A Better Perspective

	Figure 3

Relative Roles

A look at the volumes associated with the components of the water cycle (Figure 3) leads to a better perspective on the relative roles of ocean atmosphere and land. To focus only upon terrestrial fluxes, ignoring the oceanic component, would overlook the ocean-atmosphere interface that plays a critical role in maintaining the terrestrial moisture balance (Figure 3). The oceans function as a reservoir and buffer in the planetary circulation of water. Storing 23 times the water on land and a million times the water in the atmosphere, the ocean’s air-sea fluxes are many times larger than the terrestrial equivalents.

Past Limitations

Until recently, the vastness of the world’s oceans and the absence of rainfall and evaporation sensors represented a barrier to the study of the oceanic hydrologic cycle. These limitations of the past left a void in observations of precipitation or evaporation over the ocean that made quantifying the water cycle over the ocean difficult.  And mankind’s natural focus on its own water supply meant the large oceanic water cycle received little attention.  However, new satellite observations of rainfall and improved data sets of meteorological conditions over the oceans have afforded us an improved understanding of the oceanic water cycle.