The coupled ocean–atmosphere hydrologic cycle

The freshwater cycle has in the present study been traced as one integrated process in the coupled ocean–atmosphere system for both present and possible future climates simulated with an Earth-System Model. A method based on water-mass conservation was used in order to calculate mass fluxes of water from regions of evaporation to regions of precipitation. These fluxes include not only advection of moisture by the winds but also the vertical water-mass transport due to precipitation forming hence a mass-conserved 3D water-mass transport field. Six atmospheric hydrological cells were revealed, which cross the sea surface, where they join the oceanic overturning circulation. These atmospheric water cells can be interpreted as an extension of the oceanic overturning circulation, since the otherwise open ocean streamlines at the surface continue into the atmosphere due to evaporation and back into the ocean due to precipitation. Although these atmospheric water cells are related to the usual air cells, they are only half part of the coupled water cells and located differently. The future-climate scenario shows that the mid- and high-latitude atmospheric water-mass cells will transport more moisture towards the poles as well as increase of the northward cross-Equatorial atmospheric water-mass transport