Abstract
Abstract. The impact of using wind observations from the Aeolus satellite in a limited-area numerical weather prediction (NWP) system is being investigated using the limited-area NWP model Harmonie–Arome over the Nordic region. We assimilate the horizontal line-of-sight (HLOS) winds observed by Aeolus using 3D-Var data assimilation for two different periods, one in September–October 2018 when the satellite was recently launched and a later period in April–May 2020 to investigate the updated data processing of the HLOS winds. We find that the quality of the Aeolus observations has degraded between the first and second experiment period over our domain. However, observations from Aeolus, in particular the Mie winds, have a clear impact on the analysis of the NWP model for both periods, whereas the forecast impact is neutral when compared against radiosondes. Results from evaluation of observation minus background and observation minus analysis departures based on Desroziers diagnostics show that the observation error should be increased for Aeolus data in our experiments, but the impact of doing so is small. We also see that there is potential improvement in using 4D-Var data assimilation, which generates flow-dependent analysis increments, with the Aeolus data.
Highlights
It is well known that the quality of numerical weather prediction (NWP) forecasts is dependent on the accuracy of the estimation of the initial state (Simmons and Hollingsworth, 2002)
In order to have a general idea of the performance of the Aeolus horizontal line-of-sight (HLOS) winds over the MetCoOp domain, we studied the difference between the observed values and the model background, which in this case is the 3 h forecast from the previous cycle
Aeolus HLOS wind profiles have been added to the 3D-Var data assimilation in a regional high-resolution NWP system
Summary
It is well known that the quality of numerical weather prediction (NWP) forecasts is dependent on the accuracy of the estimation of the initial state (Simmons and Hollingsworth, 2002). S. Hagelin et al.: Evaluating the use of Aeolus satellite observations measurements are perpendicular to the direction of travel, hereafter referred to as the HLOS (horizontal line-of-sight) winds. The Mie winds have a stronger signal than the Rayleigh ones, and Mie winds are more precise and can be derived with a higher vertical resolution They are more concentrated to the lower part of the atmosphere. In this study we want to evaluate the suitability of using data from the Aeolus satellite in a limited-area model (LAM). The use of Aeolus observations in limited-area kilometre-scale data assimilation differs in several respects from global data assimilation. For a limited-area data assimilation system, Aeolus data are available over the domain only sometimes, and the difference in spatial scales represented by the observation and by the model, respectively, is relatively large. We will look at the overall impact of Aeolus data and the impact of the Rayleigh and Mie observations separately
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