The effect of terrain and land surface on summer monsoon convection in the

Himalayan region

Socorro Medina, Robert Houze,

Anil Kumar, and Dev Niyogi13th Conference on Mountain Meteorology), Whistler, BC, Canada, 12 August 2008

Orographic Precipitation in cold and warm climates

ALPS – MAP (1999)OR CASCADES – IMPROVE-2 (2001)

HIMALAYAS

• Terrain gradients• Land-ocean contrast• Land cover gradients

Snow/Ice

Tundra

Wetland

Forest

Irrigated crop

Crop

Savanna

Shurb/Grass

Dryland/crop

Grass

Shurb

Barren

Thar DesertGanges Delta

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 convectivesystems

Broad stratiform echoes(embedded in convective

systems)

Wide convective system in western indentation

3 September 2003

Domain 1 (dx = 9 km) Domain 2 (dx = 3 km)

Accumulated precipitation and terrain

INDIAPAK

ISTA

N

HIMALAYASHIN

DU

KU

SH

Evaluation: 3D Reflectivity structure (~22 UTC 3 Sep [~03 LST 4 Sep])OBSERVATION (TRMM-PR)

Horizontal crosssections at 4 km

Vertical crosssections alongblack line

Vertical crosssections alongred line

SIMULATION

dBZ

0 100 200Distance (km)

Hei

ght (

km)

0

8

1

6

0 100 200Distance (km)

Hei

ght (

km)

0

8

1

6

0 125 250Distance (km)

Hei

ght (

km)

0

8

1

6

0 125 250Distance (km)

Hei

ght (

km)

0

8

1

6

HYPOTHESIS: Dry line

SURFACE DEW POINT DEPRESSIONAND 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)NOAA HYSPLIT (NCEP FNL)BACKWARD TRAJECTORIES

1.0 AGL km3.5 AGL km

Valid: 18 UTC 3 Sep (23 LST) Forecast : 0 h

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

Valid: 19 UTC 3 Sep (00 LST). Forecast : 1 h

N

6.0 g kg-1

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