IUKWC Workshop November 2016: Developing Hydro-climatic Services for Water Security Session 4.2 Andrew Orr

1. Assessing WRF model experiments of precipitation in the
Himalayas
Andrew Orr
anmcr@bas.ac.uk
British Antarctic Survey

2. HKK
Himalaya
Bookhagen &
Burbank (2010)

3. Schematic drawing of a regional climate model

4. Objective: Determine the size distribution of various hydrometeors,
i.e. rain particles, cloud droplets, snow crystals, graupel particles and
ice particles
Cloud microphysics processes and precipitation
Cloud microphysics scheme Mixing ratio of
hydrometeors
Mean diameter or number
concentration of
hydrometeros
Single moment Predicted Fixed
Double moment Predicted Predicted
Key difference between single and double moment microphysics schemes

5. Scheme Single moment Double moment
WSM5 cloud, ice, rain, snow x
WDM6 ice, snow, graupel cloud, rain
Thompson cloud, snow, graupel rain, ice
Morrison cloud rain, ice, snow, graupel
Summary of the hydrometeor species represented by the WSM5, WDM6, Morrison,
and Thompson cloud microphysics schemes.

6. Experiment methodology
• Test Morrison, Thompson, WSM5, and WDM6 schemes as the
cloud microphysics option in a regional atmosphere model
• Each simulation is for a 10-day period from 1-10 July 2012.
• Regional atmosphere model employed is the Weather
Research and Forecasting (WRF) model
• Model output compared to available observations, and used
to determine key microphysical processes

7. Topography of the Langtang Valley, Nepal
Site 1 (Kyangjin) Site 2 (Near Yala)
Elevation (m asl) 3857 4831
Precipitation Tipping bucket Pluviometer
Radiation Radiometer x

8. Number of domains 4
Horizontal grid spacing 30 km, 10 km, 3.3 km, 1.1
km
Number of vertical levels 29
Model top 50 hPa
Forcing data ERA-Interim reanalysis
Boundary layer Mellor-Yamada-Nakanishi-
Niino (MYNN)
Cumulus (30 km and 10
km domains only)
Betts-Miller-Janjic (BMJ)
Shortwave radiation Dudhia scheme
Longwave radiation Rapid Radiative Transfer
Model (RRTM)
Land surface Noah land surface model
Microphysics Morrison, Thompson,
WSM3, WDM6
Summary of the WRF model setup

9. Ten-day time-series of accumulated total precipitation measured at sites 1 and 2 (thick lines)
for the period 1-10 July 2012. Dashed lines indicate simulated liquid precipitation only.

10. Histograms of frequency of 3-hourly precipitation (mm) measured at sites1 and 2
for the period 1-10 July 2012.

11. Ten-day time-series of 3-hourly incoming shortwave radiation (W m-2
) measured at
site 1 for the period 1-10 July 2012.

12. Ten-day time-series of the vertically-integrated column density (kg m-2
) of hydrometeors at sites
1 (solid lines) and 2 (dashed lines) for the period 1-10 July 2012.

13. Accumulated total precipitation (mm) over the Langtang catchment for the period 1-10 July
2012. The precipitation for Thompson, WSM5, and WDM6 is expressed as the difference with
respect to that from Morrison. The model topographic height is shown as contours (every 400

14. Ten-day average column-integrated horizontal moisture flux (vectors, kg m-1
s-1
) and
accumulated total precipitation (shading, mm) over the innermost domain for the period
1-10 July 2012. The model topographic height is shown as contours (every 2000 m).

16. (top) Air motion vectors (m s-1
) and relative humidity (%) and (bottom) hydrometeor mixing ratio
ratio (g kg-1
) along a meridional vertical cross section passing through site 1 (filled circle) using
the Morrison and Thompson schemes during the precipitation episode on 5 July 2012.

17. •Cold-rain processes are a key precipitation formation mechanism in
Langtang Valley, Himalaya.
•The choice of the microphysics scheme strongly affects
precipitation over Langtang Valley (particularly over ridges).
•As well as microphysical structure, both large-scale and localised
orographic forcing are important.
•Improved modelling of cold-rain processes are critical for a realistic
representation of cloud microphysics and precipitation.
Summary

18. • Efforts to improve model simulation of clouds urgently requires
further measurements of the microphysical properties of clouds in
the Himalayan region.
• This requires field campaigns based on use of Aerial Autonomous
Vehicles, precipitation radar, and remote sensing
• UK-India collaboration
Future work / collaboration