Global Energetic Proton Precipitation During April 2002 and Its Impact on the Ionosphere-Thermosphere System

Global energetic proton precipitation patterns during the 16-18 April 2002 magnetic storm events were generated using newly-developed data products of MEPED instruments onboard the NOAA-15 and -16 satellites. The observational data set was first sorted in 1-degree CML and 8-minute MLT bins. To achieve global coverage, the missing MLT data were then filled by interpolation techniques in each 1-degree CML interval. Four spatial interpolation approaches were carried out and compared: cosine or linear fits to data points or MLT bin averages. The resulting global proton precipitation maps, available on a 3-hour cadence, provide new information on the development and variability in the structure of incident high energy protons on a time scale commensurate with ring current growth and decay. The geoeffectiveness of 30-240 keV proton injection was assessed by running our newly-developed three-dimensional Monte Carlo ion transport model. The global characteristics of the resulting ionization and heating rates are presented. The disturbances resulted from proton precipitation were coupled into a global ionosphere-thermosphere model developed at the University of Michigan. For the first time using in situ particle flux measurements, we can examine on a planetary scale the proton role in the geoeffectiveness of storm-time particle precipitation on the thermosphere-ionosphere system. The times and places where protons significantly contribute to geoeffectiveness are described. The effect of lateral spreading of the precipitating particles is examined and discussed.