“96·7”中亚低涡持续活动能量转换和频散特征
Energy Conversion and Dispersion Characteristics of “96•7”Central Asian Vortex Persistent Activity
中文摘要：
利用NCEP/NCAR逐日再分析资料，分析了1996年7月11—22日中亚低涡持续活动发展、维持和减弱过程中三维结构及其能量转换和频散特征。结果表明：（1）中亚低涡在对流层中高层发展并向高层和低层延伸，最大正涡度中心始终位于中高层，存在300hPa以下为冷心、以上为暖心结构的气旋性深厚天气尺度系统，其发展—成熟—减弱过程最大正涡度中心由低涡中心西侧逐渐移至东侧，并对应低层辐合、中高层辐散的强上升运动。（2）扰动动能（KE）变化定量地反映中亚低涡强度变化和发展阶段，对流层中、高层KE强，同时，低涡内部的能量转换及其与外界的能量输送也主要发生在中、高层。低涡发展过程KE来源于扰动位能（AE）的转换和区域开放边界的扰动动能输入，且两者作用相当，它们使得低涡快速发展。低涡成熟期系统内部的能量转换很小，KE来自于外界扰动位能输入，消耗项为向开放边界的扰动动能输出。（3）此次低涡持续活动过程平均而言，东北大西洋反气旋式异常环流中心是罗斯贝（Rossby）波能量的频散源地，波能量向东欧—乌拉尔山频散，东欧—乌拉尔山正异常环流成为向中亚地区能量频散的“中继站”，此地重新激发罗斯贝波向中亚地区频散使得中亚低涡持续活动了12d。（4）中亚低涡不同发展阶段罗斯贝波能量频散路径有所不同。发展和稳定维持期，东北大西洋正异常环流向东欧—乌拉尔山地区的能量频散过程显著，使得东欧正异常环流强盛发展并作为能量“中继站”向中亚地区频散能量，从而导致中亚低涡快速发展和稳定维持；减弱期，东北大西洋罗斯贝波能量向东南方向频散在地中海东部地区进入亚洲副热带西风急流，然后沿亚洲急流向东频散，使得中亚低涡维持，这阶段东欧—乌拉尔山地区不再出现向中亚地区的能量频散。
中文关键词：
中亚低涡，三维结构，扰动动能转换，罗斯贝波能量频散
KeyWords：
Central Asian vortex, three-dimensional structure, eddy kinetic energy conversion, Rossby wave energy dispersion
Abstract：
Using the NCEP/NCAR reanalysis daily datasets, dynamic and thermal three-dimensional structure, energy cycle and Rossby wave energy dispersion of Central Asian vortex (CAV) persistent activity from July 11 to July 22 in 1996 are studied. The Results show that the vortex developed at the middle-upper firstly and extended upward and downward with time, which had an obvious cold core structure down 300 hPa and a warm core structure over 300 hPa along with maximal positive vorticity at the middle-upper troposphere. During its development - mature - weakened process, maximal positive vorticity moved eastward from westside of vortex center. At the same time its upper-level strong divergence, lower-level convergence and upward motion area moved eastward. Eddy kinetic energy (KE) variation can quantitatively manifest intensification change and developing stages of vortex; in the meantime KE is quite strong at the middle and upper tropospheres. Energy conversion within vortex and energy transportation with environment mostly take place over 700 hPa. The conversion term from eddy available potential energy (AE) to KE and eddy kinetic energy inflow from open atmospheric region boundaries act as main sources of the KE, and they play an equivalent role which bring about a rapid development of vortex. It keeps weak energy conversions within vortex during its mature stage, and the source and sink of KE is respectively eddy available potential energy import from environment and eddy kinetic energy outflow. For middle-range process of this vortex, the anti-cyclone anomaly center over Northeast Atlantic is the fountain of Rossby wave energy dispersion with Rossby wave propagating from Northeast Atlantic to East Europe—Urals (EAU). So the positive height anomaly circulation over EAU acts as “relay station” of energy dispersion for Central Asia. The Rossby wave emanates again from EAU and propagates to Central Asia, causing CAV persistent activity for 12 days. The characteristics of Rossby wave propagation, however, are significantly different in different periods of CAV. During developing and maintaining periods, the anti-cyclone anomaly center over Northeast Atlantic and strong wave flux divergence process are prominent and cause the positive height anomaly circulation over East Europe to develope, which acts as a "relay station" of energy and continues to propagate energy for Central Asia, consequently bringing about CAV sudden development and stable maintenance. During the weakening period, Rossby waves propagate from Northeast Atlantic to the east of the Mediterranean Sea and enter Asia subtropical jet stream to continue dispersion along with the jet stream. It is not found that Rossby wave propagates from the EAU to Central Asia.