April 23, 2012 Journal article Open Access

The February 2010 Arctic Oscillation Index

P. Ripesi; V. Pelino; F. Ciciulla; F. Maimone

Theatmosphericdynamicsduringtheoccurrenceoftheextremenegativevalueofthe ArcticOscillationIndexinFebruary2010areinvestigatedusingmeteorologicalfields from ERA-Interim and ERA-40 reanalysis data. The study focuses on the possible causes of this anomalous value, finding that it was forced by a geopotential anomaly that propagated downward from the stratosphere to the troposphere in association with a major sudden stratospheric warming event which occurred at the end of January. An analysis of the dynamics of this warming is also developed, together with a comparison with past similar events. Synoptic and spectral properties of the geopotentialfieldsareanalyzed,andthetimeseriesofthe'BaroclinicActivityIndex' are computed, finding an abrupt increase of the middle latitude baroclinic activity immediately after the central date of the warming event. A possible interpretation of this feature is proposed. Copyright c