Ionospheric Field-aligned Currents Research Articles

Relationship between large-scale ionospheric field-aligned currents and electron/ion precipitations: DMSP observations

In this study, we have derived field-aligned currents (FACs) from magnetometers onboard the Defense Meteorological Satellite Project (DMSP) satellites. The magnetic latitude versus local time distribution of FACs from DMSP shows comparable dependences with previous findings on the intensity and orientation of interplanetary magnetic field (IMF) By and Bz components, which confirms the reliability of DMSP FAC data set. With simultaneous measurements of precipitating particles from DMSP, we further investigate the relation between large-scale FACs and precipitating particles. Our result shows that precipitation electron and ion fluxes both increase in magnitude and extend to lower latitude for enhanced southward IMF Bz, which is similar to the behavior of FACs. Under weak northward and southward Bz conditions, the locations of the R2 current maxima, at both dusk and dawn sides and in both hemispheres, are found to be close to the maxima of the particle energy fluxes; while for the same IMF conditions, R1 currents are displaced further to the respective particle flux peaks. Largest displacement (about 3.5°) is found between the downward R1 current and ion flux peak at the dawn side. Our results suggest that there exists systematic differences in locations of electron/ion precipitation and large-scale upward/downward FACs. As outlined by the statistical mean of these two parameters, the FAC peaks enclose the particle energy flux peaks in an auroral band at both dusk and dawn sides. Our comparisons also found that particle precipitation at dawn and dusk and in both hemispheres maximizes near the mean R2 current peaks. The particle precipitation flux maxima closer to the R1 current peaks are lower in magnitude. This is opposite to the known feature that R1 currents are on average stronger than R2 currents.

Mid and low-latitudinal ionospheric field-aligned currents derived from the Swarm satellite constellation and their variations with local time, longitude, and season

We use the Field Aligned Currents (FAC) data of the 10 quietest days of each month of 2014–2018, the first four years of FAC observational data, derived from Swarm A and C satellites observations to study their characteristics within 15–55° latitude in the northern and −15° to −55° latitude in the southern hemispheres. Results show that in summer months, the noon time FAC have the largest variations. Over the same sector region and the same local time, the FAC have the same trend irrespective of season.Examinations of seasonal patterns indicate that, both dawn and dusk times FACs in both hemispheres always have negative (southbound) variations during summer months. In winter months the dusk time FAC becomes positive only in the southern hemisphere, while the dawn time FAC is ambiguous as it becomes negative only at low latitudes. The noon time FAC is strongly positive (northbound), in both hemispheres in summer months, but during winter months it becomes southbound at mid-latitudes and remains northbound at low latitudes. Over the African, Asian and American sectors, the summer months FAC have identical structure, while in winter months the direction of the dawn and noon times FACs are ambiguous.At the foci points of the solar quiet (SQ) current, the northern hemispheric FAC has the same variation as those observed by Park et al. (2011) and Luhr et al. (2015) during summer months, while during winter months the noon time FAC is still weakly positive. The latitudinal variation of the FAC with respect to longitudes shows that the southern hemispheric FAC at mid-latitudes is always negative at eastern longitudes irrespective of season. It suggests that the FAC is longitudinally dependent.Unlike previous ground based studies, the satellite data not only shows a single prominent negative (southbound) FAC over the African sector region around equinoxes, but it shows that during the March equinox the dusk time FAC is always negative in both hemispheres except at western longitudes 45°, where it has positive patterns. In the middle of summer and winter (months 7 and 1), the noon time FAC varies from positive in summer to negative in winter and the dawn time FAC varies from negative in summer to positive in winter which agrees with the theoretical prediction. The dusk time FAC in the northern hemisphere remains negative which agrees the observations of Park et al. (2011) and Luhr et al. (2015), while in the southern hemisphere it changes from negative in summer to positive in winter.

Observed tail current systems associated with bursty bulk flows and auroral streamers during a period of multiple substorms

Abstract. We present a multi-instrument study of a substorm bursty bulk flow (BBF) and auroral streamer. During a substorm on 25 August 2003, which was one of a series of substorms that occurred between 00:00 and 05:00 UT, the Cluster spacecraft encountered a BBF event travelling Earthwards and duskwards with a velocity of ~500 km s−1 some nine minutes after the onset of the substorm. Coincident with this event the IMAGE spacecraft detected an auroral streamer in the substorm auroral bulge in the Southern Hemisphere near the footpoints of the Cluster spacecraft. Using FluxGate Magnetometer (FGM) data from the four Cluster spacecraft, we determine the field-aligned currents in the BBF, using the curlometer technique, to have been ~5 mA km−2. When projected into the ionosphere, these currents give ionospheric field-aligned currents of ~18 A km−2, which is comparable with previously observed ionospheric field-aligned currents associated with BBFs and auroral streamers. The observations of the BBF are consistent with the plasma "bubble" model of Chen and Wolf (1993). Furthermore, we show that the observations of the BBF are consistent with the creation of the BBF by the reconnection of open field lines Earthward of a substorm associated near-Earth neutral line.

Field-aligned currents onboard the Intercosmos Bulgaria-1300 satellite in comparison with modeled FAC

The statistical field-aligned current (FAC) distribution has been demonstrated by [Iijima, T., Potemra, T.A., 1976. The amplitude distribution of field-aligned currents at northern high latitudes observed by Triad. Journal of Geophysical Research 81(13), 2165–2174] and many other authors. The large-scale (LS) FACs have been described by different empirical/statistical models [Feldstein, Ya. I., Levitin, A.E., 1986. Solar wind control of electric fields and currents in the ionosphere. Journal of Geomagnetism and Geoelectricity 38, 1143; Papitashvili, V.O., Rich, F.J., Heinemann, M.A., Hairston, M.R., 1999. Parameterization of the Defense Meteorological Satellite Program ionospheric electrostatic potentials by the interplanetary magnetic field strength and direction. Journal of Geophysical Research 104, 177–184; Papitashvili, V.O., Christiansen, F., Neubert, T., 2002. A new model of field-aligned currents derived from high-precision satellite magnetic field data. Geophysical Research Letters, 29(14), 1683, doi:10.1029/2001GL014207; Tsyganenko, N.A., 2001. A model of the near magnetosphere with a dawn–dusk asymetry (I. Mathematical structure). Journal of Geophysical Research 107(A8), doi:10.1029/2001JA000219; Weimer, D.R., 1996a. A new model for prediction of ionospheric electric potentials as a function of the IMF. In: Snowmass’96 Online Poster Session; Weimer, D.R., 1996b. Substorm influence on the ionospheric convection patterns. In: Snowmass’96 Online Poster Session; Weimer, D.R., 2001. Maps of ionospheric field-aligned currents as a function of the interplanetary magnetic field derived from Dynamic Explorer 2 data. Journal of Geophysical Research 106, 12,889–12,902; Weimer, D.R., 2005. Improved ionospheric electrodynamic models and application to calculating Joule heating rates. Journal of Geophysical Research 110, A05306, doi:10.1029/2004JA010884]. In the present work, we compare two cases of LS FAC obtained from magnetic field measurements onboard the Intercosmos Bulgaria-1300 satellite with three models: two empirical [Tsyganenko, N.A., 2001. A model of the near magnetosphere with a down-dusk asymetry (I. Mathematical structure). Journal of Geophysical Research 107(A8), doi:10.1029/2001JA000219; Weimer, D.R., 2005. Improved ionospheric electrodynamic models and application to calculating Joule heating rates. Journal of Geophysical Research 110, A05306, doi:10.1029/2004JA010884] and one computer-based MHD-simulation in “The Community Coordinated Modeling Center” (CCMC) [Toth, G., et al., 2005. Space weather modeling framework: a new tool for the space science community. Journal of Geophysical Research 110, A12226, doi:10.1029/2005JA011126]. We found that the position of the measured FAC is close to the positions predicted by the models, but the measured density can be greater than the model FAC densities. We discuss the possible reasons for the observed discrepancy between the measured and modeled FACs.