Flow at 500 mb associated with a measure of persistence over western Europe

Persistence is examined in a sector over the northeastern Atlantic and western Europe to determine whether flow associated with more or less persistence can be distinguished from one another. The data used were daily 1200 UTC 500-mb geopotential heights from January 1, 1950 through December 31, 1979. The day-to-day change in geopotential heights over an area was used as a measure of persistence. To express this change, the index developed by Lorenz (1969) was determined. Flow fields for persistent and non-persistent cases involving definitions based on 1-day lag and on 1-day through 10-day lags for winter are analyzed and results from other seasons are presented. It was found that persistence (non-persistence) in the sector is inversely (directly) proportional to the zonal wind at 55 degrees N. When persistence is measured by 1-day differences in the European sector, statistically significant changes in the flow are confined to the area near the sector. When the persistence is based on differences over a 10-day period relatively large changes in the flow are evident over the entire hemisphere.