An analysis of a relatively rare case of continental blocking

Abstract

A planetary and synoptic-scale analysis of a relatively rare continental blocking event that occurred over North America during the spring of 1980 are undertaken to determine whether or not this event was different from its counterparts which occur over oceanic regions. The planetary-scale analysis demonstrates that, during the spring season, a ridge was located further inland over the North American continent and amplified with respect to climatology. The position of this ridge may have been linked to a broad region of colder-than-normal SSTs found over the north central Pacific during the spring season and much of the previous winter. Simple "Sutcliffe-type" and thermodynamic analyses of the accompanying lower tropospheric warm anomaly associated with the ridging shows that lower tropospheric temperature advection and subsidence associated with anticyclonic vorticity advection by the time mean thermal wind produced much of the anomalous warmth.A simple synoptic-scale analysis was performed using both the Zwack-Okossi (ZO) equation and potential vorticity (PV) thinking approaches. These complementary analyses demonstrated that synoptic-scale cyclones were instrumental in the formation and maintenance (and/or intensification) of this blocking event. The PV analysis demonstrated that low-PV air was swept poleward and then was advected over the blocking region sustaining the broad region of low potential vorticity associated with the block over North America. The ZO analysis showed that the advection of anticyclonic vorticity was the most important mechanism forcing geopotential height rises at 500 hPa over the block center. The region of low PV and ZO height rises could be associated with the anticyclonic shear side of an upstream jet maximum typically found in association with developing and/or intensifying blocking event. Thus, negative PV advection correlated significantly with calculated ZO height rises. Finally, it is suggested that a favorable phase-relationship between the upstream cyclones and the large-scale ridge is necessary for block development or intensification.

A response in the ENSO cycle to an extratropical forcing mechanism during the El Niño to La Niña transition

“…This is a late-spring and summer teleconnection pattern that is similar to those such as the Pacific North America pattern (e.g. Wallace and Gutzler, 1981;Lupo and Bosart, 1999). Except for the normal OKJ action centres, an additionally significant positive correlation centre (308N, 1558W) and a less significant negative one (158N, 142.58W) that penetrated into subtropical Eastern Pacific can also be found (Fig.…”

Similarity and variability of blocked weather-regime dynamics in the Atlantic-European region

“…However, the importance of cyclone activity (e.g. Lupo and Bosart, 1999), which may imply a role of baroclinic growth, and of moist processes (e.g. Tilly et al, 2008;Pfahl et al, 2015;Steinfeld et al, 2022) for the evolution of blocking anticyclones have been emphasized also.…”