Cloud Physical Property of Sea Fog Induced by Yamase in the Sanriku Seashore

Abstract

The Pacific side of Tohoku district has been frequently suffered from cool foggy easterly (Yamase) in summer times, resulting in severe decrease of rice production. The penetration of sea fog into inland area gives important effects on solar radiation impinging on crop fields.
This study was made to make clear cloud physical characteristics of sea fogs penetrated from the sea into the Taneichi region. The observations were made during the sea fog seasons from May to August in 1990 and 1991, respectively. The fog penetrates more frequently in periods of weak or no solar radiation, such as evening, night, and morning, than in daytimes. It was also observed that the sea fog into crop field is more frequent and strong under weather conditions with the wind directions from E to S.
The size distribution of sea fogs was measured by the Poval film method at the each observation point with different distances from the Taneichi seashore. The average size of sea fogs decreases linearly with the distance from the Taneichi seashore. This reason was mainly due to water evaporation on fog droplet surface. The results were compared with average size of sea fogs estimated indirectly from Eq. (2). Although there is relatively large scatter of points, it is reasonable to say that Eq. (2) can be used to estimate average values for droplet size from the data of visivility and fog water content.