Sea Surface Conditions

Questions

1. Compare sea temperatures and surface topography in the eastern and western equatorial Pacific in normal, non- El Niño conditions.
   Check Answer

   The seawater on the surface in the eastern Pacific is much colder, and cools off with depth much faster. On the west side, there is an enormous blob of warm water that is right on the surface and also extends hundreds of meters down.

   The surface of the sea is irregular all across the Pacific, but there is a broad mound on the western side.

2. Explain how winds and currents cause these patterns.
   Check Answer

   The trade winds blow most of the time in the tropics, and start the Equatorial Currents moving just north and south of the equator. These currents push water from east to west across the Pacific. The land masses on the west side of the sea (Indonesia, the Philippines, New Guinea, etc.) block the currents, and water piles up into a low mound against the land.

   Seawater in the Equatorial Currents is heated by intense sunlight during the journey across the Pacific, and so is quite warm by the time it reaches the west side. In the east, cold water is flowing toward the equator in the Eastern Boundary Currents, so sea surface temperatures are much cooler on that side of the Pacific.

3. Now compare sea temperatures and surface topography in the eastern and western equatorial Pacific during an El Niño.
   Check Answer
   During El Niño, the surface of the Pacific slopes up toward the east. The temperature of the sea is much warmer all across the equator, both right at the surface and down several hundred meters. The hottest water is no longer on the west side of the Pacific, but between the center and east edge of the ocean.
4. Explain how winds and currents might cause these patterns.
   Check Answer
   It looks as if during El Niño, warm water is flowing east across the Pacific instead of west. This could only happen if the Trade Winds were weaker or less steady than normal, which would in turn diminish the strength of the Equatorial Currents. If the forces of wind and water moving west decline, that big mound of hot water that is usually near Indonesia would collapse, and a lot of it would flow back east in the Equatorial Countercurrents. Warm water would then build up in the eastern Pacific.