Impact of SAPHIR radiances on the simulation of tropical cyclones over the Bay of Bengal using NCMRWF hybrid-4DVAR assimilation and forecast system

• Published in: Journal of Earth System Science Vol. 129; no. 1; p. 209
• Main Authors: Choudhury, Devanil, Gupta, Ankur, Rani, S Indira, George, John P
• Format: Journal Article
• Language: English
• Published: New Delhi Springer India 01-12-2020; Springer Nature B.V
• Subjects: Assimilation; Bias; Channels; Cyclone tracks; Cyclones; Data assimilation; Earth and Environmental Science; Earth orbits; Earth Sciences; Frequency ranges; Humidity; Humidity profiles; Hurricanes; Impact analysis; Lead time; Low earth orbits; Medium-range forecasting; Ocean basins; Oceans; Satellite tracking; Satellites; Sea level pressure; Simulation; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Tropical cyclone intensities; Tropical cyclones; Vertical profiles; Weather forecasting; Indian Ocean; Bay of Bengal; tropical cyclone; hybrid-4DVAR; data assimilation; SAPHIR
• DOI: 10.1007/s12040-020-01473-2
• EISSN: 0973-774X
• ISSN: 2347-4327; 0253-4126

Observing System Experiments (OSEs) were conducted to analyze the impact of assimilation of Megha-Tropique’s (MT) Sounder for Probing Vertical Profiles of Humidity (SAPHIR) radiances on the simulation of tracks and intensity of three tropical cyclones (Kyant, Vardah, and Maarutha) formed over the Bay of Bengal during 2016–2017 North Indian Ocean cyclone period. National Centre for Medium Range Weather Forecast (NCMRWF) Unified Model (NCUM) Hybrid-4DVAR assimilation and forecast system was used for the OSEs. Assimilation of SAPHIR radiances produced an improvement of 9% and 12%, respectively, in the cyclones’ central sea level pressure (CSLP) and the maximum sustained wind (MSW), while an improvement of 38% was seen in the cyclone tracks within the forecast lead time of 120 hrs. Initial assessment shows that the improvement in the cyclone intensity is due to the assimilation of the unique surface peaking channel of SAPHIR (channel-6), whereas the improvement in the cyclone track is due to the assimilation remaining five channels of SAPHIR. Thus, the assimilation of SAPHIR radiances in the NCUM system showed improvement in both intensity and track of the cyclones over the Bay of Bengal; however, more cyclone cases over different ocean basins have to be analyzed to make a robust conclusion. This study specifies the importance of similar microwave humidity instruments in the same frequency range for the detailed exploration of cyclone track and structure.
Highlights
Impact of SAPHIR humidity channel information in the NCMRWF Hybrid-4DVar assimilation and forecast system is analysed through Observing system experiments (OSEs)
Assimilation of SAPHIR humidity information improved both track and intensity of the cyclones compared to the control experiment, and the improvement is visible upto a lead time of 5 days
It is noted that the improvement in the cyclone intensity simulation is due to the assimilation of the lowest peaking channel of the SAPHIR, while the track improvement is contributed by other channels as well.
This study underlines the importance of SAPHIR like instruments in the low earth orbiting satellites with frequent revisit time to explore the features of cyclones.