Fig1: Time variations in the intensity (1.57 - 5.70 GV) of protons, He nuclei, electrons and
positrons,during the Forbush Decrease event associated with the 13 Dec 2006 CME [5].
LOW EARTH ORBITING COSMIC RAY MISSIONS
Dr. MirkoBoezio - INFN and University of Trieste, Italy
The PAMELA[1] and the AMS-02[2] space experiments represent the state-of-the-art of the investigation of the charged Cosmic-Ray (CR) radiation in the near-Earth environment.The former waslaunched into a semi-polar (70 deginclination) and elliptical (350–610 km altitude) orbit on June 2006 onboard of the Resurs-DK1 Russian satellite; the latterwas installed in May 2011 on the ISS.Both the instruments are composed by several subdetectors, with the core constituted by a magnetic spectrometer, providingaccurateparticle identification and rigidity measurement. While the mission temporal coverage and geometric factor are limited in comparison to ground-based detectors, PAMELA and AMS-02 are able to directly measure the spectral shape and the composition of CR fluxes. The high-precision data collected at low energies are significantly improvingour understanding of the solar modulation effects on CRs, allowing the investigation of the long- and short-term CR variations between solar cycles 23 and 24 [3]. In particular, PAMELA measured the temporal evolution of different CR species (p, He, e-, e+), founding evidence ofparticle charge-sign dependent modulation effects.In addition, PAMELA is providing comprehensive observations of SEP events during the solar cycles 23 and 24, including energetic spectra and pitchangle distributions in a wide interval (80 MeV), bridging the low energy databy in-situ spacecrafts and the GLE data by the worldwide network of neutron monitors.Major PAMELA’s results include the first direct evidence of magnetosheath effects on SEPs [4]. Similar results are being achieved by AM-02 experiment at relatively higher energies, due to the higher geomagnetic cutoff related to the ISS orbit. Space- and ground-based measurements can be combined with data from NMs in order to model the directional distribution of solar events, estimating the omnidirectional density and weighted anisotropy. Finally, PAMELA and AMS-02 are performing detailed observations of geomagnetic storms andForbush Decrease (FD) effects induced byCME events. Complementing the integrated fluxes measured by NMs, PAMELA and AMS-02 provide information on the dependency of FD effects on particle composition and energy. As an example, Fig.1 reports the variations in the intensity of the different CR species (1.57 - 5.70 GV), during the FD event associated with the 13 December 2006 CME [5].
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[2] M. Aguilar et al. (2013), Phys. Rev. Lett., 110, 141102.
[3] M. Boezio et al. (2015), Proc. 34rd Intl. Cosmic Ray Conf., PoS(ICRC2015)037.
[4] O. Adrian et al. (2015), ApJ 801 L3.
[5] M. Mergé et al. (2013), Proc. 33rd Intl. Cosmic Ray Conf., 1215.