Graphical Abstract

JMSJ, 2014, Vol. 92, No. 2 (April)

Arakane, S., M. Satoh, and W. Yanase, 2014: Excitation of deep convection to the north of tropical storm Bebinca (2006). J. Meteor. Soc. Japan, 92, 141–161.
http://dx.doi.org/10.2151/jmsj.2014-201 Graphical Abstract

This study investigates the excitation of deep convection concerning the case of unusual extratropical transition (ET) of Tropical storm Bebinca (2006). The deep convection was formed to the north of Bebinca during ET of Bebinca first, and the convection strengthened and became a new cyclone. Thus, the cyclone center defined as the minimum sea level pressure appeared to be shifted from Bebinca to the new cyclone drastically.
The analyses elucidate mechanisms for excitation of deep convection, including a high convective available potential energy environment due to moisture convergence at lower levels, potential vorticity generation by a diabatic Rossby vortex mechanism (Fig. 1), and dynamical forcing formation of upward motion induced by upper levels.
Numerical simulations, including sensitivity experiments in which the vortex structure of Bebinca was changed, suggested that the Bebinca’s unusual vortex structure, which is the weak pressure gradient near the center, was fundamental for the excitation of the deep convection (Fig. 2).

Tsuguti, H., and T. Kato, 2014: Contributing factors of the heavy rainfall event at Amami-Oshima Island, Japan, on 20 October 2010. J. Meteor. Soc. Japan, 92, 163–183.
http://dx.doi.org/10.2151/jmsj.2014-202 Graphical Abstract

The low-level humid air, supplied to Amami-Oshima Island during the heavy rainfall event by strong east–northeasterly winds, originated more than 500 km to the east–northeast as low-level dry air on the northern side of a stationary front (Fig. 1).
The dry air was transformed into humid air on the way to the island by receiving large latent heat flux from the sea surface (air-parcel transformation) (Fig. 2). Warm sea surface temperatures around Amami-Oshima Island, about 2°C higher than the annual mean, contributed to this air-parcel transformation.
At Amami-Oshima Island, the collision of the humid air with a cold pool produced by pre-existed precipitation systems contributed significantly to the formation and maintenance of the precipitation systems causing the heavy rainfall event, supplemented by topographic effects of the island.