RAPID calibrations in the radiation belts Elena Kronberg 1 and Patrick W. Daly 1 (1)Max-Planck-Institute for Solar System Research, Katlenburg-Lindau, Germany; with acknowledgments to Iannis Dandouras, Reiner Friedel, Yuri Shprits, Xinlin Li, Dan Summers, Chris Perry, Jackie Davies

Outline “Volcano” effect in proton data Electrons in the inner radiation belts

“Volcano” feature Figure 1: A CAA RAPID summary plot. Since 2008 we were puzzled by so-called “volcano” feature in our summary plots, see Figure 1. Are these observations real or are these instrumental effects?

Opinion “1” – this is an instrumental effect (I. Dandouras) Figure 1: A CAA RAPID summary plot. The IIMS instrument may be affected by pile-up effects and decreased duty cycle: with high count rates, each particle activates a “start” signal which effectively deactivates the sensor for 80 ns and any additional particles arriving during this time will not be counted. The count rates are artificially lower than they should be. This can be corrected by using the start rates to correct the effective live times. Additionally false coincidences at high count rates can produce erroneously higher fluxes, which must also be flagged.

Opinion “2” – these are real measurements (our) Figure 1: A CAA RAPID summary plot. The measurements reflect a real distribution of the electrons and protons in the radiation belts. Figure 2: Equatorial omnidirectional electron flux versus L-shell for the AE5 solar-minimum radiation belt model (left); the same for proton omnidirectioanl fluxes, AP8 (right), (Kivelson and Russel; 1999). These two opinions should be investigated

Electrons in the inner radiation belts Figure 2: Equatorial omnidirectional electron flux versus L-shell for the AE5 solar- minimum radiation belt model (left); the same for protons, AP8 (right), (Kivelson and Russel; 1999). At L~2-3 the electrons can be contaminated by hard electrons (R. Friedel et al., 2005) or by the protons of about 1 MeV, see Figure 2. We check the correlation of electron intensities with the proton intensities at keV, see Figure 3. Left plot in Figure 3 does not show clear correlation between electrons and protons. However, the sharp cut from the right implies some dependence. Figure 3: Cross-calibration between RAPID/IIMS proton intensity ( keV) and RAPID/IES electron intensity ( keV) at different L shells. 2<L<34<L<5

Electrons in the inner radiation belts It is not likely that high energy electrons strongly contaminate the ~100 keV electrons according to Figure 2, where between L 2-3 no intensity maximum has been predicted. We also show the SAMPEX data for the 2.6 MeV electrons, see Figure 5. They do not show similar increases in electron intensity at these shells. Figure 5: Electrons at ~2.6 MeV measured by SAMPEX (data are provided by S. Kanekal). Figure 4: Electrons at keV measured by RAPID/IES.

Pitch-angle distribution in the inner radiation belts However, we do see background problems. Figure 6: Electron intensities (top panel); electron pitch-angle distribution at keV (middle panel) and 3-D electron distribution from L3DD data in GSE for the two time periods (bottom panel).

Electrons in the inner radiation belts: Summary The cross-calibration of the RAPID IES data ( keV) with RAPID IIMS data ( keV) in the inner radiation belts shows that the electron data are not clean. From pitch-angle plots the background problems are seen. After discussion with various people at the 10 th anniversary Cluster workshop the problem of the RAPID radiation belt data contamination the following procedure was proposed: Using Geant4 numerical modeling tool, to simulate the response of the RAPID instrument to the space environment in order to find out what is contaminating IES data in the radiation belts. Efforts: First one needs to find detailed RAPID instrument building scheme, which is somewhere buried in our institute. Second one needs to spend one month in some of USA labs (University of Colorado or UCLA) in order to learn how Geant4 works. Outcome: Hopefully we could learn what creates problems in the radiation belt data, could clean them (or at least provide a procedure of cleaning) and do some science using 4 Cluster spacecraft (e.g. particle injections).

Pitch-angle distribution in the inner radiation belts At equatorial plane the electron pitch-angle distribution does not always peak at 90° but at about 30° off from the perpendicular direction. Similar butterfly distributions are often observed in the outer radiation belt due to the drift shell splitting or losses in the magnetopause which supposedly don’t play an important role at small L-shells. Could it be related to the way as measurements are done? We don’t see in angle-angle plots any caveats related to the detectors. Figure 6: Electron intensities (top panel); electron pitch- angle distribution at keV (middle panel) and 3-D electron distribution from L3DD data in GSE for the two time periods (bottom panel).