Assimilation of horizontal line‐of‐sight winds with a mesoscale EnKF data assimilation system. (24th October 2018)

• Record Type: Journal Article
• Authors: Šavli, Matic; Žagar, Nedjeljka; Anderson, Jeffrey L.
• Is Part Of: Quarterly journal of the Royal Meteorological Society. Volume 144:Number 716(2018)
• Page Start: 2133
• Page End: 2155
• Publication Date: 2018-10-24
• Subjects: Aeolus mission -- background‐error covariances -- horizontal line‐of‐sight winds -- mesoscale ensemble Kalman filter -- observing system simulation experiment; Meteorology -- Periodicals; 551.5
• DOI: 10.1002/qj.3323
• Languages: English
• ISSNs: 0035-9009

Abstract

Abstract : This paper compares the horizontal line‐of‐sight (HLOS) wind observations with a single wind component and full wind information in a limited‐area domain over Europe and the North Atlantic. The motivation for the study is the forthcoming Aeolus mission of the European Space Agency which will provide vertical profiles of HLOS winds. A new observing system simulation experiment framework was developed using the Data Assimilation Research Testbed (DART) ensemble adjustment Kalman filter (EAKF) data assimilation with the Weather Research and Forecasting (WRF) model at a horizontal resolution of 15 km. The 50‐member EAKF/WRF is nested in the operational 50‐member ensemble prediction system of ECMWF (ENS) using model‐level data available twice per day. The ensemble spread at lateral boundaries provided by ENS, especially in the North Atlantic, is shown to be sufficient to carry out experiments without covariance inflation. Results show that the information content of HLOS winds is on average divided linearly between the zonal and meridional wind components depending on the observation azimuth. In areas of significant covariances such as fronts in the Atlantic, multivariate covariance information provides significant useful analysis increments from the HLOS wind observations, especially if observations are aligned along the front. The application of the spatially and temporally adaptive prior inflation improved all scores compared with the case without inflation. Abstract : The potential impact of the horizontal line‐of‐sight (HLOS) winds is studied in a limited‐area system using the EAKF with the WRF model nested in the ECMWF operational ensemble. OSSE experiments show that multivariate covariance information can provide useful analysis increments from a single wind component. Presented example of analysis increments on the front shows that assimilation of HLOS wind provides increments closer to the truth than assimilation of two wind components.