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
Fundamental question Why do convective systems occur and what factors determine the times and places of their occurrence?
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
Introduction
Regions
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. 1998 – Feb. 2008 DJF
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, 419-439. Romatschke U., and R. A. Houze, Jr., 2010: Extreme Summer Convection in South America, J. Climate, 23, 3761-3791. 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.
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, 419-439. Romatschke U., and R. A. Houze, Jr., 2010: Extreme Summer Convection in South America, J. Climate, 23, 3761-3791. 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.
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, 419-439. Romatschke U., and R. A. Houze, Jr., 2010: Extreme Summer Convection in South America, J. Climate, 23, 3761-3791. 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.
Classification of Precipitating Convective Systems
Classification of Extreme radar echoes Houze (2004)
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
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
Horizontal size and rain rates Examples: South Asian premonsoon and monsoon 10% 30%
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
Convective nature and rain rates Example: Medium systems in the South Asian Monsoon Subregion
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
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
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]
Synoptic background Land: influence in subtropics Example: Himalayan foothills – premonsoon – medium systems 500 mb geopotential height anomalies
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
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
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
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
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
Diurnal heating and geography Ocean Example: wide convective cores in the South Atlantic
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
Diurnal heating and geography Example: Monsoon wide convective cores at the Himalayan foothills Early Morning Evening Wide convective cores over land 00 03 06 09 12 15 18 21 00 Mean Solar Time
Diurnal heating and geography Mountain ranges and divergence EOF 1 of diurnal cycle of precipitation over land (adapted from Kikuchi and Wang 2008)
Diurnal heating and geography Sea-land-mountain effect Example: Medium systems in the South Asian monsoon 00-06 LT 12-18 LT
Diurnal heating and geography Capping effect Example: monsoon deep convective cores Sawyer 1947
Winds and specific humidity Diurnal heating and geography Capping effect Example: monsoon deep convective cores Winds and specific humidity Surface 500 mb
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
Mechanisms combine: synoptics Example: South American subtropics 500 mb geopotential height anomalies wide convective cores Surface winds [m]
Mechanisms combine: capping Example: South American subtropics Deep convective cores Winds and specific humidity Surface 500 mb Deep convective cores
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
Mechanisms combine: Diurnal cycle Example: South American subtropics Broad stratiform regions 23-05 LT 05-11 LT 11-17 LT 17-23 LT
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
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
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