OCEANOGRAPHY DICTIONARY

Left Click the icon (beside the respective word) to hear me pronounce the word (excuse my southern accent :-)

Terms contained in this document:

Corolis Force:

Downwelling:

Ekman Spiral:

El Nino:

Upwelling:

Corolis Force : The COROLIS FORCE is the apparent force that acts upon an object moving in a rotating system (ex: Earth). Although the wind may actually be traveling in a straight path on the surface of the Earth, an observer above the Earth would see the wind as if it were raveling in curve (left to right) due to the rotation of the Earth. In considering oceanography, the corolis force results in the apparent deflection of objects to the right in the northern hemisphere and to the left in the southern hemisphere.

A simple childhood analogy is : Imagine you and a friend are sitting on opposite sides of a a Merry-go-round that is rotating in a clockwise direction. You have a ball that you will pass to your friend on the other side (suppose the ball traveled in a straight path relative to the ground). Although the ball is raveling along a straight path along the ground, your friend will perceive the ball as raveling along a curved path (due to the Corolis force). The following picture illustrates this analogy.

Downwelling : In the northern hemisphere, winds blow from the south (the wind's direction is from the north in the southern hemisphere). In this process, the Corolis effect pushes the surface ocean water toward the shore. As ocean water moves to the shore, this causes water to "pile up" along the coast. As water piles up along the coast line, surface level water is pushed to deeper levels. The following animation illustrates this process.

Ekman Spiral : The EKMAN SPIRAL is a result of the corolis force. As wind blows across the ocean, surface waters move to the right of the wind and drag layers of water immediately beneath them in the northern hemisphere (waters move to the left of the wind in the southern hemisphere. As this process continues to happen, waters continue to move to right and drag water to the right at deeper levels. As the spiral gets to deeper levels, the spiral is slower due to friction. The net effect of the Ekman spiral is the movement of ocean waters at a 90 degree angle to the right of the direction of the wind along the ocean's surface in the Northern hemisphere (the ekman spiral moves in 90 degree angles to the left of the wind in the Southern hemisphere).

El Nino : This is a phenomenon that causes the surface waters to become warmer. In particular, it is the warming of surface waters in the southeastern Pacific ocean. This pattern impacts the weather patterns on a global level. El Nino typically generates drier weather in southeastern Africa, India and the western pacific. The United States tends to experience wetter conditions during El Nino. Scientists generally believe El Nino is caused by seafloor spreading activity.

Upwelling : Upwelling is the reverse pattern of Downwelling. In the northern hemisphere, winds blow from the north (the wind's direction is from the south in the southern hemisphere). In this process, the Corolis effect moves the surface ocean water away from the shore. As ocean water moves to the shore, the deeper water replaces the surface water. Since the ocean water is colder at greater depths, this replacement process causes the surface water to become colder. The following animation illustrates this process.