Bifurcation of drift shells near the dayside magnetopause

Ozturk, Mesude; Wolf, R. A.

doi:10.1029/2006ja012102

Cited by 51 publications

(77 citation statements)

References 27 publications

(39 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Therefore the following steps are carried out to obtain the outer boundary at a certain K parameter (K 0 ): (1) a bisection iterative method is applied in tracing each drift shells from the midnight meridian until the last closed drift shell L * max (α) is determined for a set of equatorial pitch angle α ranging from 20 to 90 • ; (2) the above procedure also provides the corresponding K parameter at the last closed drift shell for a specific equatorial pitch angle, i.e., K(α); (3) these L * max (K(α)) are then interpolated into L * max (K 0 ). (Shabansky, 1971;Öztürk and Wolf, 2007;Ukhorskiy et al, 2011) in which it does not come across the equator but bounces within one hemisphere, allowing a larger drift shell until it encounters the magnetopause boundary (see Kim et al, 2008, for an illustration). The quasi-periodic daily evolution of the last drift shell is caused by the warping of the tail current sheet across the magnetic equator in the T89 magnetic field model (Tsyganenko, 1989) that is used to account for the geodipole tilt angle.…”

Section: Initial Condition and Outer Boundarymentioning

confidence: 99%

Quantifying the effect of magnetopause shadowing on electron radiation belt dropouts

Koller

Morley

2013

Ann. Geophys.

View full text Add to dashboard Cite

Abstract. Energetic radiation belt electron fluxes can undergo sudden dropouts in response to different solar wind drivers. Many physical processes contribute to the electron flux dropout, but their respective roles in the net electron depletion remain a fundamental puzzle. Some previous studies have qualitatively examined the importance of magnetopause shadowing in the sudden dropouts either from observations or from simulations. While it is difficult to directly measure the electron flux loss into the solar wind, radial diffusion codes with a fixed boundary location (commonly utilized in the literature) are not able to explicitly account for magnetopause shadowing. The exact percentage of its contribution has therefore not yet been resolved. To overcome these limitations and to determine the exact contribution in percentage, we carry out radial diffusion simulations with the magnetopause shadowing effect explicitly accounted for during a superposed solar wind stream interface passage, and quantify the relative contribution of the magnetopause shadowing coupled with outward radial diffusion by comparing with GPS-observed total flux dropout. Results indicate that during high-speed solar wind stream events, which are typically preceded by enhanced dynamic pressure and hence a compressed magnetosphere, magnetopause shadowing coupled with the outward radial diffusion can explain about 60-99 % of the main-phase radiation belt electron depletion near the geosynchronous orbit. While the outer region (L * > 5) can nearly be explained by the above coupled mechanism, additional loss mechanisms are needed to fully explain the energetic electron loss for the inner region (L * ≤ 5). While this conclusion confirms earlier studies, our quantification study demonstrates its relative importance with respect to other mechanisms at different locations.

show abstract

Section: Initial Condition and Outer Boundarymentioning

confidence: 99%

Quantifying the effect of magnetopause shadowing on electron radiation belt dropouts

Koller

Morley

2013

Ann. Geophys.

View full text Add to dashboard Cite

show abstract

“…Another effect which adds to the complexity of outer belt dynamics is drift orbit bifurcations, also referred to as Shabansky orbits after Shabansky [1971]. Known for a long time [Northrop and Teller, 1960;Northrop, 1963;Roederer, 1970;Antonova et al, 2003], it recently received renewed attention [Öztürk and Wolf, 2007;Kim et al, 2008;McCollough et al, 2010;Wan et al, 2010] due to development of new particle tracing techniques and improved geomagnetic field models. In this paper we investigate the implications of drift orbit bifurcations for acceleration, transport and loss of the outer belt electrons.…”

Section: Introductionmentioning

confidence: 99%

“…Particles that undergo drift orbit bifurcations (blue color) violate the second invariant J at bifurcations, when the period of the bounce and the drift motions are no longer separated. This drives pitch angle and radial transport even when the magnetic field is constant [e.g., Antonova et al, 2003;Öztürk and Wolf, 2007;Wan et al, 2010]. Since the second invariant is not conserved, the drift orbits are not closed and the third invariant is undefined.…”

Section: Introductionmentioning

confidence: 99%

The role of drift orbit bifurcations in energization and loss of electrons in the outer radiation belt

et al. 2011

View full text Add to dashboard Cite

[1] Radiation levels in Earth's outer electron belt (L^2.5) vary by orders of magnitude on the time scales ranging from minutes to days. Multiple acceleration and loss processes operate across the belt and compete in defining its global variability. One such process is the drift orbit bifurcation effect. Caused by coupling of the drift and bounce motions, it breaks the second adiabatic invariant of radiation belt electrons producing their transport in radius and pitch angle. In this paper we investigate implications of drift orbit bifurcations to the global state and variability of the outer electron belt. For this purpose we use three-dimensional test particle simulations of electron guiding center motion in a realistic magnetic field model. We show that even at most quiet solar wind conditions bifurcations affect a broad range of the belt penetrating inside the geosynchronous orbit. This has an important practical implication for the analysis of experimental particle data: since the third adiabatic invariant is undefined for bifurcating orbit, the electron phase space density cannot be expressed in terms of three adiabatic invariants. We show that long-term transport of electrons due to drift orbit bifurcations is a complex combination of large ballistic jumps and small-amplitude diffusion in the second invariant and radial location. To model long-term transport, we derive an empirical map of the second invariant and radial jumps at bifurcations. The map can also be implemented by other radiation belt models, which cannot directly account for the physics of drift orbit bifurcations. Drift orbit bifurcations can produce electron losses through the magnetopause escape and through pitch angle scattering into the atmospheric loss cone. Most electrons, however, can stay quasi-trapped in the bifurcation regions for very long time periods. The pitch angle and radial transport due to drift orbit bifurcations lead to their meandering back and forth across the region producing mixing and recirculation of particle populations with different initial conditions. We show that this recirculation can greatly amplify electron energization by radial diffusion. Compared to the diffusion alone, the combined action of radial diffusion and drift orbit bifurcations can double electron energization at each recirculation cycle. Our results suggest that drift orbit bifurcations can play an important role in the buildup of increased electron fluxes in the storm recovery phase.

show abstract

“…Actually, the LCDS is not unique but depends on the particle pitch angle. In fact, the situation is made much more complex by the possibility of drift-orbit bifurcation (DOB), which changes the second invariant (Öztürk and Wolf, 2007) and invalidates most calculations of L * but does not cause the same rapid loss of confinement. Since low values of equatorial pitch angle are less subject to DOB, as an expedient the LCDS is found (by iterative search) for a particle with equatorial pitch angle of 40 • at midnight.…”

Section: Global Settingmentioning

confidence: 99%

Radial diffusion simulations of the 20 September 2007 radiation belt dropout

Albert

2014

Ann. Geophys.

View full text Add to dashboard Cite

Abstract. This is a study of a dropout of radiation belt electrons, associated with an isolated solar wind density pulse on 20 September 2007, as seen by the solid-state telescopes (SST) detectors on THEMIS (Time History of Events and Macroscale Interactions during Substorms). Omnidirectional fluxes were converted to phase space density at constant invariants M = 700 MeV G −1 and K = 0.014 R E G 1/2 , with the assumption of local pitch angle α ≈ 80 • and using the T04 magnetic field model. The last closed drift shell, which was calculated throughout the time interval, never came within the simulation outer boundary of L * = 6. It is found, using several different models for diffusion rates, that radial diffusion alone only allows the data-driven, time-dependent boundary values at L max = 6 and L min = 3.7 to propagate a few tenths of an R E during the simulation; far too slow to account for the dropout observed over the broad range of L * = 4-5.5. Pitch angle diffusion via resonant interactions with several types of waves (chorus, electromagnetic ion cyclotron waves, and plasmaspheric and plume hiss) also seems problematic, for several reasons which are discussed.

show abstract

Bifurcation of drift shells near the dayside magnetopause

Cited by 51 publications

References 27 publications

Quantifying the effect of magnetopause shadowing on electron radiation belt dropouts

Quantifying the effect of magnetopause shadowing on electron radiation belt dropouts

The role of drift orbit bifurcations in energization and loss of electrons in the outer radiation belt

Radial diffusion simulations of the 20 September 2007 radiation belt dropout

Contact Info

Product

Resources

About