Abstract/Summary

Diabatic processes drive surface heat fluxes and provide energy to weather systems through heating where it is warm and cooling where it is cold, globally increasing the available potential energy and giving a crucial contribution to the maintenance of midlatitude storm track regions. Locally, however, surface heat fluxes can be negatively correlated with lower-tropospheric air temperature so that cold regions are heated and warm regions are cooled. Peaks of intense air–sea thermal interaction result, on average, in the damping of the temperature variance associated with weather systems, thus depleting the potential energy available for their development, in contrast with the average positive contribution that diabatic processes give globally. In this thesis we characterise the role played by heat flux peaks in the evolution of storm tracks’ life cycle by interpreting the spatial covariance between surface heat flux and lower tropospheric air temperature as a measure of the intensity of thermodynamic activity associated with weather systems. Through the analysis of the temporal evolution of covariance we identify the average response of the atmospheric circulation to surface heat flux peaks, which are found to have the largest impact within cold sectors of weather systems, where the atmospheric boundary layer is deeper and the surface–troposphere thermal coupling is enhanced. Meridional heat fluxes also feature sporadic bursts of activity that can account for a large fraction of the total meridional heat exchange. Peaks of meridional heat flux result from both strong meridional wind–temperature correlation and variances, which play distinctive roles in the cyclical evolution of heat flux peaks depending on the relative predominance of different storm growth mechanisms. Heat-flux–temperature correlation can therefore be considered as an independent dynamical variable carrying information about the state of the atmospheric circulation and its thermal interactions.