Ocean-Atmosphere Interactions

The complex interactions between the oceans and the atmosphere are basic to understanding oceanography and meteorology. The liquid and gaseous envelopes surrounding Earth have powerful effects on weather and climate on a global scale.

Atmosphere and Ocean

The largest fraction of the heat energy the atmosphere receives toward maintaining its circulation is derived from the condensation of water vapor originating mainly from marine evaporation. Therefore, fundamental to understanding atmospheric behavior and oceanic behavior is understanding the processes occurring at the air-sea boundary. The interactions between the marine and atmospheric environments involve constant exchanges of moisture, heat, momentum, and gases.

The study of oceanic and atmospheric interactions involves a huge gaseous body and a massive liquid body, neither of which is ever homogeneous in content. The atmosphere's makeup varies continually, depending on the areas over which it flows. The content of the oceans also varies in density, temperature, salinity, rate of movement by regular currents, and surface movement under the influence of winds. As a consequence, this interaction is very complex and not entirely understood. However, certain conditions that are regularly met can act as a general guide to understanding ocean-atmosphere interactions.

Atmospheric circulations depend on heat rising from the ground surface. Because of the large area of Earth’s surface covered by oceans, the sea surface is the primary heat source to the atmosphere. In the oceans, heat is supplied primarily from the Sun, with some additional contribution from atmospheric sources. Heat-supply processes are important in developing convection currents in the ocean's surface layer for the local exchange of energy with the atmosphere and slower, deep-water circulation currents. Heat exchange between the ocean and atmosphere has a pattern similar to evaporation. Wherever the ocean's surface is warmer than the atmosphere, heat is transferred from the ocean to the air, usually as latent heat, and is moved to great heights by eddies and convection currents in the air.

The range of weather extremes is smaller over the ocean than over land because of the enormous heat-storage capacity of the ocean, which tends to stabilize atmospheric conditions and properties. The upper layer of the oceans (to a depth of approximately 70 meters) can store some thirty times more heat than the atmosphere. Ocean climate and atmospheric circulation are affected by the solar distribution over the Earth’s surface, which is a function of the latitude and the season of the year. Northern and southern latitudes receive proportionately less solar radiation than latitudes at the equator; in winter, polar latitudes receive practically no solar radiation. Because of the oceans' greater capacity to store heat, the temperature change in the atmosphere will be around thirty times greater than in the ocean for a given change in heat content. Therefore, the ocean will lose its heat content by radiation much more slowly than the air. Land, which is intermediate with regard to heat storage and heat loss, can be modified by the effect of heat storage and heat loss of the ocean.

Processes at the Air-Sea Boundary

The atmosphere adjacent to the oceans is constantly interacting with the oceans. Air does not simply flow along the sea's surface but has a frictional effect or wind stress, which causes lateral displacement of the surface water. Wind stresses on the sea surface produce ocean waves, storm surges, and shallow ocean currents. Pure wind-driven currents result from frictional wind-surface stresses and Earth’s rotational motion. This rotational motion can be seen in the Coriolis effect, by which air currents and ocean currents are deflected from true linear motion to the left in the Northern Hemisphere and the right in the Southern Hemisphere. Because the sea is continually in contact with the atmosphere, the gases that are present in the atmosphere are also found in seawater. The concentration of those gases depends on their solubilities and the chemical reactions in which they become involved. Their concentrations are affected by temperature, which is determined by many factors, wind, and wave actions.

The sea also has a large storage and regulating capacity concerning processes involving carbon dioxide in the atmosphere and the sea, including those processes relevant to photosynthesis. This whole group of reactions concerning carbon dioxide, generally referred to as the carbon cycle, is extremely complex. Carbon dioxide, a “ greenhouse gas,” has a high capacity for absorbing infrared energy or heat. Solar energy absorbed at the ground surface is radiated back into the atmosphere and is absorbed by carbon dioxide. The heated carbon dioxide molecules reradiate that infrared energy as they cool, returning at least 50 percent of the heat they have absorbed into the atmosphere and back to the surface. This “greenhouse effect” raises the functional temperature of the air and maintains it well above what it would be in the absence of the effect.

The largest fraction of radiant energy absorbed by the oceans is used in evaporation. The maximum evaporation and heat exchange between the sea and the atmosphere occurs where relatively cold continental air flows over warm ocean currents moving toward the poles. Examples of where this phenomenon is most evident include the Kuroshio ( Japan Current) and the Gulf Stream. The radiant energy absorbed and stored by the oceans at tropical latitudes may thus be moved and given off to the atmosphere elsewhere. This process is important to understand regarding the Southern Oscillation and the effect of El Niño and La Niña.

Major wind systems are responsible for forming and operating the broadly symmetrical patterns of surface-water movement known as gyres, which rotate clockwise around the North Pacific and North Atlantic and counterclockwise around the South Pacific and South Atlantic oceans. Their tropical segments are the North and South Equatorial currents, driven westward by trade winds. The Equatorial Countercurrent, a compensating flow, travels west to east in the Pacific between the North and South Equatorial currents along a course that averages a few degrees north of the equator.

Marked by warm water and high winds from the western Pacific, El Niño typically brings heavy winter rains to Peruvian deserts and warm weather to the West Coast of the United States. El Niño arises through interaction between the oceanic and atmospheric systems. During El Niño, the southeast trade winds over the equatorial Pacific collapse, allowing warm water from the western Pacific to flow eastward along the equator. This warm-water flow suppresses the normal upwelling of cold, nutrient-rich water and leads to the northward displacement of fish normally feeding in the nutrient-laden cold water.

El Niño is part of a gigantic meteorological system called the Southern Oscillation that links the ocean and atmosphere in the Pacific. This system normally functions as a kind of huge heat pump, distributing energy from the tropics at the equator to the higher latitudes through storms that develop over the warm western Pacific. Another part of the Southern Oscillation has been dubbed La Niña, which brings cold water to the central Pacific. La Niña exaggerates the normal conditions of the system. During this activity, easterly trade winds are stronger, the waters of the eastern Pacific off South America are colder, and ocean temperatures in the western equatorial Pacific are warmer. Atmospheric and oceanic conditions in the equatorial Pacific region can affect global weather. Therefore, the study of this interaction is essential.

Study of Ocean-Atmosphere Interactions

Because the study of ocean-atmosphere interactions is concerned with the boundary between marine and air masses, it is a necessity for an interdisciplinary type of study. The data used in such studies are gathered by oceanographers and meteorologists who have made this interaction the focus of their research. The same instruments are employed in oceanographic and meteorologic research, drawing heavily upon the same type of data collected but with a shift in emphasis. Because gathering data is expensive and utilizes costly specialized equipment, nearly all studies are conducted by government scientists or are sponsored by government grants.

Scientists who study ocean-atmosphere interactions are interested in seeing how these huge bodies of matter affect each other and how these effects influence the weather and climate in the rest of the world. They are also interested in the ability to predict weather and climate changes more accurately. Each element researched, such as salinity, is compared with other elements, such as temperature, to see the relationship. Air temperature and air movement are compared with wave movement, changing ocean currents, and water temperature. Each of a vast number of data points is examined for possible interrelations and interactions. When relationships are found, the data are fed into a computer model for correlation with other data. Computer models have been somewhat effective in predicting the results of interactions between marine and atmospheric environments. Separate computer models are used, with the output aimed at the interactions between these forces.

Scientists do not fully understand all the mechanisms linking certain ocean-atmosphere interactions, such as El Niño and La Niña. They hope that by studying and understanding the mechanisms involved, they may be able to make accurate long-range predictions of the amount and area of precipitation in specific regions.

Significance

The interaction between the oceans and the atmosphere can cause immense problems on a global scale. An example of this interaction and its consequences is seen in the phenomenon known as El Niño. Every three to five years, the surface waters of the central and eastern Pacific Ocean become unusually warm at the equator. Warm currents and torrential rains are brought to the normally dry desert area of central Peru, and nutrient supplies for marine life along the west coast of South America are disrupted. Hardship can occur as a result, including widespread flooding in Peru. Since 2000, El Niño events have been observed in 2002–03, 2004–05, 2006–07, 2009–10, 2014–16, 2018–19, and 2023–24.

La Niña brings an effect opposite to that of El Niño; easterly trade winds are stronger, the waters of the eastern Pacific off South America are colder, and ocean temperatures in the western equatorial Pacific are warmer than normal. As a result, the deserts in Peru and Chile become drier than normal, and the Indian subcontinent is inundated by heavier-than-usual rainfall and flooding as changes in the Southern Oscillation combine with the East Asian monsoon. In Bangladesh in late 1988, heavy rains and flooding killed more than 1,000 people, destroyed the homes of 25 million people, inundated 5 million acres of rice land, and damaged 70,000 kilometers of roads. While the storms were attributed to the La Niña phenomenon, much of the flooding was the result of massive deforestation in the Himalayas and foothills, which allowed water to rush down from the barren, eroded hills onto Bangladesh near sea level. La Niña was last active in 2020–2023, with its end in March 2023. During this three-year period, there was a rise in tropical storms and hurricanes, as well as drought and excessive heat in other areas of the United States.

Principal Terms

atmosphere: the envelope of mixed gases containing liquid and solid particles that surrounds the planet

Coriolis effect: the apparent force causing the deflection of any moving body on Earth to the west or east, depending on whether the latitude is north or south, respectively; an effect of Earth’s rotation

El Niño: an accumulation of relatively warm surface ocean waters along the west coast of tropical South America due to changes in the air pressure and wind patterns of the Southern Oscillation

gyres: generally circular oceanic current systems that have formed by a combination of the global wind system and the Coriolis effect

Kuroshio: the current, also known as the Japan Current, where cold continental air flows over warm ocean currents moving toward the poles

La Niña: the phase of the Southern Oscillation that brings cold water to the South American coasts, which makes easterly trade winds stronger, the waters of the Pacific off South America colder, and ocean temperatures in the western equatorial Pacific warmer than normal

Bibliography

Bigg, Grant. The Oceans and Climate. 2d ed., Cambridge, England: Cambridge University Press, 2003.

Chassignet, Eric P. and Jacques Verron, editors. Ocean Weather Forecasting: An Integrated View of Oceanography. Dordrecht: Springer, 2006.

Clarke, Allan J. An Introduction to the Dynamics of El Niño and the Southern Oscillation. Burlington, Mass.: Academic Press, 2008.

Curry, Judith A., and Peter Webster. Thermodynamics of Atmospheres and Oceans. San Diego, Calif.: Academic Press, 1999.

DiNezio, Pedro. “La Nina Is on its Way Back. An Atmospheric Scientist Explains What to Expect.” PBS, 12 May 2024, www.pbs.org/newshour/science/la-nina-is-on-its-way-back-an-atmospheric-scientist-explains-what-to-expect. Accessed 29 July 2024.

Docquier, David, Stéphane Vannitsem, and Alessio Bellucci. "The Rate of Information Transfer as a Measure of Ocean–Atmosphere Interactions." ESD, vol. 14, no. 3, 2023, pp. 577-591. doi.org/10.5194/esd-14-577-2023. Accessed 29 July 2024.

Hamilton, Kevin, and Wataru Ohfuchi, editors. High Resolution Numerical Modeling of the Atmosphere and Ocean. New York: Springer Science+Business Media, 2008.

Ittekko, Venugopalan, et al., editors. Particle Flux in the Ocean. New York: John Wiley & Sons, 1996.

Kagan, Boris A. Ocean-Atmosphere Interaction and Climate Modeling. Cambridge, England: Cambridge University Press, 2006.

Majumdar, Shyamal K., et al., editors. The Oceans: Physical-Chemical Dynamics and Human Impact. Easton, Pa.: Pennsylvania Academy of Science, 1994.

Marshal, John, and R. Alan Plumb. Atmosphere, Ocean and Climate Dynamics: An Introductory Text. Burlington, Mass.: Elsevier Academic Press, 2008.

“Ocean–Atmosphere Interaction.” COAPS, 2014, www.coaps.fsu.edu/~vmisra/encyclopedia.pdf. Accessed 29 July 2024.

Oceanography Course Team. Ocean Circulation. 2d ed., Oxford: Butterworth-Heinemann, 2001.

Sarachik, Edward S., and Mark A Cane. The El Niño-Southern Oscillation Phenomenon. New York: Cambridge University Press, 2010.

Schmitt, Raymond W. The Ocean Freshwater Cycle. College Station, Tex.: A&M University, 1994.

Thurman, Harold V., and Alan P. Trujillo. Introductory Oceanography. 10th ed., Upper Saddle River, N.J.: Prentice Hall, 2003.

Vallis, Geoffrey K. Atmospheric and Oceanic Fluid Dynamics: Fundamentals and Large-Scale Circulation. New York: Cambridge University Press, 2006.

Wells, Neil C. The Atmosphere and Ocean: A Physical Introduction. 3d ed., New York: John Wiley & Sons, 2012.