Ocean Currents and Atmospheric Circulation

The oceans are not stationary. Ocean currents transport heat and play a role in regulating the climate of the entire Earth.

Basic Knowledge

Ocean current: A large-scale flow that moves in a constant direction in the ocean. Its main cause is the prevailing wind (a wind that blows constantly).
Warm and cold currents:
・Warm current: Flows from low latitudes toward high latitudes. Its water temperature is higher than that of the surrounding water. It makes coastal climates warm and rainy.
・Cold current: Flows from high latitudes toward low latitudes. Its water temperature is lower than that of the surrounding water. It makes coastal climates cool and dry.
Main ocean currents near Japan:
・Kuroshio (Japan Current): A warm current flowing along the Pacific side of Japan. Its speed is approximately 1〜2 m/s, and its volume of flow is among the largest in the world.
・Oyashio (Kuril Current): A cold current flowing southward from the North Pacific. It is rich in plankton and forms excellent fishing grounds.
・Tsushima Current: A warm current flowing northward through the Sea of Japan (a branch of the Kuroshio).
・Liman Current: A cold current flowing southward through the Sea of Japan.
The ocean front where the Kuroshio and Oyashio meet is a place where warm and cold water mix and nutrients are supplied to the surface, forming some of the world's best fishing grounds (such as offshore of Sanriku).
Global atmospheric circulation consists of three cells: the Hadley circulation, in which air heated at the equator rises, cools at high latitudes, and sinks, the Ferrel circulation, and the polar circulation.

Further Exploration

On a global scale, ocean currents are affected by the Coriolis force and are deflected to the right (clockwise) in the Northern Hemisphere and to the left (counterclockwise) in the Southern Hemisphere. This forms large subtropical gyres in the Pacific and Atlantic oceans, such as the North Pacific Current and the North Atlantic Current.
The Kuroshio is written as "black current," but it actually appears bluish-black because it contains few nutrients, has high transparency, and scatters light. Oyashio means "providing nourishment like a parent" and acts like a parent by being rich in nutrients and supporting many fish species.
The El Niño phenomenon occurs when trade winds in the equatorial Pacific weaken and sea temperatures in the eastern region rise, and it is related to unusual weather in many parts of the world. During the opposite phenomenon, La Niña, the western Pacific becomes warmer.

Points to Note

① Answer accurately that the Kuroshio is a "warm current" and the Oyashio is a "cold current." ② "Warm current = warm" has a relative meaning (warmer than the surroundings); for example, the Kuroshio is not several tens of degrees Celsius even in winter. ③ The Coriolis force is not a real force but an apparent force (an inertial force in a rotating system), although it is important on the scale of the Earth.

Practice

1. Name the warm current flowing northward along Japan's Pacific side.
2. Explain why an ocean front becomes an excellent fishing ground.
3. In which direction are ocean currents in the Northern Hemisphere deflected by the Coriolis force?