Program

Tropical cyclone is an important component of Earth’s climate. It intensifies ocean mixing and deepens surface mixed layer. In so doing, it creates a cold anomaly at the surface and a warm anomaly in the subsurface, which can be considered as a downward pump of warm water (heat pump). This effect can change ocean heat uptake, poleward heat transport, and global air-sea temperatures, which is even considered as the cause of permanent El Niño in Pliocene epoch.
        Typhoon Kalmaegi passed over an array of buoys and moorings in the northern South China Sea in September 2014, leaving a rare set of observations on typhoon-induced dynamical and thermohaline responses in the upper ocean. The dynamical response was characterized by strong near-inertial currents with opposite phases in the surface mixed layer and in the thermocline, indicating the dominance of the response by the excitation of the first baroclinic mode. The thermohaline response showed considerable changes in the mean fields in addition to a near-inertial oscillation. In particular, temperature and salinity anomalies generally exhibited a three-layer vertical structure, with the surface layer becoming cooler and saltier, the subsurface layer warmer and fresher, and the lower layer cooler and saltier again. The response in the surface and subsurface layers was much stronger to the right of the typhoon track, while that in the lower layer was stronger along the track and to the left. These features of the upper ocean response were grossly reproduced by a three-dimensional numerical model. A model-based heat budget analysis suggests that vertical mixing (heat pump) was mainly responsible for the surface cooling and subsurface warming, while upwelling (cold suction) was the cause of cooling from below. Both observations and model results indicate that the whole upper ocean experienced an overall cooling in the wake of typhoon Kalmaegi. This work has just be accepted by JGR-ocean on August, 2016.
        In order to further study the general relationship between the tropical cyclones’ intensity and vertical ocean temperature structure, a one-dimensional model is formed to see the relative importance of heat pump and cold suction by changing the tropical cyclones’ wind structure, vertical mixing condition and initial stratification. The result suggests that commonly invoked heat pump theory is an oversimplification for the total effect of TCs on the ocean, and further research is needed on the tropical cyclone’s effect on meridional ocean heat transport and the whole climate or biogeochemical cycling.