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

The Effect of the Terrain on Monsoon Convection in the Himalayan Region. Socorro Medina 1 , Robert Houze 1 , Anil Kumar 2,3 and Dev Niyogi 3. 1 University of Washington; 2 RAL, NCAR ; 3 Purdue University.

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

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  1. 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

  2. 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

  3. 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

  4. Western Central Eastern 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)

  5. Example of Deep Intense Convective Core (40 dbz echo >10 km in height) 10 m winds reanalysis at 1200 UTC 14 Jun 2002 Example: Reflectivity at 0900 UTC 14 Jun 2002 Delhi sounding 00 UTC 14 Jun 2002 Orography Houze et al. (2007)

  6. dry,hot moist Similar to convective systems in Plains of US Carlson et al. (1983)

  7. Western Central Eastern 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)

  8. 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)

  9. Western Central Eastern 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)

  10. 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)

  11. 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

  12. 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

  13. 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)

  14. 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)

  15. Wide convective system simulationTime: 18-23 UTC 3 Sep 2003 (0030-0530 LST) Terrain and accumulated precipitation (mm) Pakistan India Domain 1: dx = 9 km Domain 2: dx = 3 km

  16. Pakistan India Pakistan 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)

  17. Wide convective system – Evaluation of reflectivity (22 UTC 3 Sep) Observations WRF-simulation

  18. 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

  19. Wide convective system – Hypotheses testing 0.5 km 2.5 km 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) http://www.arl.noaa.gov/ready/hysplit4.html

  20. 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)

  21. 3000 2000 1000 Wide convective system – Hypotheses testing HYPOTHESIS - Convection started where the potentially unstable column was subjected to orographic lifting CAPE (J/kg)

  22. 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)

  23. 20 18 16 12 8 4 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

  24. Dew point depression > 10°C CAPE > 1800 J/kg CIN > 150 J/kg Temperature > 31°C Mixing ratio > 20 g/kg Wide convective system – Role of the NW concave indentation of the terrain ‘Idealized’ (highly smoothed) low-level variables Relative Humidity (% ) - Shaded

  25. 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

  26. END

  27. 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

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