Gyu-Ho Lim

Variational assimilation of slant-path wet delay measurements from a hypothetical ground-based GPS network. Part I: Comparison with precipitable water assimilation

Abstract With the recent advance in Global Positioning System (GPS) atmospheric sensing technology, slant wet delay along each ray path can be measured with a few millimeters accuracy. In this study, the impact of slant wet delay is assessed on the short-range prediction of a squall line. Since the current GPS observation network in the central United States is not of high enough density to capture the mesoscale variation of moisture in time and space, a set of observing system simulation experiments is performed to assimilate slant wet delay data from a hypothetical network of ground-based GPS receivers using the four-dimensional variational data assimilation technique. In the assimilation of slant wet delay data, significant changes in moisture, temperature, and wind fields within the boundary layer were found. These changes lead to a stronger surface cold front and stronger convective instability ahead of the front. Consequently, the assimilation of slant wet delay produces a considerably improved 6-h ...

The NCAR CCM as a Numerical Weather Prediction Model

Abstract The NCAR Community Climate Model (CCM, version 3.6) is evaluated as a numerical weather prediction model. The model was run in real-time mode at relatively high resolution (T126 or approximately 1°) to produce 10-day forecasts over a 1-yr period ending 1 March 2004. The evaluation of the performance of the CCM could be useful for both the climate modeling community as well as the operational forecast centers. For climate modelers, the higher-resolution, short-range forecasts can be used to diagnose deficiencies in the physical parameterizations in the model. While climate models may produce good mean climatologies, they may fail to simulate important higher-frequency phenomena that may be important to climate. For operational centers, the examination of an open, well-developed, and studied model could provide insights that could lead to improvement in their own models. Furthermore, the CCM could be considered a candidate as a member for a suite of models for use in an operational context. And, fi...