Assimilation of INSAT-3D imager water vapour clear sky brightness temperature in the NCMRWF’s assimilation and forecast system
- 24 Downloads
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.
KeywordsINSAT-3D WV CSBT hybrid-4DVAR NCUM NWP
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.
- Das Gupta M, Priti S and Rani S I 2015 Validation of INSAT-3D atmospheric motion vectors; NMRF/RR/01/2015, 27p.Google Scholar
- Doherty A, Atkinson N, Bell W and Smith A 2015 An assessment of data from the advanced technology microwave sounder at the Met office; Adv. Meteorol. 2015 1–16, Article ID 956920, http://dx.doi.org/10.1155/2015/956920.
- George J P, Rani S I, Jayakumar A, Mohandas S, Mallick S, Lodh A, Rakhi R, Sreevathsa M N R and Rajagopal E N 2016 NCUM data assimilation system; NMRF/TR/01/2016, 20p.Google Scholar
- Kelkar R R 2019 Satellite meteorology in India: Its beginning, growth and future; Mausam 70(1) 1–14.Google Scholar
- Prasad V S 2012 Conversion of NCEP decoded data to UK MET office Obstore format; NCMR/OB/1/2012.Google Scholar
- Prasad V S 2014 Satellite data processing for NCMRWF unified model (NCUM); NMRF/RR/2/2014.Google Scholar
- Prasad V S and Rani S I 2014 Data pre-processing for NCMRWF unified model (NCUM): Version 2; NMRF/RR/01/2014, 19p.Google Scholar
- Rajagopal E N, Iyengar G R, George J P, Das Gupta M, Mohandas S, Siddharth R, Gupta A, Chourasia M, Prasad V S, Aditi S K and Ashish A 2012 Implementation of the UM model based analysis – Forecast system at NCMRWF; NMRF/TR/2012, 45p.Google Scholar
- Rani S I and Prasad V S 2013 Simulation and Validation of INSAT-3D Sounder Data at NCMRWF; https://cimss.ssec.wisc.edu/itwg/itsc/itsc19/program/papers/1_08_rani.pdf.
- Saunders R, Matricardi M, Geer A, Rayer P, Embury O and Merchant C 2010 RTTOV9 science and validation plan; NWPSAF-MO-TV-020, 2010, http://nwpsaf.eu/oldsite/deliverables/rtm/rttov9_files/rttov9_svr.pdf.
- Stengel M 2008 Assimilation of SEVIRI’s Water Vapour Channel Observations in Clear-Sky Conditions into the HIRLAM Model; Technical Report No. 68.Google Scholar
- Thepaut J N 2003 Satellite data assimilation in numerical weather prediction: An overview; In: Proceedings of ECMWF Seminar on Recent Developments in Data Assimilation for Atmosphere and Ocean, ECMWF, Reading, UK, 8–12 September 2003, pp. 75–96.Google Scholar