Electron microbursts are short (~100MS) intensifications in precipitation that have been observed by x-RAY sensing balloons and in situ by satellites since the 1960S. Despite a long history of…

This federal contract award, with ID 80NSSC19K0702, was granted by the National Aeronautics and Space Administration (NASA) to Montana State University. The $2,736,297 grant will fund a balloon-borne X-ray imaging mission to directly measure the spatial scale and distribution of electron microburst phenomena in the Earth's magnetosphere. Microbursts are short-lived, intense precipitation events that have been observed for decades, but their underlying mechanisms and importance are not well understood due to the limitations of existing satellite measurements. The proposed mission aims to provide the first direct evidence to test theories connecting microbursts to non-linear interactions between electrons and whistler-mode chorus waves. There is no set-aside designation associated with this contract award.

Electron microbursts are short (~100MS) intensifications in precipitation that have been observed by x-RAY sensing balloons and in situ by satellites since the 1960S. Despite a long history of observation much remains unknown of the phenomenon including the underlying mechanism and the relative importance of this precipitation. Two important pieces of information about microbursts that are not well measured are the scale size of bursts and the distribution of bursts across the region. Satellite observations, typically from low earth orbit, traverse the precipitation region at ~8KM/s, making determination of the scale size and distribution across the sky difficult. Bursts are often described as occurring like raindrops in the region, but the rapid cross-l cuts of even multiple spacecraft cannot see the rainstorm for the drops. Indirect measurements of microburst scale size from a LEO satellite have come up with sizes as small as a few tens of gyroradii at 600KM (~ 1 KM) [blake, 1996]. Combining ground-based measurements with sampex data, dietrech ET AL. [2010] established a statistical estimate of microbursts as SIZED30 KEV microbursts was ~40KM. No existing measurement has shown a clear distribution of scale sizes or the distribution of the bursts across the sky. The goal of the proposed mission is to directly image the spatial scale and distribution of microbursts. The discovery of intense chorus waves and subsequent statistical analyses based on cluster and themis data indicated that, during geomagnetic activity, wave amplitudes regularly exceed the threshold for non-linear trapping and that large-amplitude waves have a significant parallel component of the electric field. A landau resonance with oblique whistler waves can rapidly (less than one bounce period) accelerate and precipitate electrons, providing bursty precipitation of 20 to 200 KEV electrons. One defining characteristic of such bursty precipitations would be their spatial localization which should correspond to the localization of chorus wave generation and coherence scales (evolved from multi-spacecraft measurements) scaled to precipitation altitudes. High-timeresolution measurements of microbursts together with their spatial fine structure will provide the first direct evidence to test recent theories connecting microbursts with nonlinear whistlers and improve our knowledge of an important magnetospheric wave-particle interaction. The proposed mission is to fly a balloon-borne x-RAY imager with temporal and angular resolution capable of directly measuring the scale and distribution of microbursts. Balloon payloads are effectively stationary under the precipitation region and are sensitive to locally precipitating electrons from 20KEV to several MEV, but previous balloon payloads could not produce images at these energies at microburst timescales. Directly imaging microbursts across the field of view of the balloon will allow direct comparison to wave distributions, whistler-wave scale size, and coherence scales within whistlers. Measuring the spatial and temporal distribution on the sky will answer questions that cannot be solved by single point or even a small number of point measurements made by LEO satellites that are rapidly moving through the precipitation region. Direct measurements of the precipitation scale will also make the first quantification of electron losses in individual bursts.