Probing the Oceanic Precipitable Water Vapor Evolution Characteristics During the 2020 Tropical Cyclone Maysak Using the GNSS Radio Occultation and Satellite Microwave Radiometry Data

A tropical cyclone (TC) is a rapidly rotating storm system with complex weather phenomena, such as powerful winds, heavy rainstorms, and damaging thunderstorms. It brings enormous effects on human lives and properties over the coastal area. Moreover, the intensity of TCs is showing an increasing trend with global warming. Therefore, monitoring tropical cyclones, including the atmospheric evolution characteristics, is scientifically and practically meaningful. The Global Navigation Satellite System (GNSS) radio occultation (RO) is a powerful tool to study the atmosphere evolution during the TC period. Much more RO sounding data can be utilized than before with the completion of the new generation six-satellite Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC-2) in 2019. In this study, we analyzed the precipitable water vapor (PWV) in the upper atmosphere between 1.6 km and 40.0 km. We classified the region around the TC eye center into five bands according to the distance to the TC eye center: band 1 for the region with a radius of 0–200 km from TC eye center; band 2 for 200–400 km; band 3 for 400–600 km; band 4 for 600–800 km; and band 5 for 800–1000 km. The PWV within the band 1 showed an evident increase from August 28 with a value of ~9.5 kg/m2 to September 1, 2020 with a value of ~43.6 kg/m2, when the TC became increasingly intensified. While the PWV in bands 2 to 5 showed a decreasing trend during this period. The mean PWV gradient was −2.47 \({\text{kg}}\; \cdot \;{\text{m}}^{{2}} \cdot \left( {100\;{\text{km}}} \right)^{ - 1}\) from band 1 to band 2, −.27 \({\text{kg}}\; \cdot \;{\text{m}}^{{2}} \cdot \left( {100\;{\text{km}}} \right)^{ - 1}\) from band 2 to band 3, −1.17 \({\text{kg}} \cdot {\text{m}}^{2} \cdot \left( {100\;{\text{km}}} \right)^{ - 1}\) from band 3 to band 4, and −1.16 \({\text{kg}}\; \cdot \;{\text{m}}^{{2}} \cdot \left( {100\;{\text{km}}} \right)^{ - 1}\) from band 4 to band 5. We also analyzed PWV data from altimetry satellites and found that symmetric spatial gradient of PWV can be apparently observed. These findings can help us further understand the atmospheric evolution characteristics over ocean during the TC period, thus improve the forecast reliability and accuracy.