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The Impact of Stochastic Heat Fluxes on Sea
Surface Temperature Variability and Atmosphere-Ocean Coupling
Philip Sura
NOAA
Abstract
In this talk we study the impact of rapidly-varying (effectively
stochastic) sea surface heat fluxes on sea surface temperature (SST)
variability and atmosphere-ocean coupling. As stressed by many
previous investigators, the clear separation between the dynamical
timescales of the ocean and atmosphere allows a simple paradigm for
much air-sea interaction in which the rapidly varying component of
surface heat fluxes is approximated by a stochastic term. In many
previous studies this stochastic heat flux term is approximated by
Gaussian white-noise with fixed variance (that is, additive
noise). However, as shown from first principles, this stochastic
heat flux term depends upon not only the fast atmosphere but also upon
the slow ocean. Such state-dependent (multiplicative) noise can alter
the dynamics of SST variability and atmosphere-ocean coupling because
it induces an additional heat flux term (the noise-induced drift).
As a test of this hypothesis, daily observations at several Ocean
Weather Stations are examined in a novel stochastic framework. The
classical stochastic view with additive noise implies that SST (and
air temperature; TAIR) anomalies obey a Gaussian distribution.
However, the observations from Ocean Weather Stations reveal that
probability distribution functions (PDFs) of daily averaged SST and
TAIR anomalies are actually significantly non-Gaussian. It is shown
that it is the state-dependent character of the rapidly-varying
boundary-layer heat fluxes that appear to be responsible for the
observed non-Gaussianity of SST and TAIR anomalies. It is concluded
that the effect of state-dependent noise is crucial to understand and
model SST variability and atmosphere-ocean coupling.
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