Predecessor rain events(PREs) in the Yangtze River Delta(YRD) region associated with the South China Sea and Northwest Pacific Ocean(SCS-WNPO) tropical cyclones(TCs) are investigated during the period from 2010 to 201...Predecessor rain events(PREs) in the Yangtze River Delta(YRD) region associated with the South China Sea and Northwest Pacific Ocean(SCS-WNPO) tropical cyclones(TCs) are investigated during the period from 2010 to 2019.Results indicate that approximately 10% of TCs making landfall in China produce PREs over the YRD region;however,they are seldom forecasted. PREs often occur over the YRD region when TCs begin to be active in the SCS-WNPO with westward paths, whilst the cold air is still existing or beginning to be present. PREs are more likely to peak in June and September. The distances between the PRE centers and the parent TC range from 900 to 1700 km. The median value of rain amounts and the median lifetime of PREs is approximately 200 mm and 24 h, respectively. Composite results suggest that PREs form in the equatorward jet-entrance region of the upper-level westerly jet(WJ), where a 925-hPa equivalent potential temperature ridge is located east of a 500-hPa trough. Deep moisture is transported from the TC vicinity to the remote PREs region. The ascent of this deep moist air in front of the 500-hPa trough and frontogenesis beneath the equatorward entrance region of the WJ is advantageous for the occurrence of PREs in the YRD region. The upper-level WJ may be affected by the subtropical high and westerly trough in the Northwest Pacific Ocean, and the occurrence of PREs may favor the maintenance of the upper-level WJ. The upper-level outflow of TCs in the SCS plays a secondary role.展开更多
The three-dimensional Weather Research and Forecasting(WRF)model was used to conduct sensitivity experiments during the landfall of Typhoon Fitow(2013)to examine the impacts of cloud radiative processes on thermal bal...The three-dimensional Weather Research and Forecasting(WRF)model was used to conduct sensitivity experiments during the landfall of Typhoon Fitow(2013)to examine the impacts of cloud radiative processes on thermal balance.The vertical profiles of heat budgets,vertical velocity,and stability were analyzed to examine the physical processes responsible for cloud radiative effects on surface rainfall for Typhoon Fitow(2013).The inclusion of clouds reduced radiative cooling in ice and liquid cloud layers by reducing outgoing radiation.The suppressed radiative cooling reduced from the ice cloud layers to liquid cloud layers.This was conducive to reducing instability.The decreased instability was associated with the reduced upward motions.The reduced upward motion led to a decreased vertical mass conver-gence.Consequently,heat divergence was weakened to warm the atmosphere.Together with suppressed radiative cooling,these effects jointly suppressed net condensation and rainfall.Furthermore,the reduced rainfall due to the cloud radiative effects were mainly associated with the reduced convective and stratiform rainfall.The reduced convective rainfall was associated with the reduced net condensation,while the reduced stratiform rainfall was related to the constraint of hydrometeor convergence.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 42105004, 41930967, 42192554, and 42105011)the Natural Science Foundation of Zhejiang Province of China (Grant No. LQ20D050001)the Scientific Research Foundation of Hangzhou Normal University (Grant No. 2020QDL015)。
文摘Predecessor rain events(PREs) in the Yangtze River Delta(YRD) region associated with the South China Sea and Northwest Pacific Ocean(SCS-WNPO) tropical cyclones(TCs) are investigated during the period from 2010 to 2019.Results indicate that approximately 10% of TCs making landfall in China produce PREs over the YRD region;however,they are seldom forecasted. PREs often occur over the YRD region when TCs begin to be active in the SCS-WNPO with westward paths, whilst the cold air is still existing or beginning to be present. PREs are more likely to peak in June and September. The distances between the PRE centers and the parent TC range from 900 to 1700 km. The median value of rain amounts and the median lifetime of PREs is approximately 200 mm and 24 h, respectively. Composite results suggest that PREs form in the equatorward jet-entrance region of the upper-level westerly jet(WJ), where a 925-hPa equivalent potential temperature ridge is located east of a 500-hPa trough. Deep moisture is transported from the TC vicinity to the remote PREs region. The ascent of this deep moist air in front of the 500-hPa trough and frontogenesis beneath the equatorward entrance region of the WJ is advantageous for the occurrence of PREs in the YRD region. The upper-level WJ may be affected by the subtropical high and westerly trough in the Northwest Pacific Ocean, and the occurrence of PREs may favor the maintenance of the upper-level WJ. The upper-level outflow of TCs in the SCS plays a secondary role.
基金supported by the Natural Science Foundation of Zhejiang Province of China(No.LQ20D050001)National Natural Science Foundation of China(Grant No.42105004)the Scientific Research Foundation of Hangzhou Normal University(No.2020QDL015).
文摘The three-dimensional Weather Research and Forecasting(WRF)model was used to conduct sensitivity experiments during the landfall of Typhoon Fitow(2013)to examine the impacts of cloud radiative processes on thermal balance.The vertical profiles of heat budgets,vertical velocity,and stability were analyzed to examine the physical processes responsible for cloud radiative effects on surface rainfall for Typhoon Fitow(2013).The inclusion of clouds reduced radiative cooling in ice and liquid cloud layers by reducing outgoing radiation.The suppressed radiative cooling reduced from the ice cloud layers to liquid cloud layers.This was conducive to reducing instability.The decreased instability was associated with the reduced upward motions.The reduced upward motion led to a decreased vertical mass conver-gence.Consequently,heat divergence was weakened to warm the atmosphere.Together with suppressed radiative cooling,these effects jointly suppressed net condensation and rainfall.Furthermore,the reduced rainfall due to the cloud radiative effects were mainly associated with the reduced convective and stratiform rainfall.The reduced convective rainfall was associated with the reduced net condensation,while the reduced stratiform rainfall was related to the constraint of hydrometeor convergence.
