Structures and Seasonal Variations of Surface Winds Blowing through the Tsushima Strait

Surface winds blowing through the Tsushima Strait are statistically investigated using satellite wind measurements and atmospheric reanalysis data. This study first presents structures and seasonal variations of the northeasterly and southwesterly along-strait winds by imposing newly proposed conditions for defining them. Although the speeds of the northeasterly along-strait winds are generally high within the entire strait, the maximum wind speeds are located downwind of the two channels. The southwesterly along-strait winds start to accelerate at the west exit within the strait. Weak-wind regions are formed in the lee of Tsushima Island in both cases. The occurrence frequencies of the northeasterly and southwesterly along-strait winds are high (low) in the warm (cool) season. The northeasterly along-strait winds are more often observed than the southwesterly along-strait winds. The frequency of the northeasterly along-strait wind is extraordinarily high in September, but the averaged wind speed is comparable to those in the other months. Most of the southwesterly along-strait wind cases fall within low-Froude-number regimes, suggesting the significant effects of Tsushima Island on the wind in the strait. Synoptic situations favorable for the along-strait winds are investigated. Correlations between the along-strait wind component and sea level pressure (SLP) indicate that the along-strait winds are induced by SLP perturbations primarily over the Japan Sea and secondarily on the south of the strait. In addition, cluster analysis of the SLP fields shows four representative SLP fields favorable for the along-strait winds and their monthly occurrence frequencies.