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Diurnal Variability of Deep Tropical Convection

Diurnal Variability of Deep Tropical Convection. R. A. Houze. Lecture, Indian Institute of Tropical Meteorology, Pune, 12 August 2010. Clouds in Low Latitudes. Lecture Sequence. Basic tropical cloud types Severe convection & mesoscale systems Tropical cloud population

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Diurnal Variability of Deep Tropical Convection

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  1. Diurnal Variability of Deep Tropical Convection R. A. Houze Lecture, Indian Institute of Tropical Meteorology, Pune, 12 August 2010

  2. Clouds in Low Latitudes Lecture Sequence • Basic tropical cloud types • Severe convection & mesoscale systems • Tropical cloud population • Convective feedbacks to large-scales • Monsoon convection • Diurnal variability • Clouds in tropical cyclones

  3. This talk will illustrate that… • Diurnal cycle of tropical convection depends on: • the scale of the convective phenomenon—time scale of large systems not separable from diurnal time scale • The location of the convection—open ocean, near coastline, over mountains

  4. A Purely Oceanic Environment

  5. Convective systems over the West Pacific Cloud shield <208 K • <80 km • 80-170 km • 170-300 km • >300 km Chen & Houze 1997

  6. Convective systems over the West Pacific Cloud systems tracked in time in IR satellite data Small Large Convective systems over the West Pacific Chen & Houze 1997

  7. Convective systems over the West Pacific Time needed for large systems to reach maximum size Chen & Houze 1997

  8. Convective systems over the West Pacific Cooler than Day 1 Relationship to surface air temperature Chen & Houze 1997

  9. Convective systems over the West Pacific “Diurnal Dancing” MJO MJO Chen & Houze 1997

  10. Over Land Near Mountains

  11. Diurnal cycles of different types of extreme convective systems in mountainous regions Romatschke et al. 2010

  12. This illustrates the effect of nocturnal downslope flow on the diurnal cycle of wide convective core occurrence Wide convective core occurrence by time of day during monsoon season Romatschke et al. 2010

  13. Pre-monsoon Season in South Asia Mountains can lead to small and medium sized systems having different diurnal cycles—mesoscale lifecycle effect Δ Small 600-8,500 km2  Medium 8,500-35,000 km2 CHF MEP Romatschke et al. 2010

  14. A Coastal Environment

  15. Winter MONEX December1978January1979 Johnson & Houze 1987

  16. WINTER MONEXDiurnal variation of high cloudiness near Borneo Bintulu December 1978 Mean fractional area covered high clouds in IR images S. CHINA SEA BORNEO 08 LST 20 LST 14 LST 02 LST Houze et al. 1981

  17. WINTER MONEXDiurnal variation of precipitation near Borneo Bintulu BORNEO December 1978 Mean fractional area covered by radar echo .1 .5 Houze et al. 1981

  18. Stratiform Precipitation Radar Obs. of WINTER MONEX Borneo cloud system BORNEO S. CHINA SEA Bintulu Houze et al. 1981

  19. Andes Pacific South America Andes Pacific South America Diurnal gravity wave generation of mesoscale convection over coastal South America Mapes et al. 2003

  20. Propagational Diurnal Cycle

  21. Pre-monsoon Season in South Asia Romatschke & Houze 2010

  22. JASMINE1999 Pre-monsoon NOAA ShipRonald H. Brown Bay of Bengal Equator 100E 60E Webster et al. 2002

  23. Percent High Cloudiness in the Summer Monsoon May-September 1999 < 235 K < 210 K 850 mb wind 300 mb wind & sfc pressure Zuidema 2002

  24. Diurnalcycle, mean percent high cloudiness, 1999 Cloud Top < 210 K Zuidema 2002

  25. r = 85-140 km r < 85 km r = 140-210 km r > 210 km Location of cloud systems by horizontal dimension May-September 1999 CloudTop < 210 K Zuidema 2002

  26. JASMINE Mesoscale Convective Systems Defined & tracked by 218 K infrared threshold Zuidema 2002

  27. Propagational diurnal cycle occurs over Bay of Bengal JASMINE 1999, Ship Track & Satellite Data 85-90 E Ship Track Webster et al. 2002

  28. IR Temperature 08:30 LST

  29. IR Temperature 11:30 LST

  30. IR Temperature 14:30 LST

  31. IR Temperature 17:30 LST

  32. IR Temperature 20:30 LST

  33. IR Temperature 20:30 LST Ship radar

  34. JASMINE 1999 Ship Radar Data 2345 LST 22 May 99 0215 LST 23 May 99 0615 LST 23 May 99

  35. JASMINE 1999 Ship Radar Data Reflectivity Reflectivity Doppler Radial Velocity 22 May 1999 2300 LST

  36. 23 May 1999 0650 LST JASMINE Ship RadarData TRMM PrecipitationRadar Swath

  37. TRMM PR shows extensive stratiform structure 23 May 1999 0650 LST ~270 km

  38. Summary • Over open tropical oceans: • Small systems max in late afternoon • Large MCSs max around dawn • 2-day cycle at a given location (“diurnal dancing”) • In mountainous regions: • Isolated deep convective elements max in late afternoon • Nocturnal downslope generates early morning max MCSs • Max of small rain systems precedes max of medium systems • In coastal regions: • Large MCSs generated as response to afternoon heating over high terrain near coasts • Propagational diurnal cycles

  39. Clouds in Low Latitudes Lecture Sequence • Basic tropical cloud types • Severe convection & mesoscale systems • Tropical cloud population • Convective feedbacks to large-scales • Monsoon convection • Diurnal variability • Clouds in tropical cyclones Next

  40. This research was supported by NASA grants NNX07AD59G, NNX07AQ89G, NNX09AM73G, NNX10AH70G, NNX10AM28G, NSF grants, ATM-0743180, ATM-0820586, DOE grant DE-SC0001164 / ER-6

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