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

[摘要] A field experiment of snowfall systems, WMO-01, was conducted over the Japan Sea in the winter of 2001. During the WMO-01 period, cold-air outbreaks and passages of synoptic-scale cyclones were observed several times. By utilizing global analysis (GANAL) data, with a horizontal resolution of 1.25 degrees, the apparent heat source Q1, apparent moisture sink Q2, differential advection of moist static energy Dh, potential vorticity PV, sensible heat flux S and latent heat flux LvE were estimated to investigate characteristic features of weather over the Japan Sea. It is shown that the cold-air outbreak during 12 to 17 January was remarkable, where Q1, upper-level PV;S;LvE, and -Dh were the largest during the WMO-01 period. The cold-air was accompanied with the upper-level high PV anomaly, and the air-mass transformation took place strongly over the Japan Sea. The values of S + LvE reached approximately 600 Wm-2, and -Dh was large, indicating that the convective activity was strong. The heat and moisture budgets were compared with previous studies for the Japan Sea in winter. Generally speaking, it is shown that the budgets were similar to previous studies. Next, the 14 January case was examined in detail as a typical example of the cold-air outbreak. The convergence band (= JPCZ) was found extending southeastward from the east of joint of the Korean Peninsula to the San-in and Hokuriku areas. The L modes of convective clouds (parallel to the prevailing northwesterly wind) were seen on both sides of the JPCZ, and the T modes (normal to the NWly wind) were found on the northeastern side. A synoptic-scale cold trough was seen in eastern Asia at 500 hPa, and the polar jet was located on the southern side of the Japan Sea. Additional 1000 km-size PV anomalies slowly propagated eastward repeatedly along the northern side of the jet. This case was studied by using a non-hydrostatic cloud-resolving model with 5 km horizontal resolution (5 km-NHM). Characteristic features of the JPCZ were well reproduced. The 5 km-NHM outputs were also used to examine the heat and moisture budgets. Q*1 and Q*2 are defined similarly to Q1 and Q2, respectively, but the ice phase is included. Large differences from the GANAL analysis were found near the surface and above the height of 4 km. Near the surface, the evaporation of snow or rain may occur for the 5 km-NHM, while it may not for the analyzed Q1 and Q2 due to the vertically coarse data. The sensitivity experiments of cases with or without ice phase were also examined. It is found that the general features are similar in both cases, indicating that the ice phase is not very important for the diabatic process of clouds in this study.

[学科分类] 大气科学