On the genesis of cold layer in the Kanto Plain accompanied by cyclones passing along south coast of Japan

  • Wataru Hirata, 2012: On the genesis of cold layer in the Kanto Plain accompanied by cyclones passing along south coast of Japan .

Abstract

Cold layers often occur in the Kanto Plain during the passage of extratropical cyclones. At this time, local fronts are formed between the advection of warm air from the sea and the cold layer. It makes difficult to predict of precipitation amount and precipitation pattern. In the cold season, snowfall occurs in Kanto plain during a passage of the cyclones. There are many factors which bring snow; cyclone-track, intensity of cyclone, temperature and so on.

In this thesis, 26 approaching cyclones are researched climatologically. In addition, numerical experiments are conducted on the examples of the lows, and reveal the relationship between cold layer and snowfall.

15 out of the 26 events show the cold layers.The case that bring rainfall throughout the Kanto (March 6, 2009), cold layer occurred thickness of about 500m. Result of the numerical experiment, cold layer is not confirmed in the experiment which removed terrain. It means that blocking inland air by the terrain is a major factor in the cold layer formation.

The case that bring snowfall throughout Kanto (Feb 3, 2008), cold layer also occurred thickness of about 500m. For this case, cold layer was also confirmed in experiments to remove the terrain.On the other hand, numerical experiment which removed diabatic heating physical processes, cold layer was reduced. Therefore, cooling effect of evaporation is a major factor in the cold layer formation.

The case that bring snowfall in the Northern part of the Kanto (Feb 20, 2009), cold layer also occurred thickness of about 500m. This case has the both characteristics of former two cases.

Keywords: Cold layer, Kanto Plain, Warm air advection, Numerical experiment