Study of Intense Convection over Taiwan:

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Study of Intense Convection over Taiwan Some
Food for Thought R. Houze

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Past Observational Studies of Orographic
Precipitation

• Stable to nearly neutral environments
• Midlatitude frontal systems passing over mountain
  ranges
• Many field projects CASCADE, SCPP, COAST,
  CALJET, PACJET, IPEX, MAP, IMPROVE II
• Hobbs 1975, Marwitz 1987, Braun et al. 1997, Yu
  Smull 2000, Schultz et al. 2002, White et al.
  2003, Ralph et al. 2005, Rotunno and Houze 2007,
  many others
• Mechanisms by which flow over a mountain range
  modifies the frontal precipitation--microphysical/
  dynamical interactions
• Unstable environments
• Deep convection over and near high terrain.
• Big Thompson, Rapid City floods Maddox et al.
  1978, Caracena et al. 1979
• But, only two field projects SPACE, Cotton et
  al. 1983, and NAME

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Synoptic and topographic factors affecting
orographically influenced deep convection in
other regions
Taiwan orographic convection has some
similarities to deep convective regimes elsewhere
in Asia and elsewhere in the world.
Himalayas
Taiwan
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What could a field project in Taiwan tell us
about intense convection?

• What processes focus deep convection near the
  base of a mountain range?
• Blocking
• Diurnal effects
• Juxtaposition of moist and dry flows
• Low-level capping of convection near mountains
• In addition--Basic convective processes
• Boundary layer
• Microphysics
• Electrification

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Why do this project in Taiwan and not in the U.S.?

• Good leveraging from Taiwan
• Natural laboratory for the orographic convection
  problem
• Highly confined area amenable to setting up field
  observations
• Low-level moist flow
• Upper-level dry flow
• A region of flat land in front of the mountain
  range
• Few other complicating factors

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Lightning frequency based on TRMM satellite
observations
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Broad stratiform case11 Aug 2002
0252 UTC
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Reflectivity data for 2 monsoon seasons
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TRMM Data in the Himalayan Region
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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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A case of deep isolated 40 dBZ core14 June 2002
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Reflectivity data for 2 monsoon seasons
Convection is slightly deeper stronger over the
lowlands than the foothills