Using 19-year satellite altimetric data, variations in the eddy kinetic energy, energy exchanges and interaction between the eddy fi eld and mean fl ow are discussed for the Kuroshio south of Japan. In the seasonal cy...Using 19-year satellite altimetric data, variations in the eddy kinetic energy, energy exchanges and interaction between the eddy fi eld and mean fl ow are discussed for the Kuroshio south of Japan. In the seasonal cycle, the eddy kinetic energy level is a minimum in December/January and a maximum in April/May. In addition to seasonal variations, the eddy kinetic energy undergoes interannual changes. The energy transfers mainly from the mean fl ow to the eddy fi eld in the Kuroshio south of Japan, and dominant energy exchanges mainly occur along the Kuroshio path south of Japan in each year from 1993 to 2011. In addition, there is often barotropic instability south of Honshu. Regarding interactions between the eddy fi eld and mean fl ow, cyclonic and anticyclonic accelerations are also found along the Kuroshio path and they fl ank each other. There is cyclonic acceleration always imposed on southeast of Kyushu, and anticyclonic acceleration dominates south of Honshu from 2001 to mid-2005. Reynolds stress is used to explain the dynamic process of energy exchange. Furthermore, lag-correlation and linear regression analysis show that variability of the energy conversion rate and Reynolds stress involve responses to eddy acceleration at two time scales. The enhanced eddy acceleration induces large Reynolds stress, and enhanced Reynolds stress or barotropic instability further enforces energy transfer from the mean fl ow to the eddy fi eld.展开更多
Predicting warm-sector torrential rainfall over South China,which is famous for its destructive power,is one of the most challenging issues of the current numerical forecast field.Insufficient understanding of the key...Predicting warm-sector torrential rainfall over South China,which is famous for its destructive power,is one of the most challenging issues of the current numerical forecast field.Insufficient understanding of the key mechanisms underlying this type of event is the root cause.Since understanding the energetics is crucial to understanding the evolutions of various types of weather systems,a general methodology for investigating energetics of torrential rainfall is provided in this study.By applying this methodology to a persistent torrential rainfall event which had concurrent frontal and warm-sector precipitation,the first physical image on the energetics of the warm-sector torrential rainfall is established.This clarifies the energy sources for producing the warm-sector rainfall during this event.For the first time,fundamental similarities and differences between the warm-sector and frontal torrential rainfall are shown in terms of energetics.It is found that these two types of rainfall mainly differed from each other in the lower-tropospheric dynamical features,and their key differences lay in energy sources.Scale interactions(mainly through downscale energy cascade and transport)were a dominant factor for the warm-sector torrential rainfall during this event,whereas,for the frontal torrential rainfall,they were only of secondary importance.Three typical signals in the background environment are found to have supplied energy to the warm-sector torrential rainfall,with the quasi-biweekly oscillation having contributed the most.展开更多
利用850 hPa的纬向风异常建立一个逐候东亚-太平洋(East Asian Pacific,EAP)型指数,研究其季节内演变特征,发现东亚-太平洋型经向波列是东亚夏季风季节内变化的主要模态。其演变过程为:扰动首先出现在北太平洋中部,并通过正压不稳定过...利用850 hPa的纬向风异常建立一个逐候东亚-太平洋(East Asian Pacific,EAP)型指数,研究其季节内演变特征,发现东亚-太平洋型经向波列是东亚夏季风季节内变化的主要模态。其演变过程为:扰动首先出现在北太平洋中部,并通过正压不稳定过程从基本气流中获得能量而发展,在高层罗斯贝波能量向南频散,激发热带对流异常和赤道罗斯贝波,并相互锁相,因赤道罗斯贝波受β效应影响而共同向西移动。热带对流和环流异常在菲律宾附近达到最强,此时在东亚沿岸出现经向三极型波列,此后中低纬度异常继续向西北方向移动,使降水异常在长江流域能维持较长时间。东亚-太平洋型在东亚发展和维持有以下原因:首先,菲律宾暖水上空的对流和低层环流之间存在正反馈;其次,由于海陆热力差异导致暖大陆和冷海洋之间存在特殊的纬向温度梯度和北风垂直切变,东亚-太平洋型在经向上有向北倾斜的斜压结构,能通过斜压能量转换从平均有效位能中获得能量,同时,也能从经向温度梯度的平均有效位能中获得能量。展开更多
基金Supported by the Knowledge Innovation Program of Chinese Academy of Sciences(No.KZCX2-EW-201)the Basic Research Program of Science and Technology Projects of Qingdao(No.11-1-4-95-jch)
文摘Using 19-year satellite altimetric data, variations in the eddy kinetic energy, energy exchanges and interaction between the eddy fi eld and mean fl ow are discussed for the Kuroshio south of Japan. In the seasonal cycle, the eddy kinetic energy level is a minimum in December/January and a maximum in April/May. In addition to seasonal variations, the eddy kinetic energy undergoes interannual changes. The energy transfers mainly from the mean fl ow to the eddy fi eld in the Kuroshio south of Japan, and dominant energy exchanges mainly occur along the Kuroshio path south of Japan in each year from 1993 to 2011. In addition, there is often barotropic instability south of Honshu. Regarding interactions between the eddy fi eld and mean fl ow, cyclonic and anticyclonic accelerations are also found along the Kuroshio path and they fl ank each other. There is cyclonic acceleration always imposed on southeast of Kyushu, and anticyclonic acceleration dominates south of Honshu from 2001 to mid-2005. Reynolds stress is used to explain the dynamic process of energy exchange. Furthermore, lag-correlation and linear regression analysis show that variability of the energy conversion rate and Reynolds stress involve responses to eddy acceleration at two time scales. The enhanced eddy acceleration induces large Reynolds stress, and enhanced Reynolds stress or barotropic instability further enforces energy transfer from the mean fl ow to the eddy fi eld.
基金supported by the National Key R&D Program of China (Grant No. 2018YFC1507400)the National Natural Science Foundation of China (Grant Nos. 42075002 and 42030610)
文摘Predicting warm-sector torrential rainfall over South China,which is famous for its destructive power,is one of the most challenging issues of the current numerical forecast field.Insufficient understanding of the key mechanisms underlying this type of event is the root cause.Since understanding the energetics is crucial to understanding the evolutions of various types of weather systems,a general methodology for investigating energetics of torrential rainfall is provided in this study.By applying this methodology to a persistent torrential rainfall event which had concurrent frontal and warm-sector precipitation,the first physical image on the energetics of the warm-sector torrential rainfall is established.This clarifies the energy sources for producing the warm-sector rainfall during this event.For the first time,fundamental similarities and differences between the warm-sector and frontal torrential rainfall are shown in terms of energetics.It is found that these two types of rainfall mainly differed from each other in the lower-tropospheric dynamical features,and their key differences lay in energy sources.Scale interactions(mainly through downscale energy cascade and transport)were a dominant factor for the warm-sector torrential rainfall during this event,whereas,for the frontal torrential rainfall,they were only of secondary importance.Three typical signals in the background environment are found to have supplied energy to the warm-sector torrential rainfall,with the quasi-biweekly oscillation having contributed the most.
文摘利用850 hPa的纬向风异常建立一个逐候东亚-太平洋(East Asian Pacific,EAP)型指数,研究其季节内演变特征,发现东亚-太平洋型经向波列是东亚夏季风季节内变化的主要模态。其演变过程为:扰动首先出现在北太平洋中部,并通过正压不稳定过程从基本气流中获得能量而发展,在高层罗斯贝波能量向南频散,激发热带对流异常和赤道罗斯贝波,并相互锁相,因赤道罗斯贝波受β效应影响而共同向西移动。热带对流和环流异常在菲律宾附近达到最强,此时在东亚沿岸出现经向三极型波列,此后中低纬度异常继续向西北方向移动,使降水异常在长江流域能维持较长时间。东亚-太平洋型在东亚发展和维持有以下原因:首先,菲律宾暖水上空的对流和低层环流之间存在正反馈;其次,由于海陆热力差异导致暖大陆和冷海洋之间存在特殊的纬向温度梯度和北风垂直切变,东亚-太平洋型在经向上有向北倾斜的斜压结构,能通过斜压能量转换从平均有效位能中获得能量,同时,也能从经向温度梯度的平均有效位能中获得能量。
