Assimilation of INSAT-3D imager water vapour clear sky brightness temperature in the NCMRWF’s assimilation and forecast system

  • S Indira RaniEmail author
  • Ruth Taylor
  • Priti Sharma
  • M T Bushair
  • Buddhi Prakash Jangid
  • John P George
  • E N Rajagopal


This paper describes the direct assimilation of water vapour (WV) clear sky brightness temperatures (CSBTs) from the INSAT-3D imager in the National Centre for Medium Range Weather Forecasting (NCMRWF) Unified Model (NCUM) assimilation and forecast system. INSAT-3D imager WV CSBTs show a systematic bias of 2–3 K compared to the data simulated from the model first guess fields in the pre-assimilation study. The bias in the INSAT-3D imager WV CSBTs is removed using a statistical bias correction prior to assimilation. The impact of INSAT-3D imager WV channel CSBTs is investigated through different approaches: (i) single observation experiments and (ii) global assimilation experiments using the hybrid-four-dimensional variational technique. Single observation experiments of channels of the same frequency from different instruments like the INSAT-3D imager and sounder, and the Meteosat visible and infrared imager (MVIRI) onboard Meteosat-7, show the INSAT-3D imager and MVIRI WV channels have a similar impact on the analysis increment. Global assimilation clearly shows the positive impact of the INSAT-3D imager WV CSBTs on the humidity and upper tropospheric wind fields, whereas the impact on the temperature field, particularly over the tropics, is neutral. Validation of model forecasted parameters with the in situ radio sonde observations also showed the positive impact of assimilation on the humidity and wind fields. INSAT-3D imager WV CSBTs have been assimilated operationally in NCUM since August 2018.





The authors acknowledge the funding provided by the National Monsoon Mission (NMM) of the Ministry of Earth Sciences (MoES) for the visiting scientist programme from September 2014 to March 2015. The authors also acknowledge SAC scientists for providing the INSAT-3D CSBT data for carrying out this study and also for the near-real time availability of the product for operational assimilation. The authors acknowledge their heartfelt gratitude to the anonymous reviewer for the valuable comments which helped to improving the content of this paper.


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Copyright information

© Indian Academy of Sciences 2019

Authors and Affiliations

  • S Indira Rani
    • 1
    Email author
  • Ruth Taylor
    • 2
  • Priti Sharma
    • 1
  • M T Bushair
    • 1
  • Buddhi Prakash Jangid
    • 1
  • John P George
    • 1
  • E N Rajagopal
    • 1
  1. 1.National Centre for Medium Range Weather Forecasting (NCMRWF)Ministry of Earth Sciences (MoES)NoidaIndia
  2. 2.Satellite ApplicationsMet OfficeExeterUK

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