Diagnosis of Regional Monthly Anomalies Using the Adjoint Method. Part I: Temperature

Abstract

A one-layer, tropospherically averaged tracer model and its adjoint are used to examine observed midlatitude regional anomalies in terms of horizontal advection, and the effects of adiabatic and diabatic heat sources. The adjoint of the tracer model defines an information variable that is used to trace the airmass history of central European anomalies using observed winds. Together with a history of the tracer model's heat sources and sinks, which is also derived from observations, the adjoint integration enables the effects of heat sources and advection to be quantified, using the information tracer as a weighting function. Large January temperature anomalies are found to be primarily accounted for by horizontal advection of air masses already present on 1 January, with anomalous heating/cooling during the month playing a secondary role. Quasigeostrophic theory suggests that the small heating effects implied by the one-layer model are often associated with compensation between diabatic and adiabatic heating effects, the latter accompanying vertical motions. An attempt is made to interpret these compensating heat sources and sinks in terms of the positions of the storm tracks.