The Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) studies the loss of energetic electrons from Earth's radiation belts. BARREL's array of slowly drifting balloon payloads was designed to capitalize on magnetic conjunctions with NASA's Van Allen Probes. Two campaigns were conducted from Antarctica in 2013 and 2014. During the first campaign in January and February of 2013, there were three moderate geomagnetic storms with SYM‐H min < −40 nT. Similarly, two minor geomagnetic storms occurred during the second campaign, starting in December of 2013 and continuing on into February of 2014. Throughout the two campaigns, BARREL observed electron precipitation over a wide range of energies and exhibiting temporal structure from hundreds of milliseconds to hours. Relativistic electron precipitation was observed in the dusk to midnight sector, and microburst precipitation was primarily observed near dawn. In this paper we review the two BARREL science campaigns and discuss the data products and analysis techniques as applied to relativistic electron precipitation observed on 19 January 2013.

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[1] At suprathermal energies, interplanetary electrons commonly exhibit a magnetic field-aligned beam referred to as the strahl. The finite strahl width is a consequence of competition between magnetic focusing as the interplanetary field weakens with distance from the Sun, and particle scattering acting to broaden the strahl along its propagation path. We present a statistical survey of the strahl using ACE Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) measurements from 1998 to 2002. A systematic fitting algorithm was applied to pitch angle distributions to identify unidirectional or counterstreaming strahl features and to quantify beam widths and intensities. The analysis indicated that a strahl is present ≥75% of the time, while counterstreaming strahls were observed about 10% of the time. The strahl width ranges from 5 to 90 ; importantly, the strahl cannot be characterized by any typical width. Within counterstreaming intervals the strahl peak intensity anticorrelates with beam width while the integrated fluxes of the two simultaneously observed strahls are similar, within a factor of 2 for 75% of counterstreaming periods. Observations are consistent with a model in which integrated strahl flux leaving the corona varies over a limited range, but the degree of beam scattering along the propagation path to 1 AU varies widely. The difference between two concurrent counterstreaming strahls is likely due to different scattering profiles along the different legs of a closed field line loop, both rooted in similar coronal regions. Narrow strahls (<20 ) are strongly associated with counterstreaming intervals, as well as high-speed streams. Strahl width can either increase or decrease with energy.

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