Sack Lunch Seminar (SLS)

Hydrological cycle of the coupled ocean-atmosphere climate system

Conservation of water requires that the ocean and atmosphere transport
freshwater in equal amounts but in opposite directions. Conservation
of salt links that ocean circulation, salt stratification and
atmospheric freshwater transport. These two constraints are evident in
one of the most notable features of the present climate: that deep
water formation occurs in the North Atlantic and not North Pacific.
The Atlantic basin has a deep-reaching overturning circulation, it is
saltier and more "evaporative" than the Pacific basin and a net export
of freshwater from the Atlantic to the Pacific is observed.

Such basics aspects of the ocean-atmosphere hydrological cycle are
explored using a series of coupled climate simulations with idealized
geometries and analysed ocean fields. A novel diagnostic of freshwater
transport is used by computing ocean mass transport in salt-layers. It
is shown that a minimalist description of today's continent (two land
barriers arcing down from the north pole to delineate a small basin
and a large basin, with an unblocked circumpolar region over the south
pole) is sufficient to reproduce the observed Atlantic/Pacific
contrast and that the distribution of precipitation is key to explain
this feature.

Finally, we discuss the symmetry between ocean and atmosphere
moisture/freshwater transports. We argue that the oceanic freshwater
transport is essentially passive, responding to E-P conditions and
geometrical constraints.