A North-South asymmetry in thermospheric density

Utilizing the opportunity that our previously analyzed drag material covers the whole latitude interval between 84°N and 84°S, we have reanalyzed our 16 thousand observed total density data comparing them with model densities as a function of different parameters. A significant asymmetric dependence has been found on geographic latitudes, namely the residuals decrease continuously and evenly from the North Pole to the South Pole. The effect is significant also using data derived from the decay of several subgroups and of single satellites. Finally simple formulae are suggested for the CIRA'72, for the CIRA'86 and for the NRLMSISE-00 models explaining about 10% of the variances in all three cases.