The Effect of the Terrain on Monsoon
Convection in the Himalayan Region
Socorro Medina1, Robert Houze1, Anil Kumar2,3 and Dev Niyogi3
1University
of Washington; 2RAL, NCAR; 3Purdue University
Conference on Mesoscale Meteorology and Typhoon in East Asia (ICMCS-VI), Taipei, Taiwan, 7 November 2007
OUTLINE
• Review observations of summer monsoon
precipitating systems
• Evaluate if high-resolution models can
predict these systems
• Use simulations to investigate the role of
the terrain in monsoon convection
OUTLINE
• Review observations of summer monsoon
precipitating systems
• Evaluate if high-resolution models can
predict these systems
• Use simulations to investigate the role of
the terrain in monsoon convection
Precipitating systems from TRMM
Precipitation Radar (PR) reflectivity
Jun-Sep 2002/2003
Deep Intense
Convective Cores
40 dBZ echo
> 10 km in height
Wide Intense
Convective Cores
40 dBZ echo
> 1000 km2 area
Broad Stratiform Echo
> 50,000 km2
Houze et al. (2007)
Western
Central
Eastern
Example of Deep Intense Convective Core
(40 dbz echo >10 km in height)
Example: Reflectivity at 0900 UTC 14 Jun 2002
Delhi sounding 00 UTC 14 Jun 2002
Houze et al. (2007)
10 m winds reanalysis at
1200 UTC 14 Jun 2002
Orography
Similar to convective systems in Plains of US
Carlson et al. (1983)
Precipitating systems from TRMM
Precipitation Radar (PR) reflectivity
Jun-Sep 2002/2003
Deep Intense
Convective Cores
40 dBZ echo
> 10 km in height
Western
Central
Wide Intense
Convective Cores
40 dBZ echo
> 1000 km2 area
Broad Stratiform Echo
> 50,000 km2
Houze et al. (2007)
Eastern
Example of Wide Intense Convective Core
(40 dbz echo >1000 km2 in area)
Example: Reflectivity at 2208 UTC 3 Sep 2003
Houze et al. (2007)
Precipitating systems from TRMM
Precipitation Radar (PR) reflectivity
Jun-Sep 2002/2003
Deep Intense
Convective Cores
40 dBZ echo
> 10 km in height
Wide Intense
Convective Cores
40 dBZ echo
> 1000 km2 area
Western
Central
Broad Stratiform Echo
> 50,000 km2
Houze et al. (2007)
Eastern
Example of Broad Stratiform Echo
(>50,000 km2 in area)
Reflectivity at 0252 UTC 11 Aug 2002
10 m winds reanalysis at
00 UTC 11 Aug 2002
Houze et al. (2007)
OUTLINE
• Review observations of summer monsoon
precipitating systems
• Evaluate if high-resolution models can
predict these systems
• Use simulations to investigate the role of
the terrain in monsoon convection
NUMERICAL SIMULATIONS
• Weather Research and Forecasting (WRF
v2.1.1) model
– NCEP Reanalysis used as initial and
boundary conditions (6 hourly)
– Bulk microphysical parameterization:
WRF Single-Moment with 6 water
substances
SIMULATED SYSTEMS
• Isolated deep convective system (14
Jun 2002)  Simulation could not
capture
• Wide intense convective system (3
Sep 2003)
• Broad stratiform system (11 Aug 2002)
SIMULATED SYSTEMS
• Isolated deep convective system (14
Jun 2002)  Simulation could not
capture system
• Wide intense convective system (3
Sep 2003)
• Broad stratiform system (11 Aug 2002)
Wide convective system simulation
Time: 18-23 UTC 3 Sep 2003 (0030-0530 LST)
Terrain and accumulated precipitation (mm)
Domain 1: dx = 9 km
India
Domain 2: dx = 3 km
Wide convective system
Evaluation at 2130 UTC 03 Sep 2003 (0400 LST, t=3.5 h)
Observations
WRF-simulation
Infrared satellite temperature (shaded, K)
and low-resolution terrain (black contours, km)
Cloud top temperature (shaded, K)
and terrain (black contours, m)
Pakistan
India
Pakistan
India
Wide convective system – Evaluation of reflectivity (22 UTC 3 Sep)
Observations
WRF-simulation
OUTLINE
• Review observations of summer monsoon
precipitating systems
• Evaluate if high-resolution models can
predict these systems
• Use simulations to test hypothesis Houze
et al. 2007 – investigate role of the terrain
Wide convective system – Hypotheses testing
HYPOTHESIS - Low-level moist southwesterly flow was capped by dry
air flowing off the high Tibetan Plateau or the Afghan mountains
Surface water vapor mixing ratio (g/kg) and winds
Backward trajectories (HYSPLIT/NCEP)
0.5 km
2.5 km
http://www.arl.noaa.gov/ready/hysplit4.html
Wide convective system – Hypotheses testing
HYPOTHESIS - Low-level moist southwesterly flow was capped by dry
air flowing off the Afghan mountains
Surface dew point depression (°C)
Wide convective system – Hypotheses testing
HYPOTHESIS - Convection started where the potentially unstable
column was subjected to orographic lifting
CAPE (J/kg)
3000
2000
1000
Wide convective system – Hypotheses testing
HYPOTHESIS - Convection started where the potentially unstable
column was subjected to orographic lifting
Surface dew point depression (°C) and vertically integrated
mixing ratio of precipitating hydrometeors (mm) at 1925 UTC (t=1.25 h)
Wide convective system – Hypotheses testing
HYPOTHESIS - Convection started where the potentially unstable
column was subjected to orographic lifting
Mixing ratio (g/kg) of water vapor (shaded), cloud hydrometeors
(dark red) and precipitating hydrometeors (dark blue) at 1900 UTC
20
18
16
12
8
4
Wide convective system – Role of the NW concave indentation of the terrain
‘Idealized’ (highly smoothed) low-level variables
Dew point
depression > 10°C
CAPE > 1800 J/kg
CIN > 150 J/kg
Temperature
> 31°C
Mixing ratio > 20 g/kg
Relative Humidity (% ) - Shaded
CONCLUSIONS
Convective systems
• High-resolution model was able to predict the observed
structures (if the system is wide enough AND the model
has enough resolution)
• In Wide Intense Convective storm, the terrain appears to
play three main roles:
– The NW concave indentation of the terrain increases the existing
humidity gradients
– Elevated layer of dry, warm air originates over the Afghan
mountains and caps the moist low-level flow  allows buoyancy
to build up
– The convection is triggered at the small features of terrain (h<0.5
km): orographic lifting, convergence or both
END
Wide convective system – Hypotheses testing
HYPOTHESIS - Low-level moist southwesterly flow was capped by dry
air flowing off the Afghan mountains
Soundings at 1800 UTC
Dry side
Moist side