The generation of a localized source of electric fields known as “SAPS” is shown to enable deeper electron injections in the Earth’s radiation belts

The characteristics of particle injections in the Earth’s inner magnetosphere question our traditional representation for the large-scale electric fields. We argue that including a localized source of electric fields known as the SAPS is the key.

The big electric field measured around L=4 is a SubAuroral Polarization Stream (a “SAPS”) measured by one of the Van Allen Probes on March 1, 2013.

The interaction between the Sun and the Earth’s magnetic field often transmits significant energy to the electrons and protons present in the magnetospheric tail, a region of space located far from the Earth’s night-side. As a result, these particles move closer to the Earth. They are “injected” into the Earth’s inner space environment.

Since the 1970s, scientists have theorized that electrons and protons with the same initial kinetic energy starting from the same radial location have about the same distance of closest approach to the Earth.

Yet, recent observations from the Van Allen Probes reveal that this is not the case!

a marathon aid station in Paris, 2010

Electrons appear to be systematically injected “deeper” than protons. So what happens along the way to make electrons approach Earth at closer distances?

Our latest research combines observations from both space and the ground. We show that a localized source of electric fields called a Sub-Auroral Polarization Stream (aka a “SAPS”) is always present during these injections. We argue that a SAPS acts like a marathon aid station for electrons in that it provides them with additional energy. As a result, electrons “move faster” and approach the Earth at closer distances.


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