Accurately specifying storm‐time ULF wave radial diffusion in the radiation belts

Dimitrakoudis, Stavros; Mann, I. R.; Balasis, Georgios; Papadimitriou, Constantinos; Anastasiadis, A.; Daglis, Ioannis A.

doi:10.1002/2015gl064707

Cited by 27 publications

(34 citation statements)

References 35 publications

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“…During this intense storm, we show that the event‐specific radial diffusion coefficients do not correspond to those in Kp ‐dependent statistical models such as presented by Brautigam and Albert () and Ozeke et al (). Our results are similar to the ones obtained by Pokhotelov et al () for the October 2012 geomagnetic storm and by Dimitrakoudis et al () using analysis of 11 years of ground‐based magnetometers data. Our results imply that performing the radial diffusion simulations with Kp ‐parametrization empirical models for D LL can lead to an underestimation of the diffusion rates, especially during storm main phase.…”

Section: Introductionsupporting

confidence: 92%

On the Relative Strength of Electric and Magnetic ULF Wave Radial Diffusion During the March 2015 Geomagnetic Storm

et al. 2019

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In this paper, we study electron radial diffusion coefficients derived from Pc4-Pc5 ultralow frequency (ULF) wave power during the intense geomagnetic storm on 17-18 March 2015. During this storm the population of highly relativistic electrons was depleted within 2 hr of the storm commencement. This radial diffusion, depending upon the availability of source populations, can cause outward radial diffusion of particles and their loss to the magnetosheath, or inward transport and acceleration. Analysis of electromagnetic field measurements from Geostationary Operational Environment Satellite (GOES), Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite, and ground-based magnetometers shows that the main phase storm-specific radial diffusion coefficients do not correspond to statistical estimates. Specifically, during the main phase, the electric diffusion (D E LL ) is reduced, and the magnetic diffusion (D B LL ) is increased, compared to empirical models based on Kp. Contrary to prior results, the main phase magnetic radial diffusion cannot be neglected. The largest discrepancies, and periods of dominance of D B LL over D E LL , occur during intervals of strongly southward IMF. However, during storm recovery, both magnetic and electric diffusion rates are consistent with empirical estimates. We further verify observationally, for the first time, an energy coherence for both D B LL and D E LL where diffusion coefficients do not depend on energy. We show that, at least for this storm, properly characterizing main phase radial diffusion, potentially associated with enhanced ULF wave magnetopause shadowing losses, cannot be done with standard empirical models. Modifications, associated especially with southward IMF, which enhance the effects of D B LL and introduce larger main phase outward transport losses, are needed.Recent long-term radiation belt simulations by Drozdov et al. (2017) suggest that EMIC wave losses, parametrized in their model using solar wind dynamic pressure, may be important. However, recent studies,

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Section: Introductionsupporting

confidence: 92%

On the Relative Strength of Electric and Magnetic ULF Wave Radial Diffusion During the March 2015 Geomagnetic Storm

et al. 2019

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“…For March 2013 there remains a separation between the LCDS and the L * where the loss is observed since the LCDS does not drop below L *∼5. However, in the presence of steep gradients in phase space density and strong storm main phase ULF wave power (Dimitrakoudis et al, ; Murphy et al, ) the time scales in the modeling of Mann and Ozeke () suggest that outward radial diffusion to the LCDS could be sufficient to explain the observed rapid losses and radiation belt extinction.…”

Section: Resultsmentioning

confidence: 99%

On the Role of Last Closed Drift Shell Dynamics in Driving Fast Losses and Van Allen Radiation Belt Extinction

et al. 2018

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We present observations of very fast radiation belt loss as resolved using high time resolution electron flux data from the constellation of Global Positioning System (GPS) satellites. The time scale of these losses is revealed to be as short as ∼0.5-2 hr during intense magnetic storms, with some storms demonstrating almost total loss on these time scales and which we characterize as radiation belt extinction. The intense March 2013 and March 2015 storms both show such fast extinction, with a rapid recovery, while the September 2014 storm shows fast extinction but no recovery for around 2 weeks. By contrast, the moderate September 2012 storm which generated a three radiation belt morphology shows more gradual loss. We compute the last closed drift shell (LCDS) for each of these four storms and show a very strong correspondence between the LCDS and the loss patterns of trapped electrons in each storm. Most significantly, the location of the LCDS closely mirrors the high time resolution losses observed in GPS flux. The fast losses occur on a time scale shorter than the Van Allen Probes orbital period, are explained by proximity to the LCDS, and progress inward, consistent with outward transport to the LCDS by fast ultralow frequency wave radial diffusion. Expressing the location of the LCDS in L*, and not model magnetopause standoff distance in units of R E , clearly reveals magnetopause shadowing as the cause of the fast loss observed by the GPS satellites.

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“…Ozeke et al (2014) used statistical GOES and THEMIS measurements to derive an analytic expression for power vs. L for various geomagnetic activity levels, which can easily be incorporated into global radiation belt models. Recently, Dimitrakoudis et al (2015) found that Kp is the best single parameter to specify the statistical ULF wave power driving radial diffusion. Moreover, two-parameter ULF wave power specifications using Dst as well as Kp provide a better statistical representation of storm-time radial diffusion than any single variable alone.…”

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confidence: 99%

Calculating ultra-low-frequency wave power of the compressional magnetic field vs. <i>L</i> and time: multi-spacecraft analysis using the Van Allen probes, THEMIS and GOES

Sarris

2016

Ann. Geophys.

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Abstract. Ultra-low-frequency (ULF) pulsations are critical in radial diffusion processes of energetic particles, and the power spectral density (PSD) of these fluctuations is an integral part of the radial diffusion coefficients and of assimilative models of the radiation belts. Using simultaneous measurements from two Geostationary Operational Environmental Satellites (GOES) geosynchronous satellites, three satellites of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft constellation and the two Van Allen probes during a 10-day period of intense geomagnetic activity and ULF pulsations of October 2012, we calculate the PSDs of ULF pulsations at different L shells. By following the time history of measurements at different L it is shown that, during this time, ULF wave power is not enhanced uniformly throughout the magnetosphere but instead is mostly enhanced in the outer L shells, close to the magnetopause, and to a lesser extent in the inner magnetosphere, closer to the plasmapause. Furthermore, by using phase differences between two GOES geosynchronous satellite pairs, we estimate the daily-averaged distribution of power at different azimuthal wave numbers. These results can have significant implications in better defining the effect of radial diffusion in the phase space density of energetic particles for different wave numbers or L shell distributions of ULF power.

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Accurately specifying storm‐time ULF wave radial diffusion in the radiation belts

Cited by 27 publications

References 35 publications

On the Relative Strength of Electric and Magnetic ULF Wave Radial Diffusion During the March 2015 Geomagnetic Storm

On the Relative Strength of Electric and Magnetic ULF Wave Radial Diffusion During the March 2015 Geomagnetic Storm

On the Role of Last Closed Drift Shell Dynamics in Driving Fast Losses and Van Allen Radiation Belt Extinction

Calculating ultra-low-frequency wave power of the compressional magnetic field vs. <i>L</i> and time: multi-spacecraft analysis using the Van Allen probes, THEMIS and GOES

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Accurately specifying storm‐time ULF wave radial diffusion in the radiation belts

Cited by 27 publications

References 35 publications

On the Relative Strength of Electric and Magnetic ULF Wave Radial Diffusion During the March 2015 Geomagnetic Storm

On the Relative Strength of Electric and Magnetic ULF Wave Radial Diffusion During the March 2015 Geomagnetic Storm

On the Role of Last Closed Drift Shell Dynamics in Driving Fast Losses and Van Allen Radiation Belt Extinction

Calculating ultra-low-frequency wave power of the compressional magnetic field vs. &lt;i&gt;L&lt;/i&gt; and time: multi-spacecraft analysis using the Van Allen probes, THEMIS and GOES

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Calculating ultra-low-frequency wave power of the compressional magnetic field vs. <i>L</i> and time: multi-spacecraft analysis using the Van Allen probes, THEMIS and GOES