Low altitude energetic electron lifetimes after enhanced magnetic activity as deduced from SAC-C and DEMETER data

Benck, Sylvie; Mazzino, L.; Cyamukungu, Mathias; Cabrera, J.; Pierrard, Viviane

doi:10.5194/angeo-28-849-2010

Cited by 25 publications

(55 citation statements)

References 39 publications

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“…It is interesting to compare the analytical lifetime estimates discussed above with recent statistics of lifetimes obtained from SAC-C and DEMETER satellites for L < 5 (Benck et al, 2010) and from the SCATHA/SC3 satellite at L > 5 (Su et al, 2012) for 300 keV electrons, and with SAM-PEX lifetimes for E ∼ 2 MeV (Meredith et al, 2009;Tu et al, 2010). To this aim, the root-mean-square amplitudes of lower-band chorus measured by Cluster in the dayside outer belt (L > 4) during moderate geomagnetic activity periods (Kp ∼ 1.5 to 2) have been fitted by a formula B w ∼ 20 pT · exp(−|L − 7|/2), showing a maximum of wave intensity at L ∼ 7 and yielding the same values as in Fig.…”

Section: Global Analytical Lifetimes Compared To Recent Measurements mentioning

confidence: 99%

Parametric validations of analytical lifetime estimates for radiation belt electron diffusion by whistler waves

et al. 2013

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The lifetimes of electrons trapped in Earth's radiation belts can be calculated from quasi-linear pitch-angle diffusion by whistler-mode waves, provided that their frequency spectrum is broad enough and/or their average amplitude is not too large. Extensive comparisons between improved analytical lifetime estimates and full numerical calculations have been performed in a broad parameter range representative of a large part of the magnetosphere from L ~ 2 to 6. The effects of observed very oblique whistler waves are taken into account in both numerical and analytical calculations. Analytical lifetimes (and pitch-angle diffusion coefficients) are found to be in good agreement with full numerical calculations based on CRRES and Cluster hiss and lightning-generated wave measurements inside the plasmasphere and Cluster lower-band chorus waves measurements in the outer belt for electron energies ranging from 100 keV to 5 MeV. Comparisons with lifetimes recently obtained from electron flux measurements on SAMPEX, SCATHA, SAC-C and DEMETER also show reasonable agreement

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Section: Global Analytical Lifetimes Compared To Recent Measurements mentioning

confidence: 99%

Parametric validations of analytical lifetime estimates for radiation belt electron diffusion by whistler waves

et al. 2013

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“…Readers can find more details on the data and how they were processed and compared in Benck et al (2010).…”

Section: The Electron Data Setsmentioning

confidence: 99%

“…The determination of the loss timescales from SAC-C and DEMETER data has been presented in a previous paper (Benck et al 2010). More details on analysis procedure and results can be found therein.…”

Section: Determination Of the Loss Timescalesmentioning

confidence: 99%

“…In general, the steady-state flux level is reached after a determined lifetime which only depends on particle energy, position in space, and pitch angle. As the fluxes are assumed to decay exponentially to the quiet time level (steady state), the decay timescales, s, were obtained by fitting a linear function to the natural logarithm of the after-storm fluxes (Benck et al 2010). Figure 3, taken from Benck et al 2010, shows the mean decay timescales obtained for the indicated energy bins as a function of L for the region 1.6 L < 5 and a common region 0.22 < B < 0.46 G. Cases are observed in which enhanced fluxes do not decay according to the characteristic lifetimes.…”

Section: Determination Of the Loss Timescalesmentioning

confidence: 99%

“…As the fluxes are assumed to decay exponentially to the quiet time level (steady state), the decay timescales, s, were obtained by fitting a linear function to the natural logarithm of the after-storm fluxes (Benck et al 2010). Figure 3, taken from Benck et al 2010, shows the mean decay timescales obtained for the indicated energy bins as a function of L for the region 1.6 L < 5 and a common region 0.22 < B < 0.46 G. Cases are observed in which enhanced fluxes do not decay according to the characteristic lifetimes. Investigation of such behaviors reveals itself to be a powerful tool for the identification of the mechanisms that affect space particle flux variations, but is outside the scope of this paper.…”

Section: Determination Of the Loss Timescalesmentioning

confidence: 99%

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The transient observation-based particle (TOP) model and its potential application in radiation effects evaluation

Benck

Cyamukungu

Cabrera

et al. 2013

J. Space Weather Space Clim.

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The evaluation of the radiation hazards on components used in space environment is based on the knowledge of the radiation level encountered on orbit. The models that are widely used to assess the near-Earth environment for a given mission are empirical trapped radiation models derived from a compilation of spacecraft measurements. However, these models are static and hence are not suited for describing the short timescale variations of geomagnetic conditions. The transient observation-based particle (TOP)-model tends to break with this classical approach by introducing dynamic features based on the observation and characterization of transient particle flux events in addition to classical mapping of steady-state flux levels. In order to get a preliminary version of an operational model (actually only available for electrons at low Earth orbit, LEO), (i) the steady-state flux level, (ii) the flux enhancements probability distribution functions, and (iii) the flux decay-time constants (at given energy and positions in space) were determined, and an original dynamic model skeleton with these input parameters has been developed. The methodology is fully described and first flux predictions from the model are presented. In order to evaluate the net effects of radiation on a component, it is important to have an efficient tool that calculates the transfer of the outer radiation environment through the spacecraft material, toward the location of the component under investigation. Using the TOP-model space radiation fluxes and the transmitted radiation environment characteristics derived through GEANT4 calculations, a case study for electron flux/dose variations in a small silicon volume is performed. Potential cases are assessed where the dynamic of the spacecraft radiation environment may have an impact on the observed radiation effects.

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An empirically observed pitch‐angle diffusion eigenmode in the Earth's electron belt near L^* = 5.0

O’Brien

Claudepierre

Blake

et al. 2014

Geophysical Research Letters

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Using data from NASA's Van Allen Probes, we have identified a synchronized exponential decay of electron flux in the outer zone, near L * = 5.0. Exponential decays strongly indicate the presence of a pure eigenmode of a diffusion operator acting in the synchronized dimension(s). The decay has a time scale of about 4 days with no dependence on pitch angle. While flux at nearby energies and L * is also decaying exponentially, the decay time varies in those dimensions. This suggests the primary decay mechanism is elastic pitch angle scattering, which itself depends on energy and L * . We invert the shape of the observed eigenmode to obtain an approximate shape of the pitch angle diffusion coefficient and show excellent agreement with diffusion by plasmaspheric hiss. Our results suggest that empirically derived eigenmodes provide a powerful diagnostic of the dynamic processes behind exponential decays. IntroductionThe relativistic electrons in the Earth's outer radiation belt rarely, if ever, come to equilibrium. An equilibrium state would provide a straightforward, multidimensional probe into the dynamic processes that modify the quiescent radiation belts. However, the outer belt sometimes exhibits exponential decays lasting days, weeks, or even months [e.g., Meredith et al., 2006;Benck et al., 2010;Su et al., 2012;Fennell et al., 2013], and such decays are common in the inner zone [e.g., Baker et al., 2007]. Exponentially decaying fluxes, when they are synchronized across one or more dimensions of the radiation belt phase space, indicate the presence of a pure eigenmode of a linear time evolution operator acting in one or more of the synchronized dimensions. This arises from the fact that the eigenvalue is a characteristic of the operator-if the eigenvalue changes along one or more dimension of the phase space-the operator must be changing along that dimension too.In all likelihood, the relevant linear operator is a diffusion operator. The decay time is the negative reciprocal of the smallest eigenvalue, and the shape of the decaying eigenmode is a nearly unique transform of the diffusion coefficient. In practice, numerical uncertainty and the limitations of observations limit the derived diffusion coefficient to only part of the coordinate domain [Schulz and Lanzerotti, 1974, p 168]. Nonetheless, an eigenmode, which is a one-or higher-dimensional function, is necessarily a stronger constraint than the scalar decay time (eigenvalue) alone. The eigenmode can be synchronized in one, two, or three adiabatic invariants, depending on the order of the dominant diffusion process, although it is not necessarily possible to distinguish between multidimensional diffusion and lower order diffusion with a decay time that depends only weakly on one of the dimensions.There is a fairly extensive literature on theoretical and empirical eigenmodes. The interested reader is directed to Schulz and Lanzerotti [1974], especially section V.2 which reviews the use of pitch angle eigenmodes. Also, Albert and Shprits [2009] upda...

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Low altitude energetic electron lifetimes after enhanced magnetic activity as deduced from SAC-C and DEMETER data

Cited by 25 publications

References 39 publications

Parametric validations of analytical lifetime estimates for radiation belt electron diffusion by whistler waves

Parametric validations of analytical lifetime estimates for radiation belt electron diffusion by whistler waves

The transient observation-based particle (TOP) model and its potential application in radiation effects evaluation

An empirically observed pitch‐angle diffusion eigenmode in the Earth's electron belt near L^* = 5.0

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Low altitude energetic electron lifetimes after enhanced magnetic activity as deduced from SAC-C and DEMETER data

Cited by 25 publications

References 39 publications

Parametric validations of analytical lifetime estimates for radiation belt electron diffusion by whistler waves

Parametric validations of analytical lifetime estimates for radiation belt electron diffusion by whistler waves

The transient observation-based particle (TOP) model and its potential application in radiation effects evaluation

An empirically observed pitch‐angle diffusion eigenmode in the Earth's electron belt near L* = 5.0

Contact Info

Product

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An empirically observed pitch‐angle diffusion eigenmode in the Earth's electron belt near L^* = 5.0