Collaborative Research: Investigating the Characteristics of Lower Tropospheric Airborne GPS Radio Occultation Observations and Their Impact in Hurricane Studies

众所周知，飓风的形成过程取决于支持深层对流所需的垂直不稳定程度和调节对流活动的中层增湿。然而，由于缺乏在形成过程中的高时空观测，对增湿的时间变化知之甚少。全球定位系统(GPS)无线电掩星(RO)提供了具有很高垂直分辨率的区域平均折射率剖面(取决于湿度和温度)，这是对滴漏探测仪(逐点、高垂直分辨率)和卫星反演(高水平但低垂直分辨率)的补充。GPS RO对强降水、云和风不敏感。自星座气象、电离层和气候观测系统(COSMIC)投入使用以来，星载GPS RO资料对全球对流层中上层数值天气预报模式产生了积极的影响。然而，由于以下几个原因，低层数据的使用一直滞后：1)由于湿度的强烈水平变化而引起的复杂情况；2)信号跟踪的困难；3)中尺度系统感兴趣的窗口内的稀疏观测。这对热带气旋的形成和预报的影响很小，对对流层中层以下的影响一般也很小。机载RO可以在推进对飓风形成过程的理解方面发挥重要作用，因为使用机载系统进行密集的定向测量比使用现有的空间星座更容易进行。私人投资机构将利用一个独特的机会，在2010年8月的热带云系萧条前调查(FOREST)活动期间收集数据，这将使他们能够测试他们在热带气旋成因的数据同化方面的进展。资料同化结果应引起预报研究人员的极大兴趣，因为它们将为检验有关热带扰动演变为飓风的新假设的高分辨率模式提供更好的初始条件。更广泛的影响：该项目将向扩大的研究界推广使用机载无线电掩星，并作为飓风猎人监视任务的可行性测试，可能会从改进的业务预报中产生直接的社会效益。这项研究活动将在台湾和美国大学之间的国际合作架构中培养研究生，并促进博士后研究人员的进步。它将加强由四名女性研究人员领导的研究项目，她们将成为学生和其他年轻女性科学家的榜样。

The hurricane genesis process is known to depend on the degree of vertical instability needed to support deep convection and on mid-level moistening, which modulates convective activity. However, the time variation of moistening is poorly known due to the lack of high temporal and spatial observations during the genesis process. Global Positioning System (GPS) Radio Occultation (RO) provides area-averaged profiles of refractivity (which depends on moisture and temperature) with very high vertical resolutions that are complementary to dropsondes (pointwise, high vertical resolution) and satellite retrievals (high horizontal but poor vertical resolution). GPS RO is insensitive to heavy precipitation, clouds, and winds. Since the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) became operational, space borne GPS RO data have shown a positive impact on global numerical weather prediction models in the mid to upper troposphere range. However, the use of the data at lower levels has lagged for several reasons: 1) complications due to strong horizontal variations in moisture 2) difficulties in signal tracking and 3) sparse observations within the window of interest for mesoscale systems. This has led to minimal impact in tropical cyclone genesis and forecasting, and minimal impact below mid-troposphere in general. Airborne RO can play a major role in advancing understanding of the hurricane genesis process, because dense targeted measurements are simpler to make with an airborne system than with the existing space borne constellation. The PIs will take advantage of a unique opportunity to collect data during the Pre-Depression Investigation of Cloud Systems of the Tropics (PREDICT) campaign in August 2010, which will allow them to test their progress in data assimilation for the case of tropical cyclone genesis. The data assimilation results should be of great interest to PREDICT investigators because they will provide better initial conditions for high-resolution models for testing new hypotheses concerning the evolution of tropical disturbances into hurricanes. Broader Impacts: The project will promote the use of airborne radio occultation to an expanded research community and serve as a feasibility test for hurricane hunter surveillance missions, potentially resulting in a direct societal benefit from improved operational forecasts. This research activity will educate graduate students and promote the advancement of postdoctoral researchers within an international collaborative structure between Taiwan and US universities. It will strengthen research programs led by four female investigators, who will serve as role models for their students as well as other young female scientists.