Comments on “Magnetopause shape as a bivariate function of interplanetary magnetic field Bz and solar wind dynamic pressure” by E. C. Roelof and D. G. Sibeck

The paper "Magnetopause shape as a bivariate function of interplanetary magnetic field Bz and solar wind dynamic pressure" by Roelof and Sibeck [1993] details the development of an empirical model of the size and shape of the magnetopause from the subsolar position to a downtail distance of 20 Re for 0.5 nPa< 2 pv w < 8.0 nPa and -7 nT <B z <7 nT. One concern regarding this work is the extremely limited region of the validity of this model in IMF Bz-pV2w parameter space. Because of these limited ranges, this model is unusable during many periods of interest to magnetospheric researchers. The Roelof and Sibeck paper claims in the introduction a range of validity for IMF B z of ___7 nT, yet it displays traces of the magnetopause for values of IMF B z only between -5 and 5 nT for reasons we will illustrate below. If the model is only valid for lB z I <-5 nT, approximately 18.4 % of the time during solar maximum, and 7.2% around solar minimum, the model cannot be used 16900.