In this study, we unveil atmospheric circulation anomalies associated with the large-scale tropical teleconnections using National Center for Environmental Prediction (NCEP) reanalysis dataset. Composite analyses have...In this study, we unveil atmospheric circulation anomalies associated with the large-scale tropical teleconnections using National Center for Environmental Prediction (NCEP) reanalysis dataset. Composite analyses have been performed to know the impact of large-scale tropical circulations on the Horn of Africa. The composite analysis performed at the geopotential height of 850 Mb and 200 Mb, and precipitation rate (mm/day) during six strong El Niño and La Niña episodes revealed that the large-scale tropical variability induced climate anomalies in space and time. A substantial decrease in upper-level height (200 Mb) has been observed in the study area during El Niño composite years as compared to the La Niña years. During El Niño conditions, the upper-level divergence initiates low-level vertical motion, thereby enhancing convection, however, during La Niña composite years, nearly contrasting situations are noticed in Belg (February to May) season in Ethiopia. However, geopotential height anomalies at 850 Mb are above-normal during the strong El Niño years, suggesting suppressed convection due to vertical shrinking and enhancement of divergence at the lower level. Compared to the Belg (February to May), geopotential anomalies were generally positive during the Kiremt (June to September) season, thereby suppressing the rainfall, particularly in Southern Ethiopia and Northern Part of Kenya. In contrast, an increase in rainfall was observed during the Belg season (February to May).展开更多
According to statistic analysis on sea surface temperature(SST)anomaly features in the North Pacific in winters and springs prior to the summer flood/drought in the middle and lower reaches of the Yangtze River(hereaf...According to statistic analysis on sea surface temperature(SST)anomaly features in the North Pacific in winters and springs prior to the summer flood/drought in the middle and lower reaches of the Yangtze River(hereafter referred to as MLRY),a strong signal SST key area that affects local flood/drought is put forward,that is the equatorial eastern Pacific.The response of general circulation in the Northern Hemisphere to SST anomaly in the key area is further investigated. The low frequency wave train structure of correlation between the eastern Pacific SST and the height at 500 hPa in the Northern Hemisphere is also studied,which reflects the dynamic features of teleresponse of local flood/drought at extratropics to tropical SST anomaly. Through introducing SST anomaly in the strong signal area in numerical experiments,the flood in Yangtze River Valley is successfully simulated and the similar wave train pattern in the flow field is obtained too.Altogether,the physical picture and dynamic mode of the flood in the Yangtze River Valley are described in this work.展开更多
文摘In this study, we unveil atmospheric circulation anomalies associated with the large-scale tropical teleconnections using National Center for Environmental Prediction (NCEP) reanalysis dataset. Composite analyses have been performed to know the impact of large-scale tropical circulations on the Horn of Africa. The composite analysis performed at the geopotential height of 850 Mb and 200 Mb, and precipitation rate (mm/day) during six strong El Niño and La Niña episodes revealed that the large-scale tropical variability induced climate anomalies in space and time. A substantial decrease in upper-level height (200 Mb) has been observed in the study area during El Niño composite years as compared to the La Niña years. During El Niño conditions, the upper-level divergence initiates low-level vertical motion, thereby enhancing convection, however, during La Niña composite years, nearly contrasting situations are noticed in Belg (February to May) season in Ethiopia. However, geopotential height anomalies at 850 Mb are above-normal during the strong El Niño years, suggesting suppressed convection due to vertical shrinking and enhancement of divergence at the lower level. Compared to the Belg (February to May), geopotential anomalies were generally positive during the Kiremt (June to September) season, thereby suppressing the rainfall, particularly in Southern Ethiopia and Northern Part of Kenya. In contrast, an increase in rainfall was observed during the Belg season (February to May).
文摘According to statistic analysis on sea surface temperature(SST)anomaly features in the North Pacific in winters and springs prior to the summer flood/drought in the middle and lower reaches of the Yangtze River(hereafter referred to as MLRY),a strong signal SST key area that affects local flood/drought is put forward,that is the equatorial eastern Pacific.The response of general circulation in the Northern Hemisphere to SST anomaly in the key area is further investigated. The low frequency wave train structure of correlation between the eastern Pacific SST and the height at 500 hPa in the Northern Hemisphere is also studied,which reflects the dynamic features of teleresponse of local flood/drought at extratropics to tropical SST anomaly. Through introducing SST anomaly in the strong signal area in numerical experiments,the flood in Yangtze River Valley is successfully simulated and the similar wave train pattern in the flow field is obtained too.Altogether,the physical picture and dynamic mode of the flood in the Yangtze River Valley are described in this work.
