Statistical-dynamical analysis of wind observations usinga variational approach

Summary  In this paper, we present a variational analysis of wind and pressure data which takes into account statistical characteristics of the data and a linear model describing the dynamical relations between the analysed variables. The variational approach is used to adjust the given data to the dynamical model and it will be shown that this adjustment process can be controlled in an uncomplicated, comprehensible, and reproducible way by very few parameters only. The dependence of the analysis results on these parameters is investigated in theory and this theoretical conclusions are tested by an application. It is studied how effectively this method can be used to correct erroneous data. We apply the analysis to the COADS (Comprehensive Ocean-Atmosphere Data Set) wind and pressure data of the Januaries 1951–1993 over the North Atlantic and introduce the Ekman balance as a weak dynamical constraint. This specific data set is chosen because several previous investigations suggested that there is a spurious trend in the COADS wind speed of ∼ 1 ms⁻¹ since the mid-century. The results show that the control parameters can be effectively used to shift the wind field continuously between the identity with the input data and the exact consistency with the dynamical model. But it has to be admitted that the Ekman balance is inadequate in the tropics and that it overestimates the magnitude of the horizontal vector wind although this dynamical model is more suitable than the frequently used geostrophic balance. Received January 20, 2000 Revised April 10, 2000