Persistence of Wintertime 500 mb Height Anomalies over the Central Pacific

John D. Horel Climate Research Group. Scripps Institution of Oceanography, La Jolla, CA 92093

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Abstract

The persistence of daily 500 mb geopotential height anomalies during the 17 winters from 1966 to 1982 is documented for a region over the central Pacific that is noted for its frequent blocking activity. Persistence is expressed here in terms of the degree to which a height value remains constant during the next several days. For a 9 grid-point region centered on 50°N, 165°W, blocks (large positive geopotential height anomalies) tend to be less persistent than negative height anomalies between −100 and −200 m. The greater persistence of negative height anomalies in this region is related to periods of stronger than normal zonal flow centered near 40°N (high zonal index). These periods of stronger than normal zonal flow are more persistent than expected of a first-order autoregressive process.

Abstract

The persistence of daily 500 mb geopotential height anomalies during the 17 winters from 1966 to 1982 is documented for a region over the central Pacific that is noted for its frequent blocking activity. Persistence is expressed here in terms of the degree to which a height value remains constant during the next several days. For a 9 grid-point region centered on 50°N, 165°W, blocks (large positive geopotential height anomalies) tend to be less persistent than negative height anomalies between −100 and −200 m. The greater persistence of negative height anomalies in this region is related to periods of stronger than normal zonal flow centered near 40°N (high zonal index). These periods of stronger than normal zonal flow are more persistent than expected of a first-order autoregressive process.

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