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<h1>Report 65:&nbsp; Comparison of Variability

of the Monthly Mean Temperature of the ECMWF and NCEP Reanalyses and CCM3

and CSM Simulations</h1>

<blockquote><b>Boyle,</b> James S.</blockquote>

<ul>October 2000, 36 pp.&nbsp;

<br>Abstract

<p>The low frequency variation in the three dimensional air temperature

fields of two reanalyses and two model simulations are described.&nbsp;

The data sets used are the monthly mean temperature fields for the NCAR

Climate Simulation Model (CSM, Boville and Gent, 1998) 300 year run, an

NCAR Community Climate Model version 3 (CCM3, Kiehl et al., 1998) AMIP

type simulation, and the NCEP/NCAR and ECMWF (ERA) reanalysis data sets.&nbsp;

The variances and correlations are computed for the anomalies from the

annual cycle for each data set.

<p>In general, the reanalyses and models agree fairly well on the structure

of the temperature variance.&nbsp; The models tend to have too much variance

at the surface compared to the reanlyses.&nbsp; The CSM's poor simulation

of the SST in the eastern Pacific leads to a much reduced variance in the

Nino3 region.&nbsp; The enhanced variability over land appears to affect

the midlatitude simulation of the CSM, in that the higher surface variability

extends off the east coast of continents.&nbsp; This is not evident in

CCM3 and reanalyses where the SSTs are prescribed.

<p>At 200 hPa the CCM3 and reanalyses all evince the dumbbell pattern straddling

the Equator in the eastern Pacific, attributed by Yulaeva and Wallace (1994)

to ENSO variations.&nbsp; The CSM shows no such pattern.&nbsp;&nbsp; A

CCM3 integration using climatological SSTs displays more variance than

the CSM in this region.&nbsp; Apparently the coupling to an ocean in the

CSM suppresses the atmospheric model's variability in this locale.

<p>The correlations of the temperature fields with the surface air temperature

show that the regions of subtropical subsidence are virtually uncorrelated

to the surface at the 700 hPa level.&nbsp; The regions of the cold water

off the west coast of continents evince decoupling with the surface at

850 hPa.&nbsp; In the region from 30S to 30N the zonal mean correlation

falls to about 0.7 below 800 hPa, with this value extending up to about

600 hPa in mid and upper latitudes.&nbsp; These characteristics are consistent

across all the data sets.&nbsp; Thus, the variations of vertically integrated

measures such as MSU temperatures need not agree with observations of surface

air temperatures at the time scales examined here.

<p><font size=-1>UCRL-MI-123395</font></ul>