There is an association between High-Intensity Long-Duration Continuous AE (HILDCAA) activity intervals and the acceleration of relativistic >1 MeV electrons in the magnetosphere. All of the HILDCAAs that occurred in solar cycle 23 (SC23) from 1995 to 2008 led to the acceleration of E>0.6 MeV, >2.0 MeV, and >4.0 MeV electrons in the Earth’s outer radiation belts. What is particularly noteworthy is that the E>0.6 MeV electron acceleration was delayed ~1.0 day after the onset of the HILDCAA event, the E>2.0 MeV electrons delayed ~1.5 days after the onset of the HILDCAA event, and the E>4.0 MeV electrons delayed ~2.5 days after the onset of the HILDCAA event.

Because relativistic electrons can be damaging to spacecraft in Earth orbit, knowledge of future enhanced radiation will allow spacecraft engineers to “safe” their spacecraft from the upcoming radiation. The investigators worked to understand if it was solar and interplanetary forcing that was causing the radiation near Earth. A likely scenario is that high-speed solar wind streams come from coronal holes on the Sun. The embedded Alfvén waves in the solar wind plasma cause reconnection of magnetic fields on the dayside of the Earth’s magnetosphere, and the solar wind convects the fields and plasma to the tail. After the magnetic fields reconnect in the tail, the plasma is heated as it is injected into the nightside region of the magnetosphere. The energetic ~10 to 100 keV electrons generate electromagnetic waves called chorus waves, which interact with the ~100 keV electrons to accelerate them to ~MeV energies. Interplanetary space data and solar information gathered from NASA, ESA, and NOAA satellites were used to solve the problem.

This work was done by Bruce T. Tsurutani of Caltech; Rajkumar Hajra, Ezequiel Echer, and Walter D. Gonzalez of Institute Nacional de Pesquisas Espaciais, Sao Jose dos Campos, Brazil; and Ondrej Santolik of the Institute of Atmospheric Physics and Charles University, Prague Czech Republic, for NASA’s Jet Propulsion Laboratory. This software is available for license through the Jet Propulsion Laboratory, and you may request a license at: . NPO-49852