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Wen J.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Lai X.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Shi X.,EAAF Institute of Aeronautical Meteorology and Chemical Deference | Pan X.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute
Meteorology and Atmospheric Physics | Year: 2013

The spatial distribution of fractional vegetation coverage (FVC) over the source region of the Yellow River (SRYR) shows heterogeneity and has changed much for vegetation degradation during the past 30 years. In this paper, three numerical tests were conducted using the Weather Research and Forecasting (WRF) model for a fair weather case and a rainy case over the SRYR. The first test used FVC derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) data, the second test took a spatial constant FVC (=50 %), and the last one deployed the model default FVC. The results showed that simulated 2-m height potential temperature decreased and specific humidity increased as FVC increased for both cases. The magnitudes of the sensible and latent heat fluxes were different over the wetland at the fair day and the rainy day. There was a divergence center near the Zoige wetland in the fair weather case but a convergent center in the rainy case. As a conclusion, when the default FVC in the WRF model were replaced by the new MODIS-derived FVC data, the root-mean-square errors (RMSEs) between measurements and the simulated 2-m height air temperature and relative humidity decreased for both cases, the mean RMSEs between measurements and the simulated 2-m height air temperature and relative humidity declined by 0. 3 K and 3. 0 % in the fair day, 0. 4 K and 3. 4 % in the rainy case. The mean differences of simulated precipitation for seven ground stations were 1. 1 mm for the fair day and 4. 2 mm for the rainy case. Therefore, the updated MODIS FVC has influences on the convective environment over the SRYR. © 2013 Springer-Verlag Wien. Source


Shi X.,EAAF Institute of Aeronautical Meteorology and Chemical Deference | Shi X.,Chinese Academy of Sciences | Li Y.,EAAF Institute of Aeronautical Meteorology and Chemical Deference | Liu J.,EAAF Institute of Aeronautical Meteorology and Chemical Deference | And 5 more authors.
Journal of Natural Disasters | Year: 2012

In this paper, a rainstorm in north China was simulated by the ARPS model and the establishment and development process of its helicity was analyzed in detail. Results show that the understanding of the configuration of helicity in low level and high level is helpful to analyzing the occurrence and development of the convective systems and obtaining the location of the precipitations. Area having positive values within xy-helicity front is in favor of the occurrence of the rainstorms, but its displayed range is usually larger than that of the actual precipitation. At high level, the obvious increase of the negative z-helicity indicates the stronger development of the convective systems and more rainfall; while at low level, about 3.25km in height, the central areas of the positive z-helicity usually agree well with the precipitations. Compared with xy-helicity, z-helicity is more accurate in locating the rainfall range, and thus is a better parameter indicating the maintenance, development and the intensity of a rainstorm system. Source

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