Japan comprises a group of islands between 46° and 30°N off the east coast of Asia. The total area of the country is a bit larger than that of Germany. From north to south the main islands are Hokkaido, Honshu (the largest island and sometimes called 'the mainland'), Shikoku, and Kyushu. All the islands are hilly or even mountainous, particularly Honshu, where the highest peaks such as Fujiyama rise to over 3,600 m/12,000 ft. There are numerous other peaks rising to over 2,500 m/8,200 ft, many of which are extinct or even active volcanoes. The higher mountains in Hokkaido and Honshu are snow-covered throughout the year and there are many opportunities for winter sports.
The climate of Japan around the year is much influenced by the great seasonal wind reversal of the Asian monsoon, but there are important differences between the Korea peninsula or north China and Japan. The relatively narrow Sea of Japan separates the mainland from Japan. The Japanese islands have a climate modified and moderated by the sea; winters are less cold than in the same latitude on the continent, and precipitation is much heavier. Winter precipitation is particularly heavy on the west coast of northern Honshu and in Hokkaido. Here snowfall is heavy as the cold, outblowing winter monsoon from Siberia and Manchuria is warmed and picks up moisture over the sea. In parts of this area precipitation is greater in winter than in summer. Elsewhere in Japan winter is a relatively dry season. Much of the cloud and precipitation is associated with depressions which develop where warm, humid Pacific polar air meets cold continental air along the North Pacific polar front. Winter weather is variable and changeable over the whole of Japan, but particularly so in the north and west.
In summer and early autumn much of the heavy rain is brought by typhoons, or tropical cyclones, which move north from the South China Sea or the region east of the Philippines. In some parts of central and southern Japan there is a double rainfall maximum; one in early summer, the so-called Bai-U or plum rains, and a second in late summer or early autumn, brought by typhoons.
Winters in northern Japan, particularly in Hokkaido, are severe with heavy falls of snow. At sea level the climate is much like that of Newfoundland or northern New England (see the tables for Hakodate in southern Hokkaido and Akita in northern Honshu).
In the south of Honshu and in Kyushu and Shikoku the winters are mild and almost subtropical. This is particularly so around the coasts of the Inland Sea, or Seto-nakai,the narrow stretch of water which separates these islands. Winter rainfall is light here and snow and frost very rare (see the tables for Nagasaki and Ashizuri-misaki).
In northern Japan the summers are short but quite warm and on the eastern coasts the summers are wetter than the winters. In central and southern Japan the summers are very warm but excessively hot days are rare. Because the country is dominated by moist maritime air at this time with frequent cold, the summer heat is often sultry and oppressive, particularly in Japan's large cities.
In the mountains temperatures are sufficiently reduced by altitude as to be quite pleasant in summer. Here on sunny days in spring and summer, conditions can be quite delightful. Compare the climatic table for Oiwake, inland in the hills at 1,006 m/3,300 ft, with that for Tokyo, which is on the coast of central Honshu and is representative of some of the major cities of Japan.
In most places in Japan the daily sunshine amounts are only moderate because of the humid atmosphere and abundant rain. They are lowest in Hokkaido and northern Honshu, where they average from two to three hours a day in winter to five or six hours a day in summer. Farther south there is more sunshine, with an average of six to seven hours a day around the year. Summer sunshine is often less than that in spring, which is a drier season. Spring is perhaps the most pleasant season in Japan; the weather is usually warm and sunny, but fresher and drier than in summer or autumn.
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