Isentropic Potential Vorticity Analysis of the Outflow Layerof a Typhoon

热带气旋可以被认为是热机。它的燃料是地面空气扫向低层流入环流中心区域时聚集的潜热。在眼壁中潮湿的表面空气上升时，热量通过冷凝释放出来。在任何热机中，要将能量转化为运动动能，散热器都是必需的。在热带风暴中，这样的汇被发现在风暴中心区域的流出层(对流层上部-静止层下部)。在到达这个下沉区域之前，空气的温度、压力、湿度和三维速度发生了剧烈的变化。然而，另外两个属性保存得更好，可以用作示踪剂。这些是它的当量势温(测量它的熵)和它的势涡度(它的热稳定性和旋转运动的综合测量)。然而，这些性质的自然三维场的计算需要在热带气旋(最好是强烈的)生命周期中进行前所未有的细节和范围的测量。1990年夏季的四个观测实验应能提供分析特别是高空出流层的垂直结构所需的数据。这些分析应该会加深我们对热带气旋外流及其与对流层和平流层环境的相互作用的理解。现在有一个理想的案例可供分析，因为仪器网络部署在一个区域(西太平洋)，并在一段时间(1990年9月10日至20日)允许他们捕获超级台风Flo。这些分析可以区分当前几种热带气旋发展的理论，并为超越目前预报强度变化的统计-经验方法提供依据。此外，据估计，全球对流层和直流层之间的质量交换有5%-10%发生在这些风暴中。因此，这些分析可能有助于完善我们目前对大气化学预算的估计。美林在热带气旋分析方面建立了值得称赞的过去记录。他正得到ONR和AFGL的支持，参与1990年夏季测量的数据编辑、简化和统计旋风路径分析。该奖项支持的其他研究为补充使用这些史无前例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.