Did anomalous atmospheric circulation favor the spread of COVID-19 in Europe?

The current pandemic of coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is having negative health, social and economic consequences worldwide. In Europe, the pandemic started to develop strongly at the end of February and beginning of March 2020. Subsequently, it spread over the continent, with special virulence in northern Italy and inland Spain. In this study we show that an unusual persistent anticyclonic situation prevailing in southwestern Europe during February 2020 (i.e. anomalously strong positive phase of the North Atlantic and Arctic Oscillations) could have resulted in favorable conditions, e.g., in terms of air temperature and humidity among other factors, in Italy and Spain for a quicker spread of the virus compared with the rest of the European countries. It seems plausible that the strong atmospheric stability and associated dry conditions that dominated in these regions may have favored the virus propagation, both outdoors and especially indoors, by short-range droplet and aerosol (airborne) transmission, or/and by changing social contact patterns. Later recent atmospheric circulation conditions in Europe (July 2020) and the U.S. (October 2020) seem to support our hypothesis, although further research is needed in order to evaluate other confounding variables. Interestingly, the atmospheric conditions during the Spanish flu pandemic in 1918 seem to have resembled at some stage with the current COVID-19 pandemic.

Thin-shell instability in collisionless plasma.

Thin-shell instability is one process which can generate entangled structures in astrophysical plasma on collisional (fluid) scales. It is driven by a spatially varying imbalance between the ram pressure of the inflowing upstream plasma and the downstream's thermal pressure at a nonplanar shock. Here we show by means of a particle-in-cell simulation that an analog process can destabilize a thin shell formed by two interpenetrating, unmagnetized, and collisionless plasma clouds. The amplitude of the shell's spatial modulation grows and saturates after about ten inverse proton plasma frequencies, when the shell consists of connected piecewise linear patches.

Observations of long-lived anthropogenic halocarbons at the high-Alpine site of Jungfraujoch (Switzerland) for assessment of trends and European sources.

Anthropogenic halocarbons, such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), bromocarbons (halons) and long-lived chlorinated solvents have been measured continuously at the high-Alpine site of Jungfraujoch (Switzerland) since January 2000. Chloro- and bromo-containing halocarbons are responsible for the stratospheric ozone depletion and will be globally banned from usage within the next years. With the exception of the stable CFC-12 (CF2 Cl2), all major CFCs and chlorinated solvents show a negative trend in recent years in their background concentrations at Jungfraujoch. HCFCs, as their first-generation substitute, are still increasing with a few percent per year. However, the frequency and the strength of HCFCs pollution events, which are caused by regional European emissions, are already declining. This can be seen as a sign of the impending ban of these gases within the next years in Europe. On the other hand, HFCs as the second-generation substitutes, are increasing with relative rates of at least 10% per year (e.g. almost 5 ppt per year for HFC-134a). An allocation of European sources was attempted by combining measured concentrations with trajectories of air masses reaching the Jungfraujoch during pollution events. Potential source regions could be detected in Italy, France, Spain and Germany.