Shift and Intensification Processes of the Japan-Sea Polar-Airmass Convergence Zone Associated with the Passage of a Mid-Tropospheric Cold Core

Abstract

A mid-tropospheric mesoscale cold core passed over the Sea of Japan on 14 January 2001 during a cold air outbreak. In association with the passage of the cold core, intensification and northward and southward shifts of the Japan-Sea Polar-Airmass Convergence Zone (JPCZ) were observed. In order to clarify a response of the JPCZ to a change of upper-level environment, the shift and intensification processes associated with the passage of the cold core were studied mainly using a non-hydrostatic cloudresolving model.When the cold core approached the JPCZ, the JPCZ was intensified and shifted northward. The intensification of the JPCZ is caused by a change in a decrease of convective stability associated with the passage of the cold core. As a ridge of potential temperature is formed along the intensified updraft of the JPCZ, a leeward region of the JPCZ is locally heated by the horizontal advection in a westerly wind, which is predominant in the upper levels. This hydrostatically reduces the low-level pressure in the north of the JPCZ, and increases the wind speed blowing into the JPCZ from the south. The divergence equation indicates that the abrupt change in the pressure as well as the adjusted wind fields cause the northward shift of the JPCZ.In contrast, the JPCZ decayed and shifted southward when the cold core moved away from the JPCZ. The pressure decrease, which occurred in the north of the JPCZ, is not maintained during the southward shift, and the pressure gradient across the JPCZ becomes relatively uniform. This results in the decrease of the wind speed blowing into the JPCZ from the south, and the JPCZ shifted southward due to the advection.

Cloud-resolving simulation of heavy snowfalls in Japan for late December 2005: application of ocean data assimilation to a snow disaster

“…This model has been developed at the Hydrospheric Atmospheric Research Center, Nagoya University, Japan (Tsuboki and Sakakibara, 2001;2002), and is used for cold-air outbreaks and snowstorms (Liu et al, 2004;Maesaka et al, 2006;Ohigashi and Tsuboki, 2007).…”

The Structure and Formation Mechanism of Transversal Cloud Bands Associated with the Japan-Sea Polar-Airmass Convergence Zone

“…4f ). The movement and intensification processes of the present JPCZ cloud band have been examined by Ohigashi and Tsuboki (2007).…”

“…Nagata (1992) numerically investigated the movement and development of the JPCZ cloud band during the passage of a short-wave trough accompanied by a remarkable cold low. Ohigashi and Tsuboki (2007) clarified the dynamics of the movement and intensification of the JPCZ associated with the upper cold core by using a cloud-resolving model.…”

An Intensification Process of a Winter Broad Cloud Band on a Flank of the Mountain Region along the Japan-Sea Coast

“…Therefore, most broad cloud bands form in specific locations. Over the Sea of Japan, the broadest cloud bands form along a convergence zone in the western part of the sea (Okabayashi 1969;Yagi et al 1986;Nagata et al 1986;Nagata 1987Nagata , 1991Nagata , 1992Ohigashi and Tsuboki 2007;Eito et al 2010;Ohigashi et al 2012). The convergence zone generating the broadest cloud bands is referred to as the Japan-Sea Polar-Airmass Convergence Zone (JPCZ) (Asai 1988).…”

“…Nagata (1992) and Ohigashi and Tsuboki (2007) showed that the JPCZ cloud bands intensified under upper-level mesoscale cold lows. Takeda et al (1982) showed the intensification of isolated snow clouds near a coast.…”