The monthly probability of occurrence of southward IMF events in the GSE system in association with IMF sectors of away and toward polarity is shown to exhibit an annual variation following the heliographic latitude of earth if the IMF orientations are inferred to be in agreement with the Parker's model. Using this new idea we can infer deviations of IMF north-south (Bz components) orientations observed near earth from that predicted by Parker's model of the solar wind. Analysis of relevant earth-orbiting satellite observations of the interplanetary medium during the period 1973--80 does not reveal any systematic sunspot cycle and solar wind speed dependence for the inferred deviations of IMF from the Parker's model. However IMF north-south orientations for the year 1974, a period of recurrent high speed solar wind stream activity, show a significant departure from the Parker's model. ¿ 1998 American Geophysical Union