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<h1>Report 64:&nbsp; Interannual Variations in

Simulated and Observed MSU-2 Temperatures</h1>

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

<ul>October 2000, 48 pp.&nbsp;

<br>Abstract

<p>Microwave Sounding Unit (MSU) channel 2 temperatures are computed for

three sets of model experiments and their interannual variation is compared

to that of the observed.&nbsp; The models used are: (1) an ensemble of

ten integrations of the NCAR CCM3 using prescribed SSTs for 1979 to 1995,

(2) a 300 year integration of the NCAR/DOE Parallel Climate Model (which

has the CCM3 as the atmospheric model) and (3) a 300 year integration of

the ECHAM4/OPYC coupled model at the Max Planck Institute for Meteorology.&nbsp;

In addition, Nino34 and AO indices were computed from SST and MSLP of each

data set.&nbsp; The observed data spanned the period of 1979 to 1998.&nbsp;

The CCM3 integrations used the observed SSTs from 1979 to 1995.&nbsp; The

300 year coupled runs were divided into non-overlapping 20 year segments,

and each segment was processed independently.

<p>The EOFs of the zonally averaged, monthly mean MSU-2 anomalies were

computed.&nbsp; An SVD analysis of the covariance of the tropical (30S-30N)

precipitation and MSU-2 was carried out.

<p>The first and second modes of the observations are related to the ENSO

variations and the Arctic Oscillation, respectively.&nbsp; The Nino34 index

leads the ENSO mode by 5 months in the observations.&nbsp; For the nine

realizations of the CCM3, all have the ENSO as the leading mode, but one

does not have the AO as the second.&nbsp; The lag between the Nino34 and

leading EOF decreases to about 3 months.&nbsp; The fourteen PCM 20 year

segments show a similar variation to the CCM3, but the lag is decreased

to 2 months.&nbsp; All fourteen of the ECHAM segments have the ENSO and

AO as the leading and second modes.&nbsp; The fourteen ECHAM data sets

evince smaller variations between segments than the PCM and even the CCM3

realizations.&nbsp; The lag between the ECHAM Nino34 and the leading EOF

is about 3 months.&nbsp; Thus, both coupled models have a substantially

faster response to variations in tropical SSTs.&nbsp; This can affect the

way that these models simulate the relation between the seasonal cycle

and ENSO.</ul>

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