Presentation on theme: "Precipitation Types Global and Regional Mean Precipitation 1. Types of Precipitation: 2. Measurement: FIT, Feb 15, 2012 1."— Presentation transcript:
Precipitation Types Global and Regional Mean Precipitation 1. Types of Precipitation: 2. Measurement: FIT, Feb 15,
Global Mean Precipitation 2 Satellite measurement of precipitation What happens in Hawaii?
Hawaii Mean Precipitation 3 Precipitation measurement by Rain Gauge Mean = 70 in Without land = 25 in
Honolulu Mean Precipitation 4
Surface Analysis (Feb 11, 2012, 18 UTC) 5
Hawaii (Feb 12, 2012, 0245 UTC) 6 Radar measurement of rain
Precipitation Types 7
Precipitation Types Drizzle: diameter < 0.5 mm Rain: diameter >= 0.5 mm Where are the raindrops larger, Miami or Seattle? Raindrops almost always < 6 mm because collision among raindrops too large raindrops tend to break up Start as rain, but may fall as drizzle. Does rain always reach the surface? 8
Falling precipitation that evaporate before reaching surface - -- Virga Low humidity - - evaporation - - drops become smaller - - rate of fall decreases Strong updraft Sudden rain shower and cloudburst (Cumuliform) Rain and no-rain in places next to each other (Cumulonimbus) Continuous rain at small vertical currents (layered cloud or Nimbostratus) How does “Virga” look like and where does it happen? 9
Fig. 7-14, p. 174 Virga (Rain not reaching the surface) 10
Fig. 2, p. 175 Shape of Raindrops Spherical 2 mm (surface area / volume) is minimum for 2. 11
Table 7-2, p Intensity of Rainfall
Precipitation Types 13
Fig. 7-15, p Falling ice-crystals and snowflakes (Fallstreaks) from cirrus clouds. Snow
Fig. 7-16, p. 176 Fig. 7-17, p Common forms of ice crystal Dendrite Why is dendrite most common?
Table 7-3, p Why is dendrite most common? Growth = f(temperature, sat. vap. Pr. difference) Maximum growth rate is at -12 to -16 C, when saturation vapor pressure difference between water and ice is maximum.
Table 7-4, p Intensity of Snowfall Is visibility the best way to measure snowfall? Can wind lead to visibility problem?
Fig. 4, p Some more terms related to snowfall Flurries : light and intermittent from developing cumulus cloud Snow squall : brief but more intense than flurries, usually from cumuliform clouds Drifting snow : surface movement Blowing snow : in air movement Ground blizzard : after falling snow has ended Blanket of snow: snow covering the landscape
Fig. 4, p Snow as Sound Absorbant
Fig. 7-18, p Annual Average Snowfall over US Why is Hawaii not included?
Snow in Hawaii !! 21 Mauna Kea
Precipitation Types 22
Fig. 7-19, p Sleet and Freezing Rain Partially melted snowflake or cold raindrop - - freezes Deep freezing layer - - Sleet <= 5 mm Shallow freezing layer - - freezing rain >=0.5 mm
Fig. 7-20, p Formation of Rime Supercooled droplets in contact with object at below freezing temperature - - white milky granular ice
Fig. 7-21, p Destruction due to Freezing Rain Syracuse, New York, January 1998
Fig. 5, p Aircraft de-icing
Fig. 7-22, p Average number freezing rain/drizzle days
Fig. 7-23, p Vertical Temperature Profile and Precipitation Type
Precipitation Types 29
Fig. 4, p Snow Grains and Snow Pellets Snow GrainsSnow Pellets Diameter< 1 mm< 5 mm Showernoyes Brittleness/bouncynoyes OriginStratus cloudCumulus congestus Opaqueyes
Fig. 7-24, p Formation of Graupel / Snow Pellets Ice particle + cloud droplets -- rimed ice crystal -- graupel (dift shape than rime) -- snow pellet During summer: graupel - - large raindrop Vigorously convective cloud: graupel - - hailstones
Fig. 7-27, p Formation of Hail/Hailstone
Fig. 7-25, p. 182 Fig. 7-26, p Hail and Hailstone Dia = 17.8 cm (7 in) ; Circumference = 47.6 cm (18.7 in); weight > 1.75 lb
Table 7-5, p Summary of Precipitation Types
35 Measurement of Precipitation In-situ measurement : Rain gauge; accurate but spotty. Remote measurement : Radar, Satellite; not so accurate but large coverage. Combination of the above.
Fig. 7-29, p Components of the standard rain gauge Area of collector = 10 x area of measuring tube
Fig. 7-30, p Tipping bucket rain gauge
38 Radar Transmitted energy backscatter
Fig. 7-31a, p ReflectivityPrecipitation Oklahama, April 24, 1999
Fig. 7-31a, p Reflectivity Precipitation Precipitation due to Fay (2008)