The determination of transport coefficients from the evolution of transient perturbations is an area of active research in Tokamak physics (1). Recently, considerable effort has been devoted to the simultaneous measurement of electron density and temperature perturbations (2, 3, 4, 5) and to the analysis of these perturbations in terms of coupled transport equations (6, 7, 8, 9, 10, 11). Analytic solutions of these equations are of interest because they can provide physical insights which are not afforded by numerical simulations and because they can reduce the computer time required to analyse data.