Multi-point observation of interplanetary shock–driven asymmetry of dayside inner-magnetospheric keV particles under geomagnetically quiet conditions

We present simultaneous multi-point observation of local-time asymmetry in keV ion and electron fluxes during the interplanetary (IP) shock impact on 19 April 2014 under geomagnetically quiet conditions. During this event, Van Allen Probe-A and Probe-B were simultaneously located in the afternoon and morning sectors, respectively, for ∼20 min (18:38-18:58 UT), while sampling nearly identical radial distances (L* = 3.7 ± 0.2). This unique conjunction provides an exceptional opportunity to investigate the local-time–dependent response of inner magnetospheric particle populations to shock-driven compression. Distinct asymmetries in the ion and electron flux responses are identified during the IP shock interval. In the afternoon sector, H⁺, He⁺, and O⁺ ions exhibit pronounced multiple nose structures at energies above 5 keV that extend deeper in radial distance. In contrast, the morning sector shows fewer nose structures—particularly for O⁺ ions and the corresponding features for all ion species are considerably less deep compared to those observed in the afternoon sector. In contrast, keV electrons show an enhancement of an order of magnitude or more in the morning sector following the IP shock, whereas no significant electron response is observed in the afternoon sector during the same interval. Our results indicate that the observed dayside local-time asymmetry of keV ions is primarily governed by shock-induced asymmetric magnetospheric compression combined with the temporal variability of the convection electric field. These findings demonstrate that even weak IP shocks under quiet geomagnetic conditions can produce significant and highly asymmetric particle responses in the inner magnetosphere.