The Latitude Dependence of the Variance of Zonally Averaged Quantities

Gerald R. North Laboratory for Atmospheric Sciences, Goddard Space Flight Center, Greenbelt, MD 20771

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Fanthune J. Moeng Laboratory for Atmospheric Sciences, Goddard Space Flight Center, Greenbelt, MD 20771

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Thomas L. Bell Laboratory for Atmospheric Sciences, Goddard Space Flight Center, Greenbelt, MD 20771

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Robert F. Cahalan Laboratory for Atmospheric Sciences, Goddard Space Flight Center, Greenbelt, MD 20771

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Abstract

Zonally averaged meteorological fields can have large variances in polar regions due to purely geometrical effects, because fewer statistically independent areas contribute to zonal means near the poles than near the equator. A model of a stochastic field with homogeneous statistics on the sphere is presented as an idealized example of the phenomenon. We suggest a quantitative method for isolating the geometrical effect and use it in examining the variance of the zonally averaged 500 mb geopotential height field.

Abstract

Zonally averaged meteorological fields can have large variances in polar regions due to purely geometrical effects, because fewer statistically independent areas contribute to zonal means near the poles than near the equator. A model of a stochastic field with homogeneous statistics on the sphere is presented as an idealized example of the phenomenon. We suggest a quantitative method for isolating the geometrical effect and use it in examining the variance of the zonally averaged 500 mb geopotential height field.

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