Ionospheric Potential Research Articles

Integration of the radiation belt environment model into the space weather modeling framework

We have integrated the Fok radiation belt environment (RBE) model into the space weather modeling framework (SWMF). RBE is coupled to the global magnetohydrodynamics component (represented by the Block-Adaptive-Tree Solar-wind Roe-type Upwind Scheme, BATS-R-US, code) and the Ionosphere Electrodynamics component of the SWMF, following initial results using the Weimer empirical model for the ionospheric potential. The radiation belt (RB) model solves the convection–diffusion equation of the plasma in the energy range of 10 keV to a few MeV. In stand-alone mode RBE uses Tsyganenko's empirical models for the magnetic field, and Weimer's empirical model for the ionospheric potential. In the SWMF the BATS-R-US model provides the time dependent magnetic field by efficiently tracing the closed magnetic field-lines and passing the geometrical and field strength information to RBE at a regular cadence. The ionosphere electrodynamics component uses a two-dimensional vertical potential solver to provide new potential maps to the RBE model at regular intervals. We discuss the coupling algorithm and show some preliminary results with the coupled code. We run our newly coupled model for periods of steady solar wind conditions and compare our results to the RB model using an empirical magnetic field and potential model. We also simulate the RB for an active time period and find that there are substantial differences in the RB model results when changing either the magnetic field or the electric field, including the creation of an outer belt enhancement via rapid inward transport on the time scale of tens of minutes.

Preseismic alteration of atmospheric electrical conditions due to anomalous radon emanation

Preseismic radon (Rn-222) emanation is considered to be one of the main physical mechanisms of electromagnetic precursory phenomena. In this paper, we analyze the atmospheric radon concentration around the occurrence time of the 1995 Kobe earthquake, and evaluate the influence on the atmospheric electrical conditions based on the global electric circuit under the quasistatic state. The radon emanation increases the number density of small ions and the atmospheric conductivity and decreases the atmospheric electric field by about 40–50% in the lower atmosphere, while they show little change in the upper atmosphere. The difference in the lower and upper atmosphere induces the reduction of the ionospheric potential. The estimated quasistatic changes near the ground can explain the reported seismic precursors such as the ion number density and the electric field. At the ionospheric altitude, however, not only the quasistatic process but also the shorter-term process, i.e., a transient electrodynamic process in the atmosphere is required for the understanding of the lithosphere–atmosphere–ionosphere interaction due to the radon emanation associated with large earthquakes.

Metrics analysis of the coupled Block Adaptive‐Tree Solar Wind Roe‐Type Upwind Scheme and Fok ring current model performance

Modeling is an important tool in understanding physical processes in the solar system. Metrics analysis evaluates model performance by comparing model output to a measurable parameter of interest. In this paper we studied the performance of the coupled Block Adaptive‐Tree Solar Wind Roe‐Type Upwind Scheme (BATSRUS) global magnetosphere MHD code and the Fok ring current model (FRC) by examining in detail the geosynchronous proton fluxes during the injection event on 21–22 January 2005. The output of BATSRUS code, calculated ionospheric potential and magnetic field, as well as proton temperature and density distribution, is used as an input boundary condition for the FRC model. We also discuss another event, on 10–11 August 2000, and speculate about the reasons of an apparent difference in the performance of the coupled models for these two events. The results of the simulation are compared with two LANL satellite observations, LANL‐97A and 1994‐084. The comparison of the simulation results for strongly varying solar wind and for prolonged interval of steady solar wind with southward IMF Bz, demonstrates that coupled BATSRUS and FRC models perform fairly for the magnetosphere driven by strong solar wind disturbances and probably are missing some internal magnetosphere dynamics in the second case.

New model simulations of the global atmospheric electric circuit driven by thunderstorms and electrified shower clouds: The roles of lightning and sprites

Several processes acting below, in and above thunderstorms and in electrified shower clouds drive upward currents which close through the global atmospheric electric circuit. These are all simulated in a novel way using the software package PSpice. A moderate negative cloud-to-ground lightning discharge from the base of a thunderstorm increases the ionospheric potential above the thundercloud by 0.0013%. Assuming the ionosphere to be an equipotential surface, this discharge increases the current flowing in the global circuit and the fair-weather electric field also by 0.0013%. A moderate positive cloud-to-ground lightning discharge from the bottom of a thunderstorm decreases the ionospheric potential by 0.014%. Such a discharge may trigger a sprite, causing the ionospheric potential to decrease by ∼ 1 V . The time scales for the recovery of the ionospheric potential are shown to be ∼ 250 s , which is of the same order as the CR time constant for the global circuit. Knowing the global average rate of lightning discharges, it is found that negative cloud-to-ground discharges increase the ionospheric potential by only ∼ 4 % , and that positive cloud-to-ground discharges reduce it by ∼ 3 % . Thus, overall, lightning contributes only ∼ 1 % —an almost insignificant proportion—to maintaining the high potential of the ionosphere. It is concluded that the net upward current to the ionosphere due to lightning is only ∼ 20 A . Further, it is concluded that conduction and convection currents associated with “batteries” within thunderclouds and electrified shower clouds contribute essentially equally ( ∼ 500 A each) to maintaining the ionospheric potential.

Multi-station synthesis of early twentieth century surface atmospheric electricity measurements for upper tropospheric properties

Abstract. The vertical columnar current density in the global atmospheric electrical circuit depends on the local columnar resistance. A simple model for the columnar resistance is suggested, which separates the local boundary layer component from the upper troposphere cosmic ray component, and calculates the boundary layer component from a surface measurement of air conductivity. This theory is shown to provide reasonable agreement with observations. One application of the simple columnar model theory is to provide a basis for the synthesis of surface atmospheric electrical measurements made simultaneously at several European sites. Assuming the ionospheric potential to be common above all the sites, the theoretical air-earth current density present in the absence of a boundary layer columnar resistance can be found by extrapolation. This is denoted the free troposphere limit air-earth current density, J0. Using early surface data from 1909 when no ionospheric potential data are available for corroboration, J0 is found to be ~6 pA m−2, although this is subject to uncertainties in the data and limitations in the theory. Later (1966–1971) European balloon and surface data give J0=2.4 pA m−2.

A coupled solar wind-magnetosphere–ionosphere model for determining the ionospheric penetration electric field

The transpolar potential Φpc may be estimated from the solar wind as measured by the advanced composition explorer (ACE) satellite at the first Lagrangian point L1. In our model, the transpolar potential drives the region-1 (J1) currents through the ionosphere consistent with a solar-dependent ionospheric conductance. It is shown that the ionospheric potential may be derived from an equivalent Poisson equation, the solution of which gives the global distribution of the ionospheric electric field, including the penetration electric field near the equator. This eastward penetration electric field just past sunset, which is created by J1, is offset by a region-2 (J2) generated westward (shielding) electric field with an unknown rise time. We find that there is a correlation between storm-time potential enhancements and the presence of equatorial bubbles as measured on DMSP satellites. The magnetic storms of 6–7 April 2000 and 20–21 November 2003 are analyzed. In both cases, the observed presence of equatorial plasma bubbles showed better agreement with model predictions using a longer J2 rise time, consistent with Huang et al. [Huang, C.-S., Foster, J., Kelley, M.C., 2005. Long-duration penetration of the interplanetary electric field to the low-latitude ionosphere during the main phase of magnetic storms. Journal of Geophysical Research 110(A11309), doi:10.1029/2005JA011202].

Effects of seasonal changes in the ionospheric conductances on magnetospheric field‐aligned currents

Through the seasons of the year, the ionospheric potential doesn't change significantly, while the solar driven conductance changes dramatically. This means that the magnetospherically driven field‐aligned currents must be significantly reduced in the winter hemisphere and enhanced in the summer hemisphere. It is shown that, if this simplistic view of the conductance is used, the ratio between the maximum winter FAC and maximum summer hemisphere FAC is on the order of a factor of four. FAC data shows that the true factor is closer to two. When a seasonally dependent auroral precipitation is used to increase the auroral conductance in the winter hemisphere, the ratio between the maximum FAC in the summer and winter is reduced to 1.6. It is shown that the measured hemispheric power does indeed show a seasonal difference, with the winter hemisphere receiving more power by approximately 3.8 GW (about 20%).

Sheared magnetospheric plasma flows and discrete auroral arcs: a quasi-static coupling model

Abstract. We consider sheared flows in magnetospheric boundary layers of tangential discontinuity type, forming a structure that is embedded in a large-scale convergent perpendicular electric field. We construct a kinetic model that couples the magnetospheric structure with the topside ionosphere. The contribution of magnetospheric electrons and ionospheric electrons and ions is taken into account into the current-voltage relationship derived for an electric potential monotonically decreasing with the altitude. The solution of the current continuity equation gives the distribution of the ionospheric potential consistent with the given magnetospheric electric potential. The model shows that a sheared magnetospheric flow generates current sheets corresponding to upward field-aligned currents, field-aligned potential drops and narrow bands of precipitating energy, as in discrete auroral arcs. Higher velocity magnetospheric sheared flows have the tendency to produce brighter and slightly broader arcs. An increase in arc luminosity is also associated with enhancements of magnetospheric plasma density, in which case the structures are narrower. Finally, the model predicts that an increase of the electron temperature of the magnetospheric flowing plasma corresponds to slightly wider arcs but does not modify their luminosity.

The Global Circuit Intensity: Its Measurement and Variation over the Last 50 Years

A fundamental problem in atmospheric electric research has been measurement of the intensity and variation of Earth's electric field, which is proportional to ionospheric potential (Vi). To obtain its magnitude an electric field sounding through the atmosphere is required. Data from the three programs that have measured Vi during the last half century were combined to determine the secular variation of global circuit intensity. The average geoelectric potential (Vi) magnitude has remained relatively constant at about 240 kV, except for a temporary increase of as much as 40% following a period of intense atmospheric nuclear testing in the early 1960s. Experiments were conducted to investigate the affect of temperature on Vi. Continental-scale hourly ground-level air temperature variation modulates the intensity of Vi and there is negative feedback involving cloud development that would stabilize temperature on the diurnal time scale. However, increased temperature-driven convection will increase water vapo...

Statistical analysis of ionospheric potential patterns for isolated substorms and sawtooth events

Abstract. We present here results which contrast isolated substorms with individual sawtooth events. Sawtooth events are defined as quasi-periodic, large-amplitude oscillations in the energetic particle flux with a periodicity of 2–4 h observed at the geosynchronous orbit. Sawtooth events have several similarities to isolated substorms leading therefore, to different opinions about whether sawtooth events are just an intense periodic form of substorms or if they deserve a category of their own. To help resolve this, we examine the ionospheric potential patterns in the northern polar region for isolated substorms and sawtooth events using the assimilative mapping of ionospheric electrodynamics (AMIE) technique. First we show a statistical analysis of isolated substorm potential patterns. In order to examine the seasonal variation, isolated substorms are identified by mid-latitude positive bay in the north-south geomagnetic perturbation in each season, respectively. Superposed epoch analysis (SEA) is applied to obtain the typical polar potential patterns for each season. By examining the time evolution of the potential patterns and cross polar cap potential (CPCP) for isolated substorms during each season, we find only subtle seasonal variations in the results obtained using the AMIE analysis. This provides a basis for comparison with sawtooth events in the next step. From the averaged potential patterns of 213 isolated substorms and those of 184 individual sawtooth events, we find the sawtooth events show signatures similar to subtorms: the DP 1 potential pattern develops and dominates the polar region after the onset. However, the DP 1 potential cell of sawtooth events encompasses a larger area than that of isolated substorms. Moreover, the CPCP of sawtooth is stronger than that of isolated substorms. It is also shown that the sawtooth events displays greater variability between individual events than isolated substorms. We conclude that in terms of ionospheric electrodynamics, the sawtoothe events have features that are similar to those of isolates substorms, though larger in spatial extent and in magnitude.

The influence of convective current generator on the global current

Abstract. The mathematical generalization of classical model of the global circuit with taking into account the convective current generator, working in the planetary boundary layer was considered. Convective current generator may be interpreted as generator, in which the electromotive force is generated by processes, of the turbulent transport of electrical charge. It is shown that the average potential of ionosphere is defined not only by the thunderstorm current generators, working at the present moment, but by the convective current generator also. The influence of the convective processes in the boundary layer on the electrical parameters of the atmosphere is not only local, but has global character as well. The numerical estimations, made for the case of the convective-unstable boundary layer demonstrate that the increase of the average potential of ionosphere may be of the order of 10% to 40%.

Comment on “Shielding effects of trees on the measurement of the Earth's electric field: Implications for secular variations of the global electrical circuit” by E. Williams et al.

Comment on “Shielding effects of trees on the measurement of the Earth's electric field: Implications for secular variations of the global electrical circuit” by E. Williams et al.

An analog forecast model for the high‐latitude ionospheric potential based on assimilative mapping of ionospheric electrodynamics archives

We review an emerging technique for ionospheric forecast whereby empirical models and data assimilation techniques are combined and show that the blended technique produces a diminished result compared to using the empirical models alone. We then present a technique for the nowcast/forecast of ionospheric potential patterns using an analog forecast technique. This is a new type of model for describing ionospheric potential patterns based on matching solar wind conditions and available ground observations to previously archived assimilative mapping of ionospheric electrodynamics (AMIE) runs. The model combines the best features of a data assimilation–based model with the availability and forecast potential of an empirically based model. We define a set of comparison metrics, show quantitatively how this model compares with the Weimer (1996) model and detail the performance for a May 1998 event.

The global ionosphere–thermosphere model

The recently created global ionosphere–thermosphere model (GITM) is presented. GITM uses a three-dimensional spherical grid that can be stretched in both latitude and altitude, while having a fixed resolution in longitude. GITM is nontraditional in that it does not use a pressure-based coordinate system. Instead it uses an altitude-based grid and does not assume a hydrostatic solution. This allows the model to more realistically capture physics in the high-latitude region, where auroral heating is prevalent. The code can be run in a one-dimensional (1-D) or three-dimensional (3-D) mode. In 3-D mode, the modeling region is broken into blocks of equal size for parallelization. In 1-D mode, a single latitude and longitude is modeled by neglecting any horizontal transport or gradients, except in the ionospheric potential. GITM includes a modern advection solver and realistic source terms for the continuity, momentum, and energy equations. Each neutral species has a separate vertical velocity, with coupling of the velocities through a frictional term. The ion momentum equation is solved for assuming steady-state, taking into account the pressure, gravity, neutral winds, and external electric fields. GITM is an extremely flexible code—allowing different models of high-latitude electric fields, auroral particle precipitation, solar EUV inputs, and particle energy deposition to be used. The magnetic field can be represented by an ideal dipole magnetic field or a realistic APEX magnetic field. Many of the source terms can be controlled (switched on and off, or values set) by an easily readable input file. The initial state can be set in three different ways: (1) using an ideal atmosphere, where the user inputs the densities and temperature at the bottom of the atmosphere; (2) using MSIS and IRI; and (3) restarting from a previous run. A 3-D equinox run and a 3-D northern summer solstice run are presented. These simulations are compared with MSIS and IRI to show that the large-scale features are reproduced within the code. We conduct a second equinox simulation with different initial conditions to show that the runs converge after approximately 1.5 days. Additionally, a 1-D simulation is presented to show that GITM works in 1-D and that the dynamics are what is expected for such a model.

A possible explanation for the dominant effect of South American thunderstorms on the Carnegie curve

The Carnegie curve shows the variation of the vertical electric field near the Earth's surface with Universal Time. The largest of the three maxima in this variation occurs at the time of maximum thunderstorm activity over the Americas, although this is weaker than that over Africa. This paradoxical effect may be explained by the fact that South American thunderstorms are close to the magnetic dip equator, whereas most African thunderstorms occur over the Congo at a higher (Southern) dip latitude. Kartalev et al. [2004. A quantitative model of the effect of global thunderstorms on the global distribution of ionospheric electrostatic potential. Journal of Atmospheric and Solar-Terrestrial Physics 66, 1233–1240.] modeled the global distribution of ionospheric electrostatic potential where the equatorial (within 11 ∘ magnetic latitude of the equator) lower ionosphere accumulates all upward thunderstorm currents into one line—the dip equator. Currents flow on a spherical shell of the magnetic coordinates model, and so change the distribution of the ionospheric potential on a global scale. That global distribution of ionospheric potential determines the vertical electric field near the Earth's surface everywhere. Thus, the Carnegie curve reflects preferentially the longitudinal distribution of thunderstorms within 11 ∘ of the magnetic dip equator.

The magnetospheric and ionospheric response to a very strong interplanetary shock and coronal mass ejection

We present results from a coupled magnetospheric and ionospheric simulation of a very strong solar wind shock and coronal mass ejection (CME). The solar wind drivers that are used for this simulation were output from the Sun-to-Earth MHD simulation of the Carrington-like CME reported in Manchester et al. [Manchester IV, W., Ridley, A., Gombosi, T., De Zeeuw, D. Modeling the Sun–Earth propagation of a very fast cme. Adv. Space Res. 38 (this issue), 2006]. We use the University of Michigan’s BATS-R-US MHD code to model the global magnetosphere and coupled height integrated ionosphere. As the interplanetary shock swept over the magnetosphere, a wave is observed to propagate through the system. This is evident both in the magnetosphere and ionosphere. On the dayside, the magnetospheric bowshock is shown to bifurcate. The inner shock is pushed close to the inner boundary, where it “bounces” and propagates back outwards to meet the outer bowshock, which is propagating inwards. The inward and outward motion of the bowshocks can be observed propagating down the flanks of the magnetosphere. In the ionosphere, the wave is manifested as two pairs of field-aligned currents moving antisunward. The first pair is opposite of the normal region-1 current system, while the second pair is in the same sense as the normal region-1 system. The ionospheric potential shows a behavior consistent with the field-aligned current pattern, given the strong gradient in the conductance from the dayside to the nightside. As the magnetic cloud flows over the system, the entire magnetopause boundary is observed to move inside of geosynchronous orbit (6.6 R e). At the time of the most extreme solar wind conditions, the magnetopause boundary encounters the inner edge of the magnetospheric simulation domain. During the magnetic cloud, the ionospheric cross-polar cap potential is shown to match the Siscoe et al. [Siscoe, G.L., Erickson, G., Sonnerup, B., Maynard, N., Schoendorf, J., Siebert, K., Weimer, D., White, W., Wilson, G. Hill model of transpolar potential saturation: comparisons with MHD simulations. J. Geophys. Res. 107, 1321, doi:10.1029/2001JA009176, 2002] formulation relating the ionospheric potential to the solar wind and IMF conditions. It is shown that by using this formulation, the extremely large potentials observed in the MHD results are most likely saturated.

Antarctic polar plateau vertical electric field variations across heliocentric current sheet crossings

A superposed epoch analysis of variations of the vertical electric field measured at Vostok (78.5°S, 107°E; magnetic latitude 83.6°S) during 1998–2002 heliocentric current sheet (HCS) crossings yields no significant variation other than an association imposed by polar-cap potential differences above the site. This result contradicts published reports of a reduction ∼15% in electric field 1–3 days after HCS crossings, an observation initially made ∼30 years ago. If such a reduction had been caused by reductions in stratospheric ionising radiation, the presence of polar stratospheric clouds (PSC) would seem necessary for the occurrence of this effect. PSCs would increase the resistance of the stratosphere thus making ionisation in that region significant in the context of the ionosphere–ground current flow, in a manner analogous to the role of volcanic aerosols in the stratosphere in the explanation of the weakening of northern hemisphere winter cyclones associated with HCS crossings, the so-called ‘Wilcox effect’. However, separating the present data to correspond to the likely presence of PSC above Vostok also does not yield the reported reduction. Significant increases or decreases of the vertical electric field emerge from the observations when the HCS crossings are separated into sets depending on whether the solar wind magnetic field changes from ‘toward-to-away’ (increase of ∼11%) and ‘away-to-toward’ (decrease of ∼8%). Polar-cap potential changes above the site, inferred from solar wind parameters using the Weimer model, also show such step functions that reverse with the sign of HCS transition and are broadly consistent with the measured electric field increases or decreases. Remaining differences between the measurements and the model are consistent with a somewhat stronger solar wind speed and/or magnetic activity influence on polar-cap convection above Vostok than is predicted by the model. Variations in ground-level neutron counts, a measure of cosmic ray influence on the atmospheric conductivity, demonstrate average variations of less than 1% around HCS crossings and at this level would not contribute significantly to the electric field variations. Magnetic activity (measured using the Kp index) and solar wind speed decrease around HCS crossings independent of whether the crossings are ‘toward-to-away’ or ‘away-to-toward’. These decreases are broadly similar in shape to the previously reported Vostok electric field responses. However, their effects on ionospheric potential are included in the Weimer model, and are small. In contrast to sub-auroral latitudes, where the precipitation of MeV electrons from the radiation belts has a characteristic decrease for both types of HCS crossing, there are no known sources of stratospheric ionising radiation in the polar caps that could explain the previously reported effect. Thus, observation and theory are now in agreement for the absence of this effect.

Further signatures of long-term changes in atmospheric electrical parameters observed in Europe

Abstract. Long-term decreases found recently in both the atmospheric electrical potential gradient (PG) and the air-Earth current density (Jz), using observation series from the UK and Hungary, have motivated studies of other European data. Two surface data series somewhat longer than a decade were available: PG data obtained at Serra do Pilar (Portugal), and PG, Jz and positive air conductivity measurements at Athens (Greece). Selecting data to minimise local effects, the 1960–1971 Serra do Pilar PG values decrease at dawn and in the evening. Dawn data obtained at Athens (1967–1977) indicate a reduction in Jz, while the simultaneous PG values there increase (coincident air conductivity values decrease) for the periods investigated. The Athens PG increase is attributed to local aerosol influences, typical of urban environments. Despite the urban influence, the Athens Jz shows similarities with soundings of the ionospheric potential. The decline in Jz at Athens occurs simultaneously with a decrease reported previously in Jz at Kew (UK), indicating that, at least, a regional decrease in the global atmospheric electrical circuit occurred during part of the twentieth century. Similar surface changes occur in European atmospheric electrical parameters, with a decrease of about 0.5% to 0.7% per year between 1920 and 1970 (possibly extending back to 1898), an annual decrease of between 2.7 and 3.4%, between 1959 and 1971 and a continued decrease of about ~1% per year between 1967 and 1984, possibly still continuing. Keywords. Meteorology and atmospheric dynamics (Atmospheric electricity) – Geomagnetism and paleomagnetism (Time variations, secular and long term) – Atmospheric composition and structure (Aerosols and particles)

Effect of multiple substorms on the buildup of the ring current

The effect of magnetospheric substorms on the ring current is not completely understood. Using a combination of the University of Michigan's BAT‐S‐RUS Model and Fok Ring Current Model, we modeled the effects of multiple substorms on the ring current by modeling multiple dipolarizations in the tail. Increasing the number of substorms corresponds to increases in the number of injections into the ring current. The ionospheric potential increases during periods of southward IMF. Energy increases are more dependent on the duration of large ionospheric potential than the number of substorm dipolarizations.

Transpolar aurora: time evolution, associated convection patterns, and a possible cause

Abstract. We present two event studies illustrating the detailed relationships between plasma convection, field-aligned currents, and polar auroral emissions, as well as illustrating the influence of the Interplanetary Magnetic Field's y-component on theta aurora development. The transpolar arc of the theta aurorae moves across the entire polar region and becomes part of the opposite side of the auroral oval. Electric and magnetic field and precipitating particle data are provided by DMSP, while the POLAR UVI instrument provides measurements of auroral emissions. Ionospheric electrostatic potential patterns are calculated at different times during the evolution of the theta aurora using the KTH model. These model patterns are compared to the convection predicted by mapping the magnetopause electric field to the ionosphere using the Paraboloid Model of the magnetosphere. The model predicts that parallel electric fields are set up along the magnetic field lines projecting to the transpolar aurora. Their possible role in the acceleration of the auroral electrons is discussed. Keywords. Ionosphere (Plasma convection; Polar ionosphere) – Magnetospheric physics (Magnetosphereionosphere interactions)