Diabatic jet streak intensification during serial cyclone clustering: the North Atlantic case of February 2022

Abstract. Episodes of extratropical cyclone clustering are frequently accompanied by strengthened upper-level jet streaks. The mechanisms responsible for maintaining the associated baroclinicity, however, remain uncertain. Both diabatic processes and double-sided Rossby wave breaking have been proposed as explaining mechanisms, but their contribution is not fully understood. This study presents a jet-streak–centred diagnostic to quantify the contributions to cross-jet heating and analyse the lifecycle of a jet streak that coexists with the development of the cyclone cluster encompassing severe windstorms Dudley and Eunice over the North Atlantic in February 2022. The analysis is based on numerical simulations using the Open Integrated Forecasting System developed by the European Centre for Medium-Range Weather Forecasts.

It appears for the selected case study that the initial intensification of the jet streak along the North American East Coast is primarily driven by diabatic processes: latent heat release on the equatorward side and upstream of the jet streak maximum acts to enhance the meridional temperature gradient and therefore strengthening the upper level jet streak consistent with the thermal wind law.

Moreover, sensitivity experiments in which the magnitude of latent heat release is varied demonstrate a strong influence on jet strength: a reduced latent heat release experiment (50 % L_v) results in a substantial weaker jet streak, while a enhanced latent heat release experiment (150 % L_v) leads to a slightly stronger jet streak compared to the control experiment. The evolution of baroclinicity, as diagnosed through the Eady growth rate, is more complex and appears to result from an interplay between vertical wind shear and atmospheric stability. With reduced latent heating, stability is reduced, but does not balance the much more weaker vertical wind shear. With increased latent heating, stability is enhanced, which acts to suppress baroclinicity despite stronger vertical wind shear.

We conclude that latent heat release is the dominant mechanism driving the initial intensification of the jet streak during this February 2022 cyclone clustering event, suggesting that diabatic processes play a central role in the baroclinic environment of serial cyclone clustering.