Monitoring auroral electrojets with satellite data

Journal of geomagnetism and geoelectricity, 1988

Auroral activities on January 7, 1986, are examined with all-sky video data obtained at multiple stations. It is shown that a poleward expansion front of an expansion aurora usually consists of many northwestward protrusions which develop and decay here and there during the course of the auroral expansion. Developments of characteristic auroral protrusions are compared with magnetic field changes on the ground. The result shows that the developments of large magnetic field deflections on the ground are most likely due to enhancements of local westward electrojets associated with counterclockwise vortex currents around developing auroral protrusions in the night sector. The developments of auroral protrusions are also related to magnetic field changes at the synchronous satellites, GOES 5 and 6, conjugate with the auroral forms. Characteristic changes of magnetic field occur at GOES 5 and 6 concurrently with developments of auroral protrusions around respective magnetic footpoints of the satellites. Auroral structures within or in the vicinity of auroral protrusions are likely interlinked with the field-aligned currents around the conjugate synchronous satellites. Fast Auroral Evolution and Related Magnetic Field Changes 507

Journal of Geophysical Research, 2007

1] The equatorial electrojet (EEJ) is an eastward electric current on the day-side, flowing in a narrow band along the dip equator in the ionospheric E region. Recent magnetic observations from the CHAMP, Ørsted, and SAC-C satellites, comprising more than 95,000 dip equator crossings from 1999 to 2006, have provided an unprecedented longitudinal coverage of the EEJ magnetic signature. We have used these data to construct an empirical model of the EEJ current climatological mean and day to day variability as a function of longitude, local time, season, and solar flux. Our model has been successfully verified against vertical drift data from the JULIA radar at Jicamarca. We have also used the EEJ observations to estimate the self-correlation of the EEJ, confirming short longitudinal correlation lengths of 15°and finding a temporal correlation length of 2.4 h. Our model's predictions of the eastward electric field and its standard deviation may provide useful input to various kinds of ionospheric simulations. Coefficients and software are available online at http://models.geomag.us/EEJ.html and http://www.earthref.org.

Journal of Geophysical Research, 1996

Model calculations of the electrodynamics of the high-latitude ionosphere are compared to measurements made by the Viking satellite during July-August 1986. The model calculations are based on the IZMEM procedure, where the electric field and currents in the ionosphere are given as functions of the interplanetary magnetic field. The events chosen correspond to the growth, the expansion, and the recovery phases of substorms. During the growth and expansion phases the correlation between the model results and the satellite data is rather good. During recovery phase the correlation is not as good. The correlation between modeled and observed quantities suggest that during growth and expansion phase the magnetosphere is mainly directly driven by the solar wind, whereas during recovery phase it is mainly driven by internal processes, i.e., loading-unloading. Best fit is obtained when averaging the measured quantities over a few minutes, which means adjusting the spatial resolution of the measurements to the resolution of the model. Different time delays between the interplanetary magnetic field observations and those of Viking were examined. Best agreement was obtained, not surprisingly, for time delays corresponding to the estimated information transit time from the solar wind spacecraft to the ionosphere. In the geospace environment modeling (GEM) program, two models are considered for synthesis of sparse high-latitude data [Lotko, 1993]. Both models allow the computation of nearly instantaneous snapshots of electric field and potential distribution in the entire auroral region. The assimilative mapping of ionospheric electrodynamics (AMIE) model is used for calculation of high-latitude electric fields and currents from sets of localized observational data [Richmond and Kamide, 1988; Richmor•d et al., 1988; Richmor•d, 1992]. A similar model has also been used by Marklund et al. [1988]. See also Marklund arid Blomberg [1991] and Blomberg arid Marklur•d [1993]. The Inetitute of Terrestrial Mag-Copyright 1996 t)y the American Geophysical Union. Paper number 96JA00514. 0148-0227 / 96 / 96 J A-00514509.00 netism Electrodynamical Model (IZMEM)is another model for calculating the same parameters, but the input data are the interplanetary magnetic field (IMF) magnitude and direction [Levitir• et al., 1984; Feldsteir• arid Levitire, 1986; Papitashvili et al., 1994]. The influence of the IMF on the upper atmosphere electrodynamics is crucial also in the models of Friis-Christer•ser• et al. [1985] and Mishir• [1990]. The latter two models are used by their respective authors only, whereas the IZMEM model is publicly available through the World Data Center A for Rockets and Satellites [Bilitza, 1990]. The IZMEM model is here used to determine the global convection pattern and its temporal evolution during a number of passes of the Swedish satellite Viking over the northern high-latitude region. The model electric field is compared to the satellite observations along the trajectory, and the global convection pattern and its temporal evolution is estimated in the entire highlatitude region. The sensitivity to averaging of the correlation between the modeled and measured values is discussed. The averaging interval selected influences the sensitivity of the correlation to changes in the model, and it is of interest to determine to what extent the correlation coefficient is dependent on the correct timing of the changes between gross features of the convection system during the period studied. 19,921 19,922 FELDSTEIN ET AL.: HIGH-LATITUDE IONOSPHERE There is today a consensus that there are two processes responsible for the solar wind energy input to the magnetosphere during sUbstorms. These are direct driving and loading-unloading processes. Some fraction of the energy input is directly dissipated in the ionosphere by Joule heating and particle precipitation related to enhanced convection and enhanced ionospheric currents. This power dissipation is directly correlated with the solar wind parameters and is thus a driven process [Akasofu, 1981]. The remaining part of the power transfeted into the magnetosphere is stored temporarily in the Earth's magnetosphere and subsequently released at substorm breakup. The latter is known as loading-unloading process [Baker et al., 1984, 1993]. The delay time between a change in the IMF and the related effects in the ionosphere is different for the two processes. For the directly driven process it is 10-20 min due to the inductance of the magnetosphereionosphere system. For the loading-unloading process it is typically 40-60 min. Which one of these .processes dominates remains an open question.

Annales Geophysicae, 2008

Based on a comprehensive catalogue with more than 4000 magnetospheric substorm entries from the years 2000-2005, the spatial distribution of the substorm-related magnetic signatures at mid and low latitudes around local midnight was investigated. Superposed epoch analysis of a larger number of recent observatory data from mid and low latitudes revealed a field strength increase that is consistent with the results of earlier studies. For the first time, the magnetic signature of the substorm current wedge formation is studied also in near-Earth satellite data from CHAMP. The average maximal deflection measured on board the satellite is smaller by a factor of 2 than that determined from ground observations. The recurrence frequency of substorms as well as the amplitude of their magnetic signature depends strongly on the prevailing magnetic activity. The observed average substorm-related magnetic field signatures cannot be described adequately by a simple current wedge model. A satisfactory agreement between model results and observations at satellite height and on ground can be achieved only if the current reconfiguration scenario combines four elements:

Annales Geophysicae, 1996

Statistical models for large-scale convection and for ionospheric conductances were previously derived from observations of the incoherent-scatter radar EIS-CAT. We complete this large-scale description with statistical models of the horizontal and field-aligned currents achieved from the same data base and for the same ranges of the magnetic activity index Kp. Except for the highlatitude dayside currents generally located poleward of the radar field of view, a large part of the whole current system can be probed with EISCAT. Globally consistent with previously published models, our results also exhibit some differences, such as the asymmetry in the local-time extension of the current sheets, concentrated to a few hours around 18 MLT in the evening sector, while widely spread from premidnight to prenoon magnetic local times on the morningside. This statistical description of the current system above EISCAT allowed us to examine several aspects of the large-scale auroral electrodynamics, namely the relationships between convection, conductances, and currents, in particular in the vicinity of the Harang discontinuity, and the features of the global current circuit.

Planetary and Space Science, 1976

Ahstraet-The relationship between substorm ionospheric currents and the corresponding ground magnetic perturbations is examined, by using the height-integrated ionospheric current density deduced from the Chatanika incoherent scatter radar and the simultaneous magnetic variations along the Alaska meridian chain of stations. Although time variations of the H component near the radar site on the Earth's surface are in good agreement with those of the east-west ionospheric current, there is a substantial disagreement between the current deduced from the D perturbations and the observed north--south current in the evening sector. It is shown that the disagreement can be removed by introducing a new finding by that the upward field-aligned current on the poleward side of the aurora1 oval in the evening sector is more intense than its counterpart fieldaligned current and that it contributes greatly to the ground D perturbations.

This paper investigates the effects of geomagnetic storms of 25-27 September 2011, 16- 18 March 2013, and 6-8 September 2015 over five mid latitudes stations (Dourbes, Fairford, Moscow, Rome, and Roquetes) and performs a cross correlation analysis of ionospheric and solar parameters during these storms. We observed the highest fluctuations in ionospheric variables during the main phase of storms. In addition, there is strong evidence of pre-storm phenomenon occurring at least a few hours and more than 24 hours prior to the main phase of the geomagnetic storms. We found that the TEC and foF2 parameters have strong dependence with latitudes for the events with Sudden Storm Commencement(SSC) in mid latitude region. Relatively low TEC and foF2 can be observed in Moscow which is at the highest latitude among the five stations because of a decrease in the n(O)/n(N2) ratio through out the storm event. However, for the event with gradual storm commencement, there is no evidence of such depe...

Geophysical Research Letters, 2007

1977

Earth, Planets and Space, 2020

We report the propagation of substorm-associated magnetic fluctuations by multipoint magnetic observations from ground and space in the same meridional plane. The first Quasi-Zenith Satellite (QZS-1), which has a unique orbit of quasi-zenith orbit with an inclination of 41 • , an apogee of 7.1 R E radial distance, and an orbital period of 24 h, can stay for a long time in the near-earth magnetotail away from the magnetic equator. We examined a substorm event during 15:00-16:00 UT on July 09, 2013 when QZS-1 was located at 31 • dipole latitude and 23.5 h dipole magnetic local time. The Engineering Test Satellite VIII (ETS-VIII), Time History of Events and Macroscale Interactions during Substorms D (THEMIS-D) at a radial distance of ∼ 10 R E , and THEMIS-E at a radial distance of ∼ 7 R E were located near the equator in the similar magnetic meridian. The dipolarization was first observed at THEMIS-D at 15:14:30 UT. Then, ∼ 1 min later, magnetic fluctuations were observed by ETS-VIII and THEMIS-E. At the same time, the magnetic bay and Pi2 pulsation were observed at low-latitude magnetic observatories and the Radiation Belt Storm Probes B satellite in the inner magnetosphere. We found that QZS-1 away from the equator observed a strong azimuthal magnetic field fluctuation with a long delay of 15 min from the first dipolarization at THEMIS-D near the equator. The speed of the poleward propagating magnetic fluctuation between the ionospheric footprints is calculated to be 310 m/s , which is consistent with a typical speed of auroral poleward expansion. A similar time delay of the onset of the negative bay was observed between the Tixie (AACGM MLAT = 66.8 • ) and Kotelny (AACGM MLAT = 71.0 • ) observatories near the ionospheric footprint of satellites. We suggest that the long delay time of the magnetic fluctuation at QZS-1 was associated with the crossing of field-aligned current during the poleward expansion of the substorm current system. The distribution of azimuthal magnetic field variations in the magnetosphere indicates that the east side downward current extended more west side in the higher latitude part of the current wedge.