Characteristics and effects of ground-based GNSS zenith total delay observation errors in the convective-scale model

Abstract

In this study, we evaluated the impacts of the revised observation error on ground-based global navigation satellite system (GNSS) zenith total delay (ZTD) data in the data-assimilation system of the Korea Meteorological Administration’s 1.5 km convective-scale model. Out of the 100 total stations on the Korean Peninsula, 40 ground-based GNSS data stations were assimilated using three-dimensional variational (3D-Var) data assimilation. The ZTD observation errors were diagnosed for each station using a posteriori methods, giving errors with a variety of spatial and temporal characteristics. These station-specific error data were then implemented using the data-assimilation system, and their impacts were evaluated for a one-month period in July 2016. The root mean square error (RMSE) of the relative humidity in the lower troposphere was found to improve for the period from T+0 to T+36 hours, when using GNSS data. Replacing the errors used in the previous model with the average diagnosed errors also provided better results, but they were not as good as the results obtained using station-specific errors. The observation error is closely related to precipitable water vapor (PWV); therefore, correction values reflecting seasonal characteristics should be applied. In addition, the quantitative precipitation forecasts were improved in all experiments using GNSS data, but the effects were minimal.