ENSO-Related Variability in the Frequency of South Pacific Blocking

Abstract

Interannual variability in the frequency of atmospheric blocking events over the southern Pacific Ocean is analyzed in terms of variations in the El Niño?Southern Oscillation (ENSO) cycle, using a 16-yr record of Southern Hemisphere 500-hPa height fields. The number of days of blocking tends to increase on average during the warm phase of the ENSO cycle, particularly over the southeast Pacific during the southern spring and summer. Over the southeast Pacific between September and February, more than twice as many days of blocking are observed on average during El Niño events than during neutral or La Niña conditions. Changes in the frequency of days of blocking are found to be related to changes in the mean circulation and more strongly to changes in the variance of circulation over the South Pacific.