Impact of airborne Doppler lidar observations on ECMWF forecasts

Abstract

During the Atlantic THORPEX Regional Campaign (A-TReC) in autumn 2003, the airborne Doppler lidar of the Deutsches Zentrum f¨ur Luft- und Raumfahrt (DLR) was used to observe wind in predicted sensitive regions. In eight flights, the system measured a total of 1600 wind profiles that were experimentally assimilated in the global assimilation system at the European Centre for Medium-Range Weather Forecasts (ECMWF). The present study assesses the impact of these Doppler lidar measurements in Numerical Weather Prediction (NWP). It is shown that lidar observations have a significant impact on the analyses as well as on forecasts owing to high accuracy and spatial resolution. The measurements reduce the errors of the 1–4 day forecasts of geopotential height, wind, and humidity over Europe throughout the troposphere. On average, Doppler lidar measurements reduce the 2–4 day forecast error of geopotential height over Europe by 3%. This is a promising result, considering that observations have been gathered from only 28.5 flight hours. Dropsondes released in the same area as the Doppler lidar was operating show good agreement for measured winds, but smaller analysis impact and less reduction of the forecast error.