In this paper, the numerical simulation bias of the non-hydrostatic version GRAPES-Meso （Mesoscalc of the Global and Regional Assimilation and Prediction System） at the resolution of 0.18° for a torrential rain...In this paper, the numerical simulation bias of the non-hydrostatic version GRAPES-Meso （Mesoscalc of the Global and Regional Assimilation and Prediction System） at the resolution of 0.18° for a torrential rain case, which happened in May 31st to June 1st 2005 over Hunan province, are diagnosed and investigated by using the radiosondes, intensive surface observation, and the operational global analysis data, and the sensitivity experimental results as well. It is shown in the result that the GRAPES-Meso could reproduce quite well the main features of large-scale circulation and the distribution of the accumulated 24h precipitation and the key locations of tile torrential rainfall arc captured reasonably well by the model. I fowever, bias exist in the simulation of the mesoscale features of the torrential rain and details of the relevant systems. for example, the simulated rainfall that is too earlier in model integration and remsrkable. underpredictien of the peak value of rainfall rates over the heaviest rainfall region, the weakness of the upper jet siimulation and the overpredietion of the south-west wind in the lower troposphere etc. The investigation reveals that the sources of the simulation bias are different. The erroneous model rainfall in the earlier integration stage over the heaviest rainfall region is induced by the model initial condition bias of the wind field at ablaut 925hPa over the torrential rainfall region, where the bias grow rapidly and spread upward to about 600hPa level within the few hours into the integration and result in abnormal convergence of the wind and moisture, and thus the unreal rainfall over that region. The large bias on the simulated rainfall intensity over the heaviest rainfall region might be imputed to the following combined facters of（1） the simulation bias on the strength and detailed structures of the upper-level jet core which bring about significant, underpredictions of the dynamic conditions （including upper-level divergence and the up,yard motion for heavy rainfalt due to unfavorable mesoscale vertical coupting between the strong, upper-level divergence and Iower-level convergence; and （2） the inefficient coupling of the cumulous parameterzation scheme and the explicit moisture in the integration, which causes the failure of the explicit moisture scheme in generating grid-scale rainfall in a certain extent through inadequate convective adjustmenl and feedback to the grid-scale, In addition, the interaction of the combined two factors could form a negative feedback to the rainfall intensity simulation, and eventually lead to the obvious undcrprediction of the rainfall rate.展开更多
A cloud-resolving model simulation of a mesoscale convective system （MCS） producing torrential rainfall is performed with the finest horizontal resolution of 444 m. It is shown that the model reproduces the observed...A cloud-resolving model simulation of a mesoscale convective system （MCS） producing torrential rainfall is performed with the finest horizontal resolution of 444 m. It is shown that the model reproduces the observed MCS, including its rainfall distribution and amounts, as well as the timing and location of leading rainbands and trailing stratiform clouds. Results show that discrete convective hot towers, shown in Vis5D at a scale of 2-5 kin, are triggered by evaporatively driven cold outflows converging with the high-θe air ahead. Then, they move rearward, with respect to the leading rainbands, to form stratiform clouds. These convective towers generate vortical tubes of opposite signs, with more intense cyclonic vorticity occurring in the leading convergence zone. The results appear to have important implications for the improvement of summertime quantitative precipitation forecasts and the understanding of vortical hot towers, as well midlevel mesoscale convective vortices.展开更多
Spatial and temporal distribution characteristics and scale range of two significant areas were obtained by analyzing the relationship among summer rainfall in Yunnan province, height field and SST field (40°S –...Spatial and temporal distribution characteristics and scale range of two significant areas were obtained by analyzing the relationship among summer rainfall in Yunnan province, height field and SST field (40°S – 40°N, 30 °E – 70°W) across the North Hemisphere at 200 hPa, 500 hPa and 850 hPa for Jan. to May and correlation, and field wave structure. Remote key regions among summer rainfall in Yunnan province, height field and SST field (40°S – 40°N, 30°E – 70°W) across the North Hemisphere at 200 hPa, 500 hPa and 850 hPa were studied through further analyzing of the circulation system and its climate / weather significance. The result shows that the forecast has dependable physical basis when height and SST fields were viewed as predictors and physical models of impacts on rainy season precipitation in Yunnan are preliminarily concluded.展开更多
基金Research into the Theories and Methods for the Monitoring and Prediction of Flood-InflictingTorrential Rains in Southern China - one of Project "973"Study on the Development of Numerical PredictionModels for High-Resolution, Non-Hydrostatic Mesoscale Torrential Rains and Their Prediction Systems
文摘In this paper, the numerical simulation bias of the non-hydrostatic version GRAPES-Meso （Mesoscalc of the Global and Regional Assimilation and Prediction System） at the resolution of 0.18° for a torrential rain case, which happened in May 31st to June 1st 2005 over Hunan province, are diagnosed and investigated by using the radiosondes, intensive surface observation, and the operational global analysis data, and the sensitivity experimental results as well. It is shown in the result that the GRAPES-Meso could reproduce quite well the main features of large-scale circulation and the distribution of the accumulated 24h precipitation and the key locations of tile torrential rainfall arc captured reasonably well by the model. I fowever, bias exist in the simulation of the mesoscale features of the torrential rain and details of the relevant systems. for example, the simulated rainfall that is too earlier in model integration and remsrkable. underpredictien of the peak value of rainfall rates over the heaviest rainfall region, the weakness of the upper jet siimulation and the overpredietion of the south-west wind in the lower troposphere etc. The investigation reveals that the sources of the simulation bias are different. The erroneous model rainfall in the earlier integration stage over the heaviest rainfall region is induced by the model initial condition bias of the wind field at ablaut 925hPa over the torrential rainfall region, where the bias grow rapidly and spread upward to about 600hPa level within the few hours into the integration and result in abnormal convergence of the wind and moisture, and thus the unreal rainfall over that region. The large bias on the simulated rainfall intensity over the heaviest rainfall region might be imputed to the following combined facters of（1） the simulation bias on the strength and detailed structures of the upper-level jet core which bring about significant, underpredictions of the dynamic conditions （including upper-level divergence and the up,yard motion for heavy rainfalt due to unfavorable mesoscale vertical coupting between the strong, upper-level divergence and Iower-level convergence; and （2） the inefficient coupling of the cumulous parameterzation scheme and the explicit moisture in the integration, which causes the failure of the explicit moisture scheme in generating grid-scale rainfall in a certain extent through inadequate convective adjustmenl and feedback to the grid-scale, In addition, the interaction of the combined two factors could form a negative feedback to the rainfall intensity simulation, and eventually lead to the obvious undcrprediction of the rainfall rate.
基金supported by Jiangsu Education Science Foundation (Grant No.07KJB170065)Chinese National Science Foundation (Grant No.40775060)U.S.National Science Foundation (Grant No.ATM0758609)
文摘A cloud-resolving model simulation of a mesoscale convective system （MCS） producing torrential rainfall is performed with the finest horizontal resolution of 444 m. It is shown that the model reproduces the observed MCS, including its rainfall distribution and amounts, as well as the timing and location of leading rainbands and trailing stratiform clouds. Results show that discrete convective hot towers, shown in Vis5D at a scale of 2-5 kin, are triggered by evaporatively driven cold outflows converging with the high-θe air ahead. Then, they move rearward, with respect to the leading rainbands, to form stratiform clouds. These convective towers generate vortical tubes of opposite signs, with more intense cyclonic vorticity occurring in the leading convergence zone. The results appear to have important implications for the improvement of summertime quantitative precipitation forecasts and the understanding of vortical hot towers, as well midlevel mesoscale convective vortices.
基金Key Foundation Project of Yunnan Province (2003D0014Z)Natural Science Foundation ofChina (40065001)
文摘Spatial and temporal distribution characteristics and scale range of two significant areas were obtained by analyzing the relationship among summer rainfall in Yunnan province, height field and SST field (40°S – 40°N, 30 °E – 70°W) across the North Hemisphere at 200 hPa, 500 hPa and 850 hPa for Jan. to May and correlation, and field wave structure. Remote key regions among summer rainfall in Yunnan province, height field and SST field (40°S – 40°N, 30°E – 70°W) across the North Hemisphere at 200 hPa, 500 hPa and 850 hPa were studied through further analyzing of the circulation system and its climate / weather significance. The result shows that the forecast has dependable physical basis when height and SST fields were viewed as predictors and physical models of impacts on rainy season precipitation in Yunnan are preliminarily concluded.
