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Physical Features and Climatology of the Forecast Minus Analysis PV Field

Physical Features and Climatology of the ''Forecast Minus Analysis'' PV Field

Marco Didone and Huw C. Davies, IACETH Zurich, 2006

An alternative approach is set out for a systematic study of the difference between the forecast and contemporaneous analysis analysis field of a particular predictions system(the ECMWF). The underlying rationale is two-fold. First this perspective's intrinsic properties imply that :- (a) nonconservation of error PV signifies either isentropic advection of the error across an ambient flow's PVgradient, the misrepresentation of diabatic or frictional processes, and /or error in the analysis field at the verification time; and (b) inversion of a particular feature of the error PV-field can (via attribution) account for error of the primary flow variables in both the in-situ and far-field. Second the dynamics of rapid error growth has been linked to distinctive PV-features of the error field.

Illustrations and interpretations are proffered of this difference when viewed in terms of PV for single autumn, winter and spring (2001/02) climatology. The evolution of this pseudo-error is investigated in term of forecast length with the pseudo-errors of forecasts of different lengths. Two model versions (T511 and T711) are compared. The results point out various discrepancies e.g. in the location of the jet between analysis and forecast which increases in amplitude for longer forecast length. Intercomparison of T511 and T711 results a convergence in error structure.