A search of UARS data for ozone depletions caused by the highly relativistic electron precipitation events of May 1992

Highly relativistic electron precipitation (HRE) events containing signific ant fluxes of electrons with E > 1 MeV have been predicted by models to dep lete mesospheric ozone. For the electron fluxes measured during the great H RE of May 1992, depletions were predicted to occur between altitudes of 55 and 80 km, where HOx reactions cause a local minimum in the ozone number de nsity and mixing ratio. Measurements of the precipitating electron fluxes b y the particle environment monitor (PEM) tend to underestimate their intens ity; thus the predictions of ozone depletion should be considered an estima te of a lower limit. Since the horizontal distribution of the electron prec ipitation follows the terrestrial magnetic field, it would show a distinct boundary equatorward of the L = 3 magnetic shell and be readily distinguish ed from material that was not affected by; the HRE precipitation. To search for possible ozone depletion effects, we have analyzed data from the cryog enic limb array etalon spectrometer and microwave limb sounder instruments on UARS for the above HRE. A simplified diurnal model is proposed to unders tand the ozone data from UARS, also illustrating the limitations of the UAR S instruments for seeing the ozone depletions caused by the HRE events. Thi s diurnal analysis limits the relative ozone depletion at around 60 km alti tude to values of < 10% during the very intense May 1992 event, consistent with our prediction using ari improved Goddard Space Flight Center two-dime nsional model.