Northern Hemisphere atmospheric effects due to the July 2000 solar proton event

The third largest solar proton event in the past thirty years took place du ring July 14-16, 2000, and had a significant impact on the earth's atmosphe re. These energetic protons produced both HOx (H, OH, HO2) and NOx (N, NO, NO2) constituents in the mesosphere and upper stratosphere at polar latitud es (> 60 degrees geomagnetic) of both hemispheres. The temporal evolution o f increases in NO and NO2 during the event at northern polar latitudes were measured by the UARS HALOE instrument. Increases in mesospheric NO, of ove r 50 ppbv were found in the HALOE measurements. Measurements from the UARS HALOE and NOAA 14 SBUV/2 instruments indicate short-term (similar to day) m iddle mesospheric ozone decreases of over 70% caused by short-lived HOx dur ing the event with a longer-term (several days) upper stratospheric ozone d epletion of up to 9% caused by longer-lived NOx. We believe this is the fir st time that the three constituents NO, NO2, and ozone were all measured si multaneously during a proton event. The observations constitute a dramatic confirmation of the impact of a large particle event in the control of ozon e in the polar middle atmosphere and offer the opportunity to test theories of constituent changes driven by particle precipitation.