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We study the radial and longitudinal dependence of 4-13 and 27-37 MeV proton peak intensities and fluences measured within 1 AU of the Sun during intense solar energetic particle events. Data are from the IMP 8 and the two Helios spacecraft. We analyze 72 events and compute the total event fluence (F) and the peak intensity (J), distinguishing between the event's absolute maximum intensity and that neglecting local increases associated with the passage of shocks or plasma structures. Simultaneous measurements of individual events by at least two spacecraft show that the dominant parameter determining J and F is the longitudinal separation () between the parent active region and the footpoint of the field line connecting each spacecraft with the Sun, rather than the spacecraft radial distance (R). We perform a multiparameter fit to the radial and longitudinal distributions of J and F for events with identified solar origin and that produce intensity enhancements in at least two spacecraft. This fit determines simultaneously the radial and longitudinal dependences of J and F. Radial distributions of events observed by at least two spacecraft show ensembleaveraged variations ranging from R À2:7 to R À1:9 for 4-13 and 27-37 MeV proton peak intensities, and R À2:1 to R À1:0 for 4-13 and 27-37 MeV proton event fluences, respectively. Longitudinal distributions of J and F are approximated by the form e Àk À 0 ð Þ 2 , where 0 is the distribution centroid and k is found to vary between $1.3 and $1.0 rad À2. Radial dependences are less steep than both those deduced from diffusion transport models by Hamilton et al.

[1] We present a 3-D numerical model of atmospheric ionization due to precipitating particles with high spatial resolution. The Atmospheric Ionization Model Osnabrück (AIMOS) consists of two parts: a GEANT4-based Monte Carlo simulation and a sorting algorithm to assign observations from two polar-orbiting satellites to horizontal precipitation cells, depending on geomagnetic activity. The main results are as follows:(1) the sorting algorithm and thus the 3-D mapping of particle fluxes works reasonably well; (2) ionization rates are in good agreement with the ones from earlier models; (3) during quiet times, the major contribution to ionospheric ionization is from electrons both in the polar cap (solar electrons) as well as in the auroral oval (magnetospheric electrons) with the ionization in the auroral oval exceeding that in the polar cap; (4) during solar particle events the dominant effect in the polar cap in the stratosphere and mesosphere is from solar protons although solar electrons can contribute up to 30% to the ionization; (5) during strong shocks following a solar particle event, in the auroral oval magnetospheric electrons and protons lead to ionization rates of up to some 10% of the ones of solar particles; and (6) independent of particle source and precipitation site, in general, ionization by electrons is more important in the thermosphere.

We use atmospheric ozone density profiles between 35 and 65 km altitude derived from SCIAMACHY limb measurements to quantify the ozone changes caused by the solar proton events from 26 October to 6 November 2003, known as the “Halloween storm.” Detailed maps and daily resolved time series up to 5 weeks after the first event are compared with the results from a chemistry, transport, and photolysis model of the middle atmosphere that includes NOx and HOx production due to energetic particle precipitation. The general features of the ozone loss are captured by the model fairly well. A strong ozone depletion of more than 50% even deep into the stratosphere is observed at high geomagnetic latitudes in the Northern Hemisphere, whereas the observed ozone depletion in the more sunlit Southern Hemisphere is much weaker. Reasons for these interhemispheric differences are given. Two regimes can be distinguished, one above about 50 km dominated by HOx (H, OH, HO2) driven ozone loss, one below about 50 km, dominated by NOx (NO, NO2) driven ozone loss. The regimes display a different temporal evolution of ozone depletion and recovery. We observe for the first time an establishment of two contemporaneous maxima of ozone depletion at different altitudes, which solely can be explained by these regimes.

Solar energetic particles (SEPs) are one manifestation of violent energy releases on the Sun. The study of their acceleration and propagation reveals information about basic plasma-physical processes, such as reconnection, shock acceleration and wave-particle interaction, in astrophysical objects, such as stars, magnetospheres or the diluted plasma of the interstellar or interplanetary medium. This paper introduces the current classification scheme for solar energetic particle events, its relation to the underlying acceleration processes, and addresses open questions regarding the better understanding of SEPs as well as the underlying physical processes. Modifications to the current paradigm considering more recent observations will be suggested.