The effect of terrain and land surface on
summer monsoon convection in the
Himalayan region
Socorro Medina, Robert Houze,
Anil Kumar, and Dev Niyogi
13th Conference on Mountain Meteorology), Whistler, BC, Canada, 12 August 2008
Orographic Precipitation
in cold and warm climates
OR CASCADES –
IMPROVE-2 (2001)
ALPS – MAP (1999)
HIMALAYAS
• Terrain gradients
• Land-ocean contrast
• Land cover gradients
Snow/Ice
Thar Desert
Ganges Delta
Tundra
Wetland
Forest
Irrigated crop
Crop
Savanna
Shurb/Grass
Dryland/crop
Grass
Shurb
Barren
OBJECTIVE
• Observational studies (Sawyer et al. 1947,
Houze et al. 2007) proposed hypotheses
on how monsoon convection forms
• Objective: Test hypotheses (in following
slides) using model simulations
Model/data used
• Weather Research and Forecasting (WRF
v2.1.1) model with single-moment bulk
microphysical parameterization with 6
water substances
• Complemented with NCEP data
Dominant type of systems
Deep and wide convective
systems
Broad stratiform echoes
(embedded in convective
systems)
Wide convective system in western indentation
3 September 2003
Accumulated precipitation and terrain
Domain 1 (dx = 9 km)
INDIA
Domain 2 (dx = 3 km)
Evaluation: 3D Reflectivity structure (~22 UTC 3 Sep [~03 LST 4 Sep])
OBSERVATION (TRMM-PR)
SIMULATION
dBZ
0
Height (km)
8
0
125
Distance (km)
250
0
100
Distance (km)
200
125
Distance (km)
250
0
100
Distance (km)
200
Height (km)
8
0
Height (km)
8
0
Vertical cross
sections along
red line
0
16
0
16
Vertical cross
sections along
black line
Height (km)
8
16
16
Horizontal cross
sections at 4 km
HYPOTHESIS: Dry line
SURFACE DEW POINT DEPRESSION
AND 2 AND 4 KM TERRAIN CONTOURS
Valid: 18 UTC 3 Sep (23 LST)
Forecast : 0 h (1 h before convection
initialization)
HYPOTHESIS: Moist low-level flow from
Arabian Sea, dry flow aloft from Tibetan or
Afghan mountains
SURFACE MIXING RATIO (g/kg)
Valid: 18 UTC 3 Sep (23 LST)
Forecast : 0 h
NOAA HYSPLIT (NCEP FNL)
BACKWARD TRAJECTORIES
1.0 AGL km
3.5 AGL km
End time: 18 UTC 3 Sep (23 LST)
Elapsed period between markers: 24 h
HYPOTHESIS: High surface sensible heat flux
as low-level air moves over Thar Desert
NCEP time series

HYPOTHESIS: Convection triggered over
foothills
TERRAIN AND COLUMN
INTEGRATED
PRECIPITATION
HYDROMETEORS (10 mm)
TOTAL PRECIP. MIXING RATIO
N
6.0 g kg-1
Valid: 19 UTC 3 Sep (00 LST). Forecast : 1 h
CONCLUSIONS WIDE CONVECTIVE CASE
• Moist low-level flow from Arabian Sea heated by
passage over Thar Desert
• Western indentation of barrier allows low-level
moisture and buoyancy to build up
• Elevated layer of dry, warm air from Afghan
mountains caps the moist low-level flow
• Convection triggered by orographic lifting over
the small peaks