Robert A. Houze, Jr., Darren C. Wilton, and Bradley F. Smull

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Monsoon Convection in the Himalayan Regionas
seen by the TRMM Precipitation Radar
Robert A. Houze, Jr., Darren C. Wilton, and
Bradley F. Smull University of Washington
Thompson Lecture, NCAR, Boulder, 31 October 2006
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Monsoon Convection in the Himalayan Regionas
seen by the TRMM Precipitation Radar
Robert A. Houze, Jr., Darren C. Wilton, and
Bradley F. Smull University of Washington
Precipitation
Thompson Lecture, NCAR, Boulder, 31 October 2006
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Goal
To gain insight into the physical mechanisms by
which heavy monsoon precipitation is produced
Approach

• Use data from the Precipitation Radar (PR) on the
  Tropical Rainfall Measuring Mission (TRMM)
  satellite.
• Examine the three-dimensional structure of the
  storms producing intense monsoon precipitation.
• Determine how the 3D echo structure varies in
  relation to details of the Himalayan topography
  and proximity to surrounding oceans.

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TRMM Precipitation Radar Data Set Used in This
Study

• June-September 2002, 2003
• 1648 Overpasses over Himalayan region
• Data specially processed at UW to optimize
  vertical structure analysis

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Analysis Subregions
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TRMM Satellite Instrumentation
l 2 cm
Important! PR measures 3D structure of radar
echoes
Kummerow et al, 1998
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Analysis of three-dimensional echo regions

• Used TRMM algorithm for separating echoes into
  stratiform convective regions
• STRATIFORM identified by 2 criteria
• Non-stratiform is either CONVECTIVE or OTHER

• Used TRMM algorithm for separating echoes into
  stratiform convective regions
• STRATIFORM identified by 2 criteria
• Non-stratiform is either CONVECTIVE or OTHER

Existence of bright band
Lack of intense echo cores
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Analysis of Convective Echo Cores
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To study the vertical structure of convective
regions we first define 3D echo cores

• The TRMM Precipitation Radar data are provided in
  bins 5 km in the horizontal and 0.25 km in
  the vertical
• Echo cores 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
echocore
land
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Western
Central
Eastern
Deep Intense Cores 40 dBZ echo gt 10 km in
height
Wide Intense Cores 40 dBZ echo gt 1000 km2
area
Broad Stratiform Echo stratiform echo gt
50,000 km2
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Lightning frequency based on TRMM satellite
observations
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Carlson et al. 1983
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Sawyer 1947
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A case of deep isolated 40 dBZ core14 June 2002
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A case of deep isolated 40 dBZ core14 June 2002
0900 UTC
0930 UTC
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A case of deep isolated 40 dBZ core14 June 2002
0900 UTC
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Deep cores over the Tibetan Plateau14 July 2002
1227 UTC
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Height of 40 dBZ cores by region
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A case of wide 40 dBZ echo core22 July 2002
10 meter level
200 mb level
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A case of wide 40 dBZ echo core22 July 2002
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A case of wide 40 dBZ echo core22 July 2002
1300 UTC
1400 UTC
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A case of wide 40 dBZ echo core22 July 2002
1300 UTC
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A typical case of wide 40 dBZ echo core with line
organization
2208 UTC
3 Sep 2003
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A wide 40 dBZ echo core with squall-line
organizationrare!
2017 UTC
5 June 2003
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A of wide 40 dBZ echo core with squall-line
organizationrare!
500 mb jet over and parallel to the Himalayas
10 meter level
500 mb level
5 June 2003
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Horizontal area of 40 dBZ cores by region
Cumulative Frequency
Area (km2)
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Analysis of Stratiform Echoes
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Intraseasonal Variation of the Monsoon
Webster Tomas 1997
39 events1985-95
Day 08 mm/d5N-5S80-90E
Break
Active
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Broad stratiform case11 Aug 2002
10 meter level
200 mb level
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Broad stratiform case11 Aug 2002
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Broad stratiform case11 Aug 2002
0252 UTC
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Broad stratiform caseUpstream of mountains
0455 UTC
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Size of stratiform precipitation area by
geographical region
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Analysis of All the Reflectivity Data
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Reflectivity data for 2 monsoon seasons
Relative frequency of occurrence
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Reflectivity data for 2 monsoon seasons

• Convection is stronger deeper in west
• Stratiform more pronounced in east

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Reflectivity data for 2 monsoon seasons
Convection is slightly deeper stronger over the
lowlands than the foothills
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Summary
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Epilogue

• What has this study accomplished?
• Particular structure and organization of summer
  monsoon convection over the subcontinent of South
  Asia
• Behavior of highly convective clouds in a moist
  flow impinging on a mountain barrier
• What questions remain?
• Why does the intense convection trigger just
  upstream of the barrier?
• In depressions, what are the relative roles of
  orography and synoptic dynamics?
• Can high-resolution models predict the observed
  structures?

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Thanks