The Sea Breeze on the Pacific Side of the Shimokita Peninsula

Abstract

The Yamase wind is a cold north-easterly wind that causes summertime low temperatures in North Honshu. Because of its low elevation, the Yamase wind is affected by the mountain ranges. According to Ojika (1974), Kudo (1981) and Bokura (1990), small scale topographic features, such as the Shimokita hills (500m above sea level), are also affect the Yamase wind. However, local climate data did not show the topographic effect at the Shimokita Hills in 1987 (Kanno et al., 1989). Because the sea breeze on the Pacific side of North Honshu also causes low temperatures (Asai, 1952; Shitara, 1952, 1964), the east-west temperature contrast between the small-scale mountains may be result from not only the Yamase wind but also the sea breeze. However, the sea breeze on the Pacific side of North Honshu has not been examined since Shitara's studies in 1952 and 1964, and its vertical structure is still unknown. We here report on the results of our investigation of the sea breeze.A captive balloon observation was done on July 25 in 1989 at Tomari (Fig. 1). The Ogasawara anticyclone strongly spread (Fig. 2) and the Yamase wind did not blow on the observation day (Fig. 3). A distinct sea breeze (about 20°C) was found under about 200m elevation in the afternoon (Fig. 4). The vertical profiles of wind direction, wind speed, mixing ratio and equivalent potential temperature show that a return flow is formed in the sea breeze and the water vapor under about 100m is relatively small (Fig. 5). The temperature data of AMeDAS stations indicate that this sea breeze is restricted in the Pacific side of the Shimokita Peninsula (Fig. 6).The sea breeze observed in this work is characterized by lower elevation and higher temperature than the Yamase wind. Since the stratus and the fog were not found in the sea breeze, the sea breeze may form only by cooling from the sea surface. This process is different from the formation of the Yamase wind which results from the heating of air from the sea surface and cooling by the long wave radiation at the upper part of the stratus. Further analyses about the frequency and distribution of the sea breeze will be made in the future.