Sensitivity experiments for tropical cyclone intensity to the sea surface temperature distribution pattern around the Kuroshio currents

The ocean affects tropical cyclones (TCs) through the sea surface and greatly controls intensity of TCs (e.g., central pressure, rain rate, wind speed) by the sea surface temperature (SST). To investigate sensitivity of TC intensity to the SST distribution pattern, numerical experiments employed idealized SST distributions were performed around the Kuroshio currents in the western North Pacific, which had warm SST distribution with a quite large meridional gradient and aligned vortex patterns off Japan Honshu islands. Compared to the control experiment with observed SST, suppression of the TC central pressure was appeared in the experiments with meridionally smoothed SST in removing filament-like vortex patterns, resulting in showing the effect by zonally localized meridinal gradient of the SST and by zonal SST variation originated by vortexes. More suppression of the TC central pressure was appeared in the experiments with zonally-averaged in addition to the meridionally smoothed, which suggested that the magnitude of the meridional gradient of the SST and zonal asymmetry along the TC track of the SST controlled the TC intensity around the Kuroshio currents.

On the other hand, the ocean also varies by the air-sea interaction through mixing/upwelling in the upper layer in the ocean produced by TCs passing on the ocean surface. To investigate the intensity change of TCs with air-sea interaction, numerical experiments utilizing with atmosphere-ocean coupled model were performed; slab ocean model was for one-dimensional coupled experiments and CReSS-NHOES was for three-dimensional coupled experiments. In the comparison of the results with coupled experiments, remarkable differences of intensities resulting from air-sea interaction were represented as suppression of the TCs intensity. During the mature period of the TCs, the maximum deepening of the central minimum pressure of TCs was suppressed in the coupled experiments, especially in the three-dimensional coupled one. The three-dimensional ocean coupled experiment was represented ocean circulation including upwelling enhanced by the moving TCs, so one-dimensional vertical mixing heat transfer only in the ocean upper layer is not enough to represent the intensity of TCs. Difference of intensity suppression is remarkable in the TCs which moved slowly around the Kuroshio currents.