HOME arrow PAMELA RESULTS arrow Solar  
Solar - Read more Print
The long time in orbit of the PAMELA mission has allowed a continuous monitoring of the solar activity. The resulting modulation of the galactic cosmic rays, including the charge sign dependent eff ect, has been studied in time, and several Solar Energetic Particle (SEP) have been detected.

Solar modulation
PAMELA has been operating in these years during the very long 23rd solar minimum in Apolarity, when the magnetic dipole projection on the solar rotational axis and the rotational axis itself are anti-parallel, and it is now still acquiring data, going toward the solar maximum of cycle 24th. The last very stable solar activity minimum represents an ideal condition to study solar modulation, allowing to gain a better understanding of the mechanisms dominating the charged particle transport in the solar environment (diff usion, convection, adiabatic energy losses and, in particular, drifts). 
Figure 1  shows the low energy galactic proton absolute flux measured by PAMELA between June 2006, instrument launch date, and December 2009, when the solar activity reached its minimum. The proton flux variation during the same period, at a speci fic rigidity, is shown in Figure 2. The increasing of the fluxes with the decreasing of the solar activity is clearly visible. Figure 3 presents the galactic proton spectrum measured by PAMELA over four periods, overlaid with the corresponding computed spectra. A full three-dimensional model, based on the numerical solution of the Parker transport equation, was used to compute the di fferential intensity of cosmic-ray protons at Earth from 10 MeV to 30 GeV, allowing to achieve a better comprehension of the interplay of the major solar modulation mechanisms and to precisely determine the rigidity dependence of the di ffusion coecients.

Solar events
The Sun has long been known to be also a source of energetic particles. To fully explore the nature and capacity of solar particle acceleration processes, extremes in energy and flux of the produced particles must be studied. PAMELA, in six years of operation, has already recorded many solar energetic events associated with occurrences at the Sun. Figure 4 shows the proton flux measured by PAMELA in the energy range from 80 MeV/n up to few GeV/n during the event occurred, despite the solar minimum condition, on December 13, 2006. During the fi rst hours of the event, solar energetic particle spectrum had a quite exponential form, a demonstration of a rather signicant temporal evolution. Figure 5 shows the Helium spectrum during the same time period. The e ffect of the CME associated to the December 2006 event is clearly visible in the galactic cosmic ray flux decrease - Forbush decrease - reported in Figure 6. It is signi ficant and similar in intensity for several, di fferently charged, detected species. The flux intensity takes about 3 weeks to recover to the quiet Sun condition. Particularly interesting are the preliminary measurements of the proton  fluxes during the events occurred on March 7 and May 17, 2012, shown in Figure 7  and Figure 8 , respectively. 


Edited by Laura Marcelli