In order to investigate the effect of the factors in tower latitudes on Meiyu/Baiu front,a diagnostic analysis for the two cases during June to July of 1985 and 1986 was examined.We found that (1)when the tropical con...In order to investigate the effect of the factors in tower latitudes on Meiyu/Baiu front,a diagnostic analysis for the two cases during June to July of 1985 and 1986 was examined.We found that (1)when the tropical convective activity moves westward to 10.5-15.5′N/140°E from east side of 10.5-15.5°N/160°E,the northward shifts of the Meiyu/Baiu rain belt occurs;(2)the main factor which results in the northward and southward shifts of Meiyu/Baiu rain belt is thought as the 8,18 and 30 day oscillations of the tropical convective activity around West Pacific. Meanwhile,the wave train propagating from Lake Baikal via Okhotsk Sea to the tropics could sometimes shift Baiu rain belt southward;(3)the onsets of Meiyu in China of both cases tend to take place just when the convective activity around lower latitudes moves westward through about 140°E with the 8,18 and 30 day oscillation periods firstly coming to June.展开更多
The present reported study investigated the persistence of snow anomalies over the Tibetan Plateau(TP) from the preceding seasons to summer and the relationship between the previous snow cover anomaly and summer preci...The present reported study investigated the persistence of snow anomalies over the Tibetan Plateau(TP) from the preceding seasons to summer and the relationship between the previous snow cover anomaly and summer precipitation over East Asia. The results showed that, relative to other snow indices, such as the station observational snow depth(SOSD) index and the snow water equivalent(SWE) index, the snow cover area proportion(SCAP) index calculated from the SWE and the percentage of visible snow of the Equal-Area Scalable Earth Grids(EASE-grids) dataset has a higher persistence in interannual anomalies, particularly from May to summer. As such, the May SCAP index is significantly related to summer precipitation over the Meiyu-Baiu region. The persistence of the SCAP index can partly explain the season-delayed effect of snow cover over the TP on summer rainfall over the Meiyu-Baiu region besides the contribution of the soil moisture bridge. The preceding SST anomaly in the tropical Indian Ocean and ENSO can persist through the summer and affect the summer precipitation over the Meiyu-Baiu region. However, the May SCAP index is mostly independent of the simultaneous SSTs in the tropical Indian Ocean and the preceding ENSO and may affect the summer precipitation over the Meiyu-Baiu region independent of the effects of the SST anomalies. Therefore, the May SCAP over the TP could be regarded as an important supplementary factor in the forecasting of summer precipitation over the Meiyu-Baiu region.展开更多
In this paper, a 10-level Quasi-Lagrangian Limited Area Model is used to simulate the process of Meiyu(Baiu) front of 1979. Some physical processes, such as large-scale condensation and cumulus convection, are include...In this paper, a 10-level Quasi-Lagrangian Limited Area Model is used to simulate the process of Meiyu(Baiu) front of 1979. Some physical processes, such as large-scale condensation and cumulus convection, are included in the model. The simulation results are encouraging. 24-h numerical simulation shows that the invading of cold air from North China and rapidly northward moving of warm air from South China can be successfully reproduced. The terrain with a maximum of 4175 m is incorporated in the model. Three different kinds of terrain schemes are tested and the dynamic effect of the Plateau on the process of heavy rainfall is found to be very important.展开更多
By Doppler weather radar and satellite cloud data,the Meiyu front rainstorm which occurred in the north of Huaihe River and the north region of Yangtze-Huaihe was analyzed during July 1-2,2006.The characteristics of i...By Doppler weather radar and satellite cloud data,the Meiyu front rainstorm which occurred in the north of Huaihe River and the north region of Yangtze-Huaihe was analyzed during July 1-2,2006.The characteristics of infrared satellite cloud,radar basic reflectivity and Doppler radial velocity were discussed in this rainstorm,such as the echo intensity,the characteristics of velocity field and so on.The reasons for this rainstorm were analyzed by these characteristics.The combination of radar and satellite data in the role of forecasting Meiyu front rainstorm was studied.展开更多
概率预报是由集合预报衍生、包含不确定性信息的客观产品,对业务决策服务有重要的参考价值。传统的邻域集合概率法中,邻域半径固定不变,不符合实际天气过程中牵涉甚广的尺度谱。为此引入基于集合匹配尺度的邻域集合概率法(Neighborhood ...概率预报是由集合预报衍生、包含不确定性信息的客观产品,对业务决策服务有重要的参考价值。传统的邻域集合概率法中,邻域半径固定不变,不符合实际天气过程中牵涉甚广的尺度谱。为此引入基于集合匹配尺度的邻域集合概率法(Neighborhood Ensemble Probability based on Ensemble Agreement Scale,EAS_NEP),并在中国南方典型的梅雨锋暴雨中开展准确性和预报技巧的定量检验评估,以期验证该方法在此类过程中的适用性,并促进其在实际业务中的推广使用。联合扰动初始场、侧边界和物理过程所得到的集合预报能较好地表征实际的预报不确定性,进一步在此基础上比较了格点概率法、不同半径的邻域集合概率法以及EAS_NEP的优劣。试验结果表明,EAS_NEP能根据集合成员间的一致性程度,自适应地调整邻域半径,其在集中型降水中所确定的邻域半径通常大于分散型降水。动态调整的邻域半径既避免了半径过大时的过度平滑与关键信息丢失,又消除了半径较小所带来的奇异点,其空间分布呈阶梯型,空间连续性更优。此外,BS(布莱尔评分)、FSS(分数技巧评分)和ROC曲线(相对作用特征曲线)等定量评估结果也体现出EAS_NEP相比传统方法正的预报技巧,尤其是在分散型降水和高阈值检验时优势更明显。以上结果表明,EAS_NEP在梅雨锋暴雨的预报中具有较好的应用前景,运用在业务中能有效提升概率预报质量。展开更多
基于欧洲中期天气预报中心(European Center for Medium-range Weather Forecasts,ECMWF)集合预报资料及浙江全省自动站降水观测资料,采用贝叶斯模型平均(Bayesian Model Average,BMA)方法对2020年浙江超长梅汛期开展降水概率预报订正...基于欧洲中期天气预报中心(European Center for Medium-range Weather Forecasts,ECMWF)集合预报资料及浙江全省自动站降水观测资料,采用贝叶斯模型平均(Bayesian Model Average,BMA)方法对2020年浙江超长梅汛期开展降水概率预报订正试验。采用平均绝对误差、连续等级概率评分、布莱尔评分B_(S)、Talagrand、概率积分变换(Probability Integral Transform,PIT)直方图及属性图检验方法对本次过程BMA订正前后的概率预报进行对比分析,结果表明:(1)50 d为适用于浙江梅汛期ECMWF集合预报订正的BMA最优训练期,经最优训练期的BMA订正后,预报离散度有所增加,预报误差有所下降;(2)BMA对0.1 mm、10.0 mm和25.0 mm阈值降水的订正效果显著,经BMA订正后3个阈值的降水预报B_(S)下降率分别为25.92%、19.29%、4.76%,但对超过50.0 mm的降水订正效果不明显,且随着降水阈值增加,BMA的订正效果减弱;(3)在强降水个例中,BMA能有效减少各阈值降水预报概率大值落区偏差,使订正后的降水预报概率大值区与观测落区更一致。展开更多
基金This study is supported by National Natural Science Foundation of China under Grant No.49794030Ministry of Science Technology of China(G1998040908)
文摘In order to investigate the effect of the factors in tower latitudes on Meiyu/Baiu front,a diagnostic analysis for the two cases during June to July of 1985 and 1986 was examined.We found that (1)when the tropical convective activity moves westward to 10.5-15.5′N/140°E from east side of 10.5-15.5°N/160°E,the northward shifts of the Meiyu/Baiu rain belt occurs;(2)the main factor which results in the northward and southward shifts of Meiyu/Baiu rain belt is thought as the 8,18 and 30 day oscillations of the tropical convective activity around West Pacific. Meanwhile,the wave train propagating from Lake Baikal via Okhotsk Sea to the tropics could sometimes shift Baiu rain belt southward;(3)the onsets of Meiyu in China of both cases tend to take place just when the convective activity around lower latitudes moves westward through about 140°E with the 8,18 and 30 day oscillation periods firstly coming to June.
基金support of the National Science Foundation of China (Grant Nos. 41271434 and 41375090)the Hong Kong Research Grants Council (Grant No. CUHK403612)the Basic Research Fund of Chinese Academy of Meteorological Sciences (Grant No. 2013Z002)
文摘The present reported study investigated the persistence of snow anomalies over the Tibetan Plateau(TP) from the preceding seasons to summer and the relationship between the previous snow cover anomaly and summer precipitation over East Asia. The results showed that, relative to other snow indices, such as the station observational snow depth(SOSD) index and the snow water equivalent(SWE) index, the snow cover area proportion(SCAP) index calculated from the SWE and the percentage of visible snow of the Equal-Area Scalable Earth Grids(EASE-grids) dataset has a higher persistence in interannual anomalies, particularly from May to summer. As such, the May SCAP index is significantly related to summer precipitation over the Meiyu-Baiu region. The persistence of the SCAP index can partly explain the season-delayed effect of snow cover over the TP on summer rainfall over the Meiyu-Baiu region besides the contribution of the soil moisture bridge. The preceding SST anomaly in the tropical Indian Ocean and ENSO can persist through the summer and affect the summer precipitation over the Meiyu-Baiu region. However, the May SCAP index is mostly independent of the simultaneous SSTs in the tropical Indian Ocean and the preceding ENSO and may affect the summer precipitation over the Meiyu-Baiu region independent of the effects of the SST anomalies. Therefore, the May SCAP over the TP could be regarded as an important supplementary factor in the forecasting of summer precipitation over the Meiyu-Baiu region.
基金This research work is financially supported by the Eighth National Five-Year Scientific Project(85-906-04-02)and Nation Natural Founndation of China(4927520).
文摘In this paper, a 10-level Quasi-Lagrangian Limited Area Model is used to simulate the process of Meiyu(Baiu) front of 1979. Some physical processes, such as large-scale condensation and cumulus convection, are included in the model. The simulation results are encouraging. 24-h numerical simulation shows that the invading of cold air from North China and rapidly northward moving of warm air from South China can be successfully reproduced. The terrain with a maximum of 4175 m is incorporated in the model. Three different kinds of terrain schemes are tested and the dynamic effect of the Plateau on the process of heavy rainfall is found to be very important.
文摘By Doppler weather radar and satellite cloud data,the Meiyu front rainstorm which occurred in the north of Huaihe River and the north region of Yangtze-Huaihe was analyzed during July 1-2,2006.The characteristics of infrared satellite cloud,radar basic reflectivity and Doppler radial velocity were discussed in this rainstorm,such as the echo intensity,the characteristics of velocity field and so on.The reasons for this rainstorm were analyzed by these characteristics.The combination of radar and satellite data in the role of forecasting Meiyu front rainstorm was studied.
文摘概率预报是由集合预报衍生、包含不确定性信息的客观产品,对业务决策服务有重要的参考价值。传统的邻域集合概率法中,邻域半径固定不变,不符合实际天气过程中牵涉甚广的尺度谱。为此引入基于集合匹配尺度的邻域集合概率法(Neighborhood Ensemble Probability based on Ensemble Agreement Scale,EAS_NEP),并在中国南方典型的梅雨锋暴雨中开展准确性和预报技巧的定量检验评估,以期验证该方法在此类过程中的适用性,并促进其在实际业务中的推广使用。联合扰动初始场、侧边界和物理过程所得到的集合预报能较好地表征实际的预报不确定性,进一步在此基础上比较了格点概率法、不同半径的邻域集合概率法以及EAS_NEP的优劣。试验结果表明,EAS_NEP能根据集合成员间的一致性程度,自适应地调整邻域半径,其在集中型降水中所确定的邻域半径通常大于分散型降水。动态调整的邻域半径既避免了半径过大时的过度平滑与关键信息丢失,又消除了半径较小所带来的奇异点,其空间分布呈阶梯型,空间连续性更优。此外,BS(布莱尔评分)、FSS(分数技巧评分)和ROC曲线(相对作用特征曲线)等定量评估结果也体现出EAS_NEP相比传统方法正的预报技巧,尤其是在分散型降水和高阈值检验时优势更明显。以上结果表明,EAS_NEP在梅雨锋暴雨的预报中具有较好的应用前景,运用在业务中能有效提升概率预报质量。
文摘基于欧洲中期天气预报中心(European Center for Medium-range Weather Forecasts,ECMWF)集合预报资料及浙江全省自动站降水观测资料,采用贝叶斯模型平均(Bayesian Model Average,BMA)方法对2020年浙江超长梅汛期开展降水概率预报订正试验。采用平均绝对误差、连续等级概率评分、布莱尔评分B_(S)、Talagrand、概率积分变换(Probability Integral Transform,PIT)直方图及属性图检验方法对本次过程BMA订正前后的概率预报进行对比分析,结果表明:(1)50 d为适用于浙江梅汛期ECMWF集合预报订正的BMA最优训练期,经最优训练期的BMA订正后,预报离散度有所增加,预报误差有所下降;(2)BMA对0.1 mm、10.0 mm和25.0 mm阈值降水的订正效果显著,经BMA订正后3个阈值的降水预报B_(S)下降率分别为25.92%、19.29%、4.76%,但对超过50.0 mm的降水订正效果不明显,且随着降水阈值增加,BMA的订正效果减弱;(3)在强降水个例中,BMA能有效减少各阈值降水预报概率大值落区偏差,使订正后的降水预报概率大值区与观测落区更一致。
