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Balloon Array for Radiation Belt Relativistic Electron Losses

BARREL (Balloon Array for RBSP Relativistic Electron Losses) is a multiple-balloon investigation that will study Earth's Radiation Belts. Atmospheric losses of relativistic electrons play an important role in radiation belt dynamics; precipitation into the atmosphere may even completely deplete the radiation belts in some cases. BARREL is the first NASA Living with a Star Geospace Mission of Opportunity, and will support NASA's RBSP (Radiation Belt Storm Probes) mission.

BARREL will consist of two Antarctic balloon campaigns conducted in Austral summers of 2012 and 2013. During each campaign, a total of 20 small (~20 kg) balloon payloads will be launched to an altitude of 30-35 km to maintain an array of 5-8 payloads. Each balloon will carry a NaI scintillator to measure the bremsstrahlung X-rays produced by precipitating relativistic electrons as they collide with neutrals in Earth's atmosphere, and a DC magnetometer. The balloons will be launched from the South African Antarctic Station (SANAE IV) and the British station, Halley Bay.

We will combine the measurements of precipitation with the RBSP spacecraft measurements of waves and energetic particles, achieving the following specific science objectives during the RBSP mission:

• Determine the total electron loss rate during RBSP relativistic electron events by simultaneously measuring the precipitating flux of relativistic electrons over a wide range of local times. The loss rate will be compared with changes in the trapped flux for specific relativistic electron events to help quantify relativistic electron acceleration, and determine whether pitch-angle scattering is occurring in the strong-diffusion limit.
• Directly test models of wave-particle interactions in order to differentiate among different loss processes by combining precipitation measurements with simultaneous RBSP in situ wave and energetic particle measurements. We will quantitatively test whether EMIC waves and chorus are responsible for duskside MeV events and microburst precipitation respectively. This will be crucial for validating the models that will be used to calculate losses based only on in-situ RBSP measurements, for example during times when global precipitation measurements are not available.
• Determine the relative importance of duskside MeV events and microburst precipitation and their associated precipitation mechanisms for different magnetic activity levels. This will be achieved by comparing the precipitation loss rates due to both types of precipitation. BARREL will detect 120 duskside MeV events, allowing us to produce the first magnetic local time/L-value distribution of these events, which can then be compared to the distribution for microbursts measured by SAMPEX.
• Characterize the spatial extent and spatial structure of precipitation, which has been addressed previously only in a statistical sense. The region over which waves scatter electrons is a critical parameter for modeling electron loss timescales. This is particularly important when direct precipitation measurements are not available. BARREL will simultaneously measure precipitation at 5-8 different locations in correlation with wave measurements made by RBSP.

BARREL is one balloon project carried out by the Dartmouth Balloon Group. Click here to learn about other projects carried out by the group.