The Effect of the Terrain on Monsoon Convection in the Himalayan Region

Socorro Medina1, Robert Houze1, Anil Kumar2,3 and Dev Niyogi3

Conference on Mesoscale Meteorology and Typhoon in East Asia (ICMCS-VI), Taipei, Taiwan, 7 November 2007

1University of Washington; 2RAL, NCAR; 3Purdue University

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

WesternWesternCentralCentral

EasternEastern

Deep Intense Deep Intense Convective Cores Convective Cores 40 dBZ echo 40 dBZ echo > 10 km in height> 10 km in height

Wide Intense Wide Intense Convective CoresConvective Cores 40 dBZ echo 40 dBZ echo > 1000 km> 1000 km22 area area

Broad Stratiform EchoBroad Stratiform Echo > 50,000 km> 50,000 km22

Precipitating systems from TRMM Precipitation Radar (PR) reflectivity

Jun-Sep 2002/2003

Houze et al. (2007)

Example of Deep Intense Convective Core(40 dbz echo >10 km in height)

Example: Reflectivity at 0900 UTC 14 Jun 200210 m winds reanalysis at 1200 UTC 14 Jun 2002

Delhi sounding 00 UTC 14 Jun 2002

Houze et al. (2007)

Orography

moist

dry,hot

Similar to convective systems in Plains of US

Carlson et al. (1983)

WesternWesternCentralCentral

EasternEastern

Deep Intense Deep Intense Convective Cores Convective Cores 40 dBZ echo 40 dBZ echo > 10 km in height> 10 km in height

Wide Intense Wide Intense Convective CoresConvective Cores 40 dBZ echo 40 dBZ echo > 1000 km> 1000 km22 area area

Broad Stratiform EchoBroad Stratiform Echo > 50,000 km> 50,000 km22

Precipitating systems from TRMM Precipitation Radar (PR) reflectivity

Jun-Sep 2002/2003

Houze et al. (2007)

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)

WesternWesternCentralCentral

EasternEastern

Deep Intense Deep Intense Convective Cores Convective Cores 40 dBZ echo 40 dBZ echo > 10 km in height> 10 km in height

Wide Intense Wide Intense Convective CoresConvective Cores 40 dBZ echo 40 dBZ echo > 1000 km> 1000 km22 area area

Broad Stratiform EchoBroad Stratiform Echo > 50,000 km> 50,000 km22

Precipitating systems from TRMM Precipitation Radar (PR) reflectivity

Jun-Sep 2002/2003

Houze et al. (2007)

Example of Broad Stratiform Echo (>50,000 km2 in area)

Reflectivity at 0252 UTC 11 Aug 2002

Houze et al. (2007)

10 m winds reanalysis at 00 UTC 11 Aug 2002

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 simulationTime: 18-23 UTC 3 Sep 2003 (0030-0530 LST)

Terrain and accumulated precipitation (mm)

Domain 1: dx = 9 km Domain 2: dx = 3 km

Pakis

tan

India

Wide convective system Evaluation at 2130 UTC 03 Sep 2003 (0400 LST, t=3.5 h)

ObservationsInfrared satellite temperature (shaded, K)

and low-resolution terrain (black contours, km)

WRF-simulationCloud 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 testingHYPOTHESIS - 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)

http://www.arl.noaa.gov/ready/hysplit4.html

0.5 km2.5 km

Wide convective system – Hypotheses testingHYPOTHESIS - 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)

1000

2000

3000

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

4

8

12

16

18

20

Wide convective system – Role of the NW concave indentation of the terrain

Dew point depression > 10°C

CIN > 150 J/kg

Temperature > 31°C

‘Idealized’ (highly smoothed) low-level variables

CAPE > 1800 J/kg

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 testingHYPOTHESIS - Low-level moist southwesterly flow was capped by dry air flowing off the Afghan mountains

Soundings at 1800 UTC

Dry side

Moist side