The Variational Assimilation Experiment of GPS Bending Angle

More and more new types of observational data provide many new opportunities for improving numericalweather forecasts. Among these, the GPS (Global Positioning System) bending angle is undoubtedly veryimportant. There are many advantages of the GPS bending angle, such as high resolution, availability inall weather conditions, and global data coverage. Thus it is very valuable to assimilate GPS bending angledata into numerical weather models. This paper introduces how to obtain and assimilate the GPS bendingangle. There are two methods of assimilation: the indirect method and direct method, and they are bothintroduced in this paper. During the minimizing process of variational assimilation, calculation efficiencyis very important and the optimal step size greatly influences the algorithm efficiency. Based on thecharacteristics of the minimizing algorithm, we obtain an adaptive method for calculating the optimizingstep suitable for all kinds of minimization algorithms through mathematical deduction. Finally, a numericalvariational assimilation experiment is performed using the GPS bending angle data of 11 October 1995.The numerical results indicate the validity of the variational assimilation method and the adaptive methodintroduced here.