Various satellite data,JRA-25(Japan reanalysis of 25 years) reanalyzed data and WRF(Weather Research Forecast) model are used to investigate the in situ effect of the ESKF(East China Sea Kuroshio Front) on the MABL(ma...Various satellite data,JRA-25(Japan reanalysis of 25 years) reanalyzed data and WRF(Weather Research Forecast) model are used to investigate the in situ effect of the ESKF(East China Sea Kuroshio Front) on the MABL(marine atmospheric boundary layer).The intensity of the ESKF is most robust from January to April in its annual cycle.The local strong surface northerly/northeasterly winds are observed right over the ESKF in January and in April and the wind speeds decrease upward in the MABL.The thermal wind effect that is derived from the baroclinic MABL forced by the strong SST gradient contributes to the strong surface winds to a large degree.The convergence zone existing along the warm flank of the ESKF is stronger in April than in January corresponding to the steeper SST(sea surface temperature) gradient.The collocations of the cloud cover maximum and precipitation maximum are basically consistent with the convergence zone of the wind field.The clouds develop higher(lower) in the warm(cold) flank of the ESKF due to the less(more) stable stratification in the MABL.The lowest clouds are observed in April on the cold flank of the ESKF and over the Yellow Sea due to the existence of the pronounced temperature inversion.The numerical experiments with smoothed SST are consistent with the results from the ovservations.展开更多
Various data are used to investigate the characteristics of the surface wind field and rainfall on the East China Sea Kuroshio(ESK) in March and April, 2011. In March, the wind speed maximum shows over the ESK front(E...Various data are used to investigate the characteristics of the surface wind field and rainfall on the East China Sea Kuroshio(ESK) in March and April, 2011. In March, the wind speed maximum shows over the ESK front(ESKF) in the 10 meter wind field, which agrees with the thermal wind effect. A wind curl center is generated on the warm flank of the ESKF. The winds are much weaker in April, so is the wind curl. A rainband exists over the ESKF in both the months. The Weather Research and Forecasting(WRF) model is used for further researches. The winds on the top of the marine atmosphere boundary layer(MABL) indicate that in March, a positive wind curl is generated in the whole MABL over the warm flank of the ESKF. The thermal wind effect forced by the strong SST gradient overlying the background wind leads to strong surface northeasterly winds on the ESKF, and a positive shearing vorticity is created over the warm flank of the ESKF to generate wind curl. In the smoothed sea surface temperature experiment, the presence of the ESKF is responsible for the strong northeast winds in the ESKF, and essential for the distribution of the rainfall centers in March, which confirms the mechanism above. The same simulation is made for April, 2011, and the responses from the MABL become weak. The low background wind speed weakens the effect of the thermal wind, thus no strong Ekman pumping is helpful for precipitation. There is no big difference in rainfall between the control run and the smooth SST run. Decomposition of the wind vector shows that local wind acceleration induced by the thermal wind effect along with the variations in wind direction is responsible for the pronounced wind curl/divergence over the ESKF.展开更多
基金supported by the National Natural Science Foundation of China (No.40975003)the Ph.D.Programs Foundation of Ministry of Education of China (No.20090132110008)GYHY(QX)2007-6-31
文摘Various satellite data,JRA-25(Japan reanalysis of 25 years) reanalyzed data and WRF(Weather Research Forecast) model are used to investigate the in situ effect of the ESKF(East China Sea Kuroshio Front) on the MABL(marine atmospheric boundary layer).The intensity of the ESKF is most robust from January to April in its annual cycle.The local strong surface northerly/northeasterly winds are observed right over the ESKF in January and in April and the wind speeds decrease upward in the MABL.The thermal wind effect that is derived from the baroclinic MABL forced by the strong SST gradient contributes to the strong surface winds to a large degree.The convergence zone existing along the warm flank of the ESKF is stronger in April than in January corresponding to the steeper SST(sea surface temperature) gradient.The collocations of the cloud cover maximum and precipitation maximum are basically consistent with the convergence zone of the wind field.The clouds develop higher(lower) in the warm(cold) flank of the ESKF due to the less(more) stable stratification in the MABL.The lowest clouds are observed in April on the cold flank of the ESKF and over the Yellow Sea due to the existence of the pronounced temperature inversion.The numerical experiments with smoothed SST are consistent with the results from the ovservations.
文摘Various data are used to investigate the characteristics of the surface wind field and rainfall on the East China Sea Kuroshio(ESK) in March and April, 2011. In March, the wind speed maximum shows over the ESK front(ESKF) in the 10 meter wind field, which agrees with the thermal wind effect. A wind curl center is generated on the warm flank of the ESKF. The winds are much weaker in April, so is the wind curl. A rainband exists over the ESKF in both the months. The Weather Research and Forecasting(WRF) model is used for further researches. The winds on the top of the marine atmosphere boundary layer(MABL) indicate that in March, a positive wind curl is generated in the whole MABL over the warm flank of the ESKF. The thermal wind effect forced by the strong SST gradient overlying the background wind leads to strong surface northeasterly winds on the ESKF, and a positive shearing vorticity is created over the warm flank of the ESKF to generate wind curl. In the smoothed sea surface temperature experiment, the presence of the ESKF is responsible for the strong northeast winds in the ESKF, and essential for the distribution of the rainfall centers in March, which confirms the mechanism above. The same simulation is made for April, 2011, and the responses from the MABL become weak. The low background wind speed weakens the effect of the thermal wind, thus no strong Ekman pumping is helpful for precipitation. There is no big difference in rainfall between the control run and the smooth SST run. Decomposition of the wind vector shows that local wind acceleration induced by the thermal wind effect along with the variations in wind direction is responsible for the pronounced wind curl/divergence over the ESKF.
