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性程度以及调节对流活动的中层湿润程度。然而，由于缺乏对发生过程的高时空观测，人们对湿润的时间变化知之甚少。全球定位系统 (GPS) 无线电掩星 (RO) 提供具有极高垂直分辨率的区域平均折射率分布（取决于湿度和温度），与下投式探空仪（逐点、高垂直分辨率）和卫星检索（水平分辨率高但垂直分辨率差）互补。 GPS RO 对强降水、云和风不敏感。 自气象、电离层和气候星座观测系统（COSMIC）投入运行以来，星载GPS RO数据对全球对流层中上层数值天气预报模型产生了积极影响。 然而，较低水平数据的使用因以下几个原因而滞后：1）由于湿度水平变化较大而导致复杂化；2）信号跟踪困难；3）中尺度系统感兴趣窗口内的观测稀疏。这对热带气旋发生和预报的影响极小，对对流层中层以下的影响也极小。机载 RO 可以在增进对飓风发生过程的了解方面发挥重要作用，因为机载系统比现有的星载星座更容易进行密集的有针对性的测量。 PI 将利用 2010 年 8 月热带云系统抑郁前调查 (PREDICT) 活动期间收集数据的独特机会，这将使他们能够测试热带气旋成因情况的数据同化进展情况。 数据同化结果应该引起预测研究人员的极大兴趣，因为它们将为高分辨率模型提供更好的初始条件，以测试有关热带扰动演变为飓风的新假设。更广泛的影响：该项目将促进机载无线电掩星在更广泛的研究领域的使用，并作为飓风追踪监视任务的可行性测试，可能会因改进的业务预测而带来直接的社会效益。这项研究活动将在台湾和美国大学之间的国际合作结构中教育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.