What explains the eastward flow of the equatorial counter-current?

The eastward flow of the equatorial counter-current is primarily driven by the balance between the trade winds and the Earth's rotation. Here's a breakdown:

Trade Winds: Trade winds blow from east to west across the tropical oceans. This wind pattern pushes surface waters westward.

Ekman Transport: Due to the Earth's rotation, the Ekman transport effect causes the surface waters to move 90 degrees to the right of the wind direction in the Northern Hemisphere and to the left in the Southern Hemisphere. This effect causes the surface waters to pile up in the western part of the ocean basins.

Sea Surface Height: The accumulation of water in the western part of the ocean basins creates a higher sea surface height there compared to the eastern part. This height gradient generates a pressure gradient force that drives the water back towards the east.

Equatorial Counter-Current: This eastward flow of water near the equator, known as the equatorial counter-current, is essentially a response to the pressure gradient created by the westward-moving surface waters and the higher sea surface height in the west.

In summary, the equatorial counter-current is a result of the interaction between the trade winds, the effects of Earth's rotation, and the resulting sea surface height gradients.