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Covering about 70% of the Earth's surface, the oceans are a fundamental component of the climatic and seasonal variations in the weather. In East Asia, interactions between the rapidly mixing atmosphere and the slowly changing oceans are largely responsible for the monsoon season, particularly as they affect Korea, China and Japan. In order to better understand these patterns and to better prepare for their outcome, joint collaborative projects among these countries' top meteorologists have been launched.
In its geographical features, Korea is a transitional zone between the continental landmass of northeastern Asia and the island arc rimming the western Pacific Ocean. The western coast, which is open to continental Asia, is vulnerable to the influence of the winter monsoon. The eastern coast, on the other hand, is sheltered from the winter monsoon by the T'aebaeksan range, the backbone mountain of the Korean Peninsula. Although Korea has general characteristics of a temperate monsoonal climate, there are geographic diversities, particularly during the cold winter season.
The climate of Korea is characterized by four distinct seasons: spring, summer, autumn and winter. The contrast between winter and summer is striking. Winter is bitterly cold and is influenced primarily by the Siberian air mass. Summer is hot and humid due to the maritime pacific high. The transitional seasons, spring and autumn are sunny and generally dry. Temperatures of all season are somewhat lower than those at the corresponding latitudes in other continents, such as North America or Western Europe. The temperatures in Seoul, which is in the latitude of Richmond, VA, are closer to those in New York which is located 500 kilometers (300 miles) further north from the latitude of Seoul. The variation of annual mean temperature ranges from 10 degrees C to 16 degrees C except for the mountainous areas. August is the hottest month with with the mean temperature ranging from 20 degrees C to 26 degrees C. January is the coldest month with the mean temperature ranging from -5 degrees C to 5 degrees C. Annual precipitation is about 1,500 mm in the central region. More than a half of the total rainfall amount is concentrated in summer, while precipitation of winter is less than 10% of the total precipitation.
The prevailing winds are southeasterly in summer, and northwesterly in winter. The winds are stronger in winter, from December to February, than those of any other season. The land-sea breeze becomes dominant with weakened monsoon wind in the transitional months, September and October.
The relative humidity is the highest in July with 80-90% nationwide, and is the lowest in January and April with 30-50%. It has a moderate value of about 70% in September and October. The monsoon front approaches the Korean Peninsula from the south in late June, migrating gradually to the north. Significant rainfall occurs when a stationary front lies over the Korean Peninsula.
The rainy season over Korea, the so-called changma season, continues for a month from late June until late July. A short period of rainfall comes in early September when the monsoon front retreats back from the north. This rain occurs over a period of 30-40 days in June through July at all points of South Korea, with only some lag in time at different stations, and accounts for more than 50% of annual precipitation at most stations.
Annually, about 28 typhoons occur in the western Pacific. Generally speaking, only two or three among them approach the Korean Peninsula from June through September.
Precipitation distribution on the Korean Peninsula is mainly affected by orography. The southern coastal and its adjacent mountain regions have the largest amount of annual precipitation which is over 1,500 mm (60 inches). The sheltered upper Amnokkang (Yalu) river basin in the northern region, on the other hand, experiences less than 600 mm (24 inches). Since most of the precipitation is concentrated in the crop growing areas in the south, the water supply for agriculture is normally well met. Even though the annual mean precipitation is more than 1,200 mm (48 inches), however, Korea often experiences drought due to the large fluctuation and variation of precipitation, making the management of water resources difficult.
Information provided by the Korean Embassy