HELIOSPHERIC CURRENT SHEET INCLINATIONS PREDICTED FROM SOURCE SURFACEMAPS

The inclinations of the neutral line at the ecliptic plane derived fro m source surface model maps of coronal fields are measured for the int erval from June 1976 to March 1992. The mean and median values of 53 d egrees and 57 degrees are close to the average inclinations determined earlier from minimum variance analyses of solar wind measurements at sector boundaries, but the mode falls in the 80 degrees-90 degrees bin . This result, which is based on the model assumptions implicit in der iving the source surface maps, predicts that the heliospheric current sheet typically intersects the ecliptic plane nearly at right angles, even without steepening by stream interaction regions. High inclinatio ns dominate the solar cycle for about 7 years around solar maximum. Di ps to lower inclinations occur near solar minimum, but high variance a dmits a wide range of inclinations throughout the cycle. Compared to t he smooth solar cycle variation of the maximum latitudinal excursion o f the neutral line, often treated as the tilt angle of a flat heliosph eric current sheet, the noisy variation of the inclinations reflects t he degree to which the neutral line deviates from a sine wave, implyin g warps and corrugations in the current sheet. About a third of the ti me the neutral line so deviates that it doubles back in longitude.