Cirrus Production by Tropical Mesoscale Convective Systems

1. Cirrus Production by Tropical Mesoscale Convective Systems Jasmine Cetrone and Robert Houze8 February 2008

2. Are Cirrus Clouds Important? With high clouds Without high clouds ? Sherwood et al. (1994)

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

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

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

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

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

8. 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

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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

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

18. CloudSat Thick Anvil (>6km) 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

19. Conditional Instability W Africa Maritime Continent Bay of Bengal S S S S S S • 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

20. What Controls Anvil? S S S • 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 S S S

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

22. 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) S S S S S S

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