Precipitation

Chapter 7Chapter 7Part 2

Common ice crystal habitsCommon ice crystal habits

Dendrite snowflakesDendrite snowflakes

Average annual snowfallg

Precipitation TypesPrecipitation Types

• Sleet: air below freezing, then travels through a layer of air above freezing, g y g,begins to melt and then falls through a layer of air below freezing just above thelayer of air below freezing just above the ground surface

f f• Freezing Rain: ground surface is freezing as rain hits the surface it freezes

Formation of Sleet

RimeRime

Effects of Freezing RainEffects of Freezing Rain

Average # freezing rain/drizzle daysAverage # freezing rain/drizzle days

Effects of temperature profiles on precipitation

Precipitation TypesPrecipitation Types

• Observation: Aircraft Icing– Aviation hazard is created by the increase in y

weight as ice forms on the body of the airplanep

– Spray plane with anti-freeze

More Precipitation TypesMore Precipitation Types

• Snow Grains: solid equivalent of drizzle, no bounce or shatter

• Snow Pellets: larger than grains, bounce, break crunch underfootbreak, crunch underfoot

• Graupel: ice particle accumulation with rime

• Hail: graupel act as embryo in intense• Hail: graupel act as embryo in intense thunderstorm, grow through aggregation

h d b d ftas pushed up by updraft.

Formation of snow pelletsFormation of snow pellets

Snowflake to Snow pelletSnowflake to Snow pellet

Accumulation of HailAccumulation of Hail

Extreme HailstonesExtreme Hailstones

Measuring PrecipitationMeasuring Precipitation

• Instruments– Rain gauge: standard, tipping bucket, g g , pp g ,

weighing• Snow: average depth at 3 locations, 10:1 waterSnow: average depth at 3 locations, 10:1 water

equivalent

• Doppler RadarDoppler Radar– Transmitter generates energy toward target,

returned energy measured and displayedreturned energy measured and displayed• Brightness of echo = amount/intensity of rain

– Doppler: measures speed of horizontal rain

Standard RainGaugeGauge

Tipping Bucket Rain GaugeTipping Bucket Rain Gauge

Measuring PrecipitationMeasuring Precipitation

• Measuring from space– Specific satellites designed to assess clouds, p g ,

atmospheric moisture, and rain• Tropical Rainfall Measuring Mission (TRMM)Tropical Rainfall Measuring Mission (TRMM)• CloudSat

TRIMMTRIMM

• Measures rainfall intensity from satellitey

• Uses radar and passive remote sensing methodsremote sensing methods

• Collects radiation in the microwave, IR and visible spectrumvisible spectrum

Katrina: 28 Aug 2005Katrina: 28 Aug 2005

Katrina: 29 Aug 2005Katrina: 29 Aug 2005

CloudSatCloudSat

• Measures cloud properties from satellite• Cloudsat uses a 94 GHz (microwave)Cloudsat uses a 94 GHz (microwave)

cloud radar, providing radar backscatter from cloudsfrom clouds

CloudSatCloudSat• Quicklook example on Feb 10, 2009 (last Tues)

CloudSat ExampleCloudSat Example

CloudSatCloudSat

• Tropical Cyclone yBilly

• December 25th, 2008 as the storm moved off the coast of Western Australia. The storm contained winds of 60contained winds of 60 mph (100 km/hr) at the time of this overpass. Billy intensified as the storm moved off the Australian coast into warmer waters but later weakened as the stormweakened as the storm moved into cooler waters and stronger wind shear.

Feb 10 2009 Tornado EventFeb 10, 2009 Tornado Event

• During the afternoon and evening hours of February 10, 2009, tornadoes occurred in y , ,the central third of Oklahoma and north TexasTexas

Storm ReportsStorm Reports

Dewpoints on 2/10 at 19UTCDewpoints on 2/10 at 19UTC

Visible satellite image at 2233z Feb 10

By 2:14 PM CST, it was beginning to develop a hook echo, and by 2:18 PM CST, the hook echo was fully developed.

Feb 10 2009 Tornado EventFeb 10, 2009 Tornado Event

KTLX Radar Imagery for theEdmond OK Tornado at 256 pm CST onEdmond, OK Tornado at 256 pm CST on 2/10/2009

Feb 10 2009 Tornado EventFeb 10, 2009 Tornado Event