General features of polar lows over the Japan Sea and the Northwestern Pacific

This study of general features of occurrence frequencies, spatial distribution of locations, life-time and cloud patterns of polar lows over the Japan Sea and the neighboring Northwestern Pacific in winter of 1995/1996 based on observation and satellite satellite data showed that polar lows develop most frequently in mid-winter over the Japan Sea (35–45°N) and the Northwestern Pacific (30–50°N). They rarely form over the Eurasian Continent. Polar lows over the Northwestern Pacific are usually longlived (2–3 days). But polar lows over the Japan Sea are relatively short-lived (1–2 days), because the east-west width of the Japan Sea is relatively narrow and polar lows tend to decay after their passing over the Japan Islands. Generally speaking, polar lows over the Japan Sea are characterized by tight, spital (or comma) cloud patterns on satellite images. It was observed that polar lows over the Japan Sea have a typically spiral cloud band with clear “eye” at their mature stage. In winter, because of the effect of the warm Tsushima Current, the annual mean SST of the Japan Sea is 5–9°C higher than that of the same latitude oceans. The large sea-air temperature difference sustained over the Japan Sea provides favorable condition for polar formation. The general features of polar lows over the Japan Sea are compared with those of other areas where polar lows often occur.