Sea of Japan - Climate

Climate

The sea climate is characterized by warm waters and monsoons. This combination results in strong evaporation, which is especially noticeable between October and March when the strong (12–15 m/s or higher) northwestern monsoon wind brings cold and dry continental air. The evaporation is blown further south causing snowfall in the mountainous western coasts of Japan. This winter monsoon brings typhoons and storms with the waves reaching 8–10 meters which erode the western coasts of Japan. Tsunami waves were also recorded in the sea. In addition, the monsoon enhances the surface water convection, down to the depths of 30 meters. The coldest months are January and February with the average air temperature of −20 °C in the north and 5 °C in the south. The northern one-quarter of the sea, particularly the Siberian coast and the Strait of Tartary, freezes for about 4–5 months. The timing and extent of freezing vary from year to year, so ice may start forming in the bays as early as in October and its remains may be seen even in June. Ice cover is continuous only in the bays and forms floating patches in the open sea. Ice melting in spring results in cold currents in the northern areas.

In summer the wind weakens to 2–7 m/s and reverses its direction, blowing warm and humid air from the North Pacific onto the Asian mainland. The warmest month is August with the average air temperature of 15 °C in the north and 25 °C in the south. Annual precipitation increases from 310–500 mm in the north-west to 1,500–2,000 mm in the south-east.

A peculiar turbulent cloud pattern, named Von Karman vortices, is sometimes observed over the Sea of Japan. It requires a stable field of low clouds driven by the wind over a small (isolated) and tall obstacle, and usually forms over small mountainous islands. The Sea of Japan meets these conditions as it has frequent winds and cloudy skies, as well as compact, tall islands such as Rishiri (1,721 m), Ulleungdo (984 m) and Ōshima (732 m).