Retrieval and Application of Rapid-Scan Atmospheric Motion Vectors Using an Infrared Channel of the INSAT-3DR Satellite

摘要

The advanced Indian meteorological satellite INSAT-3DR was configured in rapid-scan mode during the formation of tropical cyclone 'Fani' over the North Indian Ocean. This study is carried out to explore the possibility of further enhancement in atmospheric motion vectors (AMVs) to understand the extreme weather event using rapid-scan observations. A novel experiment has been performed to retrieve rapid-scan AMVs (RS-AMVs) with different tracer sizes at two different temporal scales (10 and 15 min) using the Thermal Infrared (TIR)-1 channel of the INSAT-3DR satellite. The RS-AMVs are able to capture small-scale variations of winds in rapid-scan mode, compared to AMVs retrieved by the operational INSAT-3D satellite available at 30-min intervals. Initial quality assessment of retrieved RS-AMVs is performed using winds from NCEP final analysis, ERA-5 reanalysis, and radiosonde observations. The number of wind vectors are enhanced significantly in RS-AMVs against operational AMVs from INSAT-3DR. An improvement of about 12% in RS-AMVs relative to operational 30-min INSAT-3D-retrieved AMVs has been achieved. Moreover, a sensitivity study has been performed using four-dimensional variational data assimilation experiments to understand the impact of newly retrieved RS-AMVs against operational INSAT-3D-retrieved AMVs for tropical cyclone Fani. Results suggest noteworthy improvements in track prediction when RS-AMVs are used for assimilation as compared to operational AMVs. The model-simulated surface wind structures are also compared with satellite observations for the radius of the maximum winds (R-max) and the maximum radial extent of surface winds.