Journal of the Marine Biological Association of India

Volume 18 Issue 2

The ocean and the atmosphere.

R. Ananthakrishnan

MARINE meteorology is essentially concerned with the interaction between the oceans and the atmosphere and the atmospheric phenomena resulting from this interaction. The ocean and the atmosphere are two fluid media in physical contact at their interface which covers about three-quarters of the surface area of the globe. Both the fluid media are in turbulent motion in which many mutually interacting scales of motion co-exist. Exchange of heat, momentum, water, gases, salt particles, etc. takes place at the interface. These exchanges are basic for maintaining the circulations of the ocean and the atmosphere.

The oceanic waves are generated by the force which wind exerts on the water surface. The waves act as a brake on the wind and abstract momentum from it. This drag of the ocean on the wind is responsible for generating and maintaining the oceanic circulations. At the same time the atmosphere derives its water vapour from the oceans. When the vapour condenses and falls as rain the latent heat of condensation if imparted to the atmosphere, often at places far away from the place of intake of the moisture. The atmosphere derives the large bulk of its heat supply in this manner. Pressure gradients set up by differential heating give rise to the atmospheric wind systems. This shows the close links between the ocean and the atmosphere. By and large, the atmosphere supplies momentum to the ocean while the ocean supplies heat to the atmosphere.

As a consequence of the earth's rotation, largo-scale motion of the ocean and the atmosphere tend to be nearly 'geostrophic', the motion being at right angles to the pressure gradient. Since kinetic energy can be generated only by ' ageostrophic' motion, the geostrophic flow results in the storage of potential energy in the form of air-and water-mass density contrasts ; this energy is released far away in space and time from the location of input.

Date : 30-06-1976