NEW EVIDENCE FOR CHARGE-SIGN-DEPENDENT MODULATION DURING THE SOLAR MINIMUM OF 2006 TO 2009
- INFN, Sezione di Roma “Tor Vergata,” I-00133 Rome (Italy)
- INFN, Sezione di Trieste, I-34149 Trieste (Italy)
- Centre for Space Research, North-West University, 2520 Potchefstroom (South Africa)
The PAMELA space experiment, in orbit since 2006, has measured cosmic rays (CRs) through the most recent period of minimum solar activity with the magnetic field polarity as A < 0. During this entire time, galactic electrons and protons have been detected down to 70 MV and 400 MV, respectively, and their differential variation in intensity with time has been monitored with unprecedented accuracy. These observations are used to show how differently electrons and protons responded to the quiet modulation conditions that prevailed from 2006 to 2009. It is well known that particle drifts, as one of four major mechanisms for the solar modulation of CRs, cause charge-sign-dependent solar modulation. Periods of minimum solar activity provide optimal conditions in which to study these drift effects. The observed behavior is compared to the solutions of a three-dimensional model for CRs in the heliosphere, including drifts. The numerical results confirm that the difference in the evolution of electron and proton spectra during the last prolonged solar minimum is attributed to a large extent to particle drifts. We therefore present new evidence of charge-sign-dependent solar modulation, with a perspective on its peculiarities for the observed period from 2006 to 2009.
- OSTI ID:
- 22661421
- Journal Information:
- Astrophysical Journal, Vol. 834, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
TIME DEPENDENCE OF THE PROTON FLUX MEASURED BY PAMELA DURING THE 2006 JULY-2009 DECEMBER SOLAR MINIMUM
New modeling of galactic proton modulation during the minimum of solar cycle 23/24