A new combined detection algorithm for blocking and subtropical ridges

Abstract

AbstractBlockings are high-impact atmospheric systems of mid/high-latitudes and have been widely addressed in meteorological and climatological studies. However, the diversity of blocking definitions makes comparison across studies not straightforward. Here, we propose a conceptual model for the life-cycle of high-pressure systems that recognizes the multifaceted and transient characteristics of these events. A detection scheme identifies and classifies daily structures, discriminating between subtropical ridges and different types of well-established blocking patterns (omega and dipole-like Rex). This is complemented by a spatio-temporal tracking algorithm, which accounts for transitions between patterns, providing a global catalogue of events for 1950-2020. Criteria rely on simple metrics retrieved from one single-level field, and allow implementation in different datasets and climatic realms. Using reanalyses data, we provide illustrative examples, the first global and seasonal climatological assessment of the diversity of high-pressure events, their associated impacts and recent frequency changes.Results reveal that ridge and blocking events affect widespread regions from the subtropics to high-latitudes. We find remarkably distinct regional impacts among the considered types, which had been hindered in previous studies by restricted focus on Rex-like structures. This plethora of high-pressure systems is much less evident in the Southern Hemisphere, where activity is dominated by subtropical ridges and secluded blocking-like patterns. We report increasing frequencies of low-latitude systems, although with hemispheric and seasonal differences that can only be partially interpreted as a consequence of subtropical expansion. Blocking frequency trends exhibit more heterogeneous and complex spatial patterns, with no evidence of generalized significant changes.