Estimation of Dynamic Characteristic Parameters for Long-Lived Tropical Cyclone Freddy (2023) from Active/Passive Spaceborne Microwave Sensors

Spaceborne microwave instruments possess the capability of day-and-night and all-weather measurements that can penetrate clouds and fog, and directly measure tropical cyclone (TC) ocean surface winds. In this study, we establish an effective methodology to estimate TC dynamic characteristic parameters (DCP), including the storm center location, intensity, radius of maximum wind (RMW) and wind structure, purely from TC ocean winds measured by multi-platform spaceborne microwave instruments. Combining measurements from active and passive sensors can provide long time series data for monitoring changes in storm DCP. Here, the evolution of the DCP for TC Freddy (2023), from its genesis to its landfall, are evaluated using data from synthetic aperture radars (SARs), radiometer (RAD) and scatterometer (SCA) observations. Comparing the results to the best-track datasets for the longitudes and latitudes of the storm centers, we show that the root mean square errors (RMSEs) are 0.22° and 0.31°, respectively, both with a correlation of 0.99. For the detected intensity, the RMSEs are 6.8 m/s for SARs and 7.2 m/s for RADs. However, TC intensities measured by C-band SCAs are significantly underestimated, especially for wind speeds less than 50m/s. In terms of RMW and wind radii, the SARs, RADs and SCAs demonstrate good accuracy and applicability. Our investigation emphasizes the crucial role played by spaceborne microwave instruments in the study of TCs. This is helpful in monitoring, and in the future, will help improve the forecasting of TC intensities and their characteristic structures.