Abstract
Cloud streets are often observed when a cold air mass advects over a warm sea around the Japanese Islands during the winter monsoon. Thick cloud streets often appear over the southern ocean off the Japanese Islands. Visible images obtained by geostationary meteorological satellite (GMS) were analyzed to investigate the characteristics of these cloud streets during winter (January, February, December) from 1997 to 2001. The dependence of each cloud street upon the ambient wind speed and direction were investigated using reanalysis data at the level of 850hPa.
The appearance frequency of the cloud streets differs greatly. The cloud streets in the Bungo Channel, in the lee of the east Shikoku Mountains and in the lee of the Kii Mountains are the most frequently observed. However, their frequency does not appear to depend simply on the shape of windward topography.
The frequency of cloud streets depends not only on the ambient wind direction but also on the ambient wind speed. Some cloud streets are generated more frequently under stronger ambient wind, while others are generated less frequently. For example, cloud streets are generated more frequently over the ocean east of Kyushu and over the south of Shikoku when the ambient wind is stronger. On the other hand, cloud streets appearing in the lee of the Kii Mountains and on the Kii Channel are observed less frequently when the ambient wind is stronger.
The position of the starting points of some cloud streets tends to shift depending on the ambient wind velocity. For example, the starting point of the cloud streets appearing in the lee of the eastern Shikoku Mountains shifts northeastward when the ambient wind velocity becomes greater.
