Low (web) Quality - BALTEX

76
Investigation of precipitation of the contiguous China using the Weather
Research and Forecasting (WRF) model
Jian Tang and Tang Jianping
School of Atmospheric Science, Nanjing University, HanKou Road 22, Nanjing, P.R. China; tangjian@smail.nju.edu.cn
1. Introduction
The booming of the area of regional climate models
makes RCMs being more and more used in climate research
to meet the increasing demands for high resolution
simulations by its downscaling skills. Regional climate
research began in the late 1980s when the global climate
models’ (GCMs) coarse resolutions of 300-500km cannot
produce enough climate information to satisfy the needs for
investigating climate change (Leung et al., 2003). It is
commonly accepted the regional climate model driven by a
large-scale circulation (generated by either reanalysis data or
GCMs) can be integrated from an initial condition and
generate realistic high-resolution (spatial and temporal as
well) simulations. Since late 1980s, much remarkable
progress has been made in the field of the regional climate
modeling. (e.g., Dickinson et al. 1989; Giorgi 1990; Jones et
al. 1995; Fu and Giorgi 1996; Christensen et al. 1997;
Machenhauer et al. 1998). Giorgi and Mearns (1991) has
recommended that long-term continuous RCM integrations
can generate more pronouncing information than ensembles
of short simulations, including minimal effect from
atmospheric spin-up, improved equilibrium between the
regional climate and surface hydrology cycle, accurate
representation of the model internal climatology and better
detection of systematic model physics deficiencies.
China is a typical monsoon area with distinct
geographical configurations: west terrain high and low in the
east, with ocean surrounds its south and east. In this paper,
in order to understand the performance of the Weather
Research and Forecasting (WRF) model in China, we run a
twenty-year simulation to get better understanding of the
large climate variability in China. The purpose of this study
is to investigate the capability of an RCM to reproduce the
observed annual cycle of the contiguous China and to get
better understanding of model climatology biases. The
twenty-year mean climatology is long enough to be robust
significant.
2. Model simulation and validation
The WRF model, driven by the NCEP/DOE reanalysis data,
is used to simulate the regional climate change from 1982 to
2001 in China. The model was integrated form 1 December
to December 31 1981 with a resolution of 30km (Figure 1)
.The simulation results are compared to observations as well
as the NCEP/DOE reanalysis data to study the WRF’s
downscaling skill and uncertainty over China. The WRF
simulations show its remarkable downscaling skills for
precipitation and precipitation annual cycle, producing more
realistic regional details.
Figure 1. Outlined are nine key regions with
distinct climate characteristics and/or model biases.
Figure 2. Monthly 1982-2001 mean precipitation
(mm day-1) variations averaged over the nine key
regions in China for observation (OBS; thin dashed),
the WRF baseline integration (WRF; thick solid),
and the R-2 model output (R-2; thick dashed).
Figure2 compares the observed, the R-2 and WRF
simulated monthly precipitation variations averaged over
nine key regions (see specification in Fig. 1). These
regions have distinct climate characteristics and/or model
biases. The WRF simulates most accurately in the region
of Yangtze River Basin, South China and Northeast China.
In South China, the WRF simulation has corrected the R-2
precipitation seasonal cycle with less precipitation than
observation in all seasons. Similar biases exist in
Northeast China and Yangtze River Basin. The R-2 poorly
simulates the seasonal cycle and the month with maximum
precipitation has been postponed one month, and the
rainfall amount is largely overestimated. For the Yunnan-
Kweichow Plateau, North China and South of Qinghai-
Tibet Plateau, the WRF simulations are generally realistic