Report 11:  Preliminary Validation of the Low Frequency Variability of Tropospheric Temperature and Circulation Simulated for the AMIP by the ECMWF Model

Boyle, James S.
April 1993, 22 pp. 

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The ECMWF global model (cycle 36) is used to simulate the climate from 1979 to 1988. This integration is in support of the WGNE Atmospheric Model Intercomparison Project (AMIP). The model uses the observed monthly sea surface temperature for the ten year period during the integration. Anomaly correlation and RMS calculations are carried out between monthly mean observed circulation (ECMWF analyses and MSU channel 2 temperatures) and the model results, although the use of monthly mean data restricts the conclusions to the low frequency variability. The variables and regions considered are the 500 hPa geopotential and MSU temperatures for the Northern Hemisphere (30N to 70N), the 200 hPa zonal wind and MSU temperataures for the equatorial belt (15S to 15N), and the 1000 hPa zonal wind for the equatorial Pacific (15N to 15S and 120E to 100W).

The results show:(1) For the midlatitude 500 hPa geopotential there is a signal in the model results for the ENSO events of 1982/83 and 1986/87; (2) the model underestimates the midlatitude 500 hPa geopotential interannual variability as measured by the RMS but overestimates the MSU temperature variability in this region; (3) in general, outside of the ENSO periods, there is little correlation between the model and observed data anomalies of midlatitude 500 hPa geopotential; (4) in the tropics the variables evince a stronger correlation with observations in the interannual variation; (5) in the tropics the model underestimates the variability of the 200 hPa wind and MSU temperature; (6) the model, although non-interacting with the ocean, produces a credible simulation of the low frequency variability of the equatorial Pacific low level zonal wind. (pdf file)

UCRL-MI-123395