Tropical Cloud Population
Before Satellites
Visual Observation View from and aircraft flying over the South China Sea
Radiosonde Data Hot tower hypothesis Riehl & Malkus 1958
Satellite Observations
Post satellite view of tropical cloud population, ca 1970 The cirrus shield was introduced Explained satellite pictures and retained the hot tower notion and the fact that smaller clouds exist. But missing are downdrafts, mesoscale stratiform rain and thick anvils. Also assumes simple scale separation.
Radars
GATE 1974
GATE SHIP ARRAY
More Tropical Field Projects TEPPS 1997 EPIC 2001 BoB 1979 JASMINE 1999 (Dashed: No sounding network)
Figure CONVSF MCS precipitation subdivided into convective and stratiform components Houze 1997 Old convection Vigorous convection 100 km Houze 1997
Convective Vigorous convection Note Max w > (V T ) snow Height Distance Houze 1997
Stratiform Old convective material Note (V T ) snow ~1-2 m/s Height Distance Houze 1997
Idealized life cycle of tropical MCS Houze 1982
Post-GATE view of the tropical cloud population Houze et al. (1980)
Precipitation Radar in Space
The TRMM Satellite Radar TRM M Low altitude, low inclination orbit
TRMM Satellite Instrumentation! = 2 mm Important! PR measures 3D structure of radar echoes Kummerow et al, 1998
Global precipitation seen from space Combined satellite rainfall July 2000 TRMM plus passive microwave sensors + other
Latent Heating Max rain in tropics varies zonally Combined satellite rainfall July 2000
2 Years of TRMM PR data Large Cbs MCSs Small isolated Cbs Schumacher & Houze 2003
Trade Wind Regime
Indo/Pacific Warm Pool
Traditional conceptual view of mean meridional distribution of tropical convection
Trimodal distribution Johnson et al. 1999 Based on TOGA COARE data
Johnson et al. 1999 TOGA COARE
Convective Structure as a Function of Large-scale Context SST Ocean vs Land Land Surface Type Coastal Effects Mountains Synoptic Situation
SST
TRMM PR Deep Convective SST Climatology (July) July SST TRMM PR Shallow, Isolated Convective
Land vs Ocean
West African Squall Line
Global frequency and distribution of lightning as observed from space Christian et al.2002.
TRMM view of Africa vis a vis the Atlantic Rain Stratiform Rain Fraction MCSs with large 85 GHz ice scattering Lightning
South Asian Monsoon Land Surface Mountains Synoptic Context
Terrain gradients Land-ocean contrast Land cover differences Thar Desert Ganges Delta Snow/Ice Tundra Wetland Forest Irrigated crop Crop Savanna Shrub/Grass Dryland/crop Grass Shrub Barren
Mean Large-scale Flow Pattern at 1000 mb and 200 mb
Analysis Subregions N Western Subregion Mountain Foothills Lowland Central Subregion Eastern Subregion Arabian Sea INDIA Bay of Bengal E
Analysis of three-dimensional echo regions Used TRMM algorithm for separating echoes into stratiform & convective regions! STRATIFORM identified by 2 criteria: Existence of bright band Lack of intense echo cores! Non-stratiform is either CONVECTIVE or OTHER OTHER
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. echo core 3D radar echo bounded by 40 dbz contour land
Examples Deep Convective Core Wide Convective Core Stratiform Convective Broad Stratiform Region
Western Central Eastern Deep Intense Cores 40 dbz echo > 10 km in height Wide Intense Cores 40 dbz echo > 1000 km 2 area Broad Stratiform Echo stratiform echo > 50,000 km 2
Carlson et al. 1983 dry,hot moist
Sawyer 1947
Backward trajectories (HYSPLIT/NCEP) 2.5 km 1.0 km Medina et al. 2010
WRF Simulation Mixing ratio CAPE Medina et al. 2010
WRF Simulation Isochrones of integrated hydrometeor content Hydrometeor mixing ratio just after convection formed Medina et al. 2010
Intraseasonal Variation of the Monsoon 39 events 1985-95 Break Day 0: 8 mm/d 5N-5S 80-90E Active Webster & Tomas 1997
Broad stratiform case 11 Aug 2002 0252 UTC
Broad stratiform case Upstream of mountains 0455 UTC
Reflectivity data for 2 monsoon seasons " Convection is stronger & deeper in west " Stratiform more pronounced in east
Propagating MCSs
Cross section of MCS with leading line of convection and trailing stratiform precipitation Houze et al. 1989
Squall Line With Trailing Stratiform Precipitation TRMM PR data over West Africa This one propagates E to W assisted by midlevel African easterly jet
A squall-line in India rare rare! Himalayas 2017 UTC 5 June 2003
A squall-line in India rare rare! Himalayas 500 mb jet over and parallel to the Himalayas 10 meter level 500 mb level 5 June 2003
Cloud Radar in Space
Combining 3 Types of Satellite
MCSs Over the Whole Tropics Yuan and Houze 2010
MCSs Over the Whole Tropics Yuan and Houze 2010
MCSs Over the Whole Tropics Yuan and Houze 2010 Frequency of MCS anvil cloud
MCSs Over the Whole Tropics Yuan and Houze 2010 MCS Anvil cloud properties derived from CloudSat Thickness (km) West Africa Indian Ocean 0 1 2 3 4 5 Normalized Distance