Regional, Seasonal, and Diurnal Variations of Convection in the Himalayan Region

1
Regional, Seasonal, and Diurnal Variations of
Convection in the Himalayan Region

• Ulrike Romatschke
• University of Washington, University of Vienna
• Socorro Medina, Robert A. Houze Jr.
• University of Washington

13th Conference on Mountain Meteorology, 11-15
August 2008, Whistler, BC, Canada
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Objectives

• Use 3D reflectivity structure of precipitating
  systems to document
• Regional variability
• Role of topography
• Seasonal variability
• Pre-monsoon vs. monsoon
• Diurnal variability

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Data

• Tropical Rainfall Measurement Mission (TRMM)
  Precipitation Radar (PR)
• 3D reflectivity
• 1999 2006
• Pre-monsoon May
• Monsoon June September
• NCEP reanalysis
• Large-scale environment

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Classification of radar echoes within convective
systems

• Deep Convective Cores
• Convective 40 dBZ echo ? 10 km (vertical)
• Wide Convective Cores
• Convective 40 dBZ area ? 1 000 km² (horizontal)
• Broad Stratiform Echoes
• Stratiform area ? 50 000 km² (horizontal)

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Deep Convective Cores
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Deep Convective Cores

• Pre-monsoon (May)

• Monsoon (Jun-Sep)

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• Pre-monsoon

• Monsoon

Specific Humidity
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Deep Convective Cores

• Monsoon Diurnal Cycle

00 03 06 09
12 15 18 21
00
Mean Solar Time
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Wide Convective Cores
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Wide Convective Cores

• Pre-monsoon (May)

• Monsoon (Jun-Sep)

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Wide Convective Cores

• Monsoon Rain Climatology

• Monsoon Wide Convective Cores

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Land Wide Convective Cores
00 12 MST

• Monsoon Diurnal Cycle

00 03 06 09 12
15 18 21 00
Mean Solar Time
12 00 MST
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Wind composites for Wide Convective Cores at the
Himalayan foothills
1200 UTC ( 1730 MST)
0000 UTC ( 0530 MST)
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Broad Stratiform Echoes
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Broad Stratiform Echoes

• Monsoon Rain Climatology

• Monsoon Broad Stratiform Echoes

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Conclusions
Monsoon rainfall patterns strongly influenced by
convective systems of the following types

• Rain maximum over Arabian Sea and Bay of Bengal
• Convective systems with Broad Stratiform Echoes
• Rain maximum over Himalayan foothills
• Convective systems with Wide Convective Cores
  occurring late night/early morning
• Severe convection maximum in northwestern
  indentation region
• Convective systems with Deep Convective Cores

Ulrike Romatschke, University of Washington,
University of Vienna