TRMM Observations of Convection over the TRMM Observations of Convection over the Himalayan RegionHimalayan RegionR. A. Houze and D. C. WiltonR. A. Houze and D. C. Wilton

University of WashingtonUniversity of Washington

Presented 1 February 2005 at the International Brainstorming Meeting on “Modeling and Prediction over Indian Monsoon Region: Vision 2015”, National Centre for Medium Range Weather Forecasting Department of Science & Technology, Noida, UP, India

TRMM Precipitation Radar Data Set Used in TRMM Precipitation Radar Data Set Used in This StudyThis Study

• June-September 2002, 2003• 1648 Overpasses over Himalayan region

• Data specially processed at University of Washington• Cartesianized to facilitate analysis in “Mountain Zebra”

• This data set optimized to analyze vertical structure of echoes

TRMM Satellite InstrumentationTRMM Satellite Instrumentation

Kummerow et al, 1998

= 2 mmImportant! PR measures 3D structure of radar echoes

Idealized Idealized HorizontalHorizontal Pattern of the Radar Echo Pattern of the Radar Echo Pattern in a Mesoscale Convective SystemPattern in a Mesoscale Convective System

Radar reflectivity Echo type

Plan View

Houze 1997

Conceptual Model of Conceptual Model of VerticalVertical Structure Structure “Convective” Rain Elements“Convective” Rain Elements

Houze 1997

Houze 1997

Conceptual Model of Conceptual Model of VerticalVertical Structure Structure “Stratiform ” Rain Elements“Stratiform ” Rain Elements

To study the vertical structure of convective To study the vertical structure of convective regions we define 3D echo regions we define 3D echo “cores”“cores”

• The TRMM Precipitation Radar data are provided in “bins” ~5 km in the horizontal and ~0.25 km in the vertical

• Echo corecoress are formed by contiguous bins (in 3D space) of reflectivity values which exceed the threshold of 40 dBZ.

3D radar echo bounded by 40 dBZ contour

land

echocore

““Deep Convection” Core: 14 June 2002, 0859 UTCDeep Convection” Core: 14 June 2002, 0859 UTC

“deep convection” cores are those for which the maximum height of the 40 dBZ core are greater than 10 km

16

8

0 55 110

Distance (km)

Hei

ght

(km

)28N

30N

4 km level

74E 76E

Analysis SubregionsAnalysis Subregions

Arabian Sea

Bay of Bengal

°N

°E

WesternWesternSubregionSubregion

Central Central SubregionSubregion Eastern Eastern

SubregionSubregion

INDIA

Normalized Frequency Distribution Normalized Frequency Distribution of of 40 dBZ40 dBZ Convective Echo Core HeightsConvective Echo Core Heights

In western region--graupel particles

lofted to great heights by strong

updrafts

Barros et al. 2004

Lightning Frequency Based on TRMM Satellite Lightning Frequency Based on TRMM Satellite ObservationsObservations

““Wide Convection” Core: 22 July 2002, 13:09 UTCWide Convection” Core: 22 July 2002, 13:09 UTC

“wide convection” cores are those for which the area of the 40 dBZ core are greater than 1,000 km2, corresponding to a dimension of approximately 30km

16

8

Distance (km)

Hei

ght

(km

)

0 120 240

30N

34N

4 km level

72E 76E

Cumulative Distribution of Convective Core BreadthCumulative Distribution of Convective Core Breadth

In western region—wide convective

areas more frequent

Analysis of stratiform echo regionsAnalysis of stratiform echo regions

Used TRMM algorithm for separating echoes into stratiform & convective regions

Two criteria:

Existence of bright band Lack of intense echo cores

22N

30N

92E 100E

4.5 km level

22N

30N

92E 100E

Echo Classified as Stratiform

“broad stratiform” cases are those for which the area classified by the TRMM algorithm as stratiform precipitation is greater than about

50,000 km2, corresponding to a dimension of approximately 225 km

““Broad Stratiform” Case: 5 June 2003, 13:47 UTCBroad Stratiform” Case: 5 June 2003, 13:47 UTC

24N

28N

94E 98E

4.5 km level

16

8

0 576 Distance (km)

Hei

ght

(km

)288

Cross Section

Cumulative Distribution FunctionCumulative Distribution Functionfor Stratiform Precipitation Areas for Stratiform Precipitation Areas

TRMM Satellite InstrumentationTRMM Satellite Instrumentation

Kummerow et al, 1998

= 2 cmImportant! PR measures 3D structure of radar echoes

Contoured Frequency by Altitude DiagramContoured Frequency by Altitude Diagram

Relative frequency of occurrence

All data1648 overpasses

Conve

cti

veStratifor

mReflectivity Statistics by Sub-Region, Rain-Type, & AltitudeReflectivity Statistics by Sub-Region, Rain-Type, & Altitude

Convection is stronger & deeper in west

Statiform more pronounced in east

Terrain Elevation CategoriesTerrain Elevation Categories

Mountain

MountainLowland

Lowland

Foothill

Foothill

°N

°E

Lowland 0-300 m, Foothills 300-3000 m, Mountain >3000 km

Reflectivity Statistics by Subtending TerrainReflectivity Statistics by Subtending TerrainL

ow

lan

dF

oo

thill

sM

ou

nta

in

Convection is slightly deeper & stronger over the

lowlands than the foothills

Intense Convective Wide Stratiform

°N

°E

Locations of Intense Convective Cases and Wide Stratiform Locations of Intense Convective Cases and Wide Stratiform CasesCases

Concavities lead to concentration

of intense convection in

NW and stratiform

systems in NE

ConclusionsConclusions

2 years of TRMM PR data have been processed for analysis of vertical structure of convection over the Himalayan region40 dBZ cores deepest & broadest over NW region40 dBZ cores in NW region can reach 17+ km—indicating graupel lofted to high levels by strong updraftsIntense convection occurs primarily over lowlands and foothillsIntense convection is concentrated in the NW concavity of the Himalayas—continental regimeStratiform areas larger & more frequent over NE, concentrated in the NE concavity—indicating a more maritime convective regime.

End

Maheshwari & Mathur 1968

Thunderstorm over IndiaThunderstorm over India

“low echo centroid”

(coalescence & riming)

Caracena et al. 1979

Colorado Rockies Big Thompson Storm 1976Colorado Rockies Big Thompson Storm 1976

“low echo centroid”

Contoured Frequency by Altitude DiagramsContoured Frequency by Altitude Diagrams

Contoured Frequency by Altitude DiagramsContoured Frequency by Altitude Diagrams

Contoured Frequency by Altitude DiagramsContoured Frequency by Altitude Diagrams

Contoured Frequency by Altitude DiagramsContoured Frequency by Altitude Diagrams

Contoured Frequency by Altitude DiagramContoured Frequency by Altitude Diagram

Relative frequency of occurrence

All data1648 overpasses

Reflectivity by Sub-RegionReflectivity by Sub-Region

Wide Area of Convection Case: 1309 UTC 22 July 2002Wide Area of Convection Case: 1309 UTC 22 July 200200 UTC Soundings00 UTC Soundings

Wide Area of Convection Case: 1309 UTC 22 July 2002Wide Area of Convection Case: 1309 UTC 22 July 200212 UTC Soundings12 UTC Soundings

Broad Stratiform Case: 13:47 UTCBroad Stratiform Case: 13:47 UTC 5 June 2003 5 June 2003 12 UTC Soundings12 UTC Soundings

Z=R^1.25

0

5

10

15

20

25

0 10 20 30 40 50

dBZ

R (

mm

/h)

Series1

Reflectivity Related to Rain RateReflectivity Related to Rain Rate

20-year Alpine Autumn Precipitation Climatology

(rain gauge analysis by Frei and Schaer 1998)