Due to typically very heavy rains associated with tropical cyclones, the upper ocean salinity response can be affected by the fresh water flux into the ocean. Little is known about this effect because of the lack of observations. Previous studies have shown that the sea surface temperature (SST) response resembles a cold wake, which consists of a trail of decreased temperature behind the storm. Unlike the SST observations widely available from remote sensing, the sea surface salinity (SSS) data are very limited. We have therefore conducted a modeling study of the upper ocean salinity response to tropical cyclones using the Princeton Ocean Model. When studying this response, several storm factors must be taken into account. The translation speed, intensity (maximum wind speed), and size of the storm are all relevant in determining ocean changes. Our idealized experiments consisted of a tropical cyclone moving with a constant translation speed over a horizontally uniform, resting ocean.

The results are very intriguing and potentially important. In the experiments with no rain the SSS increases (positive anomalies) everywhere due to entrainment of the saltier waters from thermocline. However, when rain is included the SSS anomalies become drastically different: the SSS is significantly reduced (negative anomalies) in front of the storm center and at the periphery, while the positive anomalies become very small. Our modeling results clearly indicate for the first time that heavy rainfall typically associated with tropical cyclone can significantly affect the salinity and thus density in the upper ocean. The latter may, in turn, affect the SST response and modify the surface heat fluxes. We hypothesize that this may affect the intensity of the tropical cyclone. Further investigation of this phenomenon with the help of a fully coupled tropical cyclone-ocean model is warranted.