Ground-based Magnetometer Data Research Articles

Climatology of the open–closed boundary using ULF wave observations from South Pole, McMurdo, and distributed Antarctic AGOs

It has been shown that a proxy determination of the magnetospheric open–closed magnetic field line boundary (OCB) location can be made by examining the ultra-low-frequency (ULF) wave power in magnetometer data, with particular interest in the Pc5 ULF waves with periods of 3–10 min. In this study, we present a climatology of such Pc5 ULF waves using ground-based magnetometer data from the South Pole Station (SPA), McMurdo (MCM) station, and the Automatic Geophysical Observatories (AGOs) located across the Antarctic continent, to infer OCB behavior and variability during geomagnetically quiet times (i.e., Ap < 30 nT). For each season [i.e., austral fall (20 February 2017–20 April 2017), austral winter (20 May 2017–20 July 2017), austral spring (20 August 2017–20 October 2017), and austral summer (20 November 2017–20 January 2018)], north–south (i.e., H-component) magnetic field line residual power–spectral density (PSD) measurements taken during geomagnetically quiet periods within a 60-day window centered at the austral solstice/equinox are averaged in 10-min temporal bins to form the climatology at each station. These residual PSDs thus enable the analysis of Pc5 activity (and lower period “long-band” oscillations) and, thus, OCB location/variability as a function of season and magnetic latitude. The dawn and dusk transitions across the OCB are analyzed, with a discussion of dawn and dusk variability during nominally quiet geomagnetic periods. In addition, latitudinal dependencies of the OCB and peak Pc5 periods at each station are discussed, along with the empirical Tsyganenko model comparisons to our site measurements.

Examining Solar Flare Effects on Earth's Ionosphere Using Ground-Based Measurements

This study investigated the simultaneous effects of solar flares (SFs) on both the D and E layers of Earth's ionosphere. The analysis focused on the M and X-class SFs that occurred during the 24th solar cycle as these two classes of SFs are known to produce significant effects on Earth’s environment, particularly during the daytime period. The data utilized to detect the SF events in this study were ground-based magnetometer data from the equatorial regions. Effects of the selected SF events on the E layer were investigated based on the EUEL index constructed using the geomagnetic data. Meanwhile, the changes in the strength of radio VLF signals in the D ionospheric layer during the selected SF events were monitored using Sudden Ionospheric Disturbance (SID) data. Two case studies were performed which consisted of four SF events from a total of 23 events that were detected by geomagnetic data during the period of study. Further analysis on the selected SF events showed the common effects of SFs on the D layer, which is the increment on the VLF signal measured from the SID stations although a different response was detected in the EUEL index variations. This indicates that the VLF signal always shows an increment even though a decrement in the ionization of the E layer occurs as a result of the SF events. The difference in responses could be attributed to the distinct changes in electron density of both layers during the SF occurrence. Further studies are needed to elucidate the underlying mechanism responsible for this unique response, utilizing appropriate parameters such as total electron content, as well as the electron density data to thoroughly analyze the ionospheric response during SF events.

GMAG: An open-source python package for ground-based magnetometers

Magnetometers are a key component of heliophysics research providing valuable insight into the dynamics of electromagnetic field regimes and their coupling throughout the solar system. On satellites, magnetometers provide detailed observations of the extension of the solar magnetic field into interplanetary space and of planetary environments. At Earth, magnetometers are deployed on the ground in extensive arrays spanning the polar cap, auroral and sub-auroral zone, mid- and low-latitudes and equatorial electrojet with nearly global coverage in azimuth (longitude or magnetic local time—MLT). These multipoint observations are used to diagnose both ionospheric and magnetospheric processes as well as the coupling between the solar wind and these two regimes at a fraction of the cost of in-situ instruments. Despite their utility in research, ground-based magnetometer data can be difficult to use due to a variety of file formats, multiple points of access for the data, and limited software. In this short article we review the Open-Source Python library GMAG which provides rapid access to ground-based magnetometer data from a number of arrays in a Pandas DataFrame, a common data format used throughout scientific research.

Multi-instrument observations of polar cap patches and traveling ionospheric disturbances generated by solar wind Alfvén waves coupling to the dayside magnetosphere

Abstract. During minor to moderate geomagnetic storms, caused by corotating interaction regions (CIRs) at the leading edge of high-speed streams (HSSs), solar wind Alfvén waves modulated the magnetic reconnection at the dayside magnetopause. The Resolute Bay Incoherent Scatter Radars (RISR-C and RISR-N), measuring plasma parameters in the cusp and polar cap, observed ionospheric signatures of flux transfer events (FTEs) that resulted in the formation of polar cap patches. The patches were observed as they moved over the RISR, and the Canadian High-Arctic Ionospheric Network (CHAIN) ionosondes and GPS receivers. The coupling process modulated the ionospheric convection and the intensity of ionospheric currents, including the auroral electrojets. The horizontal equivalent ionospheric currents (EICs) are estimated from ground-based magnetometer data using an inversion technique. Pulses of ionospheric currents that are a source of Joule heating in the lower thermosphere launched atmospheric gravity waves, causing traveling ionospheric disturbances (TIDs) that propagated equatorward. The TIDs were observed in the SuperDual Auroral Radar Network (SuperDARN) high-frequency (HF) radar ground scatter and the detrended total electron content (TEC) measured by globally distributed Global Navigation Satellite System (GNSS) receivers.

Magnetospheric response to solar wind forcing: ultra-low-frequency wave–particle interaction perspective

Abstract. Solar wind forcing, e.g., interplanetary shock and/or solar wind dynamic pressure pulses impacting Earth's magnetosphere, manifests many fundamental important space physics phenomena, including producing electromagnetic waves, plasma heating, and energetic particle acceleration. This paper summarizes our present understanding of the magnetospheric response to solar wind forcing in the aspects of radiation belt electrons, ring current ions and plasmaspheric plasma physics based on in situ spacecraft measurements, ground-based magnetometer data, magnetohydrodynamics (MHD) and kinetic simulations. Magnetosphere response to solar wind forcing is not just a “one-kick” scenario. It is found that after the impact of solar wind forcing on Earth's magnetosphere, plasma heating and energetic particle acceleration started nearly immediately and could last for a few hours. Even a small dynamic pressure change in interplanetary shock or solar wind pressure pulse can play a non-negligible role in magnetospheric physics. The impact leads to generation of a series of waves, including poloidal-mode ultra-low-frequency (ULF) waves. The fast acceleration of energetic electrons in the radiation belt and energetic ions in the ring current region response to the impact usually contains two contributing steps: (1) the initial adiabatic acceleration due to the magnetospheric compression, (2) followed by the wave–particle resonant acceleration dominated by global or localized poloidal ULF waves excited at various L-shells. Generalized theory of drift and drift–bounce resonance with growth- or decay-localized ULF waves has been developed to explain in situ spacecraft observations. The wave-related observational features like distorted energy spectrum, “boomerang” and “fishbone” pitch angle distributions of radiation belt electrons, ring current ions and plasmaspheric plasma can be explained in the framework of this generalized theory. It is worth pointing out here that poloidal ULF waves are much more efficient at accelerating and modulating electrons (fundamental mode) in the radiation belt and charged ions (second harmonic) in the ring current region. The results presented in this paper can be widely used in solar wind interacting with other planets such as Mercury, Jupiter, Saturn, Uranus and Neptune and other astrophysical objects with magnetic fields.

Network community structure of substorms using SuperMAG magnetometers

Geomagnetic substorms are a global magnetospheric reconfiguration, during which energy is abruptly transported to the ionosphere. Central to this are the auroral electrojets, large-scale ionospheric currents that are part of a larger three-dimensional system, the substorm current wedge. Many, often conflicting, magnetospheric reconfiguration scenarios have been proposed to describe the substorm current wedge evolution and structure. SuperMAG is a worldwide collaboration providing easy access to ground based magnetometer data. Here we show application of techniques from network science to analyze data from 137 SuperMAG ground-based magnetometers. We calculate a time-varying directed network and perform community detection on the network, identifying locally dense groups of connections. Analysis of 41 substorms exhibit robust structural change from many small, uncorrelated current systems before substorm onset, to a large spatially-extended coherent system, approximately 10 minutes after onset. We interpret this as strong indication that the auroral electrojet system during substorm expansions is inherently a large-scale phenomenon and is not solely due to many meso-scale wedgelets.

Calculation and Characterization of the EEJ Current Density from Ground-Based Magnetometer Data Using Ampere’s Law

Calculation and Characterization of the EEJ Current Density from Ground-Based Magnetometer Data Using Ampere’s Law

Empirical model of equatorial electrojet based on ground-based magnetometer data during solar minimum in fall

In this study, we constructed an empirical model of the equatorial electrojet (EEJ), including local time and longitudinal dependence, based on simultaneous data from 12 magnetometer stations located in six longitude sectors. An analysis was carried out using the equatorial electrojet index, EUEL, calculated from the geomagnetic northward H component. The magnetic EEJ strength is calculated as the difference between the normalized EUEL index of the magnetic dip equator station and the normalized EUEL index of the off-dip equator station located beyond the EEJ band. Analysis showed that this current is always strongest in the South American sector, regardless of local time (LT), and weakest in the Indian sector during 0900 and 1000 LT, but shifted to the African sector during 1100 to 1400 LT. These longitude variations of EEJ roughly follow variations of the inversed main field strength along the dip equator, except for the Indian and Southeast Asian sectors. The result showed that the EEJ component derived from the model exhibits a similar pattern with measured EEJ from ground data during noontime, mainly before 1300 LT.

Study of simultaneous presence of DD and PP electric fields during the geomagnetic storm of November 7–8, 2004 and resultant TEC variation over the Indian Region

During very intense geomagnetic storm of November 7–8, 2004 simultaneous presence of storm time disturbance dynamo and eastward and westward directed prompt penetration electric fields inferred from the ground based magnetometer data in the 75∘ E sector is presented. Magnetometer observations show that, on the whole, average ΔH variation on 8 November remains below the night time level compared to its quiet day variation. A number of upward and downward excursions have been observed between 0130 UT and 0800 UT in the ΔH variation on 8 November. These excursions in ΔH have been attributed to the episodes of eastward and westward prompt penetrating electric fields. Ionospheric response in the equatorial ionization anomaly region along 75∘ E has also been studied using the total electron content data recorded at five GPS stations, namely Udaipur, Bengaluru (IISC), Hyderabad (HYDE), Maldives (MALD) and Diego Garcia (DGAR). Observation of markedly suppressed EIA, in conjunction with ΔH variation which was m negative during the daytime on 8 November, indicates the presence of an external field of opposite polarity (the disturbance dynamo electric field) that either undermined, or overshadowed the daytime ambient (eastward) electric field to the extent that the equatorial plasma fountain could not become effective.

Report on Science Project for Probing the High-Latitude Ionosphere with Complementary Radar and Energetic Neutral Atom (ENA) Measurements

Vast magnetospheric regions are mapped along the field lines to the narrow latitudinal band of the polar/auroral regions. Therefore monitoring of solar wind energy dissipation into the ionosphere at auroral latitudes gives unique opportunities to study geomagnetic disturbances in their complexity from a relatively well-localized vantage point. Here we introduce and present the current state of a recently proposed science project for coordinated monitoring of high-latitude activity with the EISCAT (European Incoherent Scatter) radar array supported by ground-based magnetometer and optical data and ENA (Energetic Neutral Atom) observation from the CINEMA (Cube-Sat for Ions, Neutrals, Electrons and Magnetic field) satellite system.

Spectral structure of Pc3–4 pulsations: possible signatures of cavity modes

Abstract. In this study we investigate the spectral structure of Pc3–4 pulsations observed at low and midlatitudes. For this purpose, ground-based magnetometer data recorded at the MM100 stations in Europe and at two low latitude stations in South Africa were used. In addition, fluxgate magnetometer data from the CHAMP (CHAllenging Minisatellite Payload) low Earth orbit satellite were used. The results of our analysis suggest that at least three mechanisms contribute to the spectral content of Pc3–4 pulsations typically observed at these latitudes. We confirm that a typical Pc3–4 pulsation contains a field line resonance (FLR) contribution, with latitude dependent frequency, and an upstream wave (UW) contribution, with frequency proportional to the IMF (interplanetary magnetic field) magnitude BIMF. Besides the FLR and UW contributions, the Pc3–4 pulsations consistently contain signals at other frequencies that are independent of latitude and BIMF. We suggest that the most likely explanation for these additional frequency contributions is that they are fast mode resonances (FMRs) related to cavity, waveguide, or virtual modes. Although the above contributions to the pulsation spectral structure have been reported previously, we believe that this is the first time where evidence is presented showing that they are all present simultaneously in both ground-based and satellite data.

Observations of ULF wave related equatorial electrojet and density fluctuations

We report on Pc5 wave related electric field and vertical drift velocity oscillations at the equator as observed by ground magnetometers for an extended period on 9 August 2008. We show that the magnetometer-estimated equatorial E×B drift oscillates with the same frequency as ULF Pc5 waves, creating significant ionospheric density fluctuations. We also show ionospheric density fluctuations during the period when we observed ULF wave activity. At the same time, we detect the ULF activity on the ground using ground-based magnetometer data from the African Meridian B-field Education and Research (AMBER) and the South American Meridional B-field Array (SAMBA). From space, we use magnetic field observations from the GOES 12 and the Communication/Navigation Outage and Forecast System (C/NOFS) satellites. Upstream solar wind conditions are provided by the ACE spacecraft. We find that the wave power observed on the ground also occurs in the upstream solar wind and in the magnetosphere. All these observations demonstrate that Pc5 waves with a likely driver in the solar wind can penetrate to the equatorial ionosphere and modulate the equatorial electrodynamics. While no direct drift measurements from equatorial radars exist for the 9 August 2008 event, we used JULIA 150km radar drift velocities observed on 2 May 2010 and found similar fluctuations with the period of 5–8min, as a means of an independent confirmation of our magnetometer derived drift dynamics.

Storm-time longitudinally propagating asymmetric modes at low latitudes

Abstract. The westward flowing toroidal ring current at about 2–7 RE in the Earth's equatorial plane consists of symmetric and asymmetric parts. Zonal mean of H disturbances from longitudinally distributed low latitude stations represents the symmetric contribution, whereas departure from the zonal mean gives local time dependent asymmetric component at each of the stations. Through a standard analysis of closely spaced low latitude geomagnetic data we demonstrate 24 h periodicity in the asymmetric component of the storm-time ring current, which is related to the changing local time due to rotation of the Earth. Detailed examination of shorter period oscillations, when observed globally, often show westward propagating modes. Eastward propagating mode was also observed in one case. Based on satellite and radar observations covering a narrow longitude region, westward and eastward propagating modes had been reported in earlier studies. In this study, we report that similar propagating modes which are available on global scale, can be identified using ground-based magnetometer data. These globally propagating modes, observed from ground-based studies, find obvious practical application in diagnostics of the magnetosphere, especially the ring current region. Simultaneous use of satellite and ground-based data should establish the morphology of such modes.

Study of simultaneous penetration of electric fields and variation of total electron content in the day and night sectors during the geomagnetic storm of 23 May 2002

[1] Evidence of simultaneous penetration of storm time electric fields in the day and night sectors of the globe during the geomagnetic storm of 23 May 2002 and the response of low-latitude ionosphere to such electric fields is presented. Using the ground-based magnetometer data, simultaneous penetrations of under-shielding and overshielding electric fields, and those arising owing to the unsteady ring currents, have been inferred in the day and night sectors. The ionospheric response in the day and night sectors near the northern crest of the equatorial ionization anomaly has been studied using total electron content (TEC) data. Multiple episodes of prompt penetration electric fields arising owing to the under-shielding and unsteady ring current conditions resulted in enhancement of the TEC in the day sector. These daytime TEC enhancements were reinforced by the equatorward neutral winds that also produced modulations in TEC. The presence of storm time equatorward neutral winds has been inferred from the increased thermospheric [O/N2] ratio. We also show, probably for the first time, that the same penetration fields in the night sector are responsible for the reductions in TEC on 23 May. Reduced TEC at 120°E longitude on 24 May, the day following the storm, has been attributed to the disturbance dynamo electric fields as well as to the changes in thermospheric chemical composition signified by reduced [O/N2] ratio.

Relativistic electron acceleration by compressional-mode ULF waves: Evidence from correlated Cluster, Los Alamos National Laboratory spacecraft, and ground-based magnetometer measurements

[1] Simultaneous observations by Cluster and Los Alamos National Laboratory (LANL) spacecraft and Canadian Array for Real-Time Investigations of Magnetic Activity and International Monitor for Auroral Geomagnetic Effects magnetometer arrays during a sudden storm commencement on 25 September 2001 show evidence of relativistic electron acceleration by compressional-mode ULF waves. The waves are driven by the quasiperiodic solar wind dynamical pressure fluctuations that continuously buffet the magnetosphere for ∼3 h. The compressional-mode ULF waves are identified by comparing the power of magnetic field magnitude fluctuations with the total magnetic field power. The radial distribution and azimuthal propagation of both toroidal and poloidal-mode ULF waves are derived from ground-based magnetometer data. The energetic electron fluxes measured by LANL show modulation of low-energy electrons and acceleration of high-energy electrons by the compressional poloidal-mode electric field oscillations. The energy threshold of accelerated electrons at the geosynchronous orbit is ∼0.4 MeV, which is roughly consistent with drift-resonant interaction of magnetospheric electrons with compressional-mode ULF waves.

The generator system of field-aligned currents during the April 06, 2000, superstorm

Using ground-based magnetometer data of the April 6–7, 2000, superstorm, we obtained maps of ionospheric and field-aligned currents (FACs). Based on these, we deduced the electrical circuit of the disturbed magnetosphere/ionosphere and a conceptual model of its magnetospheric generators, which supply both hemispheres. This model implies that the generator system creates primarily the Region-1 FACs of Iijima and Potemra at both hemispheres, while the Region-2 and Region-0 FACs form by spreading of the Region-1 currents through the ionosphere. This conclusion is supported by observations. A second prediction of this model turns out to be the following hypothesis, which is also based on the new empirical data. The Region-2 FAC of the dawn side in the Northern Hemisphere is connected with the global dynamo via the asymmetric ring current of the inner magnetosphere, DRP-1. Coming with the DRP-1 into the dusk side, the Region-2 FAC then splits and connects with the dusk side ionosphere of both hemispheres. This way a part of the dawn side Region-1 current becomes connected with the dusk side dynamo of the opposite hemisphere. The intensity of Region-2 and Region-1 FACs of the dusk side is therefore smaller than on the dawn side of this hemisphere, provided that the conductivity in the magnetically conjugated Region-2 ionosphere is larger than the local. Similarly, the dawn–dusk asymmetry of the FAC intensities may also be caused by an inequality of magnetic field and/or pressure gradient in the northern and southern halves of the plasma sheet where DRP-1 flows. The predicted dawn–dusk asymmetry according to such a model is supported by the observations and appears causally connected with an asymmetry between the hemispheres. This conclusion opens a new approach to study these kinds of FAC asymmetries. Further analysis led to the additional conclusion, that the global magnetospheric dynamo works as a voltage generator both during relatively quiet (average) conditions as well as under strong disturbance conditions.

Response of low-latitude ionospheric total electron content to the geomagnetic storm of 24 August 2005

[1] Response of low-latitude ionosphere to the geomagnetic storm of 24 August 2005 has been studied using total electron content (TEC) data obtained from the Global Positioning System (GPS) receivers. These studies were carried out using the receivers that were located (1) near the northern crest (∼15°N mag. Lat.) of the equatorial ionization anomaly around 56°E, 74°E, and 102°E longitude and (2) from the northern crest of the ionization anomaly down to the magnetic equator in the longitude belt 75°E ± 3°E. These studies have been substantiated with the ground-based magnetometer data at Tirunelveli and Alibag, an equatorial and off equatorial station, respectively. The ground-based ionosonde data at New Delhi, a low-latitude station, have also been used to substantiate the TEC observations. The storm day TEC shows two well-defined humps at all stations wherein enhancements of the order of 80%–100% have been observed. While the first of the enhancements has been attributed to the prompt penetration electric field associated with an interplanetary electric field (IEF Ey) of about 35 mV/m, the other one has been attributed to the second episode of the prompt penetration electric field (IEF Ey ∼ 20 mV/m) and abnormal equatorial plasma fountain in late evening hours, respectively. During the unsteady ring current conditions when the IMF Bz was still southward, penetration of a westward electric field has been inferred. Two peaks in foF2 have been observed whose time of occurrence coincides with those of the humps in the low-latitude TEC. Results from stations having nearly the same magnetic latitude show that the ionospheric response, in terms of GPS TEC, to the prompt penetration electric fields is longitudinally independent. Formation of the first hump in TEC is progressively delayed in time from low to near-equatorial latitudes for stations in different magnetic latitudes along nearly the same longitude. However, its time of appearance at Diego Garcia, a station magnetically conjugate to Udaipur, is the same as that at Udaipur. The results also reveal the poleward expansion of the ionization anomaly due to the storm. Disturbance dynamoelectric fields have been inferred to be responsible for the suppressed plasma fountain, resulting in suppressed TEC values and equatorward contraction of the ionization anomaly on 25 August, compared to a reference quiet day.

Dependence of ground-based Pc5 ULF wave power on F10.7 solar radio flux and solar cycle phase

Utilising fifteen (1990–2005) years of ground-based magnetometer data from four magnetometer stations, we characterise the statistical dependence of the Pc5 ULF wave power spectra on variations in F10.7 solar radio flux and on solar cycle phase. We show that the median Pc5 ULF wave power spectra can be characterised as a power-law with a localised Gaussian centred at a specific frequency superimposed on the power-law spectrum. Further, we demonstrate that the location of the Gaussian in frequency systematically varies with both solar cycle phase and F10.7 and is more pronounced during high-speed solar wind intervals. We postulate that the localised power spectrum enhancement (or Gaussian) is a manifestation of the local eigenfrequency of field line resonances in the Earth's magnetosphere and that the variation in the location of the Gaussian occurs as a result of increased ionospheric outflow during periods of enhanced F10.7 and active solar activity.

An anatomy of space weather's electricity market impact: Case of the PJM power grid and the performance of its 500 kV transformers

[1] The PJM Interconnection is a regional electricity transmission organization which as of 30 April 2004 coordinated the dispatch of electricity over 320,000 km of transmission lines. The backbone of PJM's transmission system is a series of 500 kilovolt (kV) transmission lines and transformers. PJM operates both hourly real-time and day-ahead markets for energy. The differences between PJM's real-time and day-ahead prices reflect unexpected operating conditions. Using ground-based magnetometer data as a proxy for geomagnetically induced currents (GICs), we present evidence that the differences between PJM's real-time and day-ahead prices are statistically related with the GIC proxy. Extra high voltage energy losses and a measure of real-time congestion costs are also shown to be statistically related with the GIC proxy. The paper investigates these statistical linkages by examining the incidence of declared constraints in the 500 kV transformers. The relationship between the GIC proxy and the incidence of declared constraints in the transformers is examined using a multivariate regression model with a dependent variable that is binary. The model is estimated using hourly data over the period 1 April 2002 through 30 April 2004. The results indicate that GICs can contribute to conditions in which the system operator declares one or more of the 500 kV transformers to be constrained. This finding takes into account forecasted load, load forecasting errors, ambient temperature, a proxy for known transmission constraints, and scheduled flows with other power grids. The results are also consistent with published findings that GICs can contribute to overheating problems in transformers.

Mapping plasma structures in the high-latitude ionosphere using beacon satellite, incoherent scatter radar and ground-based magnetometer observations

In the autumn of the year 2000, four radio receivers capable of tracking various beacon satellites were set up along the southwestern coast of Greenland. They are used to reconstruct images of the ionospheric plasma density distribution via the tomographic method. In order to test and validate tomographic imaging under the highly variable conditions often prevailing in the high-latitude ionosphere, a time interval was selected when the Sondrestrom incoherent scatter radar conducted measurements of the ionospheric plasma density while the radio receivers tracked a number of beacon satellites. A comparison between two-dimensional images of the plasma density distribution obtained from the radar and the satellite receivers revealed generally good agreement between radar measurements and tomographic images. Observed discrepancies can be attributed to F region plasma patches moving through the field of view with a speed of several hundred meters per second, thereby smearing out the tomographic image. A notable mismatch occurred around local magnetic midnight when a magnetospheric substorm breakup occurred in the vicinity of southwest Greenland (identified from ground-based magnetometer observations). The breakup was associated with a sudden intensification of the westward auroral electrojet which was centered at about 69° and extended up to some 73° corrected geomagnetic latitude. Ground-based magnetometer data may thus have the potential of indicating when the tomographic method is at risk and may fail. We finally outline the application of tomographic imaging, when combined with magnetic field data, to estimate ionospheric Joule heating rates.