Oceans and Our Atmosphere

Scientists have come to view atmosphere and ocean as part of a single engine that transports energy and heat from the equator to the poles. Even in the middle of a continent, the sky overhead is profoundly influenced by the oceans. When waters in parts of the Pacific Ocean warm as part of El Niño, for example, the result may be drought in southern Africa and wet conditions in the southeastern United States. A system of major ocean currents move warm water from the tropics to the higher latitudes and cold water back to the tropics, influencing temperatures and precipitation over wide regions. Much of northern Europe would be almost unbearably cold if it were not for the Gulf Stream, which moderates the climate by warming the waters of the nearby North Atlantic.

Scientists have come to view atmosphere and ocean as part of a single engine that transports energy and heat from the equator to the poles. The Sun sets this engine in motion, sending out energy received by our rotating planet—with the majority reaching the surface in the tropics and lower latitudes. Winds in the atmosphere and currents in the ocean redistribute the energy and associated heat across the entire globe. This motion fuels the movement of cold and warm fronts and drives powerful storm fronts thousands of miles over ocean and land.

The winds and currents interact in subtle ways. As winds blow over the ocean, they push along surface water. The moving water gradually builds up, creating disturbances deeper down that lead to motion hundreds of feet or meters beneath the surface. In this way, the flow of winds around the globe is linked to major oceanic currents, although currents move far more slowly and follow somewhat different patterns than winds.

Currents are sometimes likened to enormous rivers coursing through the oceans. Their boundaries may be defined by sharp changes in water temperature. This border area, called an oceanic front, can be turbulent as warm and cold water clash. Sometimes, a portion of the current breaks away and develops into a whirling eddy, transporting heat and salinity from one region to another.

Understanding these eddies is an important priority for researchers who track the movement of oceans and the resulting effects on climate. At NCAR, scientists have created computer models that simulate ocean eddies in remarkably fine detail, providing insights into such processes as the transport of warm water from the Indian to the Atlantic Oceans around the southern tip of Africa.

The warming or cooling of water at the ocean’s surface can have far-flung effects on the atmosphere. This is because the ocean surface and the atmosphere exchange heat and moisture, a process that is driven by the temperature difference between the water and the air just above. This exchange helps drive atmospheric circulation. For example, El Niño is associated with warmer water extending across the tropical Pacific, which helps to steer local storms and upper-level winds, thereby shaping climate across much of the globe.

Another important link between sea-surface temperatures and climate can be seen in a phenomenon known as the North Atlantic Oscillation. In recent years, this large-scale seesaw in atmospheric pressure has been causing warm, moist westerly winds to blow over Europe and Asia, warming land surfaces there, while stronger-than-usual northerly winds bluster over Greenland and northeastern Canada, carrying cold air south and chilling both land and sea. NCAR researchers attribute the behavior of this pressure seesaw to a warming of tropical ocean waters, possibly due to the buildup of greenhouse gases in the atmosphere.

Researchers also focus on salt in the oceans, which plays an important role in the movement of heat. As warm water from the tropics moves through the midlatitudes, it gradually increases in salinity because of evaporation. The saltier, denser water sinks and contributes to a current of heavy water far below the surface that spreads heat and salinity throughout the globe.

This global conveyor belt, known as the thermohaline circulation, helps regulate our climate and bring warmth to higher latitudes. The circulation pattern varied in the past, sometimes with dramatic consequences for global climate. Scientists at NCAR and other institutions have used a computer model to study the conveyor belt 21,000 years ago, when thick sheets of ice covered large parts of the planet. The results show a different thermohaline circulation pattern at that time, with water from the Antarctic penetrating farther to the North Atlantic.