Hard X ray fluxes in the energy range between 50 keV and 140 keV measured using the Army Background Experiment are found to be associated with the injection by Mount Pinatubo of a massive aerosol into the stratosphere June 14--15, 1991. Discrete X ray enhancement events are observed to increase from an average of 1.8 per month to 20 during a 1-month interval beginning 12 days after the Mount Pinatubo eruption. Systematics of these enhancements suggests a mechanism that requires a strong coupling between magnetospheric and atmospheric processes, perhaps associated with upward lightning. ¿ American Geophysical Union 1995