Premium
Relativistic electron acceleration during high‐intensity, long‐duration, continuous AE activity (HILDCAA) events: Solar cycle phase dependences
Author(s) -
Hajra Rajkumar,
Tsurutani Bruce T.,
Echer Ezequiel,
Gonzalez Walter D.
Publication year - 2014
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2014gl059383
Subject(s) - physics , solar wind , solar cycle 22 , solar minimum , solar maximum , coronal mass ejection , solar cycle , solar cycle 23 , atmospheric sciences , interplanetary magnetic field , solar cycle 24 , solar energetic particles , astrophysics , computational physics , plasma , quantum mechanics
High‐intensity, long‐duration, continuous AE activity (HILDCAA) intervals during solar cycle 23 (1995–2008) have been studied by a superposed epoch analysis. It was found that HILDCAA intervals order the solar wind velocity, temperature and density (characteristic of high‐speed solar wind intervals), the polar cap potential, and various other geomagnetic indices well. The interplanetary magnetic field B z is generally negative, and the Newell solar wind coupling function is high during HILDCAA events. The HILDCAA intervals are well correlated with an enhancement of magnetospheric relativistic ( E > 2 MeV) electron fluxes observed at geosynchronous orbit with a delay of ~1.5 days from the onset of the HILDCAAs. The response of the energetic electrons to HILDCAAs is found to vary with solar cycle phase. The initial electron fluxes are lower for events occurring during the ascending and solar maximum (AMAX) phases than for events occurring during the descending and solar minimum (DMIN) phases. The flux increases for the DMIN phase events are >50% larger than for the AMAX phase events. Although the solar wind speeds during the DMIN phases were slightly higher and lasted longer than during the AMAX phases, no other significant solar wind differences were noted. It is concluded that electrons are accelerated to relativistic energies most often and most efficiently during the DMIN phases of the solar cycle. We propose two possible solar UV mechanisms to explain this solar cycle effect.