Insight of deep convection and sea surface wind gusts link through collocated GEO and LEO data
Authors: Li Yu , La Tran Vu , Pelich Ramona-Maria , Chini Marco , Matgen Patrick , Messager Christophe 
Published: February 2023

Convective system (CS) is an extreme weather event occurring regularly over the subtropical and tropical regions such as the Gulf of Guinea, the Gulf of Mexico, Lake Victoria, Southeast Asia, India, and Australia. Certain CS types, i.e., mesoscale CS, supercell convective storms, squall lines, are disastrous for human life, infrastructures, and economic activities since they can produce strong surface winds, heavy rainfall, and significant lightning. Over the last decades, the CS observing, monitoring, and forecasting have been much improved thanks to a dense network of GEOstationary (GEO) satellites, including Meteosat, GEOS, Himawari, and Gaofen, covering Europe, Africa, America, and the Asia Pacific, respectively. However, the observation and prediction of the extreme weather events associated with deep convection are still a big challenge since they often occur suddenly, develop quickly, and become intense in a short time (several hours). Such unpredicted features are a significant issue for the numerical weather prediction models. While the prediction of intense rainfall associated with deep convection is still ongoing, the estimation of surface convective wind gusts has some important advancements. La et al. [1-2] indicated Sentinel-1 C-band Synthetic Aperture Radar (SAR) data with a high spatial resolution and wide swath bring significant advantages for observing and estimating ocean surface convective wind gusts. Indeed, through the images acquired by the Sentinel-1 Low Earth Orbit (LEO) satellite, one can observe convective wind patterns at both mesoscales and sub-mesoscales, as well as wind hot spots (15-25 m/s) at a small scale. The studies [1-2] also showed the relationship between surface wind patterns and deep convective clouds observed on Meteosat GEO images. In particular, the collocation of Sentinel-1, Aeolus Lidar, and Meteosat devices [3] enabled a multi-dimensional view of deep convection and its vertical and horizontal dynamics.Following the previous studies, we illustrate in this paper more interesting cases of multi-dimensional CS observations by the collocated GEO and LEO sensors. They include sea surface convective wind patterns observed by Sentinel-1 LEO, intense downdrafts detected by Aeolus Lidar LEO, and deep convective clouds observed by Meteosat GEO. These cases expected to strengthen the relationship between deep convection and strong surface winds over the sea. In particular, we present the assessment of surface convective wind gust estimates through comparisons to in situ wind measurements by the moored buoys and weather stations. This work is a significant step to strengthen the conclusion that the high-intensity radar backscattering observed on Sentinel-1 C-band SAR images is associated with surface convective wind gusts rather than induced by precipitation.[1] T. V. La and C. Messager, "Convective System Observations by LEO and GEO Satellites in Combination," IEEE JSTARS, vol. 14, pp. 11814-11823, 2021, doi: 10.1109/JSTARS.2021.3127401.[2] T. V. La and C. Messager, "Different Observations of Sea Surface Wind Pattern Under Deep Convection by Sentinel-1 SARs, Scatterometers, and Radiometers in Collocation," IEEE JSTARS, vol. 15, pp. 3686-3696, 2022, doi: 10.1109/JSTARS.2022.3172375.[3] La, T. V., & Messager, C. (2021). Convective system dynamics viewed in 3D over the oceans. Geophysical Research Letters, 48(5), e2021GL092397.