An Empirical Orthogonal Function Reanalysis of the Northern Polar External and Induced Magnetic Field During Solar Cycle 23

NASA Astrophysics Data System (ADS)

Shore, R. M.; Freeman, M. P.; Gjerloev, J. W.

2018-01-01

We apply the method of data-interpolating empirical orthogonal functions (EOFs) to ground-based magnetic vector data from the SuperMAG archive to produce a series of month length reanalyses of the surface external and induced magnetic field (SEIMF) in 110,000 km2 equal-area bins over the entire northern polar region at 5 min cadence over solar cycle 23, from 1997.0 to 2009.0. Each EOF reanalysis also decomposes the measured SEIMF variation into a hierarchy of spatiotemporal patterns which are ordered by their contribution to the monthly magnetic field variance. We find that the leading EOF patterns can each be (subjectively) interpreted as well-known SEIMF systems or their equivalent current systems. The relationship of the equivalent currents to the true current flow is not investigated. We track the leading SEIMF or equivalent current systems of similar type by intermonthly spatial correlation and apply graph theory to (objectively) group their appearance and relative importance throughout a solar cycle, revealing seasonal and solar cycle variation. In this way, we identify the spatiotemporal patterns that maximally contribute to SEIMF variability over a solar cycle. We propose this combination of EOF and graph theory as a powerful method for objectively defining and investigating the structure and variability of the SEIMF or their equivalent ionospheric currents for use in both geomagnetism and space weather applications. It is demonstrated here on solar cycle 23 but is extendable to any epoch with sufficient data coverage.

Spacebuoy: A University Nanosat Space Weather Mission (III)

DTIC Science & Technology

2013-10-11

ionospheric forecasting models; specifically the operational Global Assimilation of Ionospheric Measurements (GAIM) model currently used by the Air Force... ionospheric forecasting models; specifically the operational Global Assimilation of Ionospheric Measurements (GAIM) model currently used by the Air...Mission Objectives • Provide critical space weather data for use in ionospheric forecasting efforts, particularly assimilated data used in the GAIM

Modeling of HF propagation at high latitudes on the basis of IRI

NASA Astrophysics Data System (ADS)

Blagoveshchensky, D. V.; Maltseva, O. A.; Anishin, M. M.; Rogov, D. D.; Sergeeva, M. A.

2016-02-01

The paper presents the results of comparison between the modeling calculations and ionograms of oblique sounding for high-latitude HF radio paths of Arctic and Antarctic Research Institute (AARI), which was fulfilled for February 13-14, 2014 (quiet conditions). The International Reference Ionosphere 2012 model of the ionosphere (IRI-2012) was used for the study. The comparison results prove that without adaptation to current diagnostics the IRI model does not reflect the real state of high latitude ionosphere even for quiet conditions. It was found that in general the observed maximum usable frequency values (MUF) exceeded the same values obtained from the model. The adaptation of the model to current diagnostics makes the simulated MUF values significantly closer to the observed MUF. The following parameters were used for the study: critical frequencies foF2 measured by ionosondes located near the considered paths, frequencies calculated on the basis of observed TEC values and median values of the equivalent slab thickness of the ionosphere. The relative error of calculation of MUF values averaged for all the cases for one hop was 23.6% by the initial IRI model. This error was decreased by 4% for the calculations on the basis of observed ТЕС and by 6% for the adaptation to foF2. The higher the latitude of the studied radio path, the more the difference between the observed and simulated MUF values. The conclusion was made that a principal cause of this difference was the deviation of calculated maximum ionospheric height values (hmF2) from the observed hmF2. The additional model update using hmF2 values obtained from Tromso station let to better match between the calculated MUF values and the observed MUF values for all radio paths. The analysis of experimental data showed that the non-predicted events (like traveling ionospheric disturbances, M- and N-modes, lateral modes, triplets, unusual scatter effects, etc.) sometimes took place at high latitude paths even during the quiet conditions.

Comment on 'Current Budget of the Atmospheric Electric Global Circuit'

NASA Technical Reports Server (NTRS)

Driscoll, Kevin T.; Blakeslee, Richard J.

1996-01-01

In this paper, three major issues relevant to Kasemir's new model will be addressed. The first concerns Kasemir's assertion that there are significant differences between the potentials associated with the new model and the conventional model. A recalculation of these potentials reveals that both models provide equivalent results for the potential difference between the Earth and ionosphere. The second issue to be addressed is Kasemir's assertion that discrepancies in the electric potentials associated with both models can be attributed to modeling the Earth as a sphere, instead of as a planar surface. A simple analytical comparison will demonstrate that differences in the equations for the potentials of the atmosphere derived with a spherical and a planar Earth are negligible for applications to global current flow. Finally, the third issue to be discussed is Kasemir's claim that numerous aspects of the conventional model are incorrect, including the role of the ionosphere in global current flow as well as the significance of cloud-to-ground lightning in supplying charge to the global circuit. In order to refute these misconceptions, it will be shown that these aspects related to the flow of charge in the atmosphere are accurately described by the conventional model of the global circuit.

Artificial ionosphere layers for pumping-wave frequencies near the fourth electron gyroharmonic in experiments at the HAARP facility

NASA Astrophysics Data System (ADS)

Grach, S. M.; Sergeev, E. N.; Shindin, A. V.; Mishin, E. V.; Watkins, B.

2014-02-01

In this paper we consider the action (in the magnetic-zenith direction) of powerful high frequency (HF) radiation of ordinary polarization on the ionosphere F region. We deal with frequencies f 0 > 4 f ce ( f ce is the electron cyclotron frequency) of 1.7 GW equivalent radiated power. This action results in the appearance in the ionosphere of an artificial ionization layer. The layer descends with respect to the basic (unperturbed) layer at a rate of ˜500 m s-1 down to the altitude, where f 0 ≈ 4 f ce .

Field-aligned currents in the undisturbed polar ionosphere

NASA Astrophysics Data System (ADS)

Kroehl, H. W.

1989-09-01

Field-aligned currents, FAC's, which couple ionospheric currents at high latitudes with magnetospheric currents have become an essential cornerstone to our understanding of plasma dynamics in the polar region and in the earth's magnetosphere. Initial investigators of polar electrodynamics including the aurora were unable to distinguish between the ground magnetic signatures of a purely two-dimensional current and those from a three-dimensional current system, ergo many scientists ignored the possible existence of these vertical currents. However, data from magnetometers and electrostatic analyzers flown on low-altitude, polar-orbiting satellites proved beyond any reasonable doubt that field-aligned currents existed, and that different ionospheric regions were coupled to different magnetospheric regions which were dominated by different electrodynamic processes, e.g., magnetospheric convection electric fields, magnetospheric substorms and parallel electric fields. Therefore, to define the “undisturbed” polar ionosphere and its structure and dynamics, one needs to consider these electrodynamic processes, to select times for analysis when they are not strongly active and to remember that the polar ionosphere may be disturbed when the equatorial, mid-latitude and sub-auroral ionospheres are not. In this paper we will define the principle high-latitude current systems, describe the effects of FAC's associated with these systems, review techniques which would minimize these effects and present our description of the “undisturbed” polar ionosphere.

Induction signals from Callisto's ionosphere and their implications on a possible subsurface ocean

NASA Astrophysics Data System (ADS)

Hartkorn, Oliver; Saur, Joachim

2017-11-01

We investigate whether induction within Callisto's electrically conductive ionosphere can explain observed magnetic fields which have previously been interpreted as evidence of induction in a saline, electrically conductive subsurface ocean. Callisto's ionosphere is subject to the flow of time-periodic magnetized plasma of Jupiter's magnetosphere, which induces electric fields and electric currents in Callisto's electrically conductive ionosphere. We develop a simple analytic model for a first quantitative understanding of the effects of induction in Callisto's ionosphere caused by the interaction with a time-variable magnetic field environment. With this model, we also investigate how the associated ionospheric currents close in the ambient magnetospheric plasma. Based on our model, we find that the anisotropic nature of Callisto's ionospheric conductivity generates an enhancement effect on ionospheric loop currents which are driven by the time-variable magnetic field. This effect is similar to the Cowling channel effect known from Earth's ionosphere. Subsequently, we numerically calculate the expected induced magnetic fields due to Jupiter's time-variable magnetic field in an anisotropic conductive ionosphere and compare our results with the Galileo C-3 and C-9 flybys. We find that induction within Callisto's ionosphere is responsible for a significant part of the observed magnetic fields. Ionospheric induction creates induced magnetic fields to some extent similar as expected from a subsurface water ocean. Depending on currently unknown properties such as Callisto's nightside ionosphere, the existence of layers of "dirty ice" and the details of the plasma interaction, a water ocean might be located much deeper than previously thought or might not exist at all.

The two-way relationship between ionospheric outflow and the ring current

DOE Office of Scientific and Technical Information (OSTI.GOV)

Welling, Daniel T.; Jordanova, Vania Koleva; Glocer, Alex

It is now well established that the ionosphere, because it acts as a significant source of plasma, plays a critical role in ring current dynamics. However, because the ring current deposits energy into the ionosphere, the inverse may also be true: the ring current can play a critical role in the dynamics of ionospheric outflow. This study uses a set of coupled, first-principles-based numerical models to test the dependence of ionospheric outflow on ring current-driven region 2 field-aligned currents (FACs). A moderate magnetospheric storm event is modeled with the Space Weather Modeling Framework using a global MHD code (Block Adaptivemore » Tree Solar wind Roe-type Upwind Scheme, BATS-R-US), a polar wind model (Polar Wind Outflow Model), and a bounce-averaged kinetic ring current model (ring current atmosphere interaction model with self-consistent magnetic field, RAM-SCB). Initially, each code is two-way coupled to all others except for RAM-SCB, which receives inputs from the other models but is not allowed to feed back pressure into the MHD model. The simulation is repeated with pressure coupling activated, which drives strong pressure gradients and region 2 FACs in BATS-R-US. It is found that the region 2 FACs increase heavy ion outflow by up to 6 times over the non-coupled results. The additional outflow further energizes the ring current, establishing an ionosphere-magnetosphere mass feedback loop. This study further demonstrates that ionospheric outflow is not merely a plasma source for the magnetosphere but an integral part in the nonlinear ionosphere-magnetosphere-ring current system.« less

The two-way relationship between ionospheric outflow and the ring current

DOE PAGES

Welling, Daniel T.; Jordanova, Vania Koleva; Glocer, Alex; ...

2015-06-01

It is now well established that the ionosphere, because it acts as a significant source of plasma, plays a critical role in ring current dynamics. However, because the ring current deposits energy into the ionosphere, the inverse may also be true: the ring current can play a critical role in the dynamics of ionospheric outflow. This study uses a set of coupled, first-principles-based numerical models to test the dependence of ionospheric outflow on ring current-driven region 2 field-aligned currents (FACs). A moderate magnetospheric storm event is modeled with the Space Weather Modeling Framework using a global MHD code (Block Adaptivemore » Tree Solar wind Roe-type Upwind Scheme, BATS-R-US), a polar wind model (Polar Wind Outflow Model), and a bounce-averaged kinetic ring current model (ring current atmosphere interaction model with self-consistent magnetic field, RAM-SCB). Initially, each code is two-way coupled to all others except for RAM-SCB, which receives inputs from the other models but is not allowed to feed back pressure into the MHD model. The simulation is repeated with pressure coupling activated, which drives strong pressure gradients and region 2 FACs in BATS-R-US. It is found that the region 2 FACs increase heavy ion outflow by up to 6 times over the non-coupled results. The additional outflow further energizes the ring current, establishing an ionosphere-magnetosphere mass feedback loop. This study further demonstrates that ionospheric outflow is not merely a plasma source for the magnetosphere but an integral part in the nonlinear ionosphere-magnetosphere-ring current system.« less

The Rocket Investigation of Current Closure in the Ionosphere (RICCI) mission: A novel application of CubeSats from a sounding rocket platform

NASA Astrophysics Data System (ADS)

Cohen, I. J.; Anderson, B. J.; Lessard, M.; Bonnell, J. W.; Bounds, S. R.; Lysak, R. L.; Erlandson, R. E.

2017-12-01

The transfer of energy and momentum between the terrestrial magnetosphere and ionosphere is substantially mediated by large-scale field-aligned currents (FACs), driven by magnetopause dynamics and magnetospheric pressures and closing through the ionosphere where the dissipation and drag are governed. While significant insight into ionospheric electrodynamics and the nature of magnetosphere-ionosphere (M-I) coupling have been gained by rocket and satellite measurements, in situ measurement of these ionospheric closure currents remains challenging. To date the best estimates of ionospheric current densities are inferred from ground-based radar observations combining electric fields calculated from drifts with conductivities derived from densities. RICCI aims to observe the structure of the ionospheric currents in situ to determine how the altitude structure of these currents is related to precipitation and density cavities, electromagnetic dynamics, and governs energy dissipation in the ionosphere. In situ measurement of the current density using multi-point measurements of the magnetic field requires precise attitude knowledge for which the only demonstrated technique is the use of star camera systems. The low vehicle rotation rates required for miniature commercial off-the-shelf (COTS) star cameras prohibit the use of available rocket sub-payload technologies at Wallops Flight Facility (WFF) which use high rates of spin to stabilize attitude. However, CubeSat attitude systems are already designed to achieve low vehicle rotation rates, so RICCI will use a set of three CubeSat sub-payloads deployed from a main low altitude payload with apogee of 160 km to provide precise current density measurement through the ionospheric closure altitude regime, together with a second rocket with apogee near 320 km to measure the incident input energy flux and convection electric field. The two rocket payloads and CubeSate sub-payloads are all instrumented with star cameras and science-grade magnetometers. We discuss the mission design, payload complement, and science closure of this sub-orbital mission to obtain the first direct measurement of ionospheric currents associated with an auroral arc.

Agreements between ground-based and satellite-based observations. [of earth magnetospheric currents

NASA Technical Reports Server (NTRS)

Akasofu, S.-I.; Weimer, D.; Iijima, T.; Ahn, B.-H.; Kamide, Y.

1990-01-01

The polar ionospheric parameters obtained by the meridian chain of magnetometers are compared with those obtained by satellites, and a number of ionospheric quantities including the distribution of the electric potential, field-aligned currents, ionospheric currents and their equatorial counterparts, and the relationship between the AE index and the cross-polar cap potential is determined. It is noted that the agreement observed between the ground-based and satellite-based results allows to reduce the search for the driving mechanism of the ionospheric Pedersen current to identifying the driving mechanism of the Pedersen counterpart current in the equatorial plane.

The Equatorial Scintillations and Space Weather Effects on its Generation during Geomagnetic Storms

NASA Astrophysics Data System (ADS)

Biktash, Lilia

Great diversity of the ionospheric phenomena leads to a variety of irregularity types with spatial size from many thousands of kilometers to few centimeters and lifetimes from days to fractions of second. Since the ionosphere strongly influences the propagation of radio waves, signal distortions caused by these irregularities affect short-wave transmissions on Earth, transiono-spheric satellite communications and navigation. In this work the solar wind and the equatorial ionosphere parameters, Kp, Dst, AU, AL indices characterized contribution of different mag-netospheric and ionospheric currents to the H-component of geomagnetic field are examined to test the space weather effect on the generation of ionospheric irregularities producing VLF scintillations. According to the results of the current statistical studies, one can predict scintil-lations from Aarons' criteria using the Dst index, which mainly depicts the magnetospheric ring current field. To amplify Aarons' criteria or to propose new criteria for predicting scintillation characteristics is the question. In the present phase of the experimental investigations of elec-tron density irregularities in the ionosphere new ways are opened up because observations in the interaction between the solar wind -magnetosphere -ionosphere during magnetic storms have progressed greatly. We have examined scintillation relation to magnetospheric and ionospheric currents and show that the factor, which presents during magnetic storms to fully inhibit scin-tillation, is the positive Bz-component of the IMF. During the positive Bz IMF F layer cannot raise altitude where scintillations are formed. The auroral indices and Kp do better for the prediction of the ionospheric scintillations at the equator. The interplanetary magnetic field data and models can be used to explain the relationship between the equatorial ionospheric parameters, h'F, foF2, and the equatorial geomagnetic variations with the polar ionosphere cur-rents and the solar wind. Taking into account the time delay between the solar wind and the ionosphere phenomena, the relationship between the solar wind and the ionosphere parameters can be used for predicting of scintillations.

Comparison of dayside current layers in Venus' ionosphere and earth's equatorial electrojet

NASA Technical Reports Server (NTRS)

Cole, Keith D.

1993-01-01

The major physical aspects of the equatorial electrojet of Earth and the dayside ionospheric current layers of Venus are compared, viz., the electric current intensity and total current, roles of electric field, pressure and gravity, diffusion time scales, and the Bernouille effect. The largest potential differences, of the order of 10 volts, horizontally across the dayside ionosphere of Venus, have important implications for possible dynamo action in the Venus ionosphere and the application of an electric field from the lower atmosphere or from the solar wind. An upper limit to the horizontal scale of vertical magnetic fields in the Venus ionosphere is estimated thereby for the first time. New upper limits on the velocity in, and thickness of, a possible S layer at Venus are presented. If an S layer exists, it is only for extreme conditions of the solar wind. A mechanism for formation of magnetic ropes in the Venus ionosphere is also proposed.

Relationship of the interplanetary electric field to the high-latitude ionospheric electric field and currents Observations and model simulation

NASA Technical Reports Server (NTRS)

Clauer, C. R.; Banks, P. M.

1986-01-01

The electrical coupling between the solar wind, magnetosphere, and ionosphere is studied. The coupling is analyzed using observations of high-latitude ion convection measured by the Sondre Stromfjord radar in Greenland and a computer simulation. The computer simulation calculates the ionospheric electric potential distribution for a given configuration of field-aligned currents and conductivity distribution. The technique for measuring F-region in velocities at high time resolution over a large range of latitudes is described. Variations in the currents on ionospheric plasma convection are examined using a model of field-aligned currents linking the solar wind with the dayside, high-latitude ionosphere. The data reveal that high-latitude ionospheric convection patterns, electric fields, and field-aligned currents are dependent on IMF orientation; it is observed that the electric field, which drives the F-region plasma curve, responds within about 14 minutes to IMF variations in the magnetopause. Comparisons of the simulated plasma convection with the ion velocity measurements reveal good correlation between the data.

Transmission of the convection electric field to the inner magnetosphere

NASA Astrophysics Data System (ADS)

Kikuchi, T.

2003-12-01

Low latitude magnetometer observations revealed that the partial ring current started to develop within several minutes after the onset of growth of the polar cap potential (PCP), and decayed simultaneously with the decrease in the PCP (Hashimoto, Kikuchi and Ebihara., JGR 2002). The magnetometer observations also indicated that the DP2 ionospheric currents were driven by the convection electric field at mid latitudes as well as at high latitudes. These observational facts suggest that the ionospheric electric field plays a crucial role in driving the convection in the inner magnetosphere. A probable model for the electric field transmission should explain both the convection in the inner magnetosphere and the ionospheric currents at mid latitudes. The instantaneous transmission of the ionospheric electric field and currents from the polar ionosphere to the equator was explained by Kikuchi and Araki (JATP 1979) based on the TM0 mode in the Earth-ionosphere waveguide. In this paper, we attempt to explain the transmission of the convection electric field to the inner magnetosphere by applying the Earth-ionosphere waveguide. However, two issues remained unresolved in the paper by Kikuchi and Araki (1979). One is the excitation of the TM0 mode in the Earth-ionosphere waveguide, and the other is the attenuation under the nighttime ionospheric condition. To examine the excitation of the TM0 mode, we couple the Earth-ionosphere waveguide (transmission line) with a magnetospheric transmission line composed of a pair of field-aligned currents (e.g., R1 FACs). A fraction of the electromagnetic energy carried from the magnetosphere is transmitted into the Earth-ionosphere waveguide, although substantial energy is dissipated in the polar ionosphere intervening between the two transmission lines. The transmitted electromagnetic energy excites the TM0 mode in the Earth-ionosphere waveguide. We then evaluate the attenuation of the TM0 mode by calculating upward flow of energy from the waveguide into the conducting ionosphere and the magnetosphere. It is shown that the attenuation of the TM0 mode is not significant even for the nighttime condition, when compared to the geometrical attenuation due to the finite size of the polar electric field. Furthermore, it is shown that the ionospheric electric field carried by the TM0 mode is transmitted by Alfven waves upward into the inner magnetosphere along the magnetic field lines, supplying energy for the convection in the inner magnetosphere. It should be stressed that the ionosphere never creates electromagnetic energy but acts as a transmission line for the convection electric field. We conclude that the Earth-ionosphere waveguide connected with the magnetospheric transmission line explains both the instantaneous propagation of the electric field and currents in the ionosphere and of the convection electric field into the inner magnetosphere.

Shear Alfven Wave Injection in the Magnetosphere by Ionospheric Modifications in the Absence of Electrojet Currents

NASA Astrophysics Data System (ADS)

Papadopoulos, K.; Eliasson, B.; Shao, X.; Labenski, J.; Chang, C.

2011-12-01

A new concept of generating ionospheric currents in the ULF/ELF range with modulated HF heating using ground-based transmitters even in the absence of electrojet currents is presented. The new concept relies on using HF heating of the F-region to modulate the electron temperature and has been given the name Ionospheric Current Drive (ICD). In ICD, the pressure gradient associated with anomalous or collisional F-region electron heating drives a local diamagnetic current that acts as an antenna to inject mainly Magneto-Sonic (MS) waves in the ionospheric plasma. The electric field associated with the MS wave drives Hall currents when it reaches the E region of the ionosphere. The Hall currents act as a secondary antenna that inject waves in the Earth-Ionosphere Waveguide (EIW) below and shear Alfven waves or EMIC waves upwards towards the conjugate regions. The paper presents: (i) Theoretical results using a cold Hall MHD model to study ICD and the generation of ULF/ELF waves by the modulation of the electron pressure at the F2-region with an intense HF electromagnetic wave. The model solves equations governing the dynamics of the shear Alfven and magnetosonic modes, of the damped modes in the diffusive Pedersen layer, and of the weakly damped helicon wave mode in the Hall-dominated E-region. The model incorporates realistic profile of the ionospheric conductivities and magnetic field configuration. We use the model to simulate propagation and dynamics of the low-frequency waves and their injection into the magnetosphere from the HAARP and Arecibo ionospheric heaters. (ii) Proof of principle experiments using the HAARP ionospheric heater in conjunction with measurements by the DEMETER satellite This work is supported by ONR MURI grant and DARPA BRIOCHE Program

Coulomb collisions of ring current particles: Indirect source of heat for the ionosphere

NASA Technical Reports Server (NTRS)

Cole, K. D.

1975-01-01

The additional energy requirements of the topside ionosphere during a magnetic storm are less than one quarter of the ring current energy. This energy is supplied largely by Coulomb collisions of ring current protons of energy less than about 20 keV with background thermal electrons which conduct the heat to the ionosphere. Past criticisms are discussed of this mechanism for the supply of energy to the SAR-arc and neighboring regions of the ionosphere.

Saturation of the Electric Field Transmitted to the Magnetosphere

NASA Technical Reports Server (NTRS)

Lyatsky, Wladislaw; Khazanov, George V.; Slavin, James A.

2010-01-01

We reexamined the processes leading to saturation of the electric field, transmitted into the Earth's ionosphere from the solar wind, incorporating features of the coupled system previously ignored. We took into account that the electric field is transmitted into the ionosphere through a region of open field lines, and that the ionospheric conductivity in the polar cap and auroral zone may be different. Penetration of the electric field into the magnetosphere is linked with the generation of the Alfven wave, going out from the ionosphere into the solar wind and being coupled with the field-aligned currents at the boundary of the open field limes. The electric field of the outgoing Alfven wave reduces the original electric field and provides the saturation effect in the electric field and currents during strong geomagnetic disturbances, associated with increasing ionospheric conductivity. The electric field and field-aligned currents of this Alfven wave are dependent on the ionospheric and solar wind parameters and may significantly affect the electric field and field-aligned currents, generated in the polar ionosphere. Estimating the magnitude of the saturation effect in the electric field and field-aligned currents allows us to improve the correlation between solar wind parameters and resulting disturbances in the Earth's magnetosphere.

Transmission of the electric fields to the low latitude ionosphere in the magnetosphere-ionosphere current circuit

NASA Astrophysics Data System (ADS)

Kikuchi, Takashi; Hashimoto, Kumiko K.

2016-12-01

The solar wind energy is transmitted to low latitude ionosphere in a current circuit from a dynamo in the magnetosphere to the equatorial ionosphere via the polar ionosphere. During the substorm growth phase and storm main phase, the dawn-to-dusk convection electric field is intensified by the southward interplanetary magnetic field (IMF), driving the ionospheric DP2 currents composed of two-cell Hall current vortices in high latitudes and Pedersen currents amplified at the dayside equator (EEJ). The EEJ-Region-1 field-aligned current (R1 FAC) circuit is completed via the Pedersen currents in midlatitude. On the other hand, the shielding electric field and the Region-2 FACs develop in the inner magnetosphere, tending to cancel the convection electric field at the mid-equatorial latitudes. The shielding often causes overshielding when the convection electric field reduces substantially and the EEJ is overcome by the counter electrojet (CEJ), leading to that even the quasi-periodic DP2 fluctuations are contributed by the overshielding as being composed of the EEJ and CEJ. The overshielding develop significantly during substorms and storms, leading to that the mid and low latitude ionosphere is under strong influence of the overshielding as well as the convection electric fields. The electric fields on the day- and night sides are in opposite direction to each other, but the electric fields in the evening are anomalously enhanced in the same direction as in the day. The evening anomaly is a unique feature of the electric potential distribution in the global ionosphere. DP2-type electric field and currents develop during the transient/short-term geomagnetic disturbances like the geomagnetic sudden commencements (SC), which appear simultaneously at high latitude and equator within the temporal resolution of 10 s. Using the SC, we can confirm that the electric potential and currents are transmitted near-instantaneously to low latitude ionosphere on both day- and night sides, which is explained by means of the light speed propagation of the TM0 mode waves in the Earth-ionosphere waveguide.

Mars' Magnetic Atmosphere: Ionospheric Currents, Lightning (or Not), E and M Subsurface Sounding, and Future Missions

NASA Technical Reports Server (NTRS)

Espley, J. R.; Connerney, J. E. P.

2014-01-01

Mars' ionosphere has no obvious magnetic signs of large-scale, dustproduced lightning. However, there are numerous interesting ionospheric currents (some associated with crustal magnetic fields) which would allow for E&M subsurface sounding.

Application of the NASCAP Spacecraft Simulation Tool to Investigate Electrodynamic Tether Current Collection in LEO

NASA Technical Reports Server (NTRS)

Adams, Mitzi; HabashKrause, Linda

2012-01-01

Recent interest in using electrodynamic tethers (EDTs) for orbital maneuvering in Low Earth Orbit (LEO) has prompted the development of the Marshall ElectroDynamic Tether Orbit Propagator (MEDTOP) model. The model is comprised of several modules which address various aspects of EDT propulsion, including calculation of state vectors using a standard orbit propagator (e.g., J2), an atmospheric drag model, realistic ionospheric and magnetic field models, space weather effects, and tether librations. The natural electromotive force (EMF) attained during a radially-aligned conductive tether results in electrons flowing down the tether and accumulating on the lower-altitude spacecraft. The energy that drives this EMF is sourced from the orbital energy of the system; thus, EDTs are often proposed as de-orbiting systems. However, when the current is reversed using satellite charged particle sources, then propulsion is possible. One of the most difficult challenges of the modeling effort is to ascertain the equivalent circuit between the spacecraft and the ionospheric plasma. The present study investigates the use of the NASA Charging Analyzer Program (NASCAP) to calculate currents to and from the tethered satellites and the ionospheric plasma. NASCAP is a sophisticated set of computational tools to model the surface charging of three-dimensional (3D) spacecraft surfaces in a time-varying space environment. The model's surface is tessellated into a collection of facets, and NASCAP calculates currents and potentials for each one. Additionally, NASCAP provides for the construction of one or more nested grids to calculate space potential and time-varying electric fields. This provides for the capability to track individual particles orbits, to model charged particle wakes, and to incorporate external charged particle sources. With this study, we have developed a model of calculating currents incident onto an electrodynamic tethered satellite system, and first results are shown here.

Calculation of conductivities and currents in the ionosphere

NASA Technical Reports Server (NTRS)

Kirchhoff, V. W. J. H.; Carpenter, L. A.

1975-01-01

Formulas and procedures to calculate ionospheric conductivities are summarized. Ionospheric currents are calculated using a semidiurnal E-region neutral wind model and electric fields from measurements at Millstone Hill. The results agree well with ground based magnetogram records for magnetic quiet days.

Atmosphere-Ionosphere Electrodynamic Coupling

NASA Astrophysics Data System (ADS)

Sorokin, V. M.; Chmyrev, V. M.

Numerous phenomena that occur in the mesosphere, ionosphere, and the magnetosphere of the Earth are caused by the sources located in the lower atmosphere and on the ground. We describe the effects produced by lightning activity and by ground-based transmitters operated in high frequency (HF) and very low frequency (VLF) ranges. Among these phenomena are the ionosphere heating and the formation of plasma density inhomogeneities, the excitation of gamma ray bursts and atmospheric emissions in different spectral bands, the generation of ULF/ELF/VLF electromagnetic waves and plasma turbulence in the ionosphere, the stimulation of radiation belt electron precipitations and the acceleration of ions in the upper ionosphere. The most interesting results of experimental and theoretical studies of these phenomena are discussed below. The ionosphere is subject to the action of the conductive electric current flowing in the atmosphere-ionosphere circuit. We present a physical model of DC electric field and current formation in this circuit. The key element of this model is an external current, which is formed with the occurrence of convective upward transport of charged aerosols and their gravitational sedimentation in the atmosphere. An increase in the level of atmospheric radioactivity results in the appearance of additional ionization and change of electrical conductivity. Variation of conductivity and external current in the lower atmosphere leads to perturbation of the electric current flowing in the global atmosphere-ionosphere circuit and to the associated DC electric field perturbation both on the Earth's surface and in the ionosphere. Description of these processes and some results of the electric field and current calculations are presented below. The seismic-induced electric field perturbations produce noticeable effects in the ionosphere by generating the electromagnetic field and plasma disturbances. We describe the generation mechanisms of such experimentally observed effects as excitation of plasma density inhomogeneities, field-aligned currents, and ULF/ELF emissions and the modification of electron and ion altitude profiles in the upper ionosphere. The electrodynamic model of the ionosphere modification under the influence of some natural and man-made processes in the atmosphere is also discussed. The model is based on the satellite and ground measurements of electromagnetic field and plasma perturbations and on the data on atmospheric radioactivity and soil gas injection into the atmosphere.

Strike-slip earthquakes can also be detected in the ionosphere

NASA Astrophysics Data System (ADS)

Astafyeva, Elvira; Rolland, Lucie M.; Sladen, Anthony

2014-11-01

It is generally assumed that co-seismic ionospheric disturbances are generated by large vertical static displacements of the ground during an earthquake. Consequently, it is expected that co-seismic ionospheric disturbances are only observable after earthquakes with a significant dip-slip component. Therefore, earthquakes dominated by strike-slip motion, i.e. with very little vertical co-seismic component, are not expected to generate ionospheric perturbations. In this work, we use total electron content (TEC) measurements from ground-based GNSS-receivers to study ionospheric response to six recent largest strike-slip earthquakes: the Mw7.8 Kunlun earthquake of 14 November 2001, the Mw8.1 Macquarie earthquake of 23 December 2004, the Sumatra earthquake doublet, Mw8.6 and Mw8.2, of 11 April 2012, the Mw7.7 Balochistan earthquake of 24 September 2013 and the Mw 7.7 Scotia Sea earthquake of 17 November 2013. We show that large strike-slip earthquakes generate large ionospheric perturbations of amplitude comparable with those induced by dip-slip earthquakes of equivalent magnitude. We consider that in the absence of significant vertical static co-seismic displacements of the ground, other seismological parameters (primarily the magnitude of co-seismic horizontal displacements, seismic fault dimensions, seismic slip) may contribute in generation of large-amplitude ionospheric perturbations.

Field-aligned current sources in the high-latitude ionosphere

NASA Technical Reports Server (NTRS)

Barbosa, D. D.

1979-01-01

The paper determines the electric potential in a plane which is fed current from a pair of field-aligned current sheets. The ionospheric conductivity is modelled as a constant with an enhanced conductivity annular ring. It is shown that field-aligned current distributions are arbitrary functions of azimuth angle (MLT) and thus allow for asymmetric potential configurations over the pole cap. In addition, ionospheric surface currents are computed by means of stream functions. Finally, the discussion relates these methods to the electrical characteristics of the magnetosphere.

The plasma environment, charge state, and currents of Saturn's C and D rings

NASA Technical Reports Server (NTRS)

Wilson, G. R.

1991-01-01

The charge state and associated currents of Saturn's C an D rings are studied by modeling the flow of ionospheric plasma from the mid- to low-latitude ionosphere to the vicinity of the rings. It is found that the plasma density near the C and D rings, at a given radial location, will experience a one to two order of magnitude diurnal variation. The surface charge density (SCD) of these rings can show significant radial and azimuthal variations due mainly to variation in the plasma density. The SCD also depends on structural features of the rings such as thickness and the nature of the particle size distribution. The associated azimuthal currents carried by these rings also show large diurnal variations resulting in field-aligned currents which close in the ionosphere. The resulting ionospheric electric field will probably not produce a significant amount of plasma convection in the topside ionosphere and inner plasmasphere.

Current to the ionosphere following a lightning stroke

NASA Technical Reports Server (NTRS)

Hale, L. C.; Baginski, M. E.

1987-01-01

A simple analytical expression for calculating the total current waveform to the ionosphere after a lightning stroke is derived. The validity of this expression is demonstrated by comparison with a more rigorous computer solution of Maxwell's equations. The analytic model demonstrates that the temporal variation of the current induced in the ionosphere and global circuit and the corresponding return current in the earth depends on the conductivity profile at intervening altitudes in the middle atmosphere. A conclusion is that capacitative coupling may provide tighter coupling between the lower atmosphere and the ionosphere than usually considered, in both directions, which may help to explain observations which seem to indicate that magnetospheric phenomena may in some instances trigger lightning.

Features of HF Radio Wave Attenuation in the Midlatitude Ionosphere Near the Skip Zone Boundary

NASA Astrophysics Data System (ADS)

Denisenko, P. F.; Skazik, A. I.

2017-06-01

We briefly describe the history of studying the decameter radio wave attenuation by different methods in the midlatitude ionosphere. A new method of estimating the attenuation of HF radio waves in the ionospheric F region near the skip zone boundary is presented. This method is based on an analysis of the time structure of the interference field generated by highly stable monochromatic X-mode radio waves at the observation point. The main parameter is the effective electron collision frequency νeff, which allows for all energy losses in the form of equivalent heat loss. The frequency νeff is estimated by matching the assumed (model) and the experimentally observed structures. Model calculations are performed using the geometrical-optics approximation. The spatial attenuation caused by the influence of the medium-scale traveling ionospheric disturbances is taken into account. Spherical shape of the ionosphere and the Earth's magnetic field are roughly allowed for. The results of recording of the level of signals from the RWM (Moscow) station at a frequency of 9.996 MHz at point Rostov are used.

Transmission of the Magnetospheric Electric Fields to the Low Latitude Ionosphere during Storm and Substorms

NASA Astrophysics Data System (ADS)

Kikuchi, T.; Hashimoto, K. K.; Ebihara, Y.; Tanaka, T.; Tomizawa, I.; Nagatsuma, T.

2016-12-01

The solar wind energy is transmitted to the low latitude ionosphere in a current circuit from a dynamo in the magnetosphere to the equatorial ionosphere via the polar ionosphere. During the substorm growth phase and storm main phase, the dawn-to-dusk convection electric field is intensified by the southward interplanetary magnetic field (IMF), driving the ionospheric DP2 currents composed of two-cell Hall current vortices in high latitudes and Pedersen currents amplified at the dayside equator (EEJ). The EEJ-Region-1 field-aligned current (R1 FAC) circuit is completed via the Pedersen currents in midlatitude. On the other hand, the shielding electric field and the Region-2 FACs develop in the inner magnetosphere, tending to cancel the convection electric field at the mid-equatorial latitudes. The shielding often causes overshielding when the convection electric field reduces substantially and the EEJ is overcome by the counter-electrojet (CEJ), leading to that even the quasi-periodic DP2 fluctuations are contributed by the overshielding. The overshielding develop significantly during substorms and storms, leading to that the mid and low latitude ionosphere is under strong influence of the overshielding as well as the convection electric fields. The electric fields on the day- and night-sides are in opposite direction to each other, but the electric fields in the evening are anomalously enhanced in the same direction as in the day. The evening anomaly is a unique feature of the electric potential distribution in the global ionosphere. DP2-type electric field and currents also develop during the transient/short-term geomagnetic disturbances like the geomagnetic sudden commencements (SC) and ULF pulsations, which appear simultaneously at high latitude and equator within the temporal resolution of 10 sec. Using the SC, we can confirm that the electric potential and currents are transmitted near-instantaneously to low latitude ionosphere on both the day- and night-sides, which is explained by means of the light speed propagation of the TM0 mode waves in the Earth-ionosphere waveguide.

Generation of real-time global ionospheric map based on the global GNSS stations with only a sparse distribution

NASA Astrophysics Data System (ADS)

Li, Zishen; Wang, Ningbo; Li, Min; Zhou, Kai; Yuan, Yunbin; Yuan, Hong

2017-04-01

The Earth's ionosphere is part of the atmosphere stretching from an altitude of about 50 km to more than 1000 km. When the Global Navigation Satellite System (GNSS) signal emitted from a satellite travels through the ionosphere before reaches a receiver on or near the Earth surface, the GNSS signal is significantly delayed by the ionosphere and this delay bas been considered as one of the major errors in the GNSS measurement. The real-time global ionospheric map calculated from the real-time data obtained by global stations is an essential method for mitigating the ionospheric delay for real-time positioning. The generation of an accurate global ionospheric map generally depends on the global stations with dense distribution; however, the number of global stations that can produce the real-time data is very limited at present, which results that the generation of global ionospheric map with a high accuracy is very different when only using the current stations with real-time data. In view of this, a new approach is proposed for calculating the real-time global ionospheric map only based on the current stations with real-time data. This new approach is developed on the basis of the post-processing and the one-day predicted global ionospheric map from our research group. The performance of the proposed approach is tested by the current global stations with the real-time data and the test results are also compared with the IGS-released final global ionospheric map products.

An Ionosphere/Magnetosphere Coupling Current System Located in the Gap Between Saturn and its Rings

NASA Astrophysics Data System (ADS)

Khurana, K. K.; Dougherty, M. K.; Cao, H.; Hunt, G. J.; Provan, G.

2017-12-01

The Grand Finale Orbits of the Cassini spacecraft traversed through Saturn's D ring and brought the spacecraft to within 3000 km of Saturn's cloud tops. The closest approaches (CA) were near the equatorial plane of Saturn and were distributed narrowly around the local noon. The difference field (observations - internal field - magnetospheric ring current field) obtained from the Grand Finale orbits show persistent residual fields centered around the CA which diminish at higher latitudes on field lines that connect to the ring. Modeling of this perturbation in terms of internal harmonics shows that the perturbation is not of internal origin but is produced by external currents that couple the ionosphere to the magnetosphere. The sense of the current system suggests that the southern feet of the field lines in the ionosphere lead their northern footprints. We show that the observed field perturbations are consistent with a meridional Pedersen current whose strength is 1 MA/radian, i.e. comparable in strength to the Planetary-period-oscillation related current systems observed in the auroral zone. We show that the implied Lorentz force in the ionosphere extracts momentum from the faster moving southern ionosphere and passes it on to the northern ionosphere. We discuss several ideas for generating this current system. In particular, we highlight a mechanism that involves shears in the neutral winds in the thermospheric region to generate the observed magnetic field.

Ionospheric effects during severe space weather events seen in ionospheric service data products

NASA Astrophysics Data System (ADS)

Jakowski, Norbert; Danielides, Michael; Mayer, Christoph; Borries, Claudia

Space weather effects are closely related to complex perturbation processes in the magnetosphere-ionosphere-thermosphere systems, initiated by enhanced solar energy input. To understand and model complex space weather processes, different views on the same subject are helpful. One of the ionosphere key parameters is the Total Electron Content (TEC) which provides a first or-der approximation of the ionospheric range error in Global Navigation Satellite System (GNSS) applications. Additionally, horizontal gradients and time rate of change of TEC are important for estimating the perturbation degree of the ionosphere. TEC maps can effectively be gener-ated using ground based GNSS measurements from global receiver networks. Whereas ground based GNSS measurements provide good horizontal resolution, space based radio occultation measurements can complete the view by providing information on the vertical plasma density distribution. The combination of ground based TEC and vertical sounding measurements pro-vide essential information on the shape of the vertical electron density profile by computing the equivalent slab thickness at the ionosonde station site. Since radio beacon measurements at 150/400 MHz are well suited to trace the horizontal structure of Travelling Ionospheric Dis-turbances (TIDs), these data products essentially complete GNSS based TEC mapping results. Radio scintillation data products, characterising small scale irregularities in the ionosphere, are useful to estimate the continuity and availability of transionospheric radio signals. The different data products are addressed while discussing severe space weather events in the ionosphere e.g. events in October/November 2003. The complementary view of different near real time service data products is helpful to better understand the complex dynamics of ionospheric perturbation processes and to forecast the development of parameters customers are interested in.

The International Reference Ionosphere: Model Update 2016

NASA Astrophysics Data System (ADS)

Bilitza, Dieter; Altadill, David; Reinisch, Bodo; Galkin, Ivan; Shubin, Valentin; Truhlik, Vladimir

2016-04-01

The International Reference Ionosphere (IRI) is recognized as the official standard for the ionosphere (COSPAR, URSI, ISO) and is widely used for a multitude of different applications as evidenced by the many papers in science and engineering journals that acknowledge the use of IRI (e.g., about 11% of all Radio Science papers each year). One of the shortcomings of the model has been the dependence of the F2 peak height modeling on the propagation factor M(3000)F2. With the 2016 version of IRI, two new models will be introduced for hmF2 that were developed directly based on hmF2 measurements by ionosondes [Altadill et al., 2013] and by COSMIC radio occultation [Shubin, 2015], respectively. In addition IRI-2016 will include an improved representation of the ionosphere during the very low solar activities that were reached during the last solar minimum in 2008/2009. This presentation will review these and other improvements that are being implemented with the 2016 version of the IRI model. We will also discuss recent IRI workshops and their findings and results. One of the most exciting new projects is the development of the Real-Time IRI [Galkin et al., 2012]. We will discuss the current status and plans for the future. Altadill, D., S. Magdaleno, J.M. Torta, E. Blanch (2013), Global empirical models of the density peak height and of the equivalent scale height for quiet conditions, Advances in Space Research 52, 1756-1769, doi:10.1016/j.asr.2012.11.018. Galkin, I.A., B.W. Reinisch, X. Huang, and D. Bilitza (2012), Assimilation of GIRO Data into a Real-Time IRI, Radio Science, 47, RS0L07, doi:10.1029/2011RS004952. Shubin V.N. (2015), Global median model of the F2-layer peak height based on ionospheric radio-occultation and ground-based Digisonde observations, Advances in Space Research 56, 916-928, doi:10.1016/j.asr.2015.05.029.

Ionosphere Profile Estimation Using Ionosonde & GPS Data in an Inverse Refraction Calculation

NASA Astrophysics Data System (ADS)

Psiaki, M. L.

2014-12-01

A method has been developed to assimilate ionosonde virtual heights and GPS slant TEC data to estimate the parameters of a local ionosphere model, including estimates of the topside and of latitude and longitude variations. This effort seeks to better assimilate a variety of remote sensing data in order to characterize local (and eventually regional and global) ionosphere electron density profiles. The core calculations involve a forward refractive ray-tracing solution and a nonlinear optimal estimation algorithm that inverts the forward model. The ray-tracing calculations solve a nonlinear two-point boundary value problem for the curved ionosonde or GPS ray path through a parameterized electron density profile. It implements a full 3D solution that can handle the case of a tilted ionosphere. These calculations use Hamiltonian equivalents of the Appleton-Hartree magneto-plasma refraction index model. The current ionosphere parameterization is a modified Booker profile. It has been augmented to include latitude and longitude dependencies. The forward ray-tracing solution yields a given signal's group delay and beat carrier phase observables. An auxiliary set of boundary value problem solutions determine the sensitivities of the ray paths and observables with respect to the parameters of the augmented Booker profile. The nonlinear estimation algorithm compares the measured ionosonde virtual-altitude observables and GPS slant-TEC observables to the corresponding values from the forward refraction model. It uses the parameter sensitivities of the model to iteratively improve its parameter estimates in a way the reduces the residual errors between the measurements and their modeled values. This method has been applied to data from HAARP in Gakona, AK and has produced good TEC and virtual height fits. It has been extended to characterize electron density perturbations caused by HAARP heating experiments through the use of GPS slant TEC data for an LOS through the heated zone. The next planned extension of the method is to estimate the parameters of a regional ionosphere profile. The input observables will be slant TEC from an array of GPS receivers and group delay and carrier phase observables from an array of high-frequency beacons. The beacon array will function as a sort of multi-static ionosonde.

Auroral Current and Electrodynamics Structure (ACES) Observations of Ionospheric Feedback in the Alfven Resonator

NASA Technical Reports Server (NTRS)

Cohen, Ian J.; Lessard, Marc; Lund, Eric J.; Bounds, Scott R.; Kletzing, Craig; Kaeppler, Stephen R.; Sigsbee, Kristine M.; Streltsov, Anatoly V.; Labelle, James W.; Dombrowski, Micah P.;

Ionosphere-magnetosphere coupling and convection

NASA Technical Reports Server (NTRS)

Wolf, R. A.; Spiro, R. W.

1984-01-01

The following international Magnetospheric Study quantitative models of observed ionosphere-magnetosphere events are reviewed: (1) a theoretical model of convection; (2) algorithms for deducing ionospheric current and electric-field patterns from sets of ground magnetograms and ionospheric conductivity information; and (3) empirical models of ionospheric conductances and polar cap potential drop. Research into magnetic-field-aligned electric fields is reviewed, particularly magnetic-mirror effects and double layers.

ST5 Observations of the Imbalance of Region 1 and 2 Field-Aligned Currents and its Implication to Ionospheric Closure Currents

NASA Technical Reports Server (NTRS)

Le, G.

2008-01-01

A major unsolved question in the physics of ionosphere-magnetosphere coupling is how field-aligned currents (FACs) close. In order to maintain the divergence free condition, overall downward FACs (carried mainly by upward electrons) must eventually balance the overall upward FACs associated with the precipitating electrons through ionospheric Pedersen currents. Although much of the current closure may take place via local Pedersen currents flowing between Region 1 (R1) and Region 2 (R2) FACs, there is a generally an imbalance, i.e., more currents in R1 than in R2, in total currents between them. The net currents may be closed within R1 via cross-polar cap Pedersen currents. In this study, we use the magnetic field observations from Space Technology 5 mission to quantify the imbalance of R1 and R2 currents. We will determine the net R1-R2 currents under various solar wind conditions and discuss the implication of such imbalance to the ionospheric closure currents.

First demonstration of HF-driven ionospheric currents

NASA Astrophysics Data System (ADS)

Papadopoulos, K.; Chang, C.-L.; Labenski, J.; Wallace, T.

2011-10-01

The first experimental demonstration of HF driven currents in the ionosphere at low ELF/ULF frequencies without relying in the presence of electrojets is presented. The effect was predicted by theoretical/computational means in a recent letter and given the name Ionospheric Current Drive (ICD). The effect relies on modulated F-region HF heating to generate Magneto-Sonic (MS) waves that drive Hall currents when they reach the E-region. The Hall currents inject ELF waves into the Earth-Ionosphere waveguide and helicon and Shear Alfven (SA) waves in the magnetosphere. The proof-of-concept experiments were conducted using the HAARP heater in Alaska under the BRIOCHE program. Waves between 0.1-70 Hz were measured at both near and far sites. The letter discusses the differences between ICD generated waves and those relying on modulation of electrojets.

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

NASA Astrophysics Data System (ADS)

Rycroft, Michael J.; Odzimek, Anna; Arnold, Neil F.; Füllekrug, Martin; Kułak, Andrzej; Neubert, Torsten

2007-12-01

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 ˜1V. The time scales for the recovery of the ionospheric potential are shown to be ˜250s, 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 ˜20A. Further, it is concluded that conduction and convection currents associated with “batteries” within thunderclouds and electrified shower clouds contribute essentially equally (˜500A each) to maintaining the ionospheric potential.

Analysis of ionospheric refraction error corrections for GRARR systems

NASA Technical Reports Server (NTRS)

Mallinckrodt, A. J.; Parker, H. C.; Berbert, J. H.

1971-01-01

A determination is presented of the ionospheric refraction correction requirements for the Goddard range and range rate (GRARR) S-band, modified S-band, very high frequency (VHF), and modified VHF systems. The relation ships within these four systems are analyzed to show that the refraction corrections are the same for all four systems and to clarify the group and phase nature of these corrections. The analysis is simplified by recognizing that the range rate is equivalent to a carrier phase range change measurement. The equation for the range errors are given.

Associating ground magnetometer observations with current or voltage generators

NASA Astrophysics Data System (ADS)

Hartinger, M. D.; Xu, Z.; Clauer, C. R.; Yu, Y.; Weimer, D. R.; Kim, H.; Pilipenko, V.; Welling, D. T.; Behlke, R.; Willer, A. N.

2017-07-01

A circuit analogy for magnetosphere-ionosphere current systems has two extremes for drivers of ionospheric currents: ionospheric electric fields/voltages constant while current/conductivity vary—the "voltage generator"—and current constant while electric field/conductivity vary—the "current generator." Statistical studies of ground magnetometer observations associated with dayside Transient High Latitude Current Systems (THLCS) driven by similar mechanisms find contradictory results using this paradigm: some studies associate THLCS with voltage generators, others with current generators. We argue that most of this contradiction arises from two assumptions used to interpret ground magnetometer observations: (1) measurements made at fixed position relative to the THLCS field-aligned current and (2) negligible auroral precipitation contributions to ionospheric conductivity. We use observations and simulations to illustrate how these two assumptions substantially alter expectations for magnetic perturbations associated with either a current or a voltage generator. Our results demonstrate that before interpreting ground magnetometer observations of THLCS in the context of current/voltage generators, the location of a ground magnetometer station relative to the THLCS field-aligned current and the location of any auroral zone conductivity enhancements need to be taken into account.

Variation of TEC and related parameters over the Indian EIA region from ground and space based GPS observations during the low solar activity period of May 2007-April 2008

NASA Astrophysics Data System (ADS)

Chakravarty, S. C.; Nagaraja, Kamsali; Jakowski, N.

2017-03-01

The annual variations of ionospheric Total Electron Content (TEC), F-region peak ionisation (NmF2) and the ionospheric slab thickness (τ) over the Indian region during the low solar activity period of May 2007-April 2008 have been studied. For this purpose the ground based TEC data obtained from GAGAN measurements and the space based data from GPS radio occultation technique using CHAMP have been utilised. The results of these independent measurements are combined to derive additional parameters such as the equivalent slab thickness of the total and the bottom-side ionospheric regions (τT and τB). The one year hourly average values of all these parameters over the ionospheric anomaly latitude region (10-26°N) are presented here along with the statistical error estimates. It is expected that these results are potentially suited to be used as base level values during geomagnetically quiet and undisturbed solar conditions.

Earthquake-Ionosphere Coupling Processes

NASA Astrophysics Data System (ADS)

Kamogawa, Masashi

After a giant earthquake (EQ), acoustic and gravity waves are excited by the displacement of land and sea surface, propagate through atmosphere, and then reach thermosphere, which causes ionospheric disturbances. This phenomenon was detected first by ionosonde and by HF Doppler sounderin the 1964 M9.2 Great Alaskan EQ. Developing Global Positioning System (GPS), seismogenic ionospheric disturbance detected by total electron content (TEC) measurement has been reported. A value of TEC is estimated by the phase difference between two different carrier frequencies through the propagation in the dispersive ionospheric plasma. The variation of TEC is mostly similar to that of F-region plasma. Acoustic-gravity waves triggered by an earthquake [Heki and Ping, EPSL, 2005; Liu et al., JGR, 2010] and a tsunami [Artu et al., GJI, 2005; Liu et al., JGR, 2006; Rolland, GRL, 2010] disturb the ionosphere and travel in the ionosphere. Besides the traveling ionospheric disturbances, ionospheric disturbances excited by Rayleigh waves [Ducic et al, GRL, 2003; Liu et al., GRL, 2006] as well as post-seismic 4-minute monoperiodic atmospheric resonances [Choosakul et al., JGR, 2009] have been observed after the large earthquakes. Since GPS Earth Observation Network System (GEONET) with more than 1200 GPS receiving points in Japan is a dense GPS network, seismogenic ionospheric disturbance is spatially observed. In particular, the seismogenic ionospheric disturbance caused by the M9.0 off the Pacific coast of Tohoku EQ (henceforth the Tohoku EQ) on 11 March 2011 was clearly observed. Approximately 9 minutes after the mainshock, acoustic waves which propagated radially emitted from the tsunami source area were observed through the TEC measurement (e. g., Liu et al. [JGR, 2011]). Moreover, there was a depression of TEC lasting for several tens of minutes after a huge earthquake, which was a large-scale phenomenon extending to a radius of a few hundred kilometers. This TEC depression may be an ionospheric phenomenon attributed to tsunami, termed tsunamigenic ionospheric hole (TIH) [Kakinami and Kamogwa et al., GRL, 2012]. After the TEC depression accompanying a monoperiodic variation with approximately 4-minute period as an acoustic resonance between the ionosphere and the solid earth, the TIH gradually recovered. In addition, geomagnetic pulsations with the periods of 150, 180 and 210 seconds were observed on the ground in Japan approximately 5 minutes after the mainshock. Since the variation with the period of 180 seconds was simultaneously detected at the magnetic conjugate of points of Japan, namely Australia, field aligned currents along the magnetic field line were excited. The field aligned currents might be excited due to E and F region dynamo current caused by acoustic waves originating from the tsunami. This result implies that a large earthquake generates seismogenic field aligned currents. Furthermore, monoperiodical geomagnetic oscillation pointing to the epicenter of which velocity corresponds to Rayleigh waves occurs. This may occur due to seismogenic arc-current in E region. Removing such magnetic oscillations from the observed data, clear tsunami dynamo effect was found. This result implies that a large EQ generates seismogenic field aligned currents, seismogenic arc-current and tsunami dynamo current which disturb geomagnetic field. Thus, we found the complex coupling process between a large EQ and an ionosphere from the results of Tohoku EQ.

Modelling the Auroral Magnetosphere-Ionosphere Coupling System at Jupiter

NASA Astrophysics Data System (ADS)

Bunce, E. J.; Cowley, S.; Provan, G.

2016-12-01

The magnetosphere-ionosphere coupling system at Jupiter is a topic of central significance in understanding the fundamental properties of its large-scale plasma environment. Theoretical discussion of this topic typically considers the properties of the field-aligned current systems that form part of a large-scale magnetosphere-ionosphere coupling current system associated with momentum exchange between the ionosphere and the magnetosphere, communicated via the magnetic field. The current system associated with the main oval is believed to be related to centrifugally-driven outward radial transport of iogenic plasma that leads to sub-corotation in the middle magnetosphere. In addition to the magnetosphere-ionosphere coupling current system, upward-directed field-aligned currents may flow at the open-closed field line boundary due to the shear between outer closed field lines and open field lines, which may relate to emission poleward of the main oval. An axi-symmetric model of the plasma flow in the jovian system, the related coupling currents, and the consequent auroral precipitation based on these combined ideas was initially devised to represent typical steady-state conditions for the system and later extended to consider auroral effects resulting from sudden compressions of the magnetosphere. More recently, the model has been extended along model magnetic field lines into the magnetosphere in order to relate them to in situ observations from the NASA Juno spacecraft at Jupiter. The field-aligned coupling currents associated with the modelled current systems produce a readily-observable azimuthal field signature that bends the field lines out of magnetic meridians. Here we show the computed azimuthal fields produced by our model auroral current system throughout the region between the ionosphere and the magnetic equator, and illustrate the results by evaluation of various model parameters (e.g. field-aligned current density, accelerating voltages, accelerated energy flux) along the Juno orbits.

Excitation of earth-ionosphere waveguide in the ELF and lower VLF bands by modulated ionospheric current. Technical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Field, E.C.; Bloom, R.M.

1993-05-21

In this report the authors use the principal of reciprocity in conjunction with a full-wave propagation code to calculate ground-level fields excited by ionospheric currents modulated at frequencies between 50 and 100 Hz with HF heaters. Their results show the dependence on source orientation, altitude, and dimension and therefore pertain to experiments using the HIPAS or HAARP ionospheric heaters. In the end-fire mode, the waveguide excitation efficiency of an ELF HED in the ionosphere is up to 20 dB greater than for a ground-based antenna, provided its altitude does not exceed 80-to-90 km. The highest efficiency occurs for a sourcemore » altitude of around 70 km; if that altitude is raised to 100 km, the efficiency drops by about 20 dB in the day and 10 dB at night. That efficiency does not account for the greater conductivity modulation that might be achieved at altitudes greater than 70 km, however. The trade-off between the altitude dependencies of the excitation efficiency and maximum achievable modulation depends on the ERP of the HF heater, the optimum altitude increasing with increasing ERP. For HIPAS the best modulation altitude is around 70 km, whereas for HAARP there might be marginal value in modulating at attitudes as high as 100 Km. Ionospheric modification, Ionospheric currents, Ionospheric heating.« less

Role of the ionosphere for the atmospheric evolution of planets.

PubMed

Yamauchi, Masatoshi; Wahlund, Jan-Erik

2007-10-01

We have synthesized current understanding, mainly observations, with regard to ion escape mechanisms to space from the ionosphere and exosphere of Titan and Earth-type planets, with the intent to provide an improved input for models of atmospheric evolution on early Earth and Earth-type planets and exoplanets. We focus on the role of the ionosphere and its non-linear response to solar parameters, all of which have been underestimated in current models of ancient atmospheric escape (4 billion years ago). Factors that have been overlooked include the following: (1) Much larger variation of O(+) outflow than H(+) outflow from the terrestrial ionosphere, depending on solar and geomagnetic activities (an important consideration when attempting to determine the oxidized state of the atmosphere of early Earth); (2) magnetization of the ionopause, which keeps ionospheric ions from escaping and controls many other escape processes; (3) extra ionization by, for example, the critical ionization velocity mechanism, which expands the ionosphere to greater altitudes than current models predict; and (4) the large escape of cold ions from the dense, expanded ionosphere of Titan. Here we offer, as a guideline for quantitative simulations, a qualitative diagnosis of increases or decreases of non-thermal escape related to the ionosphere for magnetized and unmagnetized planets in response to changes in solar parameters (i.e., solar EUV/FUV flux, solar wind dynamic pressure, and interplanetary magnetic field).

The Role of Ionospheric Outflow Preconditioning in Determining Storm Geoeffectiveness

NASA Astrophysics Data System (ADS)

Welling, D. T.; Liemohn, M. W.; Ridley, A. J.

2012-12-01

It is now well accepted that ionospheric outflow plays an important role in the development of the plasma sheet and ring current during geomagnetic storms. Furthermore, even during quiet times, ionospheric plasma populates the magnetospheric lobes, producing a reservoir of hydrogen and oxygen ions. When the Interplanetary Magnetic Field (IMF) turns southward, this reservoir is connected to the plasma sheet and ring current through magnetospheric convection. Hence, the conditions of the ionosphere and magnetospheric lobes leading up to magnetospheric storm onset have important implications for storm development. Despite this, there has been little research on this preconditioning; most global simulations begin just before storm onset, neglecting preconditioning altogether. This work explores the role of preconditioning in determining the geoeffectiveness of storms using a coupled global model system. A model of ionospheric outflow (the Polar Wind Outflow Model, PWOM) is two-way coupled to a global magnetohydrodynamic model (the Block-Adaptive Tree Solar wind Roe-type Upwind Scheme, BATS-R-US), which in turn drives a ring current model (the Ring current Atmosphere interactions Model, RAM). This unique setup is used to simulate an idealized storm. The model is started at many different times, from 1 hour before storm onset to 12 hours before. The effects of storm preconditioning are examined by investigating the total ionospheric plasma content in the lobes just before onset, the total ionospheric contribution in the ring current just after onset, and the effects on Dst, magnetic elevation angle at geosynchronous, and total ring current energy density. This experiment is repeated for different solar activity levels as set by F10.7 flux. Finally, a synthetic double-dip storm is constructed to see how two closely spaced storms affect each other by changing the preconditioning environment. It is found that preconditioning of the magnetospheric lobes via ionospheric outflow greatly influences the geoeffectiveness of magnetospheric storms.

Excitation thresholds of field-aligned irregularities and associated ionospheric hysteresis at very high latitudes observed using SPEAR-induced HF radar backscatter

NASA Astrophysics Data System (ADS)

Wright, D. M.; Dhillon, R. S.; Yeoman, T. K.; Robinson, T. R.; Thomas, E. C.; Baddeley, L. J.; Imber, S.

2009-07-01

On 10 October 2006 the SPEAR high power radar facility was operated in a power-stepping mode where both CUTLASS radars were detecting backscatter from the SPEAR-induced field-aligned irregularities (FAIs). The effective radiated power of SPEAR was varied from 1-10 MW. The aim of the experiment was to investigate the power thresholds for excitation (Pt) and collapse (Pc) of artificially-induced FAIs in the ionosphere over Svalbard. It was demonstrated that FAI could be excited by a SPEAR ERP of only 1 MW, representing only 1/30th of SPEAR's total capability, and that once created the irregularities could be maintained for even lower powers. The experiment also demonstrated that the very high latitude ionosphere exhibits hysteresis, where the down-going part of the power cycle provided a higher density of irregularities than for the equivalent part of the up-going cycle. Although this second result is similar to that observed previously by CUTLASS in conjunction with the Tromsø heater, the same is not true for the equivalent incoherent scatter measurements. The EISCAT Svalbard Radar (ESR) failed to detect any hysteresis in the plasma parameters over Svalbard in stark contract with the measurements made using the Tromsø UHF.

Ionospheric control of the dawn-dusk asymmetry of the Mars magnetotail current sheet

NASA Astrophysics Data System (ADS)

Liemohn, Michael W.; Xu, Shaosui; Dong, Chuanfei; Bougher, Stephen W.; Johnson, Blake C.; Ilie, Raluca; De Zeeuw, Darren L.

2017-06-01

This study investigates the role of solar EUV intensity at controlling the location of the Mars magnetotail current sheet and the structure of the lobes. Four simulation results are examined from a multifluid magnetohydrodynamic model. The solar wind and interplanetary magnetic field (IMF) conditions are held constant, and the Mars crustal field sources are omitted from the simulation configuration. This isolates the influence of solar EUV. It is found that solar maximum conditions, regardless of season, result in a Venus-like tail configuration with the current sheet shifted to the -Y (dawnside) direction. Solar minimum conditions result in a flipped tail configuration with the current sheet shifted to the +Y (duskside) direction. The lobes follow this pattern, with the current sheet shifting away from the larger lobe with the higher magnetic field magnitude. The physical process responsible for this solar EUV control of the magnetotail is the magnetization of the dayside ionosphere. During solar maximum, the ionosphere is relatively strong and the draped IMF field lines quickly slip past Mars. At solar minimum, the weaker ionosphere allows the draped IMF to move closer to the planet. These lower altitudes of the closest approach of the field line to Mars greatly hinder the day-to-night flow of magnetic flux. This results in a buildup of magnetic flux in the dawnside lobe as the S-shaped topology on that side of the magnetosheath extends farther downtail. The study demonstrates that the Mars dayside ionosphere exerts significant control over the nightside induced magnetosphere of that planet.