The geomagnetic observatory on Tristan da Cunha: Setup, operation and experiences

The island Tristan da Cunha is located in the South Atlantic Anomaly, and until recently the area has been one of the largest gaps in the global geomagnetic observatory network. As part of the Danish project SAADAN we set up a geomagnetic observatory on the island. Here we report on how we established the observatory in 2009 and on its operation in 2010

Using Principal Component Analysis of Satellite and Ground Magnetic Data to Model the Equatorial Electrojet and Derive Its Tidal Composition

The intensity of the equatorial electrojet (EEJ) shows temporal and spatial variability that is not yet fully understood nor accurately modeled. Atmospheric solar tides are among the main drivers of this variability but determining different tidal components and their respective time series is challenging. It requires good temporal and spatial coverage with observations, which, previously could only be achieved by accumulating data over many years. Here, we propose a new technique for modeling the EEJ based on principal component analysis (PCA) of a hybrid ground-satellite geomagnetic data set. The proposed PCA-based model (PCEEJ) represents the observed EEJ better than the climatological EEJM-2 model, especially when there is good local time separation among the satellites involved. The amplitudes of various solar tidal modes are determined from PCEEJ based tidal equation fitting. This allows to evaluate interannual and intraannual changes of solar tidal signatures in the EEJ. On average, the obtained time series of migrating and nonmigrating tides agree with the average climatology available from earlier work. A comparison of tidal signatures in the EEJ with tides derived from neutral atmosphere temperature observations show a remarkable correlation for nonmigrating tides such as DE3, DE2, DE4, and SW4. The results indicate that it is possible to obtain a meaningful EEJ spectrum related to solar tides for a relatively short time interval of 70 days

Observations of Particle Loss due to Injection-Associated Electromagnetic Ion Cyclotron Waves

We report on observations of electromagnetic ion cyclotron (EMIC) waves and their interactions with injected ring current particles and high energy radiation belt electrons. The magnetic field experiment aboard the twin Van Allen Probes spacecraft measured EMIC waves near L = 5.5–6. Particle data from the spacecraft show that the waves were associated with particle injections. The wave activity was also observed by a ground-based magnetometer near the spacecraft geomagnetic footprint over a more extensive temporal range. Phase space density profiles, calculated from directional differential electron flux data from Van Allen Probes, show that there was a significant energy-dependent relativistic electron dropout over a limited L-shell range during and after the EMIC wave activity. In addition, the NOAA spacecraft observed relativistic electron precipitation associated with the EMIC waves near the footprint of the Van Allen Probes spacecraft. The observations suggest EMIC wave-induced relativistic electron loss in the radiation belt

In situ spatiotemporal measurements of the detailed azimuthal substructure of the substorm current wedge

The substorm current wedge (SCW) is a fundamental component of geomagnetic substorms. Models tend to describe the SCW as a simple line current flowing into the ionosphere toward dawn and out of the ionosphere toward dusk, linked by a westward electrojet. We use multispacecraft observations from perigee passes of the Cluster 1 and 4 spacecraft during a substorm on 15 January 2010, in conjunction with ground-based observations, to examine the spatial structuring and temporal variability of the SCW. At this time, the spacecraft traveled east-west azimuthally above the auroral region. We show that the SCW has significant azimuthal substructure on scales of 100km at altitudes of 4000-7000km. We identify 26 individual current sheets in the Cluster 4 data and 34 individual current sheets in the Cluster 1 data, with Cluster 1 passing through the SCW 120-240s after Cluster 4 at 1300-2000km higher altitude. Both spacecraft observed large-scale regions of net upward and downward field-aligned current, consistent with the large-scale characteristics of the SCW, although sheets of oppositely directed currents were observed within both regions. We show that the majority of these current sheets were closely aligned to a north-south direction, in contrast to the expected east-west orientation of the preonset aurora. Comparing our results with observations of the field-aligned current associated with bursty bulk flows (BBFs), we conclude that significant questions remain for the explanation of SCW structuring by BBF-driven wedgelets. Our results therefore represent constraints on future modeling and theoretical frameworks on the generation of theSCW. Key Points The substorm current wedge (SCW) has significant azimuthal structure Current sheets within the SCW are north-south aligned The substructure of the SCW raises questions for the proposed wedgelet scenari

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

Local Generation of EMIC Waves Near the Plasmapause: Coordinated Magnetosphere-ionosphere-ground Observations

We present coordinated magnetosphere-ionosphere-ground observations of EMIC waves on 17 April 2018. The EMIC waves were identified by using ground-based induction magnetometer at Neumayer station (geomagnetic latitude = 65, L = 5.6) in Antatica on the morningside (MLT = 9.5). The wave activity lasted one hour with a frequency of ~500 mHz. During the wave activity interval, Van Allen Probes-A was in the dawnside magnetosphere near the equator between 0.5 and 0.4 in magnetic latitude (MLAT) and observed EMIC waves in the frequency band centered at ~500 mHz for ~40-min interval when the spacecraft was located at L = 4.6-5.2 and MLT = 6.1-6.7 hrs, just inside the plasmapause. In the upper ionosphere, low-altitude Swarm-B satellite polar orbiting at a constant radial distance of 500 km altitude was on the morningside with a small local time separation (~1.5 hrs) between Neumayer station and Swarm-B's orbital meridian, and observed ~500-mHz waves for a short interval less than 1 min when the satellite cross a region of 66 MLAT, which is close to the magnetic latitude of Neumayer station. Since the orbital speed of Swarm-B is about 3.8/min, the occurrence region of EMIC waves in the upper ionosphere is very narrow (MLAT < 3.8) in magnetic latitude. This region corresponds to L < 0.1 in the equatorial region of the magnetosphere. The coordinated magnetosphere-ionosphere-ground observations reported here provide strong evidence for local generation of EMIC waves near the plasmapause

Using Principal Component Analysis of Satellite and Ground Magnetic Data to Model the Equatorial Electrojet and Derive Its Tidal Composition

The intensity of the equatorial electrojet (EEJ) shows temporal and spatial variability that is not yet fully understood nor accurately modeled. Atmospheric solar tides are among the main drivers of this variability but determining different tidal components and their respective time series is challenging. It requires good temporal and spatial coverage with observations, which, previously could only be achieved by accumulating data over many years. Here, we propose a new technique for modeling the EEJ based on principal component analysis (PCA) of a hybrid ground‐satellite geomagnetic data set. The proposed PCA‐based model (PCEEJ) represents the observed EEJ better than the climatological EEJM‐2 model, especially when there is good local time separation among the satellites involved. The amplitudes of various solar tidal modes are determined from PCEEJ based tidal equation fitting. This allows to evaluate interannual and intraannual changes of solar tidal signatures in the EEJ. On average, the obtained time series of migrating and nonmigrating tides agree with the average climatology available from earlier work. A comparison of tidal signatures in the EEJ with tides derived from neutral atmosphere temperature observations show a remarkable correlation for nonmigrating tides such as DE3, DE2, DE4, and SW4. The results indicate that it is possible to obtain a meaningful EEJ spectrum related to solar tides for a relatively short time interval of 70 days.Key Points: A novel technique to model the equatorial electrojet (EEJ) based on the principal component analysis of a hybrid ground‐satellite data set. The new modeling matches observations better than the EEJM‐2 model, especially when the Swarm satellites have optimum local time coverage. Time series of migrating and nonmigrating tides amplitude in the EEJ are derived from 70‐day window.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior http://dx.doi.org/10.13039/501100002322Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro http://dx.doi.org/10.13039/501100004586MEXT Japan Society for the Promotion of Science http://dx.doi.org/10.13039/50110000169

Modeling the effects of drift shell splitting in two case studies of simultaneous observations of substorm-driven Pi1B and IPDP-type EMIC waves

Intervals of Pulsations of Diminishing Periods (IPDPs) are a subtype of Electromagnetic Ion Cyclotron (EMIC) waves that can be triggered by substorm onset. Pi1B waves are Ultra Low Frequency (ULF) broadband bursts that are well correlated with substorm onset. IPDPs are associated with increased fluxes of 40-60 keV substorm-injected protons which undergo gradient-curvature drifting and interact with the cold plasmasphere population. While particle trajectories and the generation of IPDPs have been modeled in the past, those models neglect the role that drift shell splitting plays in the process. This research investigates the different pathways that Pi1B and IPDPs take from their shared origin in substorm onset to their distinct observations on the ground, including the effects of drift shell splitting en route. This paper presents two case studies using data from an array of four ground-based Antarctic magnetometers that cover the evening sector, as well as in situ magnetometer data, proton fluxes, and proton pitch angles from the Van Allen Probes spacecraft. These observations identify a separation in geomagnetic latitude between Pi1Bs and IPDPs, and pinpoint a separation in Magnetic Local Time (MLT). From these observations we model the drift shell splitting which injected particles undergo post-onset. This study shows that simulations that incorporate drift shell splitting across a full injection front are dominated by injection boundary effects, and that the inclusion of drift shell splitting introduces a slight horizontal component to the time axis of the time-frequency dependence of the IPDPs

Investigating the Relationship between IPDPs and Pi1B Waves

IPDPs (intervals of pulsations with diminishing periods) are a subset of EMIC waves. Pi1Bs (pulsations irregular 1Hz bursts) are ULF waves closely correlated with substorm onset. Prior research has indicated there may be a relationship between the two, but this relationship has not yet been fully fleshed out. In this presentation, we investigate the relationship between evening sector IPDPs and Pi1B. To do so we utilize searchcoil magnetometer, fluxgate magnetometer, riometer, and imaging riometer data from a collection of Antarctic ground stations (Halley Research Station, Neumayer, Maitri, Syowa, and Mawson) that span 10 degrees in CGM latitude, 4 hours in MLT, and L shells 4 through 9. We also utilize magnetometer data from satellites in conjunction including SWARM, which reveals a local unidentified ULF signature equatorward of the ground instrumentation (more work is required to fully understand this). From the ground instrumentation, we observe Pi1B in the late evening MLT region crossing over into the early dawn region, and IPDPs in the early evening MLT region. Despite the 4 hour range in MLT, we observe these events near simultaneously with only a ~15 minute delay between the start of the Pi1B and the start of the IPDP. We observe correlated cosmic noise absorption (CNA) that occurs simultaneously with and encompasses the full duration of these events. The ULF activity we observe aligns well with what we expect from previous work done on the subject-- IPDPs appear at lower geomagnetic latitudes (60-65 degrees) than Pi bursts, which are more prominent at ~70 degrees-- but the CNA we observe has less precedence in prior research. In this presentation, we describe our observations in detail as well as possible mechanisms that might link the Pi1B and IPDP waves, as well as the CNA