The heat and moisture available to the atmosphere from the surface of the sea is a major driver of global weather. Sea surface temperatures have such a significant impact on weather because of the high specific heat content of water, which enables the ocean to store vast amounts of heat that can be released to the atmosphere as either latent or sensible heat. Sea surface temperatures follow a predicable gradient, hotter at the equator and colder at the poles, get distributed by ocean currents, and vary according to season. However, sea surface temperatures show much less variability compared to air and land temperatures, and small changes (temperatures 3° C hotter than the climatological average is considered to be a fairly large positive temperature anomaly) can have a big impact on global weather.
Warm tropical oceans influence climate worldwide. Because tropical waters are so warm, a lot of water evaporates from the sea surface. This is why the tropics are so humid. Due to convective forces, this humid air is readily transported to the upper levels of the troposphere and from there it can travel around the world. In fact, most of the precipitable water available worldwide has its origins in tropical waters. Water travels from from the tropics to the mid-latitudes and beyond in plumes known as atmospheric rivers, and the intensity of these rivers can have a big impact on the severity of weather events in the mid-latitudes. When sea surface temperatures in the tropics are high, increased evaporation injects more precipitable water into the atmosphere resulting in large atmospheric rivers with a very high moisture content. Atmospheric rivers with large amounts of precipitable water can cause extreme rainfall and flooding events. In the Pacific northwest, atmospheric rivers from the tropical waters near Hawaii are known as the Pineapple Express, and result in warm and wet conditions in the region.
Tropical storms and hurricanes are developed, maintained, and intensified by latent heat energy from warm tropical waters. Higher temperatures mean that storms are more likely to develop and will be more intense. The energy provided by warm tropical waters can sustain these systems inland for long distances and well into the cooler waters of the midlatitudes. Furthermore, the El Nino southern oscillation is a sea surface temperature anomaly in the eastern tropical Pacific which impacts patterns of rainfall and tropical storm development worldwide.
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