Multi-scale analysis of the impact of soil moisture and boundary layer processes on convective precipitation

点击翻译按钮获取中文摘要

Within the framework of this project, a strategy to study the effects of soil moisture (SM), evapotranspiration and water vapour in the planetary boundary layer (PBL) on QPF will be applied on different scales (local to regional). The aim is to identify the dependence of convectively and orographically induced precipitation on the variability of the SM field and the corresponding processes in the PBL. This is made possible by an innovative measurement approach using a very high number of different SM sensors on various scales, which are partly supplied by the IMK from other sources and partly included in the overall COPS application. This application includes the implementation of a SM station network based on presently uncoordinated measurements of various organisations and supplemented by a large number of low-cost SM probes, 2D moisture measurements using geophysical methods (up to 1 km) and integrating SM measurements using FreeLineSensing and reflecting GPS signals (up to 40 km). These innovative techniques have been developed at the applicants institute. A minor part of this proposal covers improvements of such instruments to reach operationaiity, since the COPS application considers only proven measurement techniques. The measurements will form essential parts of the General Observation Period (GOP) and the Convectively and Orographically induced Precipitation Study (COPS) in 2007 and will provide important guidelines on the required size and resolution of SM station arrays for future operational measurement networks. Suitable quality control routines and upscaling algorithms for SM data from point measurements to the grid size of the operational forecast model LM (Lokal-Modell) of the German Wearther Service (DWD) will be developed. The water and energy fluxes at the surface and in the PBL will become available as a central part of the COPS experiment under IMK responsibility. The optimised SM and atmospheric fields arejg compared to their related representation within the LM and the global model GME. LM model runs will be initiated with the optimised fields to study the impact of surface and PBL processes on convective precipitation. LM model results are compared to observations during the COPS campaign for several case studies. The combination of dense observations with LM simulations permits a rigourous analysis of the water transfer process chain from soil moisture and fluxes in the PBL to convection initiation and precipitation. The work constitutes a central part of the overall COPS strategy by thorough analyses of the measurement data and aims to improve the QPF by better process representation in the weather prediction model LM.