1. Tropical and subtropical convection in South Asia and South America
Defensio dissertationis
Tropical and subtropical convection in South Asia and South America
Annual precipitation 5 10 15 20
[mm/d]
Zipser et al. 2006
Ulrike Romatschke
University of Washington, University of Vienna
Meteorologisch-Geophysikalisches Kolloquium, December 13, 2010, University of Vienna

2. Fundamental question
Why do convective systems occur and what factors determine the times and places of their occurrence?

3. Specific questions Physical properties Mechanisms
Horizontal and vertical size
Convective or stratiform nature
Rain rate
Mechanisms
Synoptic background
Seasonal and diurnal changes
Moisture
Geography
terrain shape, height, orientation, and gradient
land versus ocean

4. Introduction

5. Regions

6. Data
Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR)
Resolution
horizontal: 4.3 km x 4.3 km (5 km x 4.2 km) before (after) 08/2001
vertical: 250 m
Area: 38°S to 38°N
Swath width: 215 km (247 km)
NCEP-NCAR reanalysis
Resolution: 2.5˚ x 2.5˚
South Asia 1999 – 2006
MAM (premonsoon), JJAS (monsoon)
South America: Dec – Feb. 2008
DJF

7. Publications
Romatschke, U., S. Medina, and R. A. Houze, Jr., 2010: Regional, Seasonal, and Diurnal Variations of Extreme Convection in the South Asian Region, J. Climate, 23,
Romatschke U., and R. A. Houze, Jr., 2010: Extreme Summer Convection in South America, J. Climate, 23,
Romatschke U., and R. A. Houze, Jr., 2010: Characteristics of Precipitating Convective Systems in the South Asian Monsoon, J. Hydrometeorol., in press.
Romatschke U., and R. A. Houze, Jr., 2010: Characteristics of Precipitating Convective Systems in the Premonsoon Season of South Asia, J. Hydrometeorol., in press.

8. Publications
Romatschke, U., S. Medina, and R. A. Houze, Jr., 2010: Regional, Seasonal, and Diurnal Variations of Extreme Convection in the South Asian Region, J. Climate, 23,
Romatschke U., and R. A. Houze, Jr., 2010: Extreme Summer Convection in South America, J. Climate, 23,
Romatschke U., and R. A. Houze, Jr., 2010: Characteristics of Precipitating Convective Systems in the South Asian Monsoon, J. Hydrometeorol., in press.
Romatschke U., and R. A. Houze, Jr., 2010: Characteristics of Precipitating Convective Systems in the Premonsoon Season of South Asia, J. Hydrometeorol., in press.

9. Publications
Romatschke, U., S. Medina, and R. A. Houze, Jr., 2010: Regional, Seasonal, and Diurnal Variations of Extreme Convection in the South Asian Region, J. Climate, 23,
Romatschke U., and R. A. Houze, Jr., 2010: Extreme Summer Convection in South America, J. Climate, 23,
Romatschke U., and R. A. Houze, Jr., 2010: Characteristics of Precipitating Convective Systems in the South Asian Monsoon, J. Hydrometeorol., in press.
Romatschke U., and R. A. Houze, Jr., 2010: Characteristics of Precipitating Convective Systems in the Premonsoon Season of South Asia, J. Hydrometeorol., in press.

10. Classification of Precipitating Convective Systems

11. Classification of Extreme radar echoes
Houze (2004)

12. Specific questions Physical properties Mechanisms
Horizontal and vertical size
Convective or stratiform nature
Rain rate
Mechanisms
Synoptic background
Seasonal and diurnal changes
Moisture
Geography
terrain shape, height, orientation, and gradient
land versus ocean

13. Specific questions Physical properties Mechanisms
Horizontal and vertical size
Convective or stratiform nature
Rain rate
Mechanisms
Synoptic background
Seasonal and diurnal changes
Moisture
Geography
terrain shape, height, orientation, and gradient
land versus ocean

14. Horizontal size and rain rates Examples: South Asian premonsoon and monsoon
10%
30%

15. Specific questions Physical properties Mechanisms
Horizontal and vertical size
Convective or stratiform nature
Rain rate
Mechanisms
Synoptic background
Seasonal and diurnal changes
Moisture
Geography
terrain shape, height, orientation, and gradient
land versus ocean

16. Convective nature and rain rates Example: Medium systems in the South Asian Monsoon
Subregion

17. Specific questions Physical properties Mechanisms
Horizontal and vertical size
Convective or stratiform nature
Rain rate
Mechanisms
Synoptic background
Seasonal and diurnal changes
Moisture
Geography
terrain shape, height, orientation, and gradient
land versus ocean

18. Specific questions Physical properties Mechanisms
Horizontal and vertical size
Convective or stratiform nature
Rain rate
Mechanisms
Synoptic background
Seasonal and diurnal changes
Moisture
Geography
terrain shape, height, orientation, and gradient
land versus ocean

19. Broad stratiform regions
Synoptic background – Ocean: strong influence Examples: Bay of Bengal, western South Atlantic
Large systems
500 mb geopot. height anom.
Broad stratiform regions
[m]

20. Synoptic background Land: influence in subtropics Example: Himalayan foothills – premonsoon – medium systems
500 mb geopotential height anomalies

21. Specific questions Physical properties Mechanisms
Horizontal and vertical size
Convective or stratiform nature
Rain rate
Mechanisms
Synoptic background
Seasonal and diurnal changes
Moisture
Geography
terrain shape, height, orientation, and gradient
land versus ocean

22. Surface winds and specific humidity
Seasonal changes and moisture Example: wide convective cores in premonsoon and monsoon
Premonsoon
Premonsoon
Surface winds and specific humidity
Monsoon
Monsoon
Probability
10 m/s

23. Specific questions Physical properties Mechanisms
Horizontal and vertical size
Convective or stratiform nature
Rain rate
Mechanisms
Synoptic background
Seasonal and diurnal changes
Moisture
Geography
terrain shape, height, orientation, and gradient
land versus ocean

24. Diurnal heating and geography Mountain ranges and divergence
Monsoon
06 UTC ~02 LT
00 UTC
~ 0530 LT
Surface winds and divergence
18 UTC ~14 LT
12 UTC
~ 1730 LT

25. Broad stratiform regions
Diurnal heating and geography Ocean Examples: wide convective cores and broad stratiform regions
Wide convective cores
Broad stratiform regions
Bay of Bengal
South Atlantic

26. Diurnal heating and geography Ocean Example: wide convective cores in the South Atlantic

27. Diurnal heating and geography Example: Monsoon systems at the Himalayan foothills
[mm/h]
Precipitation
12 UTC
~ 1730 LT
00 UTC
~ 0530 LT
00-06 LT
12-18 LT
0.6
Small
0.4
Medium
0.2

28. Diurnal heating and geography
Example: Monsoon wide convective cores at the Himalayan foothills
Early Morning
Evening
Wide convective cores over land
Mean Solar Time

29. Diurnal heating and geography Mountain ranges and divergence
EOF 1 of diurnal cycle of precipitation over land
(adapted from Kikuchi and Wang 2008)

30. Diurnal heating and geography Sea-land-mountain effect Example: Medium systems in the South Asian monsoon
00-06 LT
12-18 LT

31. Diurnal heating and geography Capping effect Example: monsoon deep convective cores
Sawyer 1947

32. Winds and specific humidity
Diurnal heating and geography Capping effect Example: monsoon deep convective cores
Winds and specific humidity
Surface
500 mb

33. Specific questions Physical properties Mechanisms
Horizontal and vertical size
Convective or stratiform nature
Rain rate
Mechanisms
Synoptic background
Seasonal and diurnal changes
Moisture
Geography
terrain shape, height, orientation, and gradient
land versus ocean

34. Mechanisms combine: synoptics Example: South American subtropics
500 mb geopotential height anomalies wide convective cores
Surface winds
[m]

35. Mechanisms combine: capping Example: South American subtropics
Deep convective cores
Winds and specific humidity
Surface
500 mb
Deep convective cores

36. Mechanisms combine: Diurnal cycle Example: South American subtropics
Wide convective cores
06 UTC ~02 LT
23-05 LT
05-11 LT
11-17 LT
17-23 LT

37. Mechanisms combine: Diurnal cycle Example: South American subtropics
Broad stratiform regions
23-05 LT
05-11 LT
11-17 LT
17-23 LT

38. Conclusions More precipitation near mountains favored by
Large systems
Systems with large convective fraction
Synoptic influence on large systems
Strong over oceans and in subtropics
Moist large-scale environment
Essential for existence and horizontal growth of convection
Capping
Extremely deep afternoon convection near mountains
Diurnal cycle
Small systems over mountains in daytime
Medium (mesoscale) systems over foothills in morning
Small/medium diurnal systems over coastal mountains
Large ocean systems weakened by daytime converg. over land

39. Acknowledgements Prof. Houze
Dr. Medina and the Mesoscale Group at the University of Washington
Prof. Grubišić and Dr. Volkert
Prof. Meurers and Prof. Steinacker
Family and friends
Paul and Doris

40. Future work Precipitating convective systems in South America
Other seasons
Other locations (Australia, Africa,…)
Midlatitudes: Global Precipitation Measurement (GPM) data
Combination with other satellite data
CloudSat: Precipitating and non-precipitating systems
Temporally contiguous satellite data
Test hypotheses with mesoscale models
Implement new knowledge in weather forecasting and climate models