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
Cloud and Precipitation Seminar, University of Washington, Seattle, 25 October 2007
Precipitation distribution in relation to terrain
Orography (km)
Jun-Aug precipitation (mm/month)
(Climatology from TRMM-PR data from 1997-2004)
Arabian
Sea
Xie et al. (2006)
Bay of
Bengal
MOTIVATION –
MONSOON 2007
(Jun-Aug)
Precipitation (mm)
Anomaly (%)
MONSOON CONVECTION IN THE
HIMALAYAN REGION – Three part study
1
Houze, Wilton, and Smull (2007) – 3D structure
of intense storms and their distribution in
relation to topography and surrounding oceans
2
Ulrike Romatschke (Ulli) – Is extending Houze
et al. (2007) study
 Cloud and Precipitation Seminar Nov 15th
3
Analyze numerical simulations to investigate
the detailed role of the terrain – preliminary
results
MONSOON CONVECTION IN THE
HIMALAYAN REGION – Three part study
1
Houze, Wilton, and Smull (2007) – 3D structure
of intense storms and their distribution in
relation to topography and surrounding oceans
2
Ulrike Romatschke (Ulli) – Is extending Houze
et al. (2007) study
 Cloud and Precipitation Seminar Nov 15th
3
Analyze numerical simulations to investigate
the detailed role of the terrain – preliminary
results
Houze, Wilton, and Smull (2007) study
• Data from Precipitation Radar (PR) on the
Tropical Rainfall Measuring Mission
(TRMM) satellite (June-September
2002/2003)
• Found contiguous radar echoes that
exceeded some size threshold
• Analyzed separately convective and
stratiform radar echoes
Convective and stratiform radar
reflectivity echoes
Horizontal cross-section
Vertical cross-section convective echo
Vertical cross-section stratiform echo
Houze (1997)
Results of Houze et al. (2007):
Western
Central
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
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
Carlson et al. 1983
Results of Houze et al. (2007):
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
stratiform echo
> 50,000 km2
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)
Results of Houze et al. (2007):
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
stratiform echo
> 50,000 km2
Eastern
Example of Broad Stratiform Echo
(>50,000 km2 in area)
00 UTC 11 Aug 2002
Tengchong sounding
Example: Infrared satellite temperature
and reflectivity at ~03 UTC 11 Aug 2002
10 m winds reanalysis at
00 UTC 11 Aug 2002
Houze et al. (2007)
MONSOON CONVECTION IN THE
HIMALAYAN REGION – Three part study
1
Houze, Wilton, and Smull (2007) – 3D structure
of intense storms and their distribution in
relation to topography and surrounding oceans
2
Ulrike Romatschke (Ulli) – Is extending Houze
et al. (2007) study
 Cloud and Precipitation Seminar Nov 15th
3
Analyze numerical simulations to investigate
the detailed role of the terrain – preliminary
results
MONSOON CONVECTION IN THE
HIMALAYAN REGION – Three part study
1
Houze, Wilton, and Smull (2007) – 3D structure
of intense storms and their distribution in
relation to topography and surrounding oceans
2
Ulrike Romatschke (Ulli) – Is extending Houze
et al. (2007) study
 Cloud and Precipitation Seminar Nov 15th
3
Analyze numerical simulations to investigate
the detailed role of the terrain – preliminary
results
OBJECTIVES
• Evaluate if high-resolution models can predict the
structures observed by Houze et al. (2007)
• Test the ideas put forward in that study:
– Investigate why the intense convection is often
observed over the foothills
– Analyze the relative roles of orography and synoptics
in systems observed in association with Bay of
Bengal depressions
NUMERICAL SIMULATIONS
•
Weather Research and Forecasting (WRF v2.1.1) model (runs
conducted by Anil Kumar, NCAR/Purdue University)
– NCEP Reanalysis used as initial and boundary conditions (6
hourly)
– Bulk microphysical parameterization: WRF Single-Moment with 6
water substances
• Isolated deep convective system: dx1=9 km; dx2 = 3 km (14
Jun 2002)  Simulation couldn’t capture system
• Wide intense convective system (3 Sep 2003)
• Broad stratiform system (11 Aug 2002)
•
HYSPLIT model trajectories using NCEP reanalysis
(http://www.arl.noaa.gov/ready/hysplit4.html)
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 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 at 2230 UTC 03 Sep 2003 (0500 LST, t=4.5 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 at 2300 UTC 03 Sep 2003 (0530 LST, t=5.0 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
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 - Low-level moist southwesterly flow was capped by dry
air flowing off the Afghan mountains
Soundings at 1800 UTC
Dry side
Moist side
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 1815 UTC
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 1830 UTC
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 1845 UTC
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
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
Broad stratiform system simulation
Time: 12 UTC 10 Aug – 03 UTC 11 Aug 2003 (1830-0930 LST)
Terrain and accumulated precipitation (mm)
Domain 1: dx = 27 km
Domain 2: dx = 9 km
Broad stratiform system –
Evaluation of low-levels winds at 00 UTC 11 Aug 2002
Observations
10 m winds and wind speed (m/s)
WRF-simulation
Surface winds and wind speed (m/s)
and terrain (red contours)
Broad stratiform system – Evaluation of IR temperature and reflectivity
Observations
WRF-simulation
Broad stratiform system –
Sounding at Tengchong at 00 UTC 11 Aug 2002
Observations
WRF-simulation
Broad stratiform system – Role of the Bay of Bengal Depression
‘Idealized’ (highly smoothed) low-level variables
Rainrate > 5 mm/hr
Mixing ratio > 21 g/kg
LOW
Wind speed
> 5m/s
SLP
PRELIMINARY CONCLUSIONS –
Broad stratiform system
• The high-resolution model was able to predict
the observed structures
• The Bay of Bengal depression provides lowlevel moisture and cross-barrier flow
• Low-level flow channeled between individual
ranges and impinges into the NE indentation of
the Himalayas
Concluding remark….
Schultz et al. 2000
“In diagnosing precipitation
processes, assessing the
mechanism for forcing ascent
should be the primary concern. The
degree of instability… merely
modulates the response to the
forcing”
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
Equivalent potential
temperature > 364 K
Wide convective system – Hypotheses testing
HYPOTHESIS - Convection started where the potentially unstable
column was subjected to orographic lifting
CAPE (for parcel with max theta_e, J/kg)
CIN (for parcel with max theta_e, J/kg)
Wide convective system
Evaluation at 1830 UTC 03 Sep 2003
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 at 1900 UTC 03 Sep 2003
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 at 2100 UTC 03 Sep 2003 (XXX LST, t=X 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
Broad stratiform system simulation
Terrain and accumulated precipitation (mm)
Broad stratiform system – Hypotheses testing
HYPOTHESIS – The flow over the terrain enhances the mesoscale
precipitation areas
Vertically integrated precipitating mixing ratio over 15 h (mm)
Broad stratiform system – Hypotheses testing
HYPOTHESIS – The flow over the terrain enhances the mesoscale
precipitation areas
Cloud water mixing ratio and vertical velocity
Stratiform case
Broad stratiform system –
Evaluation of 200 mb winds at 00 UTC 11 Aug 2002
Observations
wind speed (m/s)
WRF-simulation
wind speed (m/s)
and terrain (red contours)
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 1800 UTC
20
18
16
12
8
4