Atmospheric Fronts and Their Association with Day-to-Day Temperature Difference: A European Climatology

The advance of computers has allowed, among others, the frontal analysis to be objectivized. With objectively defined fronts at hand, it was a relatively short step to produce climatology of their occurrence frequency. Along with frontal climatology, the associations between the presence of fronts and precipitation have been investigated quite thoroughly in the past decade.

The link between atmospheric fronts and surface temperature, and in particular with its changes from one day to the next, has not been studied yet from a climatological point of view. Although fronts are typically looked at as discontinuities in the temperature field, it is temperature aloft, not surface temperature, on which the definition of a front is based. Surface temperature is modified by a variety of boundary layer and surface processes, which makes its behaviour in the vicinity of fronts and during their passage complex, and therefore far from trivial and worth investigating.

This contribution presents climatology of occurrence of fronts, separately for cold and warm ones, in the Euro-Atlantic domain, as identified in the ERA-5 reanalysis, for period 1961-2020. In the objective localization of fronts, we utilize temperature frontal parameter, which is defined as a second derivative of temperature in the direction perpendicular to the front. The position of each front is paired with temperature difference with the 24-hour step between after and before a passage of the front over a gridpoint. As a result, we obtain climatology of day-to-day temperature differences in the presence of a warm / cold front, which is then compared to climatology in the absence of a front. We find that strong day-to-day coolings are significantly more frequently associated with passages of cold fronts than with front-free conditions in summer over most of European continent; this is, however, not true in winter.