Formation of temperature anomalies in descending dry intrusions

Dry intrusions are a dominant feature in midlatitude cyclonic systems and play a central role in the development of high‐impact weather, including temperature extremes. They are large‐scale, quasi‐isentropic, descending flows originating from the upper troposphere and can reach the surface. In this work we present the first global Lagrangian quantification of the dynamical and thermodynamical processes governing the formation of the temperature anomaly at the outflow of dry intrusions. Through a decomposition of the temperature anomaly, we quantify the adiabatic, advective and diabatic contributions to the formation of the anomaly along the dry‐intrusion trajectory. We find that cold temperature advection counterbalances the adiabatic heating during the descent. The advective term in the Lagrangian temperature budget is dependent on the latitudinal extent and isentropic surface of the airmass. In addition, diabatic cooling increases in the last 24 hours of descent as the airmass reaches the boundary layer and evaporative cooling enhances the negative temperature anomaly. Trajectories that remain above the boundary layer experience little diabatic cooling and typically retain a positive temperature anomaly. Our results formulate the balance between the different processes controlling the temperature anomaly at the outflow of the dry intrusion. In addition, the results emphasise the importance of cross‐scale interactions between synoptic‐scale descent, mesoscale transport and boundary layer diabatic processes.