Middle atmosphere research has suggested the importance of charged particle precipitation for several minor species. To experimentally investigate these effects requires observations of both the minor species and particle precipitation. Particle precipitation is organized in a geomagnetic coordinate system, yet data are persistently presented in geographic coordinates. This has serious implications, as quantified here for nitric oxide observations, which could lead to erroneous conclusions regarding particle effects. In geographic coordinates UARS/HALOE measurements of high latitude NO at equinox show a 25% hemispheric asymmetry that disappears when the data are replotted in magnetic coordinates. This result is applicable to all high latitude particle effects and is important for understanding magnetospheric and solar influences on various minor species in the mesosphere and stratosphere. ¿ 1999 American Geophysical Union