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Spatial Synoptic Classification (SSC)

Spatial Synoptic Classification (SSC). A method of synoptic weather-typing; the classification of ambient weather conditions into categories Surface weather types 4x Daily surface obs at individual stations Temp, dp, wind, pressure, cloud cover http://sheridan.geog.kent.edu/ssc.html.

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Spatial Synoptic Classification (SSC)

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  1. Spatial Synoptic Classification (SSC) • A method of synoptic weather-typing; the classification of ambient weather conditions into categories • Surface weather types • 4x Daily surface obs at individual stations • Temp, dp, wind, pressure, cloud cover • http://sheridan.geog.kent.edu/ssc.html

  2. SSC History • Kalkstein and Greene (Kalkstein et al. 1996) • Stations east of Rockies • winter and summer • Sheridan 2000 (Sheridan 2002) • Expanded to 300+ stations U.S. and Canada • All seasons • Bower, McGregor (mid 2000’s) • Expanded into Europe • Slightly different methodology

  3. Methods • Hybrid scheme • Weather types first identified manually • Seasonal typical seed days were then picked for each weather type for every station • Algorithms then use hypothetical seed days 365 days a year • Actual daily conditions then compared to seed day conditions • Day is classified into a weather type that most closely resembles the seed day

  4. Weather Types • DP (dry polar) is synonymous with the traditional cP air mass classification. This air mass is generally advected from polar regions around a cold-core anticyclone, and is usually associated with the lowest temperatures observed in a region for a particular time of year, as well as clear, dry conditions.

  5. Dry Moderate • DM air is mild and dry. It has no traditional analog, but is often found with zonal flow in the middle latitudes, especially in the lee of mountain ranges. It also arises when a traditional air mass such as cP or mT has been advected far from its source region and has thus modified considerably.

  6. Dry Tropical • DT (dry tropical) weather type is similar to the cT air mass; it represents the hottest and driest conditions found at any location. There are two primary sources of DT: either it is advected from the desert regions, such as the Sonoran or Sahara Desert, or it is produced by rapidly descending air, whether via orography (such as the chinook) or strong subsidence.

  7. Moist Polar • MP air is a large subset of the mP air mass; weather conditions are typically cloudy, humid, and cool. MP air appears either by inland transport from a cool ocean, or as a result of frontal overrunning well to the south of the region. In can also arise as a modified cP air mass, especially downwind of the Great Lakes.

  8. Moist Moderate • MM is considerably warmer and more humid than MP. The MM air mass typically appears in a zone south of MP air, still in an area of overrunning but with the responsible front much nearer. It can also arise within an mT air mass on days when high cloud cover suppresses the temperature.

  9. Moist Tropical • MT analogous to the traditional mT air mass, is warm and very humid. It is typically found in warm sectors of mid-latitude cyclones or in a return flow on the western side of an anticyclone; as one approaches the tropics this weather type dominates. • MT+ is a subset of MT that was derived after the initial classification, to account for the lack of utility of a weather-type scheme in the warm subtropics when one weather type dominates most of the year. It is defined as an MT day where both morning and afternoon temperatures are above seed day means, and thus captures the most "oppressive" subset of MT days.

  10. Transitional • TR days are defined as days in which one weather type yields to another, based on large shifts in pressure, dew point, and wind over the course of the day.

  11. Weather Type Considerations • Within the SSC scheme, weather-type characteristics change from station to station and day to day. • Moist Tropical weather type is hotter and more humid in the southeastern US, nearer its source region, than in the northeastern US, after it has modified somewhat. • MT is warmer at all locations in July than in January.

  12. Experimental SSC Climate Zones

  13. Southeastern Zone • Southeast60 stationsCapital: Jackson, MS • distinct seasonality • variable winter calendar • During the summer, the subtropical Bermuda High controls the weather • Moist Tropical (and Moist Moderate on cloudier days) account for nearly 3/4ths of all days.

  14. Basin and Range • Basin and range34 stationsCapital: Amarillo, TX • elevated arid areas • second-most affected by dry weather types • nearly half of all days DM.

  15. Laurentian • Laurentian58 stationsCaptial: Alpena, MI • considerable difference between winter and summer • presence of all weather types throughout the summer • limited tropical influence in the winter.

  16. Northern Rockies • Northern Rockies33 stationsCapital: Glasgow, MT • limited MT-penetration • high terrain nearby • some incidence of DT year-round • greater MP occurrence than in other temperate zones

  17. Mid-Latitude • True mid-latitude54 stationsCapital: Washington, DC • summer significant MT occurrence, and more limited polar-weather type influcence than 3a or 3b • only climate zone that is influenced by all weather types year-round.

  18. Arctic • Arctic37 stationsCaptial: Schefferville, QC • abundance of polar weather types • DP peaking in late winter • MP peaking at the autumn ice minimum.

  19. Tropical • Tropical13 stationsCapital: Key West, FL • MT monopoly in the summer • limited variability in the winter • only zone with the same weather type making up more than 50% of the calendar in every month of the year.

  20. Boreal Coast • Boreal coast15 stationsCapital: Yakutat, AK • adjacent cold ocean waters • dominated by MP • Dry Polar is common in the winter months • MM occurrence varies from station to station, based on proximity to a milder oceanic fetch on occasion.

  21. Sonoran • Sonoran5 stationsCapital: Phoenix, AZ • dominated by DT • five stations in this zone have two distinct summer patterns • Phoenix and Yuma heavily affected by the (MT) monsoon, and Las Vegas, Tucson, and Daggett not. • Resulting climograph is midway between the two.

  22. Marine • Marine16 stationsCapital: Halfiax, NS • similar to Boreal • warmer waters bring MM days more frequently • MT occurring on occasion in summer • has the highest TR frequency

  23. European • European58 stationsCapitals: Seattle, WA and Stuttgart, Germany • western Europe, with a few Pacific US stations included • Similar to zones 3a and 3c, all weather types have a presence • MM is more prominent here than in any other zone.

  24. Polar Air Mass Frequency (Jan) DP MP

  25. Polar Air Mass Frequency (July) DP MP

  26. Moderate Air Mass Frequency (Jan) DM MM

  27. Moderate Air Mass Frequency (July) DM MM

  28. Tropical Air Mass Frequency (Jan) DT MT

  29. Tropical Air Mass Frequency (July) DT MT

  30. Transition Jan July Oct April

  31. SSC Applications • Bioclimate • Human • Human Health/Mortality • Air pollution/Aerosols • Behavior/suicide/crime • Agriculture and Forest • Urban Heat Islands • Temp and Precip modification • Cryosphere/Snow • Heat Waves/Drought • Synoptic Climatology • Atmospheric circulation

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