Analytic expressions for ULF wave radiation belt radial diffusion coefficients

Ozeke, L. G.; Mann, I. R.; Murphy, K. R.; Rae, I. J.; Milling, D. K.

doi:10.1002/2013ja019204

Cited by 191 publications

(739 citation statements)

References 43 publications

(139 reference statements)

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“…Recent studies of the magnetic ULF PSDs using GOES data (e.g. Ozeke et al, 2012Ozeke et al, , 2014 also showed magnetic PSDs close to the power law, similar to those in Fig. 1.…”

Section: Discussion and Summarysupporting

confidence: 78%

The influence of solar wind variability on magnetospheric ULF wave power

Pokhotelov¹,

Rae²,

Murphy

et al. 2015

Ann. Geophys.

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Abstract. Magnetospheric ultra-low frequency (ULF) oscillations in the Pc 4-5 frequency range play an important role in the dynamics of Earth's radiation belts, both by enhancing the radial diffusion through incoherent interactions and through the coherent drift-resonant interactions with trapped radiation belt electrons. The statistical distributions of magnetospheric ULF wave power are known to be strongly dependent on solar wind parameters such as solar wind speed and interplanetary magnetic field (IMF) orientation. Statistical characterisation of ULF wave power in the magnetosphere traditionally relies on average solar wind-IMF conditions over a specific time period. In this brief report, we perform an alternative characterisation of the solar wind influence on magnetospheric ULF wave activity through the characterisation of the solar wind driver by its variability using the standard deviation of solar wind parameters rather than a simple time average. We present a statistical study of nearly one solar cycle (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)) of geosynchronous observations of magnetic ULF wave power and find that there is significant variation in ULF wave powers as a function of the dynamic properties of the solar wind. In particular, we find that the variability in IMF vector, rather than variabilities in other parameters (solar wind density, bulk velocity and ion temperature), plays the strongest role in controlling geosynchronous ULF power. We conclude that, although time-averaged bulk properties of the solar wind are a key factor in driving ULF powers in the magnetosphere, the solar wind variability can be an important contributor as well. This highlights the potential importance of including solar wind variability especially in studies of ULF wave dynamics in order to assess the efficiency of solar wind-magnetosphere coupling.

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“…Recent studies of the magnetic ULF PSDs using GOES data (e.g. Ozeke et al, 2012Ozeke et al, , 2014 also showed magnetic PSDs close to the power law, similar to those in Fig. 1.…”

Section: Discussion and Summarysupporting

confidence: 78%

The influence of solar wind variability on magnetospheric ULF wave power

Pokhotelov¹,

Rae²,

Murphy

et al. 2015

Ann. Geophys.

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“…Such enhanced Pc5 wave activity penetrating deep in the magnetosphere and its effects on particle motion are linked with radial diffusion (Ukhorskiy et al, 2009;Ozeke et al, 2012Ozeke et al, , 2014. Semi-periodic variations in magnetic and electric fields steering the drift motion of trapped electrons lead to particle diffusion across drift shells from regions of lower magnetic field strength to regions of increased magnetic field strength.…”

Section: Discussionmentioning

confidence: 99%

“…Radial diffusion requires a population of seed electrons of a few hundred kiloelectron volts which are supplied by substorms and subsequently energized by Pc5 waves. Depending on the general particle distribution, radial diffusion may act to increase electron flux levels in the inner magnetosphere as electrons diffuse earthward, breaking the drift invariant, , while maintaining the gyro invariant, µ, and bounce invariant, J , associated with the trapped particles' motion (Ukhorskiy et al, 2009;Ozeke et al, 2012Ozeke et al, , 2014. Radial diffusion may also act as a loss process as the aggregate of particles drift outward and are lost to the magnetopause (Turner et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Association of radiation belt electron enhancements with earthward penetration of Pc5 ULF waves: a case study of intense 2001 magnetic storms

et al. 2015

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Abstract. Geospace magnetic storms, driven by the solar wind, are associated with increases or decreases in the fluxes of relativistic electrons in the outer radiation belt. We examine the response of relativistic electrons to four intense magnetic storms, during which the minimum of the Dst index ranged from −105 to −387 nT, and compare these with concurrent observations of ultra-low-frequency (ULF) waves from the trans-Scandinavian IMAGE magnetometer network and stations from multiple magnetometer arrays available through the worldwide SuperMAG collaboration. The latitudinal and global distribution of Pc5 wave power is examined to determine how deep into the magnetosphere these waves penetrate. We then investigate the role of Pc5 wave activity deep in the magnetosphere in enhancements of radiation belt electrons population observed in the recovery phase of the magnetic storms. We show that, during magnetic storms characterized by increased post-storm electron fluxes as compared to their pre-storm values, the earthward shift of peak and inner boundary of the outer electron radiation belt follows the Pc5 wave activity, reaching L shells as low as 3-4. In contrast, the one magnetic storm characterized by irreversible loss of electrons was related to limited Pc5 wave activity that was not intensified at low L shells. These observations demonstrate that enhanced Pc5 ULF wave activity penetrating deep into the magnetosphere during the main and recovery phase of magnetic storms can, for the cases examined, distinguish storms that resulted in increases in relativistic electron fluxes in the outer radiation belts from those that did not.

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“…ULF wave power measurements on the ground or in situ have led to various attempts to derive an analytic expression for their effect on the diffusion coefficient of particles, as a function of some geophysical index or solar wind parameter [e.g., Brautigam and Albert, 2000;Brautigam et al, 2005;Ozeke et al, 2012Ozeke et al, , 2014.…”

Section: Introductionmentioning

confidence: 99%

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

Dimitrakoudis

Mann

Balasis

et al. 2015

Geophysical Research Letters

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Ultralow frequency (ULF) waves can contribute to the transport, acceleration, and loss of electrons in the radiation belts through inward and outward diffusion. However, the most appropriate parameters to use to specify the ULF wave diffusion rates are unknown. Empirical representations of diffusion coefficients often use Kp; however, specifications using ULF wave power offer an improved physics‐based approach. We use 11 years of ground‐based magnetometer array measurements to statistically parameterize the ULF wave power with Kp, solar wind speed, solar wind dynamic pressure, and Dst. We find that Kp is the best single parameter to specify the statistical ULF wave power driving radial diffusion. Significantly, remarkable high energy tails exist in the ULF wave power distributions when expressed as a function of Dst. 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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Analytic expressions for ULF wave radiation belt radial diffusion coefficients

Cited by 191 publications

References 43 publications

The influence of solar wind variability on magnetospheric ULF wave power

The influence of solar wind variability on magnetospheric ULF wave power

Association of radiation belt electron enhancements with earthward penetration of Pc5 ULF waves: a case study of intense 2001 magnetic storms

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

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