Stratospheric Final Warmings fall into two categories with different evolution over the course of the year

Abstract

In early spring the stratospheric zonal circulation reverses from westerly to easterly. The transition, called Stratospheric Final Warming (SFW), may be smooth and late, mainly controlled by the solar radiative heating of the polar region, or early and abrupt with rapid increase of polar temperature and deceleration of the zonal wind, forced by the planetary wave activity. Here we present a study, based on 71 years meteorological reanalysis data. Two composites of radiative and dynamical SFWs have been built. There is a very significant difference in the evolution during the year of polar temperature and 60°N zonal wind between the two composites. The state of the polar vortex on given month is anticorrelated with its state 2 to 3 months earlier. Early winter is anticorrelated with mid-winter and mid-winter with late winter/early spring. The summer stratosphere keeps a memory of its state in April–May after the SFW until late June.

Classification of Stratosphere Winter Evolutions Into Four Different Scenarios in the Northern Hemisphere

“…Thus, the three perturbed scenarios identified here confirm the result found in Hauchecorne et al. (2022), especially from the mid‐winter, that is, the vortex state on a given month is anti‐correlated with its state 2–3 months earlier and are therefore further evidence of the stratospheric memory existence.…”

“…Accordingly, the conclusion in Hauchecorne et al. (2022) is confirmed here with these first three scenarios, that is, the vortex on a given month is anti‐correlated with its state 2–3 months earlier.…”

“…Moreover, Butler and Domeisen (2021), who studied FSWs from 1958 to 2019 in the NH, classified these both winters with a "late" FSW. Consequently, and to keep a consistency with the classification carried out by Hauchecorne et al (2022), these two winters are considered as having a late and radiative end for the remaining of this study.…”

“…In contrast, wave-2 events are the precursor of an elongated or split vortex over Canada and eastern Asia. Hauchecorne et al (2022), in addition to their new classification of FSWs from 1950 to 2020 according to their nature and their occurrence, either "dynamical" or "radiative" events, investigated the seasonal memory of the stratosphere. They found that the polar vortex on a given month is anti-correlated with its state 2-3 months earlier and that the stratosphere keeps a memory of its state of April-May until at least July.…”

“…This work aims to improve our overall understanding of the handling of winters by investigating principal winter typologies and inferring how the early winter is related to the mid-winter and then how the mid-winter influences the early spring. The novelty here is that we pursue the investigation of the stratosphere memory initiated by Hauchecorne et al (2022) over the same period with a new technique of classification of winters based on the principal component analysis of the evolution of the polar vortex. To our knowledge, it is the first time that this type of classification has been undertaken and, in addition, by using the new ERA-5 reanalyzes of wind at 10 hPa-60°N produced by the European Center for Medium-Range Weather Forecasts (ECMWF).…”