Life cycle of a midlatitude cyclone Cyclogenesis: 13 b. Life cycle of a midlatitude cyclone Cyclogenesis - 1 Begins B i with ith a disruption di ti off the th polar l frontal boundary 14 Textbook figure 10-1 b. Life cycle of a midlatitude cyclone Cyclogenesis - 2 “kink” kink in boundary; cold air pushes S, warm air pushes N Creates counterclockwise rotation 15 Textbook figure 10-1 b. Life cycle of a midlatitude cyclone Cyclogenesis - 2 Low pressure deepens Warm and cold fronts emerge “Mature” “M t ” cyclone l 16 Textbook figure 10-1 b. Life cycle of a midlatitude cyclone Mature cyclone: Precipitation along frontal boundaries bou da es Probability of precipitation increases towards the center of the cyclone NW Winds SE Winds SW Winds Cumuliform clouds 17 Textbook figure 10-2 b. Life cycle of a midlatitude cyclone Occlusions End of cyclone’s cyclone s life…. 18 Textbook figure 10-1 b. Life cycle of a midlatitude cyclone Passage of a cyclone: 1. Cloud cover deepens; possible precip. (warm front) 2 Precip give way to warmer 2. warmer, clear conditions; winds shift form S to SW 3 Clear 3. Cl conditions diti give i way to t a cold ld front: f t fast-moving, heavy band of clouds and precip. i 4. Cold front passes and brings clear, cold conditions 19 b. Life cycle of a midlatitude cyclone Passage of a cyclone: http://www.opc.ncep.noaa.gov/Loops/UA_CONUS_hires/UA_CONUS_hires_03_Day.shtml 20 Textbook figure 10-3 Midlatitude Cyclones GEOG 303 6 Nov., Nov 2008 a. Polar front theory b. Life cycle of a midlatitude cyclone c. Upper troposphere and s surface rface processes d. Upper-level pp flow and large-scale weather e Conveyor Belt model e. 21 c. Upper troposphere processes Vorticity: rotation of a fluid positive vorticity: air flow in direction off E Earth’s th’ rotation t ti negative g vorticity: y air flow in opposite pp direct of Earth’s rotation Vorticity changes in the upper atm. atm lead to pressure changes near the surface… f 22 c. Upper troposphere processes Vorticity: Increased vorticity Æ convergence Decreased vorticity Æ divergence Rossby wave 23 Textbook figure 10-4 c. Upper troposphere processes Vorticity: Increased vorticity Æ convergence Decreased vorticity Æ divergence Rossby wave 24 Textbook figure 10-7 c. Upper troposphere processes Vorticity: Cyclones develop downwind of troughs Anticyclones develop upwind of troughs (downwind of ridges) Rossby wave 25 Textbook figure 10-7 c. Upper troposphere processes 26 http://weather.unisys.com/upper_air/ua_500.html c. Upper troposphere processes 27 http://weather.unisys.com/upper_air/ua_500.html c. Upper troposphere processes Dynamic low (cold-core low): low low-pressure pressure systems (cyclones) resulting from tropospheric motions Thermal low ((warm-core low): ) low-pressure caused by localized heating from below 28 Textbook figure 10-9 c. Surface processes Differences in surface temperature lead to upper pp level pressure p gradients g 29 Textbook figure 10-9 c. Surface processes Thus, near-surface temperatures strongly g y influence upper-level pp pressure p distribution – e.g. jet stream is above polar frontal boundary. 30 Midlatitude Cyclones ERTH 303 17 Nov., Nov 2009 a. Polar front theory b. Life cycle of a midlatitude cyclone c. Upper troposphere and s surface rface processes d. Upper-level pp flow and large-scale weather e Conveyor Belt model e. 31 d. Upper-level flow and large-scale weather Zonal flow: (W-E) Calm conditions No areas of widespread precip. 32 d. Upper-level flow and large-scale weather Meridional flow: (N-S) Favors formation of cyclones y and anticyclones y 33 d. Upper-level flow and large-scale weather Steering of midlatitude cyclones Systems y p parallel 500 mb flow,, at ½ speed p Winter = strong flow aloft; more frequent storms 34 Textbook figure 10-16 Midlatitude Cyclones ERTH 303 17 Nov., Nov 2009 a. Polar front theory b. Life cycle of a midlatitude cyclone c. Upper troposphere and s surface rface processes d. Upper-level pp flow and large-scale weather e Conveyor Belt model e. 35 e. Conveyor Belts Conveyor Belt Model: Modern view of midlatitude cyclones Warm conveyor belt Originates near surface in warm sector Frontal lifting g results in p precipitation p Cold conveyor belt Enters as an easterly belt flowing westward Dry conveyor belt Upper-level, westerly flow 36 e. Conveyor Belts Conveyor Belt Model: 37 e. Conveyor Belts Conveyor Belt Model: Cold Belt Dry Belt W Warm Belt B lt 38 10.01 In a middle latitude cyclone cyclone, this stage is called ______. 1. cyclogenesis y g 2. occlusion 3. maturityy 4. senescence 10.01 In a middle latitude cyclone cyclone, this stage is called ______. 1. cyclogenesis y g 2. occlusion 3. maturityy 4. senescence 10.02 In a middle latitude cyclone cyclone, this stage is called ______. 1. cyclogenesis y g 2. occlusion 3. maturityy 4. senescence 10.02 In a middle latitude cyclone cyclone, this stage is called ______. 1. cyclogenesis y g 2. occlusion 3. maturityy 4. senescence 10.05 This diagram illustrates a _______. 1. middle latitude cyclone y 2. cold front 3. flow in the stratosphere p 4. Rossby wave 10.05 This diagram illustrates a _______. 1. middle latitude cyclone y 2. cold front 3. flow in the stratosphere p 4. Rossby wave 10.08 Jet stream divergence causes _______. 1. middle latitude cyclones y 2. sinking air 3. chaotic flow 4. anticyclones 10.08 Jet stream divergence causes _______. 1. middle latitude cyclones 2. sinking air 3. chaotic flow 4. anticyclones 10.12 On this map map, the surface low is located here because of _______. 1. a barotrophic p atmosphere 2. divergence aloft 3. convergence aloft 4. negative relative vorticity ti it 10.12 On this map map, the surface low is located here because of _______. 1. a barotrophic p atmosphere 2. divergence aloft 3. convergence aloft 4. negative relative vorticity ti it 10.15 This upper air flow pattern is best termed “____.” 1. baroclinic 2. zonal 3. meridional 4. mythical 10.15 This upper air flow pattern is best termed “____.” 1. baroclinic 2. zonal 3. meridional 4. mythical
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