Cirrus Production by Tropical Mesoscale Convective Systems Jasmine Cetrone and Robert Houze 8 February 2008

Are Cirrus Clouds Important? Sherwood et al. (1994) ? With high cloudsWithout high clouds

Global Distribution of High Clouds Majority of high clouds confined to the tropics Wylie et al. (1994) JJA DJF

Cirrus and Precipitation Precipitation intimately tied to cirrus ISCCP High Cloud Amounts Schumacher and Houze (2003)

MCSs as Major Contributors to Upper- level Hydrometeors Houze (1982)

Distribution of MCS Properties TRMM TMI 85-GHz ice scattering TRMM-derived summer time stratiform rain fraction

Water Budget of a MCS SW LW Adapted from Houze et al. (1980)

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

Regions of Interest Schumacher and Houze (2003) Summer time SF rain frac Continental Monsoon Oceanic Monsoon Maritime Continent Monsoon

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

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

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

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 – Monsoon season in Maritime Island –Use of hourly IR geostationary satellite data insured selection of MCS cases

TRMM PR Convective CFADs 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 W AfricaMaritime Continent Bay of Bengal

TRMM PR Stratiform CFADs 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 W AfricaMaritime Continent Bay of Bengal

TRMM PR Convective Rain Fraction 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 W AfricaMaritime Continent Bay of Bengal

CloudSat Anvil CFADs W Africa anvil clouds shallower! Maritime anvil clouds reach the highest W AfricaMaritime Continent Bay of Bengal

CloudSat Thick Anvil (>6km) CFADs 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 W AfricaMaritime Continent Bay of Bengal

Conditional Instability 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 SSS SSS W AfricaMaritime Continent Bay of Bengal

What Controls Anvil? 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 regions…so smaller stratiform precipitation areas leads to less anvil SSS SSS

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

Preliminary Conclusions SSS SSS 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)

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