A conceptual model of the salinity distribution in the atmosphere–ocean
Hadley cell is presented. The model pertains to the region of tropical east-
erly surface winds, where the surface salinity increases poleward from a local
salinity minimum near the equator to a subtropical salinity maximum. A
fundamental constraint is that the meridional freshwater transports in the
atmosphere and the ocean have the same magnitude but opposite directions.
A key assumption is that the strengths of the meridional overturning cells in
the atmosphere and the ocean are proportional and set by the surface-layer
Ekman transport. It is further assumed that the meridional salinity varia-
tion in the Hadley cell, to the lowest order of approximation, is controlled
by zonally-symmetric physics, i.e. effects related to east–west variations of
the flow are neglected. The model predicts that the salinity variation in
the oceanic cell is directly proportional to the specific humidity of the near-
surface air, but independent of the meridional mass transport (as long as the
atmospheric and oceanic mass transports remain proportional). If the rela-
tive humidity of the near-surface air is constant, the salinity variation in the
Hadley cell varies with the surface temperature according to the Calusius–
Clapeyron expression for the saturation vapor pressure.

Last Updated: 2008-07-02