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Precipitation Types. Global and Regional Mean Precipitation 1. Types of Precipitation: 2. Measurement:. FIT, Feb 15, 2012. Global Mean Precipitation. Satellite measurement of precipitation What happens in Hawaii?. Hawaii Mean Precipitation. Mean = 70 in Without land = 25 in.

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slide1

Precipitation Types

Global and Regional Mean Precipitation

1. Types of Precipitation:

2. Measurement:

FIT, Feb 15, 2012

slide2

Global Mean Precipitation

Satellite measurement of precipitation

What happens in Hawaii?

hawaii mean precipitation
Hawaii Mean Precipitation

Mean = 70 in

Without land = 25 in

Precipitation measurement by Rain Gauge

slide6

Hawaii (Feb 12, 2012, 0245 UTC)

Radar measurement of rain

slide8

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?

slide9

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?

slide11

Shape of Raindrops

Spherical < 2 mm ; Parachute > 2 mm

(surface area / volume) is minimum for 2.

Fig. 2, p. 175

slide12

Intensity of Rainfall

Table 7-2, p. 175

slide14

Snow

c

Falling ice-crystals and snowflakes (Fallstreaks)

from cirrus clouds.

Fig. 7-15, p. 176

slide15

Common forms of ice crystal

Fig. 7-16, p. 176

Why is dendrite

most common?

Dendrite

Fig. 7-17, p. 178

slide16

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 7-3, p. 176

slide17

Intensity of Snowfall

Is visibility the best way to measure snowfall?

Can wind lead to visibility problem?

Table 7-4, p. 178

slide18

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

slide20

Annual Average Snowfall over US

Why is Hawaii not included?

Fig. 7-18, p. 179

slide23

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. 7-19, p. 180

slide24

Formation of Rime

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

Fig. 7-20, p. 180

slide25

Destruction due to Freezing Rain

Syracuse, New York, January 1998

Fig. 7-21, p. 180

slide26

Aircraft de-icing

Fig. 5, p. 181

slide31

Formation of Graupel / Snow Pellets

gr

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. 7-24, p. 182

slide33

Hail and Hailstone

Dia = 17.8 cm (7 in) ;

Circumference = 47.6 cm (18.7 in);

weight > 1.75 lb

Fig. 7-25, p. 182

Fig. 7-26, p. 183

slide35

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.

slide36

Components of the standard rain gauge

Area of collector = 10 x area of measuring tube

Fig. 7-29, p. 184

slide37

Tipping bucket rain gauge

Fig. 7-30, p. 185

slide38

Transmitted energy

backscatter

Radar

slide39

Reflectivity

Precipitation

Oklahama, April 24, 1999

Fig. 7-31a, p. 187

slide40

Precipitation due to Fay (2008)

Precipitation

Reflectivity

Fig. 7-31a, p. 187

slide46

Fig. 7-28a, p. 184

Fig. 7-28b, p. 184

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