An Analysis~of Forecast Error in the NMC Hemispheric Primitive Equation Model

John M. Wallace Department of Atmospheric Sciences, University of Washington. Seattle 98195

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James K. Woessner Department of Atmospheric Sciences, University of Washington. Seattle 98195

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Abstract

Errors in 72 h forecasts of 500 and 1000mb height and 1000-500mb thickness from the NMC hemispheric primitive equation model during six recent winter seasons are examined in order to determine the geographical distribution of the systematic and non-systematic components of the forecast error. The systematic errors are in the sense as to make the equator-to-pole temperature gradient, the time-averaged jet streams,and the standing waves weaker in the forecasts than in the observed climatology. The non-systematic forecast errors are closely related to the observed high-frequency temporal variability, with largest values in the storm tracks. The systematic error accounts for up to about one-third of the mean-square forecast error in middle latitudes.

Abstract

Errors in 72 h forecasts of 500 and 1000mb height and 1000-500mb thickness from the NMC hemispheric primitive equation model during six recent winter seasons are examined in order to determine the geographical distribution of the systematic and non-systematic components of the forecast error. The systematic errors are in the sense as to make the equator-to-pole temperature gradient, the time-averaged jet streams,and the standing waves weaker in the forecasts than in the observed climatology. The non-systematic forecast errors are closely related to the observed high-frequency temporal variability, with largest values in the storm tracks. The systematic error accounts for up to about one-third of the mean-square forecast error in middle latitudes.

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