An Overview of the Field Experiment "Winter Mesoscale Convective Systems (MCSs) over the Japan Sea in 2001", and Comparisons of the Cold-air Outbreak Case (14 January) between Analysis and a Non-hydrostatic Cloud-resolving Model

Features of the polar-air outbreak and the energy balance in the transformed air-mass over the Japan Sea, during a period of strong polar-air outbreak in 1977, are studied by using upper observation data on a research vessel (Keifu-maru) and two coastal stations (Akita and Wajima). The analysis is made over an area of 3.8 Â (100 km) 2 using vertically dense (25-hPa interval) data interpolated from data at standard pressure levels and significant levels.The mixed layer capped by the stable layer is formed in the transformed air-mass. The large apparent heat and moisture sources are evaluated within the mixed layer. The apparent heat and moisture sources decrease abruptly at the top of the mixed layer. The large kinetic energy dissipation due to the sharing stress in the lower layer almost offsets the large generation of the kinetic energy due to the work down by the pressure gradient force.The present analysis indicates that the use of vertically dense data is important to resolve the multilayer structure of the transformed air-mass, and to obtain accurate vertical distribution of apparent energy sources, in the transformed airmass.The results of the present analysis are consistent, in general, with numerical simulations on the airmass transformation over the Japan Sea. However, the apparent heat and moisture sources in the lower portion of the boundary layer in this study are considerably small as compared with results of the simulation studies. This discrepancy will be due to the use of data at the land stations on the outflow side of the budget analysis area.

Section: Comparison With the Results Of Numerical Simulation Over The mentioning

confidence: 99%

“…Detailed observational studies are also needed for the verification of the vertical distribution of the heat and moisture sources obtained in numerical experiments on the polar-air outbreak over the Japan Sea (e.g., Yamagishi 1980b; Yoshizaki et al 2004;Ninomiya et al 2006). This is the basic motivation of this article.…”

Section: Introductionmentioning

confidence: 99%

Features of the Polar Air Outbreak and the Energy Balance in the Transformed Air-Mass Observed over the Japan Sea

Ninomiya

2006

“…Several observational and numerical studies (e.g., Matsumoto et al 1967;Ninomiya 1989;Ninomiya and Hoshino 1990;Nagata 1993;Ninomiya et al 1996Ninomiya et al , 2004Yoshizaki et al 2004) showed that mesoscale circulation systems were generated in the polar-air streams over the Japan Sea, under the influence of the synoptic-scale disturbances. Such phenomena are not studied in this report, because of the insufficient time and horizontal resolution of the observations.…”

Section: Discussionmentioning

confidence: 99%

“…Detailed studies about variations of the polar-air outbreak over the Japan Sea are also needed for the verification of simulations by regional models (e.g., Yamagishi 1980b;Nagata 1993;Yoshizaki et al 2004) and simulations by the atmospheric general circulation models (e.g., Ninomiya et al 2006) of the polar-air outbreak and the airmass transformation. This is the basic motivation of this article.…”

Section: Introductionmentioning

confidence: 99%

Synoptic-Scale Variations in the Polar Air-Mass Transformed over the Japan Sea

Ninomiya

2007

The present report studies synoptic-scale variations of the polar air-mass transformed over the Japan Sea, during the ''East Japan Sea Observation'' in the winters of 1976 and 1977. Rawinsonde observation data at a research vessel are used, in addition to data at operational upper observation stations and the objective analysis data.The multi-layer structure of the transformed air-mass, including the unstable lowest layer and the mixed layer capped by the stable layer, is formed in the transformed airmass over the Japan Sea. The mixed layer, which includes the sub-cloud layer and the cloud layer, is characterized by nearly vertically-uniform equivalent potential temperature. The height of the mixed layer top is 1000-1500 m, on the average, over the Japan Sea. The height increases toward the south, and reaches 2000-2500 m over the coastal area of Japan.The height of the mixed layer top, and the apparent total heat source in the transformed air-mass, vary widely in association with the synoptic-scale changes of polar-air outbreak. The height of the mixed layer top tends to increase in association with the increase of the apparent total heat source in the mixed layer, and the decrease of the vertical stability in the lower-middle troposphere. The snowfall depth over the coastal area of Japan tends to increase in association with the increase of the apparent total heat source over the Japan Sea. The important synoptic conditions for the occurrence of the heavy snowfalls are the intense polar-air outbreak, and/or the passage of the cold vortex or the deep cold trough over the Japan Sea.

“…2. Regional objective analysis (RANAL) with a horizontal resolution of 20 km (30 N and 60 N) and 21 levels (surface and 1000, 950,925,900,850,800,700,600,500,400,300,250,200,150,100,70,50,30,20,and 10 hPa) (Yoshizaki et al 2001;Yoshizaki et al 2004). 6.…”

Section: Datamentioning

confidence: 99%

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

Ohigashi

Tsuboki

2007

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.