NORTH PACIFIC ISLANDS ARCS
Ryukyu Islands
http://pacificinfo.ru/climate/arcvad/3/ (in Russian)
The Ryukyu (Nansei) range separates the East China Sea from the open part of the Pacific Ocean-the basin of the Philippine Sea. The Ryukyu archipelago is a typical twin island arch with a volcano belt from the internal (continental) side including several active volcanoes and an external chain of nonvolcanic islands. The archipelago is elongated in the form of an arch from the northeast to the southwest over a distance of approximately 1200 km between the Kyusyu and Taiwan islands. The archipelago consists of six groups of islands (Osumi, Tokara, Amami, Okinawa, Miyako, and Yakima; the two latter groups are often united under the Sakisima name). The archipelago includes 98 islands (in the Japanese literature, the name Ryukyu is commonly related only to the middle and southwestern parts of the island arch consisting of 55 islands). The main deepest and widest straits are the southern strait of the archipelago near the eastern coast of Taiwan Island (East Taiwan Strait) with a maximal depth of approximately 1900 m and a width of 100 miles, the central strait south of the Okinawa Islands (Okinawa Strait) with a depth greater than 1000 m and a width about 120 miles, and the northern strait near the Tokara archipelago (Tokara Strait) with a depth down to 900 m and a width of approximately 100 miles.
Similar to the Far East seas, the East China Sea located at the boundary between the southeastern periphery of Asia and the Pacific Ocean lies in the zone of a monsoon climate. The annual precipitation amount ranges here from about 1146 mm in the west to 2244 mm in the east with a maximum in the summer period. In the winter, northerly and northwesterly winds with velocities from 6 to 15 m/s prevail over the sea. The mean monthly air temperature in January pronouncedly increases from the north to the south (in the central regions of the sea, it is equal to 8--10°C, and, in the south, it is about 25°C). In the summer, southeasterly and southerly winds with velocities from 2 to 6 m/s are predominantly observed over the sea. The mean monthly air temperature in August ranges from 24 to 28°C.
Tidal phenomena are characteristic features of the hydrological regime in the region studied. The velocities of the tidal currents in deep and wide straits between the islands of the archipelago reach 1 m/s, and, in the shallow water straits, they are as high as 2.5 m/s. The tidal fluctuations of the sea level in the region of the archipelago reach 1-2 m. Near Taiwan Island, they increase up to 5-6 m (the greatest tides are recorded in the summer and winter, while the smallest are in the spring and autumn). Tidal mixing caused by strong tidal currents plays a significant role in the transformation of the waters in the zones near the islands.
The structure and dynamics of the water are studied on the basis of hydrological and meteorological long-term data combined with the materials of field observations over a period longer than half a century in the region of the Ryukyu archipelago. New data about the hydrological characteristics of the waters were obtained. Characteristic differences of waters of various modifications in the main straits between the islands are demonstrated. The dependence of the water structure formation in the straits on the seasonal variability of the water exchange through the straits is distinguished.
(K.T. Bogdanov, V.V. Moroz. Structure, dynamic and acoustical water characteristics peculiarities of the Ryukyu ridge straits and adjacent area – Vladivostok, Dalnauka, 2008. 141p.)