Diagnosis of Regional Monthly Anomalies Using the Adjoint Method. Part II: Potential Vorticity

Abstract

An equivalent barotropic tracer model and its adjoint are used to examine observed central European anomalies of potential vorticity (PV) in terms of advection and diabatic effects. The PV viewpoint yields a similar picture of six January anomalies to that found using a one-layer tropospheric temperature model, with the main component of the largest anomalies resulting from advection of PV present at the beginning of the month. Remote PV plays a larger role due to more rapid advection at upper levels. Anomalous diabatic effects are estimated as a residual from the tracer model itself. They are found to be of similar importance for the PV anomalies as are the (residual) source terms in the one-layer thermodynamic equation in the tropospheric temperature case. However, the spatial fields of the residual monthly averaged diabatic effects are noisier and more difficult to interpret than in the temperature case. An interpretation in terms of an estimate of the cross-isentropic mass flux at the base of the model is attempted.