Hi,

Some of us noticed a substantial change in the underlying climatology of
the data used in the FNMOC SST anomaly charts some while ago, and I took
the liberty of trying to track down what had happened. I have at last
received a helpful explanation and include it here for the interest of
those who use that particular site.


'We implemented some changes to our NCODA analysis system on the date
that you noticed the change in the climate anomaly fields. The change
you noticed is due to a change in the underlying climatology used in the
NCODA system.

Previously, the Reynolds surface climatology (an older version) was used
for surface analyses and the GDEM climatology was used for subsurface
analyses. Since the change, the GDEM climatology is used for both
surface and subsurface analyses.

This does not affect the actual surface temperatures because the
observational data dominates the solution once the analysis is "spun
up".
It does however affect the climate anomaly graphics very dramatically,
as
you noticed. The two climatologies look quite different in some of the
high
latitude regions.

You are not the only person to have noticed the rather abrupt change.
We
are considering using the most recent Reynolds SST climatology as the
basis for the climate anomaly graphics so that our graphics are more
directly comparable to those produced by others; the actual analysis
would not be affected. Unfortunately, I cannot tell you when this might
happen.'


Cheers
James
--
James Brown

"James Brown" wrote :

Some of us noticed a substantial change in the underlying climatology of
the data used in the FNMOC SST anomaly charts some while ago, and I took
the liberty of trying to track down what had happened. I have at last
received a helpful explanation and include it here for the interest of
those who use that particular site.


'We implemented some changes to our NCODA analysis system on the date that
you noticed the change in the climate anomaly fields. The change you
noticed is due to a change in the underlying climatology used in the NCODA
system.

Previously, the Reynolds surface climatology (an older version) was used
for surface analyses and the GDEM climatology was used for subsurface
analyses. Since the change, the GDEM climatology is used for both surface
and subsurface analyses.

This does not affect the actual surface temperatures because the
observational data dominates the solution once the analysis is "spun up".
It does however affect the climate anomaly graphics very dramatically, as
you noticed. The two climatologies look quite different in some of the
high
latitude regions.

You are not the only person to have noticed the rather abrupt change. We
are considering using the most recent Reynolds SST climatology as the
basis for the climate anomaly graphics so that our graphics are more
directly comparable to those produced by others; the actual analysis would
not be affected. Unfortunately, I cannot tell you when this might
happen.'

Thanks James. Getting an explanatory response like that is very
useful. It pretty much confirms what some of us suspected, but
hadn't bothered to check out.

Philip