Assimilation of ASCAT winds using 4DVAR: an impact study

Abstract

Sea surface wind vectors from Advanced Scatterometer (ASCAT) onboard MetOP satellites are pivotal inputs to NWP models, especially during cyclone period. NCMRWF regularly receives these winds from NOAA through ftp and routinely assimilates in the operational global models. The impact of ASCAT winds in the NCMRWF Unified Model (NCUM) assimilation and forecast system during the cyclone Chapala period from 28 October 2015 to 4 November 2015 is studied. Before assimilating, these winds are validated against in-situ observations from buoy platforms over the North Indian Ocean (NIO). It is found that the errors in the ASCAT winds are well within the limit of mission goal (<2m/s). After the successful validation, numerical experiments are designed in such a way that 10-day forecasts are generated from two different initial conditions. In the control run (CTL), ASCAT winds are removed from the Observation Processing System (OPS) and Variational Assimilation (VAR) systems of NCUM, while in the experiment run (AST) ASCAT winds are included in both OPS and VAR. Forecasts from both the runs are analysed to see the movement and intensification of the cyclonic system in due course. The results show that the experiments with ASCAT winds improved the track and intensity of the NIO cyclonic system.

IMDAA Regional Reanalysis: Performance Evaluation During Indian Summer Monsoon Season

“…These observations come from the worldwide Global Telecommunications System (GTS) and from satellite-based data sets. IMDAA also benefited from extra surface observations recovered from the archives of IMD and NCMRWF in the later years, since 1995 (Mahmood et al, 2018;Srinivas et al, 2016), which may not be part of global GTS data set. However, during the study period (1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993) no additional observations from IMD/NCMRWF archive were used in the reanalysis.…”