Life histories of low-level misocyclones, one of which corresponded to a tornado vortex within a winter storm in the Japan Sea coastal region on 1 December 2007, were observed from close range by X-band Doppler radar of the East Japan Railway Company. Continuous plan position indicator (PPI) observations at 30-s intervals at the low-elevation angle revealed at least four cyclonic misocyclones within the head of the comma-shaped echo of the vortical disturbance under winter monsoon conditions. The meso-b-scale vortical disturbance developed within the weak frontal zone at the leading edge of cold-air outbreaks.High-resolution observation of misocyclones revealed the detailed structures of these misocyclones and their temporal evolution. As the parent storm evolved, a low-level convergence line was observed at the edge of the easternmost misocyclone. This convergence line was considered to be important for the initiation and development of the misocyclones and the tornado through vortex stretching. The strongest misocyclone gradually intensified as its diameter contracted until landfall, and then began to dissipate soon after landfall. The temporal evolution of the misocyclones through landfall is discussed.Surface wind and pressure variations suggested a cyclonic vortex passage, which was consistent with the passage of the radar-derived misocyclone. The observed pressure drop was also consistent with that computed from the cyclostrophic equation for the modified Rankine vortex. The observed behavior of two adjacent misocyclones was primarily consistent with the rotational flow associated with the other misocyclone. The generation and development processes of the tornado and misocyclones are discussed.

In order to study changes in the regional climate in the vicinity of Japan during the summer rainy season due to global warming, preliminary experiments by a semi-cloud resolving non-hydrostatic model with a horizontal resolution of 5 km (NHM-5km) are conducted from June to October between 2002 and 2006 using 20-km horizontal grid operational regional analysis data of Japan Meteorological Agency (JMA) as the initial and boundary conditions.The total precipitation amount and appearance frequency for daily precipitation amount simulated by the NHM-5km show notable agreement with those of the surface observation data of Automated Meteorological Data Acquisition System (AMeDAS) of JMA. The temporal and spatial characteristics of maximum daily precipitation amounts (MDPs) from June to October also agree well with the observational results. The regional largest values among MDPs (R-MDPs) for 6 regions of the Japanese Islands are also estimated for the simulation results of the nearest grid points for each AMeDAS station and the AMeDAS observations. Those comparisons conclude the high performance of the NHM-5km for the reproducibility of MDPs and R-MDPs, which are highly related to extreme events.

A 5-km-mesh nonhydrostatic cloud-system-resolving regional climate model (NHM-5km) has been developed at the Meteorological Research Institute (MRI) of the Japan Meteorological Agency (JMA) by improving upon the JMA operational mesoscale model (MSM). Three major changes have been made to MSM: the Kain-Frisch convective parameterization scheme has been improved to reduce the incidence of false predictions of rainfall areas along coastlines during the warm season, a spectral nudging method has been introduced to avoid phasegap between the inner model (NHM-5km) and the outer model, and a Simple Biosphere model has been applied for sophisticated representation of land surface processes. This article presents details of the first two of these modifications.A present-day climate simulation is performed using NHM-5km by nesting within the results of a 20-kmmesh atmospheric global climate model (MRI-AGCM3.2S). Taylor's skill score is used to compare the performances of NHM-5km and MRI-AGCM3.2S in terms of reproducing the spatial pattern of precipitation-based extreme indices over the Japanese Islands. The comparison shows that NHM-5km yields a significant improvement in reproducing the present-day climatology (e.g., the maximum number of consecutive dry days and the simple daily precipitation intensity index), suggesting that NHM-5km is a reliable tool for accurately predicting future changes in extreme weather at a fine spatial resolution.

The Japan Meteorological Agency (JMA) completed its second global atmospheric reanalysis, the Japanese 55-year Reanalysis (JRA-55). However, the horizontal spatial resolution of JRA-55, TL319 (about 55 km), is insufficient for representing the hilly topography of the Japanese islands. Therefore, to reproduce extreme events caused by the hilly topography and their long-term climatological change in Japan, JMA has conducted a dynamical regional downscaling, called DSJRA-55, based on JMA's operational mesoscale model, which has a horizontal resolution of 5 km. DSJRA-55 receives its initial field and boundary conditions from the JRA-55 reanalysis. DSJRA-55 is historically the first products in the world that covers very long term for 55 years with very high resolution in 5 km. Furthermore, DSJRA-55 does not perform data assimilation; instead, initial field and boundary conditions are given at frequent intervals to the downscaled model and short-range forecasts are performed. Then, successive forecasts are connected continuously to create the DSJRA-55 product. In early evaluation results, DSJRA-55 was able to reproduce observed temperature and precipitation during 1958−2012. Although it showed a systematic temperature bias in some regions and seasons and it underestimated the frequencies of heavy-rain days and heavy-rain hours, DSJRA-55 reproduced the overall distribution of orographic precipitation well. DSJRA-55 is therefore expected to be useful for analyzing past extreme events and for statistical studies of long-term climate.(Citation: Kayaba, N

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