夏季沿西亚急流Rossby波活动异常的波源和能量传播及转换特征

Wave sources, energy propagation and conversion for anomalous Rossby wave activities along West Asian jet stream.

    摘要
  • 摘要: 用1958—2003年NCEP/NCAR再分析资料，利用涡度源方程、Eliassen-Palm通量（EP通量）和非绝热效应的波能方程，分析了夏季沿西亚急流Rossby波活动（WAJRA）异常的波源、能量传播和转换特征，从大气动力学内部机制上进一步认识WAJRA异常的成因，提高对中高纬大气环流异常机理的理解。研究表明，对流层高层位于地中海和北大西洋—斯堪的纳维亚半岛的负涡度源区和EP通量强辐散区为夏季WAJRA异常的波源区。当波源区位置和强度出现异常时，波源所激发东传的Rossby波活动也出现异常，从而导致WAJRA强弱变化。WAJRA强（弱）年冰岛—斯堪的那维亚半岛（斯堪的那维亚半岛以东）EP通量强辐散区激发Rossby波并沿2条路径向东传播，一支向东传播在乌拉尔山附近转向东南并在里海、咸海—新疆上空进入亚洲副热带西风急流传播增强（减弱），另一支直接向东南方向传播在地中海东部—黑海附近进入亚洲西风急流增强（减弱），此外，地中海上空EP通量辐散也增强（减弱），它们共同作用使得WAJRA增强（减弱）。沿西亚地区副热带西风急流（简称西亚急流，指亚洲副热带西风急流的15°—60°E部分）非绝热加热产生扰动有效位能远大于基本气流动能向扰动动能的转换和基本气流有效位能向扰动有效位能的转换。西亚急流Rossby波活动强年（弱年）伊朗高原及其北侧的西亚地区非绝热加热产生的有效位能增强（减弱）显著，是WAJRA增强（减弱）的能量源。

     

    Abstract: Characteristics of the wave sources，energy propagation and conversion for anomalous Rossby wave activities(RWA) along West Asian jet stream (WAJS) in summer are examined based on the NCEP/NCAR reanalysis dataset from 1958 to 2003 by using vorticity source equation, EliassenPalm (EP) flux, and wave energy equation with diabatic heating. As a result, the causes of RWA anomalies along WAJS are further comprehended from the atmospheric dynamic mechanism to improve understanding of mid-high latitude circulation anomalies. The results show that the negative vorticity source and the strong EP flux divergence over the Mediterranean Sea and the North Atlantic-Scandinavian Peninsula area act as the wave sources of RWA anomalies along WAJS. When the intensity and position of the wave sources are anomalous, the excited eastwardpropagation RWA along WAJS also behaviors anomalously. In strong (weak) years of RWA along WAJS, Rossby waves excited by the strong divergence of EP fluxes over the Iceland-Scandinavian Peninsula area (east to Scandinavian Peninsula) propagate eastward and southeastward. The eastward propagating waves strengthen (weaken) after turning southeastwards near the Ural Mountain and then entering into the Asian subtropical westerly jet stream(ASWJS) over the Caspian Sea -Aral Sea -Xinjiang, and the southeastward propagating waves strengthen (weaken) after directly entering into the ASWJS over the eastern Mediterranean-the Black Sea. Furthermore, the divergence of EP flux over the Mediterranean also strengthens (weakens) in the strong (weak) years, so they jointly bring about strong (weak) RWA along WAJS. Besides the perturbation available potential energy (PAPE) along WAJS(15°-60°E )produced by diabatic heating is far greater than the conversion from the kinetic energy of basic flow into perturbation kinetic energy and from the available potential energy of basic flow into PAPE. The RWA along WAJS looks stronger (weaker) than normal, when the PAPEs produced by diabatic heating over the Iran Plateau and west Asia obviously strengthen (weaken), therefore they are also the energy sources of RWA anomalies.

     

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