Observations in the vicinity of ocean fronts indicate that sea surface temperature (SST) is positively correlated
with near-surface wind speed such that stronger winds are found over warmer SST. This indicates that the ocean
is forcing the atmosphere, and is opposite to what is commonly observed on large scales, where a negative correlation
is indicative of the atmosphere driving the ocean. I have been exploring several aspects of the coupling near
ocean fronts, including the behavior in strong cross-front, mid-latitude regimes and the feedback of such
coupling on the ocean circulation. Traditional mechanisms for the acceleration of near-surface winds over
warm water are an adjustment to local pressure gradients and the downward mixing of high momentum from aloft
due to increased instability of the planetary boundary layer over warm water. A third mechanism appears to
be important for mid-latitude fronts when the cross front wind is suffienctly strong, namely the conversion of
along front momentum to across front momentum through the Coriolis term (J. Climate paper below). It
is also shown that winds from the warm side of the front to the cold side of the front can enhance the
baroclinic instability of the ocean front, while winds from the cold side to the warm side tend to stabilize the
front. A nondimensional parameter is derived that characterizes the strength of this coupling, which is
strongest at low latitudes, for weak ocean flows, and in shallow water.
This work has been generously supported through grants from the
Office of Naval Research.
Recent manuscripts on these subjects :
Spall, M. A., 2007. Mid-latitude wind stress / sea surface temperature coupling in the
vicinity of oceanic fronts. Journal of Climate , 20, 3785-3801.
Spall, M. A., 2007. Effect of Sea Surface Temperature / Wind Stress Coupling on Baroclinic
Instability in the Ocean. Journal of Physical Oceanography , 37, 1092-1097.
A recent review paper:
Small, R. J., and others 2007. Air-Sea Interaction over Ocean Fronts and Eddies.
in press: Dynamics of Atmospheres and Oceans .