Inner-Core Sea Surface Cooling Induced by a Tropical Cyclone

As a key to modulate the negative feedback to tropical cyclone (TC) intensity, the TC-induced inner-core sea surface cooling (SSCIC) is poorly understood. Using a linear two-layer theory and OGCM experiments, this study illustrates that the pattern of the inner-core mixing can be well interpreted by the wind-driven currents in the mixed layer (ML). This interpretation is based on 1) the mixing is triggered by the ML bulk shear instability and 2) the lag of upwelling makes the inner-core bulk shear equivalent to the inner-core wind-driven currents. Overall, the patterns of the inner-core bulk shear and mixing resemble the crescent body of a sickle. As an accumulative result of mixing, the SSCIC is clearly weaker than the maximum cold wake because of the weaker mixing ahead of the inner core and nearly zero mixing in a part of the inner core. The SSCIC induced by a rectilinear-track TC is mainly dominated by the inner-core mixing. Only for a slow-moving case, upwelling and horizontal advection can make minor contributions to the SSCIC by incorporating them with mixing. The SSCIC strength is inversely proportional to the moving speed, suggesting the mixing time rather than the mixing strength dominates the SSCIC. Despite inability in treating the mixing strength, this study elucidates the fundamental dynamical mechanisms of SSCIC, especially emphasizing the different roles of mixing, upwelling, and horizontal advection for fast- and slow-moving TCs, and thus provides a good start point to understand SSCIC.