## The Statistical Atmospheric Model

The atmospheric model calculates the winds that blow on the ocean model's
surface. Rather than use a full atmospheric general circulation model for
this task, we use a statistical atmospheric model. There are two reasons
we do this. The first is pragmatic: the statistical model runs 100
times faster than a full general circulation model. This lets us do many
more experiments than we would otherwise be able to do in a given amount
of time. The second is philosophical: when we construct the statistical
model, we go through many steps intended to filter out noise that we believe
only degrades the predictive performance of the model. There is no easy
or self-consistent way to remove such noise from a general circulation
model.

The statistical model is made from observations, as follows. First we
decompose historically observed variability in sea surface temperature
(SST) into a set of patterns called empirical orthogonal functions
(EOFs). We then decompose the historically observed wind field in the same
fashion. Lastly, we see, from the historical record, how likely it is that
each wind pattern will be associated with each SST pattern. We save all
this information in a file. When we go to use the statistical atmospheric
model, we simply decompose the model's SST field into the same patterns
as historically observed, then apply the wind patterns that are associated
with those SST patterns to the ocean model's surface.

*Last modified*: 25 June 1997

*Contact*: dpierce@ucsd.edu

Copyright © 2000 David W. Pierce. All rights reserved.