Extreme Convection Near the Himalayas and Andes Robert A. Houze, Jr.
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Extreme Convection Near the Himalayas and Andes Robert A. Houze, Jr. Ulrike Romatschke, Socorro Medina, Kristen Rasmussen Dev Niyogi, Anil Kumar Gerald R. North Symposium, Texas A&M University, College Station, June 8, 2009 Sponsored in part by: NSF Award# ATM-0505739 NSF Award# ATM-0820586 NASA Award# NNX07AD59G Data & Models TRMM PR 3D reflectivity Sample, 1998-2008 South Asia: March-April, 1999-2006 South America: December-February, 1998-2008 NCEP reanalysis Large-scale environment WRF model Simulation of representative cases Himalayan Region Terrain gradients • Land-ocean contrast • Land cover differences Snow/Ice Thar Desert Ganges Delta Tundra Wetland Forest Irrigated crop Crop Savanna Shrub/Grass Dryland/crop Grass Shrub Barren SFC SFC 500 hPa 500 hPa 200 hPa 200 hPa Wind & Moisture Climatology Convective systems Convective component Stratiform component Extreme characteristic Extreme characteristic Contiguous convective echo 3D volume 40 dBZ Contiguous stratiform echo Horizontal area 50 000 km2 “Broad stratiform region” Top height 10 km “Deep convective core” Horizontal area 1 000 km2 “Wide convective core” Examples Deep Convective Core Stratiform Wide Convective Core Convective Broad Stratiform Region Pre-Monsoon Deep Convective Cores Climatology of Extreme Convective Features Wide Convective Cores Broad Stratiform Regions Monsoon Pre-Monsoon Monsoon Deep Convective Cores Climatology of Extreme Convective Features Wide Convective TRMM Cores Rainfall Broad Stratiform Regions May July Pre-Monsoon Deep Convective Cores Climatology of Extreme Convective Features Wide Convective Cores Broad Stratiform Regions Monsoon Example of a wide convective core system in the western region Backward trajectories (HYSPLIT/NCEP) 2.5 km 1.0 km Sawyer 1947 Houze et a. 2007 Observations WRF-simulation Infrared satellite temperature (shaded, K) Cloud top temperature (shaded, K) and low-resolution terrain (black contours, km) and terrain (black contours, m) Pakistan India Pakistan India TRMM PR Observations WRF Simulation WRF Simulation Mixing ratio CAPE WRF Simulation Isochrones of integrated hydrometeor content Hydrometeor mixing ratio just after convection formed Diurnal Variability in the Himalayan Region Deep convective cores (mostly land) Wide convective cores: Land Wide convective cores: Ocean Broad stratiform regions: Ocean Wide convective cores Nocturnal formation in Himalayan foothills Composite winds Wide convective core cases 1130 2330 1730 0530 Nocturnal downslope flow in Himalayan foothills Andes Region Regions of analysis Foothills North Foothills South La Plata Basin Summer Season (DJF) Deep convective Cores Wide convective cores Broad stratiform regions Precip. climatology Example of a Wide Convective Core Wide Convective Case (37,901 km2 40 dBZ echo) QuickTime™ and a H.264 decompressor are needed to see this picture. 0 UTC (20 LT on the previous day) 925 mb NCEP/NCAR Reanalysis Air Temperature and Vector Winds Time of TRMM Swath is 4:13 UTC (00:13 LT) 6 UTC (2 LT) 500 mb Geopotential Height Anomaly for 11/12/2003 925 mb Geopotential Height Anomaly for 11/12/2003 Composite of NCEP Data For wide convective cores in SOUTH 500 mb geopotential height anomaly Surface pressure anomaly [mb] Surface winds (~02 LT) Composites For wide convective cores in SOUTH 500 mb geopotential height anomaly Surface winds & divergence Divergence Divergence 06 UTC ~02 LT 18 UTC ~14 LT 10 m s-1 Region of Eastern Himalayas and Bay of Bengal Pre-Monsoon Deep Convective Cores Climatology of Extreme Convective Features Wide Convective Cores Broad Stratiform Regions Monsoon Example of a Bay of Bengal Case WRF simulation Surface wind Total Rain TRMM PR (a) WRF Simulation WRF Simulation WRF Simulation QuickTime™ and a Animation decompressor are needed to see this picture. WRF Simulation Summary Black--850 mb wind vectors WRF Simulation Summary Black--850 mb wind vectors Yellow--850 wind speed WRF Simulation Summary Black--850 mb wind vectors Yellow--850 wind speed White--LH flux WRF Simulation Summary Black--850 mb wind vectors Yellow--850 wind speed White--LH flux Blue--Precipitable water WRF Simulation Summary Black--850 mb wind vectors Yellow--850 wind speed White--LH flux Blue--Precipitable water Red--Precip WRF Simulation Summary Black--850 mb wind vectors Yellow--850 wind speed White--LH flux Blue--Precipitable water Red--Precip White--850 mb height WRF Simulation Summary Black--850 mb wind vectors Yellow--850 wind speed White--LH flux Blue--Precipitable water Red--Precip White--850 mb height Yellow--500 mb vertical velocity WRF Simulation Summary Black--850 mb wind vectors Yellow--850 wind speed White--LH flux Blue--Precipitable water Red--Precip White--850 mb height Orange--500 mb vertical velocity Red--Precip Conclusions Deep convective cores • associated with daytime heating • rare over ocean • often in arid regions • low-level moist jet overrun by dry flow from high terrain Wide convective cores • both land and ocean • associated with systems that develop broad stratiform regions • affected by nocturnal downslope flow • line structures common in S. America, not in S. Asia Broad stratiform regions • most common over ocean and wetlands • likely later stage of MCS • over land--strongly reinforced by flow interaction with mountains • over ocean--weak diurnal cycle but max in midday over oceans End
