Cirrus Production by Tropical Mesoscale Convective Systems

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Cirrus Production by Tropical Mesoscale
Convective Systems
Jasmine Cetrone and Robert Houze8 February 2008
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Are Cirrus Clouds Important?
With high clouds
Without high clouds
Sherwood et al. (1994)
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Global Distribution of High Clouds

• Majority of high clouds confined to the tropics

JJA
DJF
Wylie et al. (1994)
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Cirrus and Precipitation

• Precipitation intimately tied to cirrus

ISCCP High Cloud Amounts
Schumacher and Houze (2003)
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MCSs as Major Contributors to Upper-level
Hydrometeors
Houze (1982)
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Distribution of MCS Properties
TRMM-derived summer time stratiform rain fraction
TRMM TMI 85-GHz ice scattering
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Water Budget of a MCS
SW
LW
LW
Adapted from Houze et al. (1980)
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Goals

• Establish climatologies of precipitation and
  anvil regions of MCSs over regions of the tropics
• Determine relationships between the precipitation
  and anvil regions of MCSs
• Complete the conceptual model of cloud and
  precipitation structure of MCSs

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Regions of Interest
ContinentalMonsoon
OceanicMonsoon
Summer timeSF rain frac
Maritime ContinentMonsoon
Schumacher and Houze (2003)
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West Africa

• Influenced by African Monsoon during NH summer
  months (continental monsoon climate)
• Many squall-like MCSs
• Summer 2006 AMMA project
• Scanning precipitation radar
• 4xdaily soundings
• Vertically pointing cloud radar

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Maritime Continent

• Influenced by Australian Monsoon during SH summer
  months (island monsoon climate)
• Massive MCSs influenced by monsoonal flow
• Long-term dataset at Darwin, Australia
• 2 scanning precipitation radars (dual-Doppler)
• Vertically pointing cloud radar
• 2xdaily soundings
• Satellite coverage

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Bay of Bengal

• Influenced by Asian Monsoon during NH summer
  months (oceanic monsoon climate)
• Southward-propagating leading-convection,
  trailing stratiform type MCSs
• May 1999 JASMINE project
• Scanning precipitation radar
• 3-hourly soundings
• Vertically pointing cloud radar

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Methodology

• TRMM PR and CloudSat reflectivity data from over
  three regions only from MCSs
• 2006 Monsoon season in W Africa
• 2006 Monsoon season in Bay of Bengal
• 2006-2007 Monsoon season in Maritime Island
• Use of hourly IR geostationary satellite data
  insured selection of MCS cases

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TRMM PR Convective CFADs
W Africa
Maritime Continent
Bay of Bengal

• Convective precip in W Africa MCSs are taller and
  more intense
• Convective precip in Maritime and Bengal MCSs is
  similar, with Maritime being slightly taller

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TRMM PR Stratiform CFADs
W Africa
Maritime Continent
Bay of Bengal

• Stratiform precip in W Africa MCSs taller and
  high reflectivities at high altitudes (indicating
  large ice aloft, consistent with Nesbitt et al
  2000.)
• Stratiform precip in Maritime MCSs slightly
  taller and with higher reflectivities aloft than
  Bengal

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TRMM PR Convective Rain Fraction
W Africa
Maritime Continent
Bay of Bengal

• Very high convective rain fractions in W Africa
  MCSs, indicating stratiform regions that are
  smaller and/or shorter in duration
• Maritime has lowest convective rain fraction,
  influence of monsoonal systems with large, long
  lasting stratiform regions
• Bengal distribution indicates moderate convective
  rain fraction, and narrow shows that MCSs in that
  region are very similar to each other

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CloudSat Anvil CFADs
W Africa
Maritime Continent
Bay of Bengal

• W Africa anvil clouds shallower!
• Maritime anvil clouds reach the highest

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CloudSat Thick Anvil (gt6km) CFADs
W Africa
Maritime Continent
Bay of Bengal

• W Africa anvils have high frequency of high
  reflectivity near cloud bottom(large crystals)
• Maritime and Bengal distributions similar
• Evidence of aggregation below thick anvil?
• High IWP for W Africa anvils compared to
  Bengal/Maritime anvils

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Conditional Instability
W Africa
Maritime Continent
Bay of Bengal
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• W Africa has layer of strong instability from
  surface to 600 hPa, leads to violent convective
  updrafts
• Maritime has layer of instability from surface to
  600 hPa, while Bengal has more shallow layer of
  instability

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What Controls Anvil?
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• Bengal and Maritime MCSs show many similarities
  in anvil, while W Africa MCSs have different
  anvil features
• W Africa MCSs have precipitation CFADs that show
  deeper, more intense convection
• Possibly the intensity of convection and/or
  fraction of convective rainfall affects the type
  of anvil
• Much anvil comes out of stratiform precipitation
  regionsso smaller stratiform precipitation areas
  leads to less anvil

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Convection and Anvils in MCSs
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• When deep, intense, continental convection is
  present, see a settling of the anvil
• Overshooting top
• Large ice falling

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Preliminary Conclusions

• W Africa MCSs
• Deep, intense convection, small stratiform area
• Anvils shallower, but high IWP
• Maritime MCSs
• Moderate convection, large stratiform areas
• Deep anvils
• Bengal MCSs
• Moderate convection, moderate stratiform areas
• Deep anvils
• Anvil height and density in MCSs influenced by
  convective intensity and amount
• Anvil longevity possibly moderated by amount of
  stratiform precipitation (need case studies)

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Future Work
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• Environmental conditions also a factor
• Case studies in each region for different
  environmental conditions
• Examine TRMM / CloudSat coincident cases for
  coherent view

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