What characterizes an El Niño event?

An El Niño event is primarily characterized by the pooling of unusually warm water in the eastern tropical Pacific Ocean. This phenomenon significantly influences weather patterns not just in the Pacific but around the globe. The warming occurs because, during an El Niño, the normal trade winds weaken, which allows warm water that is typically located in the western Pacific to shift eastward. This alteration affects ocean temperatures and atmospheric conditions, leading to various weather impacts such as increased rainfall in some regions and droughts in others.

In contrast, the other options refer to characteristics associated with either normal conditions or opposite phenomena, such as La Niña. For example, pooling of cold water in the eastern tropical Pacific is associated with La Niña conditions, where trade winds strengthen, promoting upwelling of cold, nutrient-rich water. The consistent upwelling of nutrient-rich water typically occurs in non-El Niño conditions and supports higher levels of marine life and fishing activity. Similarly, stabilization of trade winds tends to occur during periods of neutral conditions or La Niña, rather than during an El Niño. Thus, the unique warming of the eastern Pacific during an El Niño is what sets this event apart and defines its impact.