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1FIREBIRD Science Overview

Marcello RuffoloNathan HyattJordan Maxwell2 August 2013FIREBIRD ScienceFIREBIRDFocused Investigations of Relativistic Electron Burst Intensity, Range, and Dynamics1.5-unit cube-satellite mission investigating relativistic electron microburstsTwo low-earth-orbiting satellites studying radiation belt dynamics

22 August 2013FIREBIRD ScienceFundamental ConceptsRadiation BeltsL-ShellElectron MicroburstsWhistler-Mode ChorusRadiation Belt ElectronsLoss ConeGyro-Resonant Interaction

32 August 2013FIREBIRD ScienceL-Shell42 August 2013FIREBIRD Science

Magnetic field strength calculated using L-shell, location, and time

L-Shell52 August 2013FIREBIRD Science

Radiation BeltsBands of charged particles trapped in Earths magnetic fieldsInner belt from L=1.5 to L=2Outer belt from L=4 to L=6

62 August 2013FIREBIRD Science

Magnetic Local TimeMeasurement of time with axis about the magnetic pole

72 August 2013FIREBIRD Science

Electron MicroburstsLocalized region of precipitating electronsLost from the Van Allen radiation belts and precipitate down onto the ionosphere (upper atmosphere)Occur on a short timescale (~0.2s)Observed predominantly from L=4 to L=6 in the morning sector (3MLT to 9MLT)Believed to be correlated to chorus waves generated in the near equatorial region

82 August 2013FIREBIRD ScienceElectron MicroburstsMay occur in trains ranging from 10s to several hours with ~0.5s spacing between bursts

92 August 2013FIREBIRD Science

Black-dashed line: Estimate of locally-trapped population

Blue-dotted line: Position in L-Shell

Orange spikes: Relativistic Microburst events

Whistler-Mode ChorusBursts of very-low frequency (VLF) electromagnetic emissionsPropagate within plasma in radiation beltsFrequencies range from hundreds of Hz to several kHzTimescale of ~1s, but may occur in trainsTrain timescales match those of microburstsRight-hand polarized (RHP) waves

102 August 2013FIREBIRD ScienceWhistler-Mode Chorus112 August 2013FIREBIRD Science

Whistler-Mode Chorus122 August 2013FIREBIRD ScienceChorus appears in two bandsUpper-Band ChorusLower-Band ChorusCorrelation with energy bands of microbursts

Bell et al 2009Radiation Belt ElectronsElectrons have right-hand cyclotron motion about field linesCyclotron frequency: Electrons >1 MeV are relativistic:

132 August 2013FIREBIRD Science

Loss ConeShape in velocity spaceRepresents probability that electrons will precipitate off the magnetic field linesDimensions determined by angle between velocity and magnetic field lines (pitch angle)Condition for a loss cone: Where is measured on a specific L-shellPitch angle:

142 August 2013FIREBIRD Science

Gyro-Resonant InteractionInteraction between radiation-belt electrons and whistler-mode chorus wavesConditions for interactionWave frequency equals electron gyro-resonant frequencyWave frequency less than electron cyclotron frequencyRequires that wave and electron be travelling toward each other, so that Doppler-shift can allow for comparable frequencies

Wave and electron must be similarly polarizedWhistler-mode chorus and electron cyclotron both RHP

152 August 2013FIREBIRD Science

Gyro-Resonant InteractionGyro-resonant interaction scatters electron pitch anglesSome electrons have low enough pitch angles to enter loss cone and precipitate into ionosphereThis precipitation is an electron microburstMost accepted theory

162 August 2013FIREBIRD ScienceFIREBIRD MissionThe FIREBIRD mission consists of two satellites operating simultaneously to answer the following:What is the spatial scale size of an individual microburst?What is the energy dependence of an individual microburst?How much total electron loss from the radiation belts do microburst's produce globally?

172 August 2013FIREBIRD ScienceSpatial Scale SizeMulti-point measurement required to determine spatial scale sizeFIREBIRD payloads separate at ~8 cm/sCurrent orbital scenarios estimate payloads will exceed 150 km (a landmark value mentioned in the FIREBIRD proposal) after about 2.5 monthsGPS coordinates resolved with science data will provide estimates of spatial scale size

182 August 2013FIREBIRD ScienceEnergy DependenceLower energy bursts (tens to hundreds of keV) can resonate at the equator with whistler-mode chorus waves Higher energy bursts typically occur between 60- 66 latitudeEnergy of microburst's correlated with chorus bands.

192 August 2013FIREBIRD ScienceGlobal Electron LossUse data from RBSP and BARREL to complement FIREBIRDMicrobursts are believed to be a primary loss mechanism of radiation-belt electrons

202 August 2013FIREBIRD Science

Global Electron LossRemove charged particles from the radiation beltsVarious mechanismsMicroburstsGeneral precipitationOther less prevalent mechanisms (account for small percentage of loss)

212 August 2013FIREBIRD ScienceWhy do we care?Fill in gaps in understanding of radiation-belt phenomenaStrengthening correlation between EMBs and whistler-mode chorusEnhancing conclusions drawn by past and present satellite missions by providing missing informationEducational opportunity for students involved

222 August 2013FIREBIRD ScienceQuestions?232 August 2013FIREBIRD Science