Analysis of Flow Variability during the Terrain-influenced Monsoon Rainfall Experiment (2008)

The Terrain-influenced Monsoon Rainfall Experiment (TiMREX) - 2008 was a field campaign conducted to observe features of the East Asian monsoon, with particular focus on precipitation variability in and near Taiwan, where society is strongly impacted by rainfall amounts that can exceed 2 m over the course of a day in the presence of monsoon convection. Following quality-check procedures, all available operational and experimental observations collected during the TiMREX time period (15 May-6 June), which include data from high-frequency soundings and multiple dropsonde missions, were used to generate time-dependent, 0.25-degree gridded analyses by employing the three-dimensional variational data assimilation system (3DVAR) included with the Weather Research and Forecasting model (WRFDA) and gridded fields from the NCEP-Global Forecast System model (as first guess for WRFDA). Validation of the resulting analyses, which are a combination of observations and the first guess model, were performed via comparison with rainfall estimates from the Tropical Rainfall Measuring System, radar observations, as well as other observations utilized by WRFDA to generate the analyses. Previous research suggests that the nature of the flow (i.e., velocity and vertical stability) around Taiwan and other islands strongly determines how the flow navigates the island obstacle. It follows that the degree and nature of flow blocking significantly influences precipitation rate and location (e.g., whether precipitation systems maximized upstream of Taiwan or along the inland foothills of Taiwan). The characteristics of flow blocking in relation to flow velocity and vertical stability as well as associated impacts on precipitation will be investigated by examining multiple cases in the gridded analyses generated using WRFDA and observations from TiMREX 2008.