Unusually High Fog Frequency at Kushiro, Japan, during Early Autumn in 2012

Abstract

Fog frequency at Kushiro, Hokkaido Island, Japan, during midsummer depends strongly on the advection of sea fog from the ocean onto the land, which itself depends on the behavior of the North Pacific High (NPH). This study investigates the relationship between unusually high fog frequency at Kushiro during early autumn in 2012 and the NPH extension. The total fog frequency during mid-August through mid-September in 2012 was the highest over the past 32 years. A northwestward expansion of the NPH caused anomalous southerly winds, that transported warm moist air onto the southeast coast of Hokkaido Island. This warm moist southerly flow favors the onshore advection of sea fog, as it does during midsummer. During early autumn in 2012, the warm advection also results in a large temperature difference between atmosphere and sea over the cold Oyashio current, which suggests that an increase in sea fog generation is another important factor for the high fog frequency at Kushiro.