7: Ocean-Atmosphere Interactions
- Page ID
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CC1 Density and Layering in Fluids: Fluids, including the oceans and atmosphere, are arranged in layers sorted by their density. Air density can be reduced by increasing its temperature, and by increasing its concentration of water vapor causing the air to rise. This is the principal source of energy for Earth’s weather.
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CC3 Convection and Convection Cells: Evaporation or warming at the sea surface decreases the density of the surface air mass and causes it to rise. The rising air mass cools by adiabatic expansion, and eventually loses water vapor by condensation, which increases temperature as latent heat is released. As air continues to rise, adiabatic expansion and radiative heat loss then cool the air and increase its density so that it sinks. These processes form the atmospheric convection cells that control Earth’s climate.
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CC4 Particle Size, Sinking, Deposition, and Resuspension: Suspended particles (either in ocean water or in the atmosphere) sink at rates primarily determined by particle size: large particles sink faster than small particles. This applies to water droplets in the atmosphere. The smallest droplets sink very slowly and form the clouds, while larger droplets fall as rain.
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CC5 Transfer and Storage of Heat by Water: Water’s high heat capacity allows large amounts of heat to be stored in the oceans and released to the atmosphere without much change of ocean water temperature. Water’s high latent heat of vaporization allows large amounts of heat to be transferred to the atmosphere in water vapor and then transported elsewhere. Water’s high latent heat of fusion allows ice to act as a heat buffer reducing climate extremes in high latitude regions.
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CC8 Residence Time: The residence time is the average length of time that molecules of contaminants such as chlorofluorocarbons spend in the atmosphere before being decomposed or removed in precipitation or dust. Long residence time allows such contaminants to diffuse upwards into the ozone layer in the upper atmosphere.
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CC9 The Global Greenhouse Effect: The oceans and atmosphere are both important in studies of the greenhouse effect, as heat, carbon dioxide and other greenhouse gases are exchanged between atmosphere and oceans at the sea surface. The oceans store large amounts of heat, and larger quantities of carbon dioxide both in solution and as carbonates.
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CC10 Modeling: The complex interactions between the oceans and atmosphere that control Earth’s climate and affect the fate of greenhouse gases can best be studied by using mathematical models, many of which are extremely complex and require massive computing resources.
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CC11 Chaos: The nonlinear nature of ocean-atmosphere interactions makes at least part of this system behave in sometimes unpredictable ways and makes it possible for climate and ecological changes to occur in rapid, unpredictable jumps from one set of conditions to a completely different set of conditions.
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CC12 The Coriolis Effect: Water and air masses move freely over the Earth and ocean surface while objects on the Earth’s surface, including the solid Earth itself, are constrained to move with the Earth in its rotation. This causes moving water or air masses to appear to follow curving paths across the Earth’s surface. The apparent deflection, called the Coriolis Effect, is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The effect is at a maximum at the poles, and is reduced at lower latitudes, becoming zero at the equator
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CC13 Geostrophic Flow: Air and water masses flowing on horizontal pressure gradients are deflected by the Coriolis Effect until they flow across the gradient such that the pressure gradient force and Coriolis Effect are balanced, a condition called geostrophic flow. This causes ocean currents and winds to flow around high and low pressure regions in near circular paths. The familiar rotating cloud formations of weather systems seen on satellite images are formed by air masses flowing geostrophically.
The Earth’s climate (temperature, rainfall, etc., averaged over several decades of prior data) and weather (temperature, rainfall, etc., occurring at a specific time) are determined by the distribution of heat and water vapor in the atmosphere. The oceans play an important role in controlling this distribution.
Ocean-atmosphere interactions are also important because ocean currents are generated by winds as well as density differences between water masses. Seawater density is determined primarily by changes in temperature and salinity that occur at the ocean surface (Chap. 4). Surface water temperature is controlled by solar heating and radiative cooling, and salinity is altered by evaporation and precipitation.
The ocean contains many times more heat energy than the atmosphere does. This is because water is denser than air, and the total mass of ocean water is more than 200 times the total mass of air in the atmosphere. In addition, water has a much higher heat capacity per unit mass than air (or the rocks and soil of the land). Just the top few meters of ocean water have the same heat capacity as the entire atmosphere.
The oceans contain more than 97% of the world’s water. The ocean surface covers more than 70% of the Earth’s surface. The transfers of heat and water vapor between the ocean and the atmosphere that occur at the ocean surface are the main driving forces that determine the world’s climate.
Studies of the complex interactions between the oceans and atmosphere have been important since oceanographic science began. However, such studies have received more intensive attention because of potential climate changes as a result of the enhanced greenhouse effect (CC9). We cannot understand such climate changes without understanding ocean-atmosphere interactions.