Precipitation Types

Global and Regional Mean Precipitation

1. Types of Precipitation:

2. Measurement:

FIT, Feb 15, 2012 1

Global Mean Precipitation

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Satellite measurement of precipitationWhat happens in Hawaii?

Hawaii Mean Precipitation

3Precipitation measurement by Rain Gauge

Mean = 70 in Without land = 25 in

Honolulu Mean Precipitation

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Surface Analysis (Feb 11, 2012, 18 UTC)

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Hawaii (Feb 12, 2012, 0245 UTC)

6 Radar measurement of rain

Precipitation Types

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Precipitation Types

Drizzle: diameter < 0.5 mmRain: 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?

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Does rain always reach the surface?

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?

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Fig. 7-14, p. 174

Virga (Rain not reaching the surface)

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Fig. 2, p. 175

Shape of Raindrops

Spherical < 2 mm ; Parachute > 2 mm(surface area / volume) is minimum for 2.

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Table 7-2, p. 175

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Intensity of Rainfall

Precipitation Types

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Fig. 7-15, p. 176

14Falling ice-crystals and snowflakes (Fallstreaks) from cirrus clouds.

Snow

Fig. 7-16, p. 176

Fig. 7-17, p. 178

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Common forms of ice crystal

DendriteWhy is dendrite most common?

Table 7-3, p. 176

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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. 178

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Intensity of Snowfall

Is visibility the best way to measure snowfall? Can wind lead to visibility problem?

Fig. 4, p. 179

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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. 179

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Snow as Sound Absorbant

Fig. 7-18, p. 179

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Annual Average Snowfall over US

Why is Hawaii not included?

Snow in Hawaii !!

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Mauna Kea

Precipitation Types

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Fig. 7-19, p. 180

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Sleet and Freezing Rain

Partially melted snowflake or cold raindrop - - freezesDeep freezing layer - - Sleet <= 5 mmShallow freezing layer - - freezing rain >=0.5 mm

Fig. 7-20, p. 180

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Formation of Rime

Supercooled droplets in contact with object at below freezing temperature - - white milky granular ice

Fig. 7-21, p. 180

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Destruction due to Freezing Rain

Syracuse, New York, January 1998

Fig. 5, p. 181

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Aircraft de-icing

Fig. 7-22, p. 181

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Average number freezing rain/drizzle days

Fig. 7-23, p. 182

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Vertical Temperature Profile and Precipitation Type

Precipitation Types

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Fig. 4, p. 179

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Snow Grains and Snow Pellets

Snow Grains Snow Pellets

Diameter < 1 mm < 5 mm

Shower no yes

Brittleness/bouncy no yes

Origin Stratus cloud Cumulus congestus

Opaque yes yes

Fig. 7-24, p. 182

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Formation of Graupel / Snow Pellets

Ice particle + cloud droplets -- rimed ice crystal -- graupel (dift shape than rime) -- snow pelletDuring summer: graupel - - large raindropVigorously convective cloud: graupel - - hailstones

Fig. 7-27, p. 183

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Formation of Hail/Hailstone

Fig. 7-25, p. 182Fig. 7-26, p. 183

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Hail and Hailstone

Dia = 17.8 cm (7 in) ;Circumference = 47.6 cm (18.7 in); weight > 1.75 lb

Table 7-5, p. 185

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Summary of Precipitation Types

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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. 184

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Components of the standard rain gauge

Area of collector = 10 x area of measuring tube

Fig. 7-30, p. 185

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Tipping bucket rain gauge

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Radar

Transmitted energy

backscatter

Fig. 7-31a, p. 187

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Reflectivity Precipitation

Oklahama, April 24, 1999

Fig. 7-31a, p. 187

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Reflectivity Precipitation

Precipitation due to Fay (2008)

THE END

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Fig. 7-23a, p. 182

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Fig. 7-23b, p. 182

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Fig. 7-23c, p. 182

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Fig. 7-23d, p. 182

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Fig. 7-28a, p. 184 Fig. 7-28b, p. 184

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Fig. 7-32, p. 189

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Fig. 7-32, p. 189

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