Robert A. Houze, Jr., Darren C. Wilton, and Bradley F. Smull University of Washington

1. Monsoon Convection in the Himalayan Regionas seen by the TRMM Precipitation Radar Robert A. Houze, Jr., Darren C. Wilton, and Bradley F. Smull University of Washington Thompson Lecture, NCAR, Boulder, 31 October 2006

2. Monsoon Convection in the Himalayan Regionas seen by the TRMM Precipitation Radar Robert A. Houze, Jr., Darren C. Wilton, and Bradley F. Smull University of Washington Precipitation Thompson Lecture, NCAR, Boulder, 31 October 2006

3. Goal To gain insight into the physical mechanisms by which heavy monsoon precipitation is produced Approach • Use data from the Precipitation Radar (PR) on the Tropical Rainfall Measuring Mission (TRMM) satellite. • Examine the three-dimensional structure of the storms producing intense monsoon precipitation. • Determine how the 3D echo structure varies in relation to details of the Himalayan topography and proximity to surrounding oceans.

4. TRMM Precipitation Radar Data Set Used in This Study • June-September 2002, 2003 • 1648 Overpasses over Himalayan region • Data specially processed at UW to optimize vertical structure analysis

5. Analysis Subregions °N WesternSubregion Mountain Foothills Lowland Central Subregion Eastern Subregion Arabian Sea Bay of Bengal INDIA °E

6. TRMM Satellite Instrumentation l = 2 cm Important!PR measures 3D structure of radar echoes Kummerow et al, 1998

7. Analysis of three-dimensional echo regions • Used TRMM algorithm for separating echoes into stratiform & convective regions • STRATIFORM identified by 2 criteria: • Non-stratiform is either CONVECTIVE or “OTHER” • Used TRMM algorithm for separating echoes into stratiform & convective regions • STRATIFORM identified by 2 criteria: • Non-stratiform is either CONVECTIVE or “OTHER” Existence of bright band Lack of intense echo cores

8. Analysis of Convective Echo Cores

9. To study the vertical structure of convective regions we first define 3D echo “cores” • The TRMM Precipitation Radar data are provided in “bins” ~5 km in the horizontal and ~0.25 km in the vertical • Echo cores are formed by contiguous bins (in 3D space) of reflectivity values which exceed the threshold of 40 dBZ. 3D radar echo bounded by 40 dBZ contour echocore land

10. Western Central Eastern Deep Intense Cores 40 dBZ echo > 10 km in height Wide Intense Cores 40 dBZ echo > 1000 km2 area Broad Stratiform Echo stratiform echo > 50,000 km2

11. Lightning frequency based on TRMM satellite observations

12. Carlson et al. 1983 dry,hot moist

13. Sawyer 1947

14. A case of deep isolated 40 dBZ core14 June 2002 10 meter level 200 mb level

15. A case of deep isolated 40 dBZ core14 June 2002 0900 UTC 0930 UTC

16. A case of deep isolated 40 dBZ core14 June 2002 0900 UTC

17. Deep cores over the Tibetan Plateau14 July 2002 1227 UTC

18. Height of 40 dBZ cores by region In western region--graupel particles lofted to great heights by strong updrafts

19. A case of wide 40 dBZ echo core22 July 2002 10 meter level 200 mb level

20. A case of wide 40 dBZ echo core22 July 2002

21. A case of wide 40 dBZ echo core22 July 2002 1300 UTC 1400 UTC

22. A case of wide 40 dBZ echo core22 July 2002 1300 UTC

23. A typical case of wide 40 dBZ echo core with line organization 2208 UTC 3 Sep 2003

24. A wide 40 dBZ echo core with squall-line organization—rare! 2017 UTC 5 June 2003

25. A of wide 40 dBZ echo core with squall-line organization—rare! 500 mb jet over and parallel to the Himalayas 10 meter level 500 mb level 5 June 2003

26. Horizontal area of 40 dBZ cores by region In western region—wide convective areas more frequent Cumulative Frequency Area (km2)

27. Analysis of Stratiform Echoes

28. Intraseasonal Variation of the Monsoon Webster & Tomas 1997 Day 0:8 mm/d5N-5S80-90E 39 events1985-95 “Break” “Active”

29. Broad stratiform case11 Aug 2002 10 meter level 200 mb level

30. Broad stratiform case11 Aug 2002

31. Broad stratiform case11 Aug 2002 0252 UTC

32. Broad stratiform caseUpstream of mountains 0455 UTC

33. Size of stratiform precipitation area by geographical region

34. Analysis of All the Reflectivity Data

35. Reflectivity data for 2 monsoon seasons Relative frequency of occurrence

36. Reflectivity data for 2 monsoon seasons • Convection is stronger & deeper in west • Stratiform more pronounced in east

37. Reflectivity data for 2 monsoon seasons Convection is slightly deeper & stronger over the lowlands than the foothills

38. Summary • Strongest over lowlands • Vertical cells • Wide cores—amorphous or parallel to mt. range • Lots of lightning • No squall lines • West: “Deep” & “wide” cores prone to occur just upstream & over the foothills, esp. in the west, near confluence of dry downslope & maritime flows. • Squall lines when jet parallel to Himalayas • Isolated cells over plateau • Central: Get both deep and wide cores, as in west, but not as frequent. • Mesoscale systems like oceanic convection with large stratiform regions • Get broad stratiform regions associated with depressions propagating from equatorial region • East: Get mesoscale, partially stratiform cloud systems associated with depressions over the Bay of Bengal

39. Epilogue • What has this study accomplished? • Particular structure and organization of summer monsoon convection over the subcontinent of South Asia • Behavior of highly convective clouds in a moist flow impinging on a mountain barrier • What questions remain? • Why does the intense convection trigger just upstream of the barrier? • In depressions, what are the relative roles of orography and synoptic dynamics? • Can high-resolution models predict the observed structures?

40. Thanks