Four Seas

The Four Seas (Chinese: 四海; pinyin: Sìhǎi) were four bodies of water that metaphorically made up the boundaries of ancient China. There is a sea for each for the four cardinal directions. The West Sea is Qinghai Lake, the East Sea is the East China Sea, the North Sea is Lake Baikal, and the South Sea is the South China Sea. Two of the seas were symbolic until they were tied to genuine locations during the Han Dynasty's wars with the Xiongnu. The lands "within the Four Seas", a literary name for China, are alluded to in Chinese literature and poetry.

History

The original Four Seas were a metaphor for the borders of pre-Han Dynasty China. Only two of the Four Seas were tied to real locations, the East Sea with the East China Sea and the South Sea with the South China Sea. During the Han Dynasty, wars with the Xiongnu brought them north to Lake Baikal. They recorded that the lake was a "huge sea" (hanhai) and designated it the mythical North Sea. They also encountered Qinghai Lake, which they called the West Sea, and the lakes Lop Nur and Bostang in Xinjiang. The Han Dynasty expanded beyond the traditional West Sea and reached Lake Balkash, the westernmost boundary of the empire and the new West Sea of the dynasty. Expeditions were sent to explore the Persian Gulf, but went no further. The military expansion of the dynasty ended in 36 BC after the Battle of Zhizhi.

List of seas

The word sea can, aside from referring to the World Ocean, also mean a specific, much smaller body of water, such as the North Sea or the Red Sea. There is no sharp distinction between a sea in this sense and an ocean, though seas are generally smaller, and are often partly (as marginal seas) or wholly (as inland seas) bordered by land. However, the Sargasso Sea has no coastline and lies within a circular current, the North Atlantic Gyre. It is a distinctive body of water with brown Sargassum seaweed and calm blue water, very different from the rest of the Atlantic Ocean. Seas are generally larger than lakes, and contain salt water rather than freshwater, but some geographic entities known as "seas" are enclosed inland bodies of water that are not salty: for instance, the Sea of Galilee is a freshwater lake. The Law of the Sea states that all of the ocean is "sea".

Seas (disambiguation)

Seas may mean:

Wind wave

In fluid dynamics, wind waves, or wind-generated waves, are surface waves that occur on the free surface of oceans, seas, lakes, rivers, and canals or even on small puddles and ponds. They result from the wind blowing over an area of fluid surface. Waves in the oceans can travel thousands of miles before reaching land. Wind waves range in size from small ripples, to waves over 100 ft (30 m) high.

When directly generated and affected by local winds, a wind wave system is called a wind sea. After the wind ceases to blow, wind waves are called swells. More generally, a swell consists of wind-generated waves that are not significantly affected by the local wind at that time. They have been generated elsewhere or some time ago. Wind waves in the ocean are called ocean surface waves.

Wind waves have a certain amount of randomness: subsequent waves differ in height, duration, and shape with limited predictability. They can be described as a stochastic process, in combination with the physics governing their generation, growth, propagation and decay—as well as governing the interdependence between flow quantities such as: the water surface movements, flow velocities and water pressure. The key statistics of wind waves (both seas and swells) in evolving sea states can be predicted with wind wave models.