1. Diurnal Variability of Deep Tropical Convection R. A. Houze Lecture, Summer School on Severe and Convective Weather, Nanjing, 11-15 July 2011

2. Convective Clouds Lecture Sequence 1.Basic convective cloud types 2.Severe convection & mesoscale systems 3.Tropical cloud population 4.Convective feedbacks to large-scales 5.Extreme convection 6.Diurnal variability 7.Clouds in tropical cyclones

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

4. A Purely Oceanic Environment

5. Convective systems over the West Pacific 1<80 km 280-170 km 3170-300 km 4>300 km Cloud shield <208 K Chen & Houze 1997

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

7. Convective systems over the West Pacific Chen & Houze 1997 Cloud systems tracked in time in IR satellite data Small (<80 km)Large (80-170 km)

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

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

10. Over Land Near Mountains

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

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

13. Example from pre-monsoon season in South Asia Romatschke et al. 2010 Mountains can lead to small and medium sized systems having different diurnal cycles— mesoscale lifecycle effect Δ Small 600-8,500 km 2  Medium 8,500-35,000 km 2 IEC

14. Propagational Diurnal Cycle

15. Equator NOAA Ship Ronald H. Brown Webster et al. 2002 60E 100E JASMINE 1999 Pre-monsoon Bay of Bengal

16. South Asian Topography

17. Diurnal cycle, mean percent high cloudiness, 1999 Cloud Top < 210 K Zuidema 2002

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

20. IR Temperature 08:30 LST

21. IR Temperature 11:30 LST

22. IR Temperature 14:30 LST

23. IR Temperature 17:30 LST

24. IR Temperature 20:30 LST

25. IR Temperature Ship radar 20:30 LST

26. 2345 LST 22 May 990215 LST 23 May 990615 LST 23 May 99 JASMINE 1999 Ship Radar Data

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

28. Johnson & Houze 1987 December 1978 January 1979

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

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

31. 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 Downstream of mountains and/or coastlines: –Large MCSs generated apparently as response to afternoon heating over high terrain propagate away from the mountainous region or coastline 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 Downstream of mountains and/or coastlines: –Large MCSs generated apparently as response to afternoon heating over high terrain propagate away from the mountainous region or coastline

32. Convective Clouds Lecture Sequence 1.Basic convective cloud types 2.Severe convection & mesoscale systems 3.Tropical cloud population 4.Convective feedbacks to large-scales 5.Extreme convection 6.Diurnal variability 7.Clouds in tropical cyclones Next

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

34. Extra Slides

35. Romatschke et al. 2010 Monsoon Season Composite Surface Winds for Cases of Wide Convective Systems

36. 300 mb wind & sfc pressure850 mb wind Percent High Cloudiness in the Summer Monsoon 1999 May-September 1999 < 235 K< 210 K Zuidema 2002

37. r < 85 km r = 140-210 km r = 85-140 km r > 210 km Location of cloud systems by horizontal dimension May-September 1999 Cloud Top < 210 K

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

39. A Coastal Environment

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

41. WINTER MONEX Diurnal variation of precipitation near Borneo December 1978 Mean fractional area covered by radar echo BORNEO Bintulu.1.5

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

43. JASMINE Ship Radar Data TRMM Precipitation Radar Swath 23 May 1999 0650 LST

44. TRMM PR shows extensive stratiform structure ~270 km

45. Example from pre-monsoon season in South Asia Romatschke et al. 2010 Δ Small 600-8,500 km 2  Medium 8,500-35,000 km 2 CHF Mountains can lead to small and medium sized systems having different diurnal cycles— mesoscale lifecycle effect