Abstract
Recent analysis of energetic electron measurements from the Magnetic Electron Ion Spectrometer instruments onboard the Van Allen Probes showed a local time variation of the equatorial electron intensity in the Earth’s inner radiation belt. The local time asymmetry was interpreted as evidence of drift shell distortion by a large-scale electric field. It was also demonstrated that the inclusion of a simple dawn-to-dusk electric field model improved the agreement between observations and theoretical expectations. Yet, exactly what drives this electric field was left unexplained. We combine in-situ field and particle observations, together with a physics-based coupled model, the Rice Convection Model (RCM) Coupled Thermosphere-Ionosphere-Plasmasphere-electrodynamics (CTIPe), to revisit the local time asymmetry of the equatorial electron intensity observed in the innermost radiation belt. The study is based on the dawn-dusk difference in equatorial electron intensity measured at L = 1.30 during the first 60 days of the year 2014. Analysis of measured equatorial electron intensity in the 150–400 keV energy range, in-situ DC electric field measurements and wind dynamo modeling outputs provide consistent estimates of the order of 6–8 kV for the average dawn-to-dusk electric potential variation. This suggests that the dynamo electric fields produced by tidal motion of upper atmospheric winds flowing across Earth’s magnetic field lines - the quiet time ionospheric wind dynamo - are the main drivers of the drift shell distortion in the Earth’s inner radiation belt.
Highlights
The Van Allen Probes (Mauk et al, 2013) have provided unprecedented amounts of high quality energetic (10–100 keV) electron flux measurements near the magnetic equator in the inner belt and slot region (Reeves et al, 2016) below an equatorial altitude of about 3 Earth Radii (L < 3)
During the first 60 days of 2014, the Van Allen Probes crossings of L 1.30 are in the dusk-premidnight region (20–22 magnetic local time (MLT)) during inbound, φ1, and in the dawn (4-6 MLT) sector during outbound, φ2 (Figure 1A)
The similarity is remarkable given that: 1) the neutral winds and associated wind dynamo vary from day to day and 2) every method was applied under a unique set of conditions
Summary
The Van Allen Probes (Mauk et al, 2013) have provided unprecedented amounts of high quality energetic (10–100 keV) electron flux measurements near the magnetic equator in the inner belt and slot region (Reeves et al, 2016) below an equatorial altitude of about 3 Earth Radii (L < 3). These new measurements confirmed known dynamical features such as “zebra stripe” patterns in the spectrograms of energetic electrons (Imhof and Smith, 1965; Ukhorskiy et al, 2014) and energetic electron injections deep into the inner magnetosphere (Pfitzer and Winckler, 1968; Turner et al, 2015). The observed local time asymmetry of the equatorial electron intensity at fixed L values below L 1.4 challenged the latter, suggesting a drift shell distortion by a quasi-static electric field
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
