A Basis for Achieving Economic, Societal and Environmental Goals in Illinois
Xin-Zhong Liang
Surface Boundary Conditions
Liang, X.-Z., H. Choi, K.E. Kunkel, Y.
Dai, E. Joseph, J.X.L. Wang, and P. Kumar, 2004: Development of the regional
climate-weather research and forecasting model (CWRF). Part A: Surface boundary
conditions. Illinois State Water Survey Research Report, in press.
ABSTRACT. The CWRF is
the climate
extension of the Weather
Research and Forecasting model (
WRF), incorporating all its
functionalities for numerical weather predictions while enhancing the
capability for climate applications.
This paper focuses on the construction and implementation of the surface
boundary conditions (SBCs) that are specifically
designed for
CWRF mesoscale
modeling applications
. The
primary
SBCs include surface topography (mean
elevation, slope, curvature, and their standard deviations); bedrock, lakebed
or seafloor depth; soil sand and clay fraction profile; surface albedo
localization factor; bottom soil temperature; surface characteristic
identification; land cover category; fractional vegetation cover; leaf and stem
area index; sea surface temperature, salinity and current; and sea temperature
and salinity profile.
They are
currently presented onto a CWRF domain suitable for the U.S applications at
30-km spacing. The raw data
sources and processing procedures, however, are elaborated in detail, by which
the SBCs can be readily constructed for any specific
CWRF domain over the globe. For a specific field, alternative data sources, if
available, are compared to quantify uncertainties and suggest the choice or
improvement.
CWRF-CMM5 Comparison
We have
so far conducted various sensitivity and validation experiments of the initial CWRF
(without the latest updates) for the 1993 U.S. Midwest flood case, where the
LBCs were constructed from the NCEP-DOE AMIP-II reanalysis (Kanamitsu et al.
2002).
compares CWRF simulated regional mean rainfall daily variations during May
2-July 31, with observations and CMM5 outputs. For the
Midwest
major flood area, the CMM5 reproduces different climate regimes, where observed
rainfall was identified with the periodic (5-day) passage of mid-latitude
cyclones in June and persistent synoptic circulations in July. The CWRF
realistically simulates the June variations, but has less skill in July with
insufficient rainfall between days 4-18
.
This deficiency likely results from incomplete representation of regional water
recycling processes, which is anticipated to be largely eliminated by the
latest updates. In particular, the incorporation of more realistic
surface boundary conditions (Liang et al. 2004b), including new surface albedo
parameterization, bedrock depth, soil and vegetation properties, will
significantly improve regional climate simulations.
On the other hand, both CWRF and CMM5 produce an excellent simulation of
observed rainfall variations during the whole period over Cascade, where the
orographic effect dominates. Over the U.S. Northeast, the observed
temporal evolution is generally well simulated by both RCMs, with somewhat
overestimated (underestimated) rainfall intensity in CWRF (CMM5).
Note that the rainfall associated with the
North American summer monsoon over Mexico is totally missed in the CMM5,
while the geographic distributions and daily variations are very realistically
reproduced by the CWRF. The rainfall intensity seems to be overestimated in the
CWRF, though the observed data has a coarse resolution and large uncertainty.
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