Use of Global Positioning Satellites (GPS) Occultation Data in Numerical Weather Prediction

已作出广泛努力，将来自公海的遥感大气数据适当地纳入数值预报模式，在这些海域，常规数据稀少。沿着这一思路，PI寻求通过改进旧方法以及探索新方法来推进全球定位卫星(GPS)掩星数据的同化。GPS发射的无线电信号的折射程度取决于信号通过的大气特性，因此可以用来获得大气热力学状态的知识。本研究项目分为四个方面：1)改进PI在以前的研究中使用的光线跟踪方法(一种将弯曲角轮廓与观测轮廓相匹配的正演模拟计算)的计算效率，并改进其在对流层低层的性能；2)通过估计射线路径上的平均大气折射率信息来开发一种高效的折射率同化方法，以获得折射率指数的综合影响；3)评估和量化GPS导出的折射率数据中的误差；4)利用GPS数据反演的信息来评估和检查现有的物理参数化方案。考虑到GPS数据在未来可能发挥的作用，这项研究对天气预报的潜在影响是重大的。

Extensive efforts have been made to properly incorporate remotely sensed atmospheric data from open oceans where conventional data are sparse into the numerical prediction models. Along this line, the PI seeks to advance the assimilation of the Global Positioning Satellites (GPS) occultation data by improving old approaches as well as exploring a new method. The degree of refraction of the radio signals transmitted by the GPS depends on the properties of the atmosphere through which the signals travel, and thus can be used to gain the knowledge of the atmospheric thermodynamic state. This research project is divided into four areas: 1) Improve the computational efficiency of the raytracing approach (a forward modeling calculation to match the bending angle profile with the observed profile) used by the PI in her previous study and improve its performance in the lower troposphere; 2) Develop an efficient refractivity assimilation method by estimating the averaged atmospheric refractivity information along the ray path to obtain the integrated effect of refractivity index; 3) Assess and quantify errors in the GPS-derived refractivity data; 4) Evaluate and examine existing physical parameterization schemes using the information retrieved by the GPS data. The potential impact of this study on weather predictions is significant considering the role that GPS data likely will play in the future.