Abstract: This paper examines the response of the bandpass filter with Gauss weighting to arbitrary two-dimensional fields and suggests a new concept: Relative Response Function. Based on the nature of relative response function, satisfactory weighting parameters C1, C2 are obtained. By studying of selected case, the procedure of using structure function curves to choose the maximum response wavelength is formulated. It is shown that bandpass filtering offers some improvements to the analysing and forecasting of mesoscale weather processes.