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
The midwinter suppression(MWS) of the North Pacific storm track(NPST) has been an active research topic for decades. Based on the daily-mean NCEP/NCAR reanalysis from 1948 to 2018, this study investigates the MWS-rela...The midwinter suppression(MWS) of the North Pacific storm track(NPST) has been an active research topic for decades. Based on the daily-mean NCEP/NCAR reanalysis from 1948 to 2018, this study investigates the MWS-related atmospheric circulation characteristics in the Northern Hemisphere by regression analysis with respect to a new MWS index, which may shed more light on this difficult issue. The occurrence frequency of the MWS of the upper-tropospheric NPST is more than 0.8 after the mid-1980 s. The MWS is accompanied by significantly positive sea-level pressure anomalies in Eurasia and negative anomalies over the North Pacific, which correspond to a strengthened East Asian winter monsoon. The intensified East Asian trough and atmospheric blocking in the North Pacific as well as the significantly negative low-level air temperature anomalies, lying upstream of the MNPST, are expected to be distinctly associated with the MWS. However, the relationship between the MWS and low-level atmospheric baroclinicity is somewhat puzzling.From the diagnostics of the eddy energy budget, it is identified that the inefficiency of the barotropic energy conversion related to the barotropic governor mechanism does not favor the occurrence of the MWS. In contrast, weakened baroclinic energy conversion, buoyancy conversion, and generation of eddy available potential energy by diabatic heating are conducive to the occurrence of the MWS. In addition, Ural blocking in the upstream region of the MNPST may be another candidate mechanism associated with the MWS.展开更多
利用欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)提供的全球再分析数据,使用局地多尺度能量涡度分析法(localized Multiscale Energy and Vorticity Analysis,MS-EVA)分析了初夏影响江淮流域极端...利用欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)提供的全球再分析数据,使用局地多尺度能量涡度分析法(localized Multiscale Energy and Vorticity Analysis,MS-EVA)分析了初夏影响江淮流域极端干旱发生的欧洲关键区动能变率的时间特征及其动能收支。结果表明:初夏欧洲关键区高层动能有增长趋势时,我国江淮流域极易发生极端干旱事件。该处增长的动能主要来自天气尺度动能的传输,其次来自气压梯度力做功和动能的垂直输送;动能向有效位能的转换和季节平均尺度动能的传输是高层动能流失的原因。深入研究三项动能来源因子后发现:上层增加的动能一部分来自低层北大西洋东岸和欧洲大陆西南地区的动能东传,在欧洲辐合后向上输送,为高层传递能量;同时,由于关键区地面热强迫增强,使垂直风切变增大,大气斜压稳定度降低,气压梯度力做功项增大,使得高层动能得到补充。在此期间,由于地面加热,天气尺度传输项对高层动能的传输量也增多。关键区增加的净能量经西风环流在江淮地区辐合,有助于该地上空的脊增强,促进了极端干旱事件发生。该结果从能量转换角度探究了江淮流域干旱发生的部分成因,为干旱预估提供依据。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 Research and Development Program of China(Grant No.2018YFC1505901)the National Natural Science Foundation of China(Grant Nos.41490642,4160501,and 41520104008)。
文摘The midwinter suppression(MWS) of the North Pacific storm track(NPST) has been an active research topic for decades. Based on the daily-mean NCEP/NCAR reanalysis from 1948 to 2018, this study investigates the MWS-related atmospheric circulation characteristics in the Northern Hemisphere by regression analysis with respect to a new MWS index, which may shed more light on this difficult issue. The occurrence frequency of the MWS of the upper-tropospheric NPST is more than 0.8 after the mid-1980 s. The MWS is accompanied by significantly positive sea-level pressure anomalies in Eurasia and negative anomalies over the North Pacific, which correspond to a strengthened East Asian winter monsoon. The intensified East Asian trough and atmospheric blocking in the North Pacific as well as the significantly negative low-level air temperature anomalies, lying upstream of the MNPST, are expected to be distinctly associated with the MWS. However, the relationship between the MWS and low-level atmospheric baroclinicity is somewhat puzzling.From the diagnostics of the eddy energy budget, it is identified that the inefficiency of the barotropic energy conversion related to the barotropic governor mechanism does not favor the occurrence of the MWS. In contrast, weakened baroclinic energy conversion, buoyancy conversion, and generation of eddy available potential energy by diabatic heating are conducive to the occurrence of the MWS. In addition, Ural blocking in the upstream region of the MNPST may be another candidate mechanism associated with the MWS.
文摘利用欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)提供的全球再分析数据,使用局地多尺度能量涡度分析法(localized Multiscale Energy and Vorticity Analysis,MS-EVA)分析了初夏影响江淮流域极端干旱发生的欧洲关键区动能变率的时间特征及其动能收支。结果表明:初夏欧洲关键区高层动能有增长趋势时,我国江淮流域极易发生极端干旱事件。该处增长的动能主要来自天气尺度动能的传输,其次来自气压梯度力做功和动能的垂直输送;动能向有效位能的转换和季节平均尺度动能的传输是高层动能流失的原因。深入研究三项动能来源因子后发现:上层增加的动能一部分来自低层北大西洋东岸和欧洲大陆西南地区的动能东传,在欧洲辐合后向上输送,为高层传递能量;同时,由于关键区地面热强迫增强,使垂直风切变增大,大气斜压稳定度降低,气压梯度力做功项增大,使得高层动能得到补充。在此期间,由于地面加热,天气尺度传输项对高层动能的传输量也增多。关键区增加的净能量经西风环流在江淮地区辐合,有助于该地上空的脊增强,促进了极端干旱事件发生。该结果从能量转换角度探究了江淮流域干旱发生的部分成因,为干旱预估提供依据。
