FEATURES OF VARIATION IN TOTAL,BAROTROPIC AND BAROCLINIC KINETIC ENERGY WITH THE MECHANISM EXPLORED AROUND THE 1998 SCS SUMMER MONSOON ONSET

This paper concerns atmospheric kinetic energy variation related to the onset of summer monsoon in May,1998 over the SCS (South China Sea).Results show that around the onset, noticeable conversion occurs in atmospheric total,barotropic and baroclinic kinetic energy (KE) at 300-1000 hPa;three days before the onset,total and barotropic KE are already growing markedly and baroclinic KE increases simultaneously with the onset:the monsoon's onset is associated closely to the meridional propagation of barotropic and baroclinic KE in the SCS region and study of equations of barotropie/baroclinic KE indicates that the net production term is the dominant factor for the change of the two forms of KE,the term of fluxes plays a part in weakening the energies and the conversion term is responsible for transforming barotropic into baroclinic KE.

Two Modes of the Silk Road Pattern and Their Interannual Variability Simulated by LASG/IAP AGCM SAMIL2.0

In this study, two modes of the Silk Road pattern were investigated using NCEP2 reanalysis data and the simulation produced by Spectral Atmospheric Circulation Model of IAP LASG, Version 2 （SAMIL2.0） that was forced by SST observation data. The horizontal distribution of both modes were reasonably reproduced by the simulation, with a pattern correlation coefficient of 0.63 for the first mode and 0.62 for the second mode. The wave train was maintained by barotropic energy conversion （denoted as CK） and baroclinic energy conversion （denoted as CP） from the mean flow. The distribution of CK was dominated by its meridional component （CKy） in both modes. When integrated spatially, CKx was more efficient than its zonal component （CKx） in the first mode but less in the second mode. The distribution and efficiency of CK were not captured well by SAMIL2.0. However, the model performed reasonably well at reproducing the distribution and efficiency of CP in both modes. Because CP is more efficient than CK, the spatial patterns of the Silk Road pattern were well reproduced. Interestingly, the temporal phase of the second mode was well captured by a single-member simulation. However, further analysis of other ensemble runs demonstrated that the successful reproduction of the temporal phase was a result of internal variability rather than a signal of SST forcing. The analysis shows that the observed temporal variations of both CP and CK were poorly reproduced, leading to the low accuracy of the temporal phase of the Silk Road pattern in the simulation.

DEVELOPMENT OF A TROPICAL CYCLONE IN BAROTROPIC ENVIRONMENTAL FLOWS

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The decadally modulating eddy field in the upstream Kuroshio Extension and its related mechanisms

Both the level of the high-frequency eddy kinetic energy（HF-EKE） and the energy-containing scale in the upstream Kuroshio Extension（KE） undergo a well-defined decadal modulation, which correlates well with the decadal KE path variability. The HF-EKE level and the energy-containing scales will increase with unstable KE path and decrease with stable KE path. Also the mesoscale eddies are a little meridionally elongated in the stable state, while they are much zonally elongated in the unstable state. The local baroclinic instability and the barotropic instability associated with the decadal modulation of HF-EKE have been investigated. The results show that the baroclinic instability is stronger in the stable state than that in the unstable state, with a shorter characteristic temporal scale and a larger characteristic spatial scale. Meanwhile, the regional-averaged barotropic conversion rate is larger in the unstable state than that in the stable state. The results also demonstrate that the baroclinic instability is not the dominant mechanism influencing the decadal modulation of the mesoscale eddy field, while the barotropic instability makes a positive contribution to the decadal modulation.

BAROTROPIC AND BAROCLINIC DIVERGENCE QUASI ENERGY EQUATIONS AND THEIR APPLICATION TO A BLOCKING EVENT

As in the case of the expression for enstrophy (1/2ζ~2) and equations for barotropic and baroclinic enstrophy,this paper presents an expression of divergence assumed to have its quasi energy because of flows (DQE,or 1/2 D^2) with which to establish the equations of barotropie and baroclinic DQE,each consisting of five factors responsible for changes in these equations:the terms of energy flux,production,conversion,geostrophic effect and dissipation,and also a case study of a blocking event over the Sea of Okhotsk whose development is characterized largely by changes in barotropic and baroclinic DQE's on the strength of upper-level strong divergence and low-level vigorous convergence.During the event's strengthening,the baroclinic net production (inclusive of geostrophie effect) mechanism acts as the dominant factor for the enhancement of the baroclinic DQE,with its net transport outward offsetting part of its growth but the conversion mechanism augmenting its growth,and during the weakening the outward net transport of baroclinic DQE is the predominant factor of its enfeebling,baroclinic net DQE production (inclusive of geostrophic effect) and the conversion mechanisms make the baroclinic DQE increased,thereby alleviating the weakening in intensity.

东亚-太平洋型季节内演变和维持机理研究

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。

北太平洋风暴轴“深冬抑制”现象的能量分析

采用欧洲中期天气预报中心逐日再分析资料(ERA-40),从局地能量变化方程出发,通过分析北太平洋风暴轴区域对流层不同层次局地能量的季节演变过程,对风暴轴区域各能量项在"深冬抑制"现象中的作用进行了深入探讨。结果表明,天气尺度扰动动能的季节变化可以很好地反映北太平洋风暴轴的"深冬抑制"现象,并且该现象在对流层上层最为显著,其发生概率约为80%,其中20世纪70年代中后期到80年代前期抑制最强。从同期各能量项的变化来看,扰动动能的变化主要受斜压能量转换项、涡动非地转位势通量的散度项和正压能量转换项的影响。在深冬季节,由于消耗扰动动能的正压能量转换项虽有些微弱减少从而使得扰动动能有所增加,但为风暴轴提供扰动动能的斜压能量转换项和涡动非地转位势通量的散度项减少的幅度却更大,因而总的效果是扰动动能大为减小,这可能是造成北太平洋风暴轴"深冬抑制"现象的直接原因。

2004年冬季风期间一次强寒潮过程的能量收支研究1

利用1°(纬度)×1°(经度)的NCEP再分析资料和常规站点观测资料对2004年12月28～31日的一次强寒潮、冷涌过程作了研究,研究结果表明:(1)此次强寒潮事件在我国南海引发了强烈的冷涌,该支冷涌一直向南越过赤道影响南半球。大尺度环境场有利于此次寒潮、冷涌事件的爆发,本次寒潮属于"横槽转竖型",其中200hPa的西风带大槽经历了一次调整,500hPa经历了一次明显的横槽转竖过程,对流层低层蒙古高压稳定维持,其东侧的偏北大风是冷空气南下的有利条件。(2)此次寒潮大风区内的动能制造以正压动能制造和斜压动能制造为主,寒潮爆发初期,以正压制造过程为主,此后,由于有效位能释放的作用增强,斜压制造过程与正压制造强度相当,大风区随着动能制造的增强而增强;当斜压、正压动能制造均减弱,大风区亦随之减弱。(3)有效位能收支表明,整层有效位能的释放与大风区相对应,有效位能的释放有利于寒潮、冷涌的维持。寒潮大风区内,对流层高层受有效位能释放的影响最大,有效位能和风能可以互相转换;对流层中层所受的影响最小,且以风能向有效位能转换为主;对流层低层则以有效位能向动能转化为主,十分有利于低层风速的增大和维持。

北上台风暴雨过程涡散场的能量收支和转换特征

利用辐散风和旋转风的动能收支方程，对北方一次北上台风倒槽暴雨过程暴雨区内的涡散场能量收支和转换进行了计算。结果表明：暴雨区内动能的增加是暴雨增幅的一个主要原因。暴雨发展时，就旋转风动能（ Ｋ Ｒ） 而言，旋转风动能通量（ Ｈ Ｆ Ｒ） 辐合是主要能源，而旋转风的动能产生项（ Ｇ Ｒ） 是主要能汇；就辐散风动能（ Ｋ Ｄ） 而言，辐散风的动能产生项（ Ｇ Ｄ） 是主要能源，辐散风动能通量（ Ｈ Ｆ Ｄ） 辐散是主要能汇；总动能水平通量（ Ｈ Ｆ） 提供的辐合主要表现于对流层中、低层，这就使得低层辐合加强，上升运动加强，有利于暴雨的增幅。在暴雨过程中次网格尺度效应由能源转变为能汇，在暴雨发展之时能汇减小；能量的转换项 Ｃ（ Ｋ Ｄ， Ｋ Ｒ）总为正值，在转换项中，地转效应项的贡献很大。说明暴雨过程能量均由 Ｋ Ｄ 向 Ｋ Ｒ 转换，也就是说有效位能经 Ｋ Ｄ 向 Ｋ Ｒ 转换， 充分说明了在整个暴雨过程中， 尽管辐散风动能变化（ Ｋ Ｄ／ｔ） 很小，但是它在其中充当“桥梁”作用， Ｃ（ Ｋ Ｄ， Ｋ Ｒ） 在暴雨发展时达到最大，此时能量转换最为旺盛；对流层低层辐散风动能向旋转风动能的转换是暴雨产生和发展的重要条件。此次暴雨过程，在暴雨区内表现为斜压?

北半球中高纬月平均环流正压斜压动能的年变化特征

本文利用多年月平均资料计算了北半球中高纬月平均环流正压、斜压动能的年变化特征。结果表明无论正压、斜压动能都具有明显的年变化,而且两者的变化趋势也是一致的,但是正压动能要比斜压动能对总动能的贡献大得多。环流异常具有相当正压的垂直结构。有关结论可为长期数值预报模式的简化提供依据。

亚洲季风变动与大气正压/斜压运动动能变化的气候特征

使用 NCEP/NCAR 40年 ( 1 95 8～ 1 997年 )月平均再分析资料 ,通过动力学诊断研究了大气斜压 /正压运动动能的变化及其相互转换 ,分析了亚洲季风变动与这两种动能变化的联系。指出 :季风区大气运动动能的组成和变化具有独特的特征。冬季风时期 ,大气斜压运动动能与正压运动动能具有正相关线性关系 ,斜压运动动能向正压运动动能转换 ;春、秋季无论是东亚还是印度季风区斜压运动动能与正压运动动能之间的转换都处于极小值 ,只是印度季风区始终是斜压动能向正压动能转换 ,而东亚季风区则出现正压动能向斜压动能的转换。夏季风时期季风区以斜压运动动能为主 ,而中、高纬度地区一直以正压运动动能为主。由冬至夏季风区正压动能减少并在盛夏达到极小值。春夏转换时期季风区斜压运动动能和转换因子曲线的随时间的变化位相与夏季风建立的位相同步 。

A comparison of two kinds of eastward-moving mesoscale vortices during the mei-yu period of 2010

During the mei-yu period,the east edge of the Tibetan Plateau and the Dabie Mountain are two main sources of eastward-moving mesoscale vortices along the mei-yu front(MYF).In this study,an eastward-moving southwest vortex(SWV) and an eastward-moving Dabie vortex(DBV) during the mei-yu period of 2010 have been investigated to clarify the main similarities and differences between them.The synoptic analyses reveal that the SWV and DBV were both located at the lower troposphere;however,the SWV developed in a "from top down" trend,whereas the DBV developed in an opposite way.There were obvious surface closed low centers corresponding to the DBV during its life span,whereas for the SWV,the closed low center only appeared at the mature stage.Cold and warm air intersected intensely after the formation of both the vortices,and the cold advection in the SWV case was stronger than that in the DBV case,whereas the warm advection in the DBV case was more intense than that in the SWV case.The Bay of Bengal and the South China Sea were main moisture sources for the SWV,whereas for the DBV,in addition to the above two moisture sources,the East China Sea was also an important moisture source.The vorticity budget indicates that the convergence was the most important common factor conducive to the formation,development,and maintenance of the SWV and DBV,whereas the conversion from the vertical vorticity to the horizontal one(tilting) was the most important common factor caused the dissipation of both of the vortices.The kinetic energy(KE) budget reveals that the KE generation by the rotational wind was the dominant factor for the enhancement of KE associated with the SWV,whereas for the DBV,the KE transport by the rotational wind was more important than the KE generation.The KE associated with the SWV and the DBV weakened with different mechanisms during the decaying stage.Furthermore,the characteristics of baroclinic and barotropic energy conversions during the life spans of both vortices indicate that the SWV and DBV both belong to the kind of subtropical mesoscale vortices.

夏威夷群岛背风逆流区涡动能的年际变化及其机制诊断分析

夏威夷群岛以西背风逆流区流系复杂,是中尺度涡高发区,该海域中尺度涡活动对大尺度环流变化、海气交换以及海洋生物分布等具有重要意义。利用1993—2020年的再分析数据,研究了夏威夷群岛背风逆流区涡动能的年际变化特征及其机制。根据涡动能分布情况,将夏威夷群岛以西背风逆流区分为2个区域(离岛区域和近岛区域)开展研究,主要结论如下:(1)离岛和近岛区域涡动能均有显著的年际变化,近岛区域超前离岛区域涡动能变化。超前12个月时,与离岛涡动能相关系数最大为0.57。(2)涡动能的年际变化主要受正压不稳定、斜压不稳定、平流和风应力做功调控。涡动能收支诊断分析发现离岛区域涡动能的年际变化主要受斜压不稳定变化控制,近岛区域涡动能年际变化主要受风应力做功变化控制。(3)涡动能年际变化受大尺度年际信号调控。离岛区域涡动能年际变化与太平洋年代际振荡信号指数显著相关,超前太平洋年代际振荡信号指数10个月时相关系数最大为0.85。近岛区域涡动能年际变化超前太平洋年代际振荡信号指数2个月时,相关系数最大为0.40。