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Iizuka S.,Japan National Research Institute for Earth Science and Disaster Prevention | Shiota M.,Japan Meteorological Agency | Kawamura R.,Kyushu University | Hatsushika H.,Toyama Prefectural Environmental Science Research Center
Scientific Online Letters on the Atmosphere | Year: 2013

The possible impact of the winter monsoon intensity and sea surface temperature (SST) gradient on the activity of explosively developing extratropical cyclones around Japan is investigated using the Weather Research Forecasting model. Two independent long-term integrations over 18 winters from 1993/94 to 2010/2011 are conducted using prescribed observed SST data (OS run) and spatially smoothed data (SS run). The OS run is successful in reproducing the spatial distributions of the explosive cyclone activity in the vicinity of Japan under both strong and weak winter monsoon conditions. Under strong monsoon conditions, the Kuroshio, the Kuroshio Extension, and the Japan Sea subpolar fronts give rise to enhanced near-surface baroclinicity through the increase in heat and moisture fluxes from the ocean surface, resulting in frequent occurrence of the explosive cyclone activity along those fronts. © 2013, the Meteorological Society of Japan. Source


Kawase H.,Japan Agency for Marine - Earth Science and Technology | Yoshikane T.,Japan Agency for Marine - Earth Science and Technology | Hara M.,Japan Agency for Marine - Earth Science and Technology | Fujita M.,Japan Agency for Marine - Earth Science and Technology | And 3 more authors.
Scientific Online Letters on the Atmosphere | Year: 2012

We focus on the dramatic decrease in the snow cover on the Japan Sea side of Central Japan in the late 20th century. Using a regional climate model, a control experiment (CTL) was conducted, and it accurately simulated the dramatic decrease in maximum snow depth (SNDmax) between the 1980s and the 1990s. We then conducted a pseudo climate simulation (PCS) in the 1990s, which assumes the mean atmospheric fields in the 1990s and the perturbation from the mean atmospheric fields in the 1980s. The PCS method is expected to evaluate only the impacts of changes in the mean atmospheric fields on the snow cover changes. The PCS simulates the decreases in SNDmax over the coastal area, which are comparable to the changes simulated by the CTL. On the other hand, changes in SNDmax are negligible in the PCS over the mountainous area, where the slight increases in SNDmax are simulated by the CTL. Therefore, the changes in the mean atmospheric fields, especially, the mean temperature rise, are main factors of the snow cover decrease over the coastal area, while changes in both the mean atmospheric fields and the perturbation contribute to the snow cover changes over the mountainous area. © 2012, the Meteorological Society of Japan. Source


Kawase H.,Japan Agency for Marine - Earth Science and Technology | Hara M.,Japan Agency for Marine - Earth Science and Technology | Yoshikane T.,Japan Agency for Marine - Earth Science and Technology | Ishizaki N.N.,Japan Agency for Marine - Earth Science and Technology | And 3 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013

The Sea of Japan side of Central Japan is one of the heaviest snowfall areas in the world. We investigate near-future snow cover changes on the Sea of Japan side using a regional climate model. We perform the pseudo global warming (PGW) downscaling based on the five global climate models (GCMs). The changes in snow cover strongly depend on the elevation; decrease in the ratios of snow cover is larger in the lower elevations. The decrease ratios of the maximum accumulated snowfall in the short term, such as 1 day, are smaller than those in the long term, such as 1 week. We conduct the PGW experiments focusing on specific periods when a 2 K warming at 850 hPa is projected by the individual GCMs (PGW-2K85). The PGW-2K85 experiments show different changes in precipitation, resulting in snow cover changes in spite of similar warming conditions. Simplified sensitivity experiments that assume homogenous warming of the atmosphere (2 K) and the sea surface show that the altitude dependency of snow cover changes is similar to that in the PGW-2K85 experiments, while the uncertainty of changes in the sea surface temperature influences the snow cover changes both in the lower and higher elevations. The decrease in snowfall is, however, underestimated in the simplified sensitivity experiments as compared with the PGW experiments. Most GCMs project an increase in dry static stability and some GCMs project an anticyclonic anomaly over Central Japan, indicating the inhibition of precipitation, including snowfall, in the PGW experiments. Key Points Dynamical downscaling of snow cover changes using a regional climate model Snow cover changes around the complex terrain on the Sea of Japan side Impact of sea surface temperature and atmospheric circulation changes on snow ©2013. American Geophysical Union. All Rights Reserved. Source


Yamashita Y.,University of Toyama | Kawamura R.,University of Toyama | Iizuka S.,Japan National Research Institute for Earth Science and Disaster Prevention | Hatsushika H.,Toyama Prefectural Environmental Science Research Center
Journal of the Meteorological Society of Japan | Year: 2012

The activity of explosively developing extratropical cyclones in the vicinity of Japan in intimate association with the occurrence of heavy snowfall on the Japan Sea side of central Japan is examined using Japanese long-term reanalysis projected data (JRA-25), with additional data from the Japan Meteorological Agency climate data assimilation system (JCDAS). On a monthly basis, the explosive extratropical cyclone tracks tend to concentrate around the Kuroshio Current off the Pacific coast of Japan and the Japan Sea at the heavy snowfall phase, whereas the tracks disperse over the broader areas in the light snowfall phase. The heavy and light snowfall phases correspond well to the strong and weak phases of the East Asian winter monsoon circulation respectively, and the monsoon variability influences the local monthly snowfall on the Japan Sea side of central Japan through change in the explosive cyclone activity. On a daily basis, stationary Rossby wave packets propagating eastward along the northern Eurasian and South Asian waveguides, i.e., subpolar and subtropical teleconnection types, contribute to the occurrence of extraordinarily heavy snowfall events through the development of explosive cyclones. The subpolar teleconnection type facilitates not only the intensification and southward migration of a cold continental high in East Asia, but also the rapid growth of an explosive cyclone around Japan by inducing the equatorward advection of higher potential vorticity from high latitudes. Both developments lead to the reinforcement of an east-west gradient in sea level pressure (SLP) across Japan, thereby providing a favorable condition for the heavy snowfall events. For the subtropical teleconnection type, the explosive cyclone system is primarily responsible for the occurrence of extremely heavy snowfall events through enhanced zonal SLP gradient. It is also found that the explosive cyclone activity differs in terms of geographical location and track between the subpolar and subtropical teleconnection types. © 2012, Meteorological Society of Japan. Source


Shimizu A.,Japan National Institute of Environmental Studies | Sugimoto N.,Japan National Institute of Environmental Studies | Matsui I.,Japan National Institute of Environmental Studies | Mori I.,Japan National Institute of Environmental Studies | And 2 more authors.
Scientific Online Letters on the Atmosphere | Year: 2011

Dust extinction coefficients near the ground surface, based on National Institute for Environmental Studies lidar network measurements, were directly compared with mass densities measured simultaneously by filter sampling during several heavy dust events in Japan. The ratio between them varied from 0.5 to 2 g m -1, and depended more on the observatory, than on the dust event being observed. This variation could not be accounted for by the change in particle size distribution during long-distance transport from the source region to Japan, but internal mixing of dust with spherical particles might explain the observed results. © 2011, the Meteorological Society of Japan. Source

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