Earth's Ring Current Research Articles

What Drove the Carrington Event? An Analysis of Currents and Geospace Regions

AbstractThe 1859 Carrington event is the most intense geomagnetic storm in recorded history, and the literature provides numerous explanations for what drove the negative H perturbation on the Earth. There is debate on what dominated the event. Our analysis shows a combination of causes of similar orders of magnitude. Previous analyses generally rely upon the observed H perturbation at Colaba, India; historic newspaper reports; and empirical models. We expand the analysis using two Space Weather Modeling Framework simulations to examine what drove the event. We compute contributions from currents and geospace regions to the northward B field on Earth's surface, BN. We examine magnetospheric currents parallel and perpendicular to the local B field, ionospheric currents, and gap region field–aligned currents (FACs). We also evaluate contributions from the magnetosheath, near–Earth, and neutral sheet regions. A combination of currents and geospace regions significantly contribute to BN on the Earth's surface, changing as the storm evolves. At storm onset, magnetospheric currents and gap–region FACs dominate in the equatorial region. At auroral latitudes, gap–region FACs and ionospheric currents are the largest contributors. At storm peak, azimuthal magnetospheric currents and gap–region FACs dominate at equatorial latitudes. Gap–region FACs and ionospheric currents dominate in the auroral zone, down to mid‐latitudes. Both the magnetosheath and FACs contribute at storm peak, but are less significant than that from the near–Earth ring current. During recovery, the near–Earth ring current is the largest contributor at equatorial latitudes. Ionospheric currents and gap–region FACs dominate in the auroral zone.

New Findings From Explainable SYM‐H Forecasting Using Gradient Boosting Machines

AbstractIn this work, we develop gradient boosting machines (GBMs) for forecasting the SYM‐H index multiple hours ahead using different combinations of solar wind and interplanetary magnetic field (IMF) parameters, derived parameters, and past SYM‐H values. Using Shapley Additive Explanation values to quantify the contributions from each input to predictions of the SYM‐H index from GBMs, we show that our predictions are consistent with physical understanding while also providing insight into the complex relationship between the solar wind and Earth's ring current. In particular, we found that feature contributions vary depending on the storm phase. We also perform a direct comparison between GBMs and neural networks presented in prior publications for forecasting the SYM‐H index by training, validating, and testing them on the same data. We find that the GBMs yield a statistically significant improvement in root mean squared error over the best published black‐box neural network schemes and the Burton equation.

Acceleration of Ring Current Protons Driven by Magnetosonic Waves: Comparisons of Test Particle Simulations with Quasilinear Calculations

Abstract Wave–particle interactions play important roles in local acceleration and pitch angle scattering loss of charged particle dynamics in astrophysics and space physics, and energy transfer between plasma waves and particles is a key problem in plasma physics. Using full relativistic test particle simulations, we quantitatively evaluate the magnetosonic wave-driven acceleration of Earth's ring current protons both inside and outside the plasmapause at L = 4.5. Analysis of resonance conditions indicates that the broadband magnetosonic waves can affect protons by multiple harmonic cyclotron resonances. With a representative amplitude ∼200 pT, magnetosonic waves can produce energy diffusion coefficients, obtained from test particle simulations, at rates of ∼10−4 s−1 for protons ∼1–3 keV inside the plasmapause and ∼3–30 keV outside the plasmapause, both at equatorial pitch angles ∼75°–90°. Compared with the quasilinear theory calculations, the test particle diffusion coefficients exhibit a difference due to the nonresonant transit time effect outside the plasmapause. Subsequent 2D Fokker–Planck simulations indicate that on a timescale of ∼2 days, magnetosonic waves can effectively enhance the phase space density of the ring current protons ∼10 keV inside the plasmapause and ∼100 keV outside the plasmapause at equatorial pitch angles ∼60°–90°, thereby leading to the evolvement of the ring current proton distribution from a Kappa-type to a 90°-peaked profile. Our results demonstrate that the local acceleration of the ring current protons by magnetosonic waves is an important process of energy transfer between different populations of magnetospheric protons and hence contributes to the dynamic evolution of Earth's ring current.

Influence of the Earth's ring current strength on Størmer's allowed and forbidden regions of charged particle motion

Abstract. Størmer's particles' trapping regions for a planet with an intrinsic dipolar magnetic field are considered, taking into account the ring current which arises due to the trapped particles' drift for the case of the Earth. The influence of the ring current on the particle trapping regions' topology is investigated. It is shown that a critical strength of the ring current exists under which further expansion of the trapping region is no longer possible. Before reaching this limit, the dipole field, although deformed, retains two separated Størmer regions. After transition of critical magnitude, the trapping region opens up, and charged particles, which form the ring current, get the opportunity to leave it, thus decreasing the ring current strength. Numerical calculations have been performed for protons with typical energies of the Earth's radiation belt and ring current. For the Earth's case, the Dst index for the critical ring current strength is calculated.

Simulation and TWINS observations of the 22 July 2009 storm

TWINS is the first mission to perform stereo imaging of the Earth's ring current. The magnetic storm on 22 July 2009 was at the time the largest storm observed since TWINS began routine stereo imaging in June 2008. On 22 July 2009, the Dst dropped to nearly −80 nT at 0700 and 1000 UT. During the main phase, and at the peak of the storm, TWINS 1 and 2 were near apogee and moving between predawn and postdawn local time. The energetic neutral atom (ENA) imagers on the two spacecraft captured the storm intensification and the formation of the partial ring current. The peak of the high‐altitude ENA emissions was seen in the midnight‐to‐dawn local time sector. The development of this storm has been simulated using the comprehensive ring current model (CRCM) to understand and interpret the observed signatures. We perform CRCM runs with constant and time‐varying magnetic field. The model calculations are validated by comparing the simulated ENA and ion flux intensities with TWINS ENA images and in situ ion data from a THEMIS satellite. Simulation with a static magnetic field produces a strong shielding electric field that skews the ion drift trajectories toward dawn. The model's corresponding peak ENA emissions are always more eastward than those in the observed TWINS images. On the other hand, the simulation with a dynamic magnetic field gives better spatial agreement with both ENA and in situ particle data, suggesting that temporal variations of the geomagnetic field exert a significant influence upon global ring current ion dynamics.

Comprehensive computational model of Earth's ring current

A comprehensive ring current model (CRCM) has been developed that couples the Rice Convection Model (RCM) and the kinetic model of Fok and coworkers. The coupled model is able to simulate, for the first time using a self‐consistently calculated electric field, the evolution of an inner magnetosphere plasma distribution that conserves the first two adiabatic invariants. The traditional RCM calculates the ionospheric electric fields and currents consistent with a magnetospheric ion distribution that is assumed to be isotropic in pitch angle. The Fok model calculates the plasma distribution by solving the Boltzmann equation with specified electric and magnetic fields. To combine the RCM and the Fok model, the RCM Birkeland current algorithm has been generalized to arbitrary pitch angle distributions. Given a specification of height‐integrated ionospheric conductance, the RCM component of the CRCM computes the ionospheric electric field and currents. The Fok model then advances the ring current plasma distribution using the electric field computed by the RCM and at the same time calculates losses along particle drift paths. We present the logic of CRCM and the first validation results following the H+ distribution during the previously studied magnetic storm of May 2, 1986. The H+ fluxes calculated by the coupled model agree very well with observations by AMPTE/CCE. In particular, the coupled model is able to reproduce the high H+ flux seen on the dayside at L ∼ 2.3 that the previous simulation, which employed a Stern‐Volland convection model with shielding factor 2, failed to produce. Though the Stern‐Volland and CRCM electric fields differ in several respects, the most notable difference is that the CRCM predicts strong electric fields near Earth in the storm main phase, particularly in the dusk‐midnight quadrant. Thus the CRCM injects particles more deeply and more quickly.

Dynamics of the earth's ring current: Theory and observation

The development of currents within an arbitrary distribution of particles trapped in the geomagnetic field is described. These currents combine to form the earth's ring current and thus are responsible for the worldwide depressions of surface magnetic field strength during periods of magnetic activity known as magnetic storms. Following a brief review of trapped particle motion in magnetic fields, ring current development is described and presented in terms of basic field and particle distribution parameters. Experimental observations then are presented and discussed within the theoretical framework developed earlier. New results are presented which, in the area of composition and charge state observations, hold high promise in solving many long standing ring current problems. Finally, available experimental results will be used to assess our present understanding as to ring current sources, generation, and dissipation.

The Ampte charge Composition Explorer and the 4-7 September 1984 geomagnetic storm

The orbit and payload of the AMPTE (active magnetospheric particle tracer explorer) Charge Composition Explorer (CCE) satellite, which provide an exellent opportunity for observing the geomagnetically trapped particle population in general and the earth's ring current in particular, are described. A global view of the September 4, 1984 geomagnetic storm is presented and the initial findings of the CCE investigators on the earth's ring current are given. It is shown that the CCE ring-current results pertain to an unusual asymmetric ring current and may not be applicable to a more typical ring-current development and decay.

The Earth's ring current: Causes, generation, and decay

The Earth's ring current: Causes, generation, and decay

Ring current composition and sources: An update

The composition of the Earth's ring current was reviewed at the Chapman Conference on “Magnetospheric Substorms and Related Plasma Processes,” held at Los Alamos Scientific Laboratory, Los Alamos, NM., 9–13 October 1978 (Akasofu, 1980; Williams, 1980a). It was found that the composition of the bulk of the ring current energy distribution had not been measured and several source mechanisms were possible. In this note we update that review and present recent results from Prognoz, GEOS, and ISEE instruments. Composition data and results concerning the general behavior of storm time energetic particles are shown. It is found that the ring current energy density composition still has not been observed and that the recent equatorial low energy composition results add to the particle type (charge state) and source possibilities.

Inference of the ring current ion composition by means of charge exchange decay

The analysis of data from the Explorer 45 (S³‐A) electrostatic analyzer in the energy range 5–30 keV has provided some new results on the ring current ion composition. It has been well established that the storm time ring current has a decay time of several days, during which the particle fluxes decrease nearly monotonically. In the past, ring current studies have assumed or stated that hydrogen was the dominant ion in the earth's ring current. By analyzing the measured ion fluxes during the several day storm recovery period and assuming that beside hydrogen other ions were present and that the decays were exponential in nature, we were able to establish three separate lifetimes for the ions. These fitted decay lifetimes are in excellent agreement with the expected charge exchange decay lifetimes for H+, O+, and He+ in the energy and L value range of the data. This inference technique thus establishes the presence of measurable and appreciable quantities of oxygen and helium ions as well as protons in the storm time ring current; we also find indications that He++ may also be present under these same conditions. The existence of additional ions is not ruled out by this technique.