Space-time analysis of geopotential height and SLP, intraseasonal oscillations, weather regimes, and local climates over the North Atlantic and Europe

Abstract

We extract coherent and robust oscillations at the intraseasonal time scale using multi-channel singular spectrum analysis (MSSA). Three daily fields are compared, namely sea-level pressure (SLP) and geopotential heights at 500 and 700 hPa (Z500 and Z700). The data set extends from 1958 to 1997 and covers the same North Atlantic-European domain. Three oscillations stand out with periods of 30-35, 65-70 and 120-130 d respectively. A comparison shows that the same period oscillations at different levels are highly correlated. Moreover, it is shown that these modes are phase-locked and thus should come out from a single limit cycle. When these oscillations are compared with the succession of weather regimes (WRs), it can be shown that WR occurrences are indeed strongly influenced by particular phases of the 30-35 and 65-70 d modes. Transition from one WR to another is also shown to be favored by the life cycle of the previous modes. For instance, zonal regimes are followed preferably by blocking ones. Thus, regime transitions are indeed not random but are somehow steered by the dynamical behavior of a low-dimensional atmospheric attractor. We then explore the links between the intraseasonal modes and the local temperatures over France and Western Europe as well as precipitations over France. Once again, we conclude that bursts of low-frequency oscillations, such as the ones detected, significantly influence local surface weather conditions.