Observations of the latitude dependence of the location of the martian magnetic pileup boundary: FIELDS EFFECTS ON MARTIAN MPB LOCATION

We report observations that show the dependence of the altitude of the magnetic pileup boundary (MPB) at Mars on planetary latitude. As seen by the Mars Global Surveyor Magnetometer/Electron Reflectometer instrument, the MPB is further away from Mars on average at southern latitudes than at northern latitudes. The data are consistent with a MPB distance mapped to the terminator plane that does not vary with latitude in the northern hemisphere, but increases with increasing southern latitude in the southern hemisphere. We also report increased variability in the MPB distance within the longitude range 90–270° E. longitude in the southern hemisphere which is the region that contains the strongest crustal magnetic fields. These trends are most obvious in a planet-fixed coordinate system, indicating a planet-fixed driver of the MPB location. The proposed mechanism is the local diversion of shocked solar wind flow by crustal magnetic fields.