Isentropic Potential Vorticity Analysis of the Outflow Layerof a Typhoon

热带气旋可以看作是一台热机。它的燃料是表面空气被扫向低空流入环流的中心区域时所收集的潜热。热是在眼壁潮湿的表面空气上升过程中通过凝结释放出来的。在任何热机中，为了将能量转化为运动的动能，都需要一个散热片。在热带风暴中，这种汇存在于风暴中心区域流出的低空层（对流层上层-平流层下层）。温度、压力、湿度和空气的三维速度在到达这个下沉区域之前发生了巨大的变化。然而，另外两种性质保存得更好，可以作为示踪剂。它们是它的等效势温（熵的一种度量）和势涡（热稳定性和旋转运动的一种综合度量）。然而，要计算这些特性的自然三维场，就需要在热带气旋（最好是强热带气旋）的整个生命周期中测量前所未有的细节和范围。1990年夏季进行的四次观测实验应能提供分析特别是高架流出层垂直结构所需的数据。这些分析有助于我们进一步了解热带气旋外流及其与对流层和平流层环境的相互作用。由于仪器网部署在一个区域（西太平洋）并在一段时间（1990年9月10日至20日）期间捕捉到了超级台风弗洛，因此现在有了一个理想的分析案例。这些分析有助于区分目前几种热带气旋发展理论，并为超越目前预测强度变化的统计经验方法提供基础。此外，据估计，对流层和平流层之间的全球质量交换的5- 10%发生在这些风暴中。因此，这些分析有助于改进我们目前对大气化学收支的估计。美林过去在热带气旋分析方面建立了可靠的记录。他正在ONR和AFGL的支持下参与1990年夏季测量数据的数据编辑、减少和统计旋风轨迹分析。该奖项支持的额外研究为补充使用这些前所未有的数据集提供了机会。

A tropical cyclone may be considered to be a heat engine. Its fuel is the latent heat gathered by surface air as it is swept toward the central region of a low-level inflow circ- ulation. The heat is released by condensation during ascent of the moist surface air in the eye-wall. In any heat engine, a heat sink is required for energy to be converted to the kinetic energy of motion. In a tropical storm, such a sink is found in an ele- vated (upper troposphere-lower statosphere) layer of outflow from the storm's central region. The temperature, pressure, humidity, and three-dimensional velocity of the air change drastically before reaching this sink region. However, two other properties are better conserved, that can serve as tracers. These are its equivalent potential temperature (a measure of its entropy) and its potential vorticity (a combined measure of its thermal stability and rotational motion). Calculation of natural three-dimensional fields of these properties requires, however, measurements of unprecedented detail and extent through the life- cycle of a (preferably intense) tropical cyclone. Four observational experiments in the summer of 1990 should provide the data needed to analyze, in particular, the vertical structure of the elevated outflow layer. These analyses should further our understanding of tropical cyclone outflow and its interaction with its tropospheric and stratospheric environment. An ideal case is now available for analysis, since the instru- mental networks were deployed in a region (the western Pacific) and during a period (10-20 September 1990) that allowed them to capture Super-typhoon Flo. The analyses could serve to discriminate between a few cur- rent theories of tropical cyclone development and provide a basis for advancing beyond current statistical-empirical methods for forecasting intensity changes. Also, it is estimated that 5- 10% of the global mass exchange between troposphere and strato- sphere occurs in these storms. Thus, the analyses could help refine our present estimates of atmospheric chemical budgets. Merrill has established a creditable past record in tropical cyclone analyses. He is being supported by ONR and AFGL to par- ticipate in the data editing, reduction and statistical cyclone- track analyses of the summer 1990 measurements. The additional research supported under this award provides an opportunity for complementary use of these unprecedented data sets.