About Microbursts in the Radiation Belts
Microbursts are short-duration (~100ms) bursts of relativistic electrons precipitating from the radiation belts. Microbursts are capable of losing large numbers of electrons; it may be possible to empty a pre-storm electron belt in one day.
This sporadic, short time-scale electron dumping from the radiation belts into the upper atmosphere was discovered decades ago. Beginning in 1992, low altitude observations from the SAMPEX Small Explorer satellite provided insight into the morphology of these electron microbursts. They occur in "clusters" consisting of many individual microbursts. Single satellites, like SAMPEX, are unable to discern the spatio-temporal behavior of electron microbursts at the cluster level and at the individual microburst scale. The two-satellite FIREBIRD mission will resolve the spatio-temporal variations of individual microbursts.
Scientific Objectives
Firebird will answer three critical questions:- What is the spatial scale size of an individual burst?
This information will provide better insight into causes and into total radiation belt loss due to microbursts. The two FIREBIRD spacecraft will fly within ~400 km of one another for up to four months, allowing sampling across many spatial scales. As the spacecraft drift apart, they will help resolve spatial/temporal ambiguity and determine the size of the microburst region. - What is the energy dependence of an individual burst?
This will help us to determine what resonance conditions are occurring. We know that there is a high level of energy coherence in microbursts. FIREBIRD will provide enough counts for a high time-resolution measurement. We will have 6 on-orbit programmable energy channels between >200keV and >1MeV. With these we will find the decorrelation length in the energy spectra. - How much total electron loss do bursts produce locally?
While questions 1 and 2 constrain the physical process that generates relativistic electron microbursts, question 3 quantifies its geoeffectiveness and overall space weather impact. The answer to question 3 requires cross-track separations of multiple hours of MLT on the dawn side, which is not possible within the resources available for the FIREBIRD mission alone. However, FIREBIRD would be able to answer Question 3 with the aid of other planned assets (e.g., the BARREL balloon mission, the NASA Van Allen Probes, and the Colorado Student Space Weather Experiment).