Towards triple collocation analysis of 4D wind observations

2021 EUMETSAT Meteorological Satellite Conference, 20-24 September 2021, Bucharest, Romania
The resolution of regional numerical weather prediction (NWP) models has continuously been increased over the past decades, in part, thanks to the improved computational capabilities. At such small scales, the fast weather evolution is driven by wind rather than by temperature and pressure. Over the ocean, where global NWP models are not able to resolve wind scales below 150 km, regional models provide wind dynamics and variance equivalent to 25 km or lower. However, although this variance is realistic, it often results in spurious circulation (e.g., moist convection systems), thus misleading weather forecasts and interpretation. An accurate and consistent initialization of the evolution of the 3-dimensional (3-D) wind structure is therefore essential in regional weather analysis. The research will focus on a comprehensive characterization of the spatial scales and measurement errors for the different operational space-borne wind products currently used and/or planned to be used in regional models. In addition, a thorough investigation and improvement of the 4-D (including time) consistency between different horizontal and/or vertical satellite wind products will be carried out. Such products include the Ocean and Sea Ice Satellite Application Facility (OSI SAF) scatterometer-derived sea-surface wind fields, the Nowcasting and Very Short-Range Forecasting (NWC) SAF Atmospheric Motion Vectors (AMVs), Aeolus and/or Infrared Atmospheric Sounding Interferometer (IASI) wind profiles. Densely sampled aircraft wind profiles (Mode-S) will be used to verify and characterize the satellite products. To this end, the experience of the NWC, OSI, and NWP SAFs will be exploited. Moreover, data assimilation experiments of the consistent datasets into the HARMONIE-AROME regional model will be carried out in two different regions, i.e., the Netherlands and the Iberian Peninsula regional configurations. Regarding the characterization of the spatial scales and measurement errors, the widely used triple collocation analysis in scatterometry is further analyzed and adapted for the purpose of this project. Scatterometer winds are collocated with buoy observations and ECMWF model output during a period of 14 months on a global scale over the oceans. Different techniques to estimate the representativeness errors of the collocated data sets are inter-compared and their inconsistencies analyzed. The triple collocation method is then exploited to characterize the errors of the different sources at different scales. The analysis is performed for different oceanic regions and seasons.
Finally, an algorithm for collocating 4D wind observations from Aeolus, Mode-S data, and ECMWF model output over a region of Western Europe is currently being developed. Moreover, experimental 4D wind data from IASI are analyzed to evaluate its possible use as an additional source of wind observations for regional data assimilation