| 1998年夏第二阶段梅雨期乌拉尔山阻塞形势的维持 |
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| 作者姓名： | Li Shuanglin Ji Liren Lin Wantao Ni Yunqi |
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| 作者单位： | Li Shuanglin，Ji Liren and Lin Wantao (LASG，Institute of Atmospheric Physics，Chinese Academy of Sciences，Beijing 100029) Ni Yunqi (Chinese Academy of Meteorological Sciences，Beijing 100081) |
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| 基金项目： | the CAS Key project KZCX2-203 the Research Program for the Excellent State Key Laboratory! (Grant No.49823002)，the Study on F |
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| 摘 要： | １９９８年夏季长江流域发生了近５０年来最严重的洪水。洪水形成最直接、最主要的原因是梅雨异常。异常梅雨的形成与东亚夏季风偏弱及热带外环流持续异常有关，其中一个明显特征是乌拉尔山地区长时间维持阻塞形势。本文结合诊断分析和数值试验，从瞬变对基本流的强迫（大气内部强迫）及热带热源强迫（外源强迫）两方面，分析了与第二段梅雨相对应的乌拉尔长时间阻塞的维持机制。利用共轭敏感性分析方法，计算了最有利于乌拉尔阻塞发展和维持的敏感扰动，发现扰动的分布位置，刚好与观测到的，从东大西洋到欧洲区域的异常增强的瞬变活动区相重叠。Ｅ矢量及斜压线性静止波模式的诊断进一步表明，异常期间的增强瞬变活动有利于乌拉尔出现正高度异常。计算了持续异常期间的高空急流及大气加热场，发现北美到大西洋的高空急流及热带加热都出现明显异常。中期天气预报模式 ＩＡＰ Ｔ４２Ｌ９的集合预报试验表明，热带地区的加热异常，尤其是热带中西太平洋和大西洋的加热异常，有利于乌拉尔正高度异常的形成。最后，提出了一种热带异常热源驱动下，瞬变波与定常波双向相互作用的阻塞形成与自维持的可能机制。
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| 关 键 词： | 乌拉尔阻塞 热带加热 瞬变 行星波 双向相互作用 |
| 收稿时间： | 10 November 1999 |
The maintenance of the blocking over the ural mountains during the second Meiyu period in the summer of 1998 |
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| Li Shuanglin,Ji Liren,Lin Wantao,Ni Yunqi.The maintenance of the blocking over the ural mountains during the second Meiyu period in the summer of 1998[J].Advances in Atmospheric Sciences,2001,18(1):87-105. |
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| Authors: | Li Shuanglin Ji Liren Lin Wantao Ni Yunqi |
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| Institution: | LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029,LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029,LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029,Chinese Academy of Meteorological Sciences, Beijing 100081 |
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| Abstract: | The 1998 summer-time floods at the Yangtze River basin of China, the severest in last 50 years or so,directly resulted from the abnormal extension of Meiyu (rainy season), which was related to a weak East Asian summer monsoon and persistent anomalies of extratropical circulation. The long persistence of blocking over the Ural Mountains is a conspicuous feature. The physical processes responsible for the prolonged maintenance of this key system are investigated in terms of internal forcing (transient eddy upon basic flow)and external forcing (tropical heating forcing) via diagnosis and numerical experiments in the paper. Using the adjoint method, the location and structure of optimal perturbations favorable for the development and maintenance of Ural blocking are identified, which shows an apparent coincidence with the observed storm track at the eastern Atlantic to Europe sector. The diagnosis of E-vector and the response of baroclinic stationary wave to transient forcing both suggest further that the enhanced transient eddy activity favors the occurrence and maintenance of positive anomalies. The upper-level jet and heat sources (sinks) during that period are calculated, and the results indicate that the anomaly of upper jet and tropical heating is evident. The ensemble forecasting experiments by a GCM, IAP T42L9 show that the anomalous heating over the tropics, especially over the central-western Pacific and Atlantic, favors the formation of positive anomalies of height at the Ural region. Finally, a self-sustain mechanism of positive anomalies through two-way interaction between planetary stationary wave and transient eddy under the stimulation of anomalous tropical heating is proposed. |
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| Keywords: | 1998 floods in China Blocking high over the Ural Mountains Tropical abnormal heating Transient eddy Two-way interaction |
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