Persistence of Wintertime 500 mb Height Anomalies over the Central Pacific

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.