An Analysis of Snow Simulations in a Regional Climate Model with an Advanced Snow Scheme
Jiming Jin and Norman L. Miller
Earth Sciences Division, Lawrence Berkeley National Lab, Berkeley, California
6-hourly precipitation simulation at (-129.49oW, 51.14oN)
Introduction
• The Penn State-National Center for Atmospheric Research fifth-generation
Mesoscale Model (MM5) has been broadly used to perform regional weather,
climate, and water resources forecast and research.
• The latest version of MM5 has three land surface schemes; the bucket model,
the Pleim-Xiu model, and the NOAH model. These land surface models
include a simple slab snow scheme, which is unable to explicitly and
physically describe snow processes.
• Community Land Model version 3 (CLM3) has an advanced snow component
which will improve simulations of regional snowpack and related processes.
• Hypothesis: MM5 regional climate simulations will have improved water and
energy budgets if the current Land Surface Model is replaced with CLM3.
Compared with the Satellite snow cover
data, the faster snow melt in MM5/NOAH
results in a smaller snow cover due to its
simple snow physics. However, the
sophisticated snow model in MM5/CLM3
improves snow cover simulations.
Surface Albedo Simulation
Observation (SeaWiFS) (4kmx4km)
Two-way 60-km and 20-km nested domains. The
large box is for 60 km resolution and the smaller one
is for 20km resolution.
Snow water Equivalent (mm)
Latent Heat Flux Simulation (W m-2)
The components of CLM3
MM5-OLD (20km x 20km)
• Biogeophysics:
•5-layer snow
•10-layer soil
•1-layer vegetation.
• Hydrological Cycle:
•Hillslope processes
•lake hydrology
2 meter height air temperature (oC)
MM5-NEW (20km x 20km)
•Biogeochemistry:
•Carbon cycling
•organic matter
•dust, etc.
•Dynamic vegetation:
•Plant Function Types
Courtesy of G. Bonan
Precipitation (mm)
Both MM5/NOAH and MM5/CLM3 give reasonable
simulations for diurnal cycles of surface air
temperature and precipitation. However, MM5/CLM3
suppresses the exaggerated precipitation in
MM5/NOAH, which is caused by the earlier
snowmelt and stronger evaporation (latent heat flux)
in the spring season.
Comparison of CLM and the NOAH Model
CLM2
NOAH
Vegetation
Soil
Up to 4
vegetation
types in a
grid cell
10-layer soil
including
frozen soil
processes
Only one
vegetation
type in a
grid cell
Snow
4-layer soil
without
frozen soil
Lake
River
Routing
5-layer snow A 10-layer A simple
including
lake model DEM used
solid ice,
included
to calculate
liquid water,
water flow
and
directions.
compaction
processes
One layer
N/A
N/A
snow
lumped with
top soil layer
The simulations of SWE, surface air temperature and
precipitation. The time series are for averages of the Snotel
stations over the Columbia River Basin. Compared with
MM5/NOAH (old), MM5/CLM3 significantly improves
simulations in SWE, surface air temperature, and
precipitation.
Snow Cover Simulation
OBS (MODIS 5 km x 5km)
6-hourly surface air temperature simulation at (-129.49oW, 51.14oN)
Conclusions
• The coupling of MM5 with CLM3 significantly improves the
snow depth, snow cover, and surface albedo simulations.
• The faster snow melt is caused by unrealistic descriptions of
the surface energy balance in MM5/NOAH, which is greatly
alleviated due to the reasonable treatment of snow physics in
MM5/CLM3.
• The earlier snow melt in MM5/NOAH results in stronger
evaporation in the late spring, which causes exaggerated
precipitation. MM5/CLM3 produces lower evaporation during
the same time as a result of a better snowpack simulation,
thus suppressing the overestimated precipitation.
References
The Datasets
MM5-OLD (20km x 20km)
• The automated Snowpack Telemetry (SnoTel) stations over the
Columbia River Basin.
Cayan, D.R., 1996: Interannual climate variability and snowpack
in the western United States. J. Climate, 9, 928-948.
• The daily snowdepth, surface air temperature, and precipitation data
are from the Western Regional Climate Center.
Clark, M.P., M.C. Serreze, and G.J. McCabe, 2001: The historical
effect of El Nino and La Nina events on the seasonal evolution
of the montane snowpack in the Columbia and Colorado River
basins. Water Resour. Res., 37, 741-756.
• The temperature and precipitation data from the regular
meteorological stations.
Jin, J. and N.L. Miller, 2004: An analysis of climate variability
and snowmelt mechanisms in mountainous regions.
Submitted to Journal of Hydrometerology.
MM5-NEW (20km x 20km)
• 5 km x 5 km MODIS/Terra snow cover data, and 4 km x 4 km SeaWiFS
surface albedo data.
• Two sets of 60 km and 20 km hourly model output from March 1 to
May 31, 2002 were produced by MM5/NOAH (Old) and MM5/CLM3
(New). Only the 20 km resolution data were analyzed.
Acknowledgement
This study was supported by the California Energy
Commission Grant (46507). Work for the Department of
Energy is under contract DE-AC03-76SF00098.