海洋风暴形成的一种动力学机制

A DYNAMICAL MECHANISM OF MARINE STORM GENESIS

文中从观测统计学、瞬变涡动能量学和 MM5中尺度数值模拟角度 ,研究了海洋风暴 (爆发性气旋 )形成的气候特征及其可能的动力学机制 ,揭示了一幅爆发性发展的物理图像。结果表明 ,在冷季大气特别是日本以东洋面上大气特有的热力气候背景下 ,通过同海洋风暴过程相联系的涡动热通量 vθ的向极地输送 (- vθ· θm>0 ) ,将季节尺度的时间平均有效位能向瞬变涡旋时间尺度的涡动有效位能转换 ,是海洋风暴形成的主要动力机制。在该过程中转换来的具有最大贡献的涡动有效位能 ,连同具有次大贡献的积云加热制造的涡动有效位能(q3 )一起 ,通过暖异常区 (α >0 )暖湿空气上升运动 (-ω >0 )的斜压转换 (-ωα) ,促使涡动动能增长。同时 ,补充的涡动有效位能又加强了暖异常区的暖湿空气上升运动 ,进而产生积云对流活动及其潜热释放的正反馈过程 ,最终导致涡动动能急剧增长和海洋风暴的形成。海-气潜热输送的作用是在风暴形成初期提供后来积云尺度对流活动及潜热释放的水汽潜力。研究还表明 ,海洋风暴主要发生在冷季月份 1 3 0°E以东的中高纬洋面上 ,这种对特定季节和特定海域的依赖性是大气和海洋气候背景的动力

Climatological characteristics and a dynamical mechanism of marine storm genesis (explosive cyclone) are investigated in the paper from observation statistics, transient eddy energetics and mesoscale numerical simulation of MM5. The results show that under the circumstance of favorable atmospheric thermodynamic background especially over the eastern ocean of Japan during the cold seasons, via poleward transfer of eddy heat fluxes associated with a marine storm the energy conversion from P m on seasonal scale to P e on transient eddy scale is a dynamic mechanism of marine storm genesis. The converted greater eddy potential energy, along with the secondary one made by cumulus heating, is further transferred to eddy kinetic energy via upward motion of anomaly warm air, hence enhancing the growth of eddy kinetic energy. Meanwhile, the compensatory eddy potential energy also enhances the upward motion of anomaly warm air that leads to cumulus convective activities and ensuing latent heat release. This builds a positive feedback process and results in the rapid growth of eddy kinetic energy and marine storm genesis. Latent heat flux from the ocean during the incipient storm provides a potential for cumulus convective and condensation latent release during explosive development. The results also show that marine storm occurs preferentially over the mid- and high-latitude ocean east of 130°E during the cold seasons. The dependence property on special locations and seasons results from the synthetic dynamic/thermodynamic role of atmospheric and oceanic climatological background.