Effect of Swarm A/C Orbital Configuration and Magnetic Field Inclination on the Spherical Elementary Current Systems (SECS) Analysis Method
1Oulu university, Finland; 2Finnish Meteorological Institute, Helsinki, Finland
The method of Spherical Elementary Current Systems (SECS) was adapted for analyzing magnetic data from the Swarm mission by Amm et al. (2015). The method can be used to estimate not only the field-aligned current (FAC), but also the ionospheric sheet current in a narrow strip around the A and C satellites' track. If the B satellite is close to the A/C pair, as happened frequently during the first mission year, it can also be included in the analysis.
The recent results by Juusola et al. (2016), who compared ground-based equivalent current estimates with the divergence-free part of the current as inferred from Swarm data, show that large-scale electrojet-type sheet current systems can be determined from the satellite data with good accuracy. However, they concluded that the Swarm satellites' altitude and the longitudinal separation of the A/C pair severely limits our ability to resolve smaller scale structures in the horizontal sheet current. Using synthetic but realistic models of various ionospheric current systems, we will investigate how much the SECS results could be improved by tuning the orbital configuration of the A/C pair.
In the present form the SECS analysis method is limited to high magnetic latitudes, due to the simplifying assumption of radial FAC direction. We will describe some proposed efforts to include a more realistic description of the FAC geometry, so that the SECS-based Swarm analysis method could be extended to middle and low latitudes.
Amm et al. (2015): https://dx.doi.org/10.1002/2014JA020154
Juusola et al. (2016): https://dx.doi.org/10.1002/2016JA022961
A Tentative Procedure to Assess / Optimize the Swarm Electric Field Data and Derive the Ionospheric Conductance in the Auroral Region
1Institute for Space Sciences, Bucharest, Romania; 2University of Oulu, Oulu, Finland; 3Finnish Meteorological Institute, Helsinki, Finland; 4Jacobs University Bremen, Bremen, Germany
Electric field is essential to understand the coupling processes in the magnetosphere-ionosphere-thermosphere (M-I-T) system and, as such, is one of the key quantities measured onboard Swarm. This paper introduces a procedure, illustrated with a couple of event studies, that may help the assessment and, when necessary, optimization of the electric field data, at the same time with providing estimates of the ionospheric conductance. The procedure applies primarily in the auroral region and relies, essentially, on the closure of the field-aligned current (FAC) by ionospheric current, on Ohm’s law that relates the ionospheric current, electric field, and conductance, as well as on a conductance proxy (Robinson et al., 1987), based on the energy flux and average energy of the precipitating electrons. The ionospheric current can be derived from Swarm magnetic field observations by the technique of Spherical Elementary Current Systems (SECS – introduced by Amm, 1997, and adapted for Swarm by Amm et al., 2015). Further on, by plugging the derived ionospheric current together with the observed electric field into the Ohm’s law, one can estimate the ionospheric Pedersen and Hall conductance (with a precision that depends on the quality of the electric field data) along the footprints of individual satellite tracks. At the same time, by following Robinson et al. (1987), the ratio of the Hall to Pedersen conductance can be used to infer the average electron energy (over upward current regions), the electron energy flux can be derived by multiplying the electron energy by the number flux inferred from the (upward) FAC density, and eventually one can derive an alternative estimate of the Pedersen conductance. Finally, by comparing the two estimates of the Pedersen conductance, one can assess the quality of the electric field data. Moreover, the minimization of the root mean square difference of the two conductance estimates provides a potentially powerful tool to optimize the electric field data in the auroral region and to derive reliable conductance information.
Field-Aligned Current Response to Increasing Solar Indices
Virginia Tech, United States of America
While many studies of field-aligned current (FAC) response to driving parameters have been done, few have focused on the impacts of changing solar radiative index. A new FAC model has been developed utilizing magnetometer measurements from the CHAMP, Orsted, and Swarm missions. Using this model, an analysis of changing solar radiative index has been done. What has been found is that there is a nonlinear behavior in response to increases in the F10.7, S10.7, and M10.7 indices, while the Y10.7 index remains very linear. This may suggest that the height integrated conductivity does not have a linear response with increasing F10.7, S10.7, and M10.7 indices. Surprisingly, the Y10.7 response is highly linear, which may be due to it's relation to the D-region of the ionosphere, while most of the current closes in the E- and F- regions.
Analysis of Thick, Finite, and Non-Planar Field-Aligned Currents in the Polar Regions with Swarm Magnetic Field Measurements
Institut de Recherche en Astrophysique et Planétologie (IRAP), France
The calculation of field aligned currents and the study of their morphology has long been a crucial problem in space plasma physics. The most commonly used method is to use the magnetic field vector measurement of a single satellite, subtracting a proper background field, to approximately calculate the current density under the assumption of a planar and infinite current sheet. When multipoint measurements are available (Cluster, Swarm), one can calculate the curl of magnetic field and infer the field-aligned current density from the Ampere’s law (curlometer technique). In this work, we take advantage of the two Swarm satellites flying side by side (Swarm A and C) to establish a model of finite, thick, and non-planar current sheet. We shall present the underlying formalism of our model and its capabilities: not only does it derive the magnitude of the current, but also the morphology parameters of the current sheet, including curvature, radius and spatial extent.
Multi-point Analysis of Current Structures in the Inner Magnetosphere
1BUAA, China, People's Republic of; 2RAL_space, STFC, UK; 3China Earthquake Administration, Beijing 100085, China.
The RC and connecting R2 FACs influence the geomagnetic field at low Earth orbit (LEO) and are both sampled in situ by the four Cluster spacecraft, while FACs are sampled by Swarm. Here, the capability of Swarm-Cluster coordination for probing the behaviour of the field aligned currents (FAC) at medium and low orbits and signatures both adjacent to and within the ring current (RC) is explored. Joint signatures of R1 and R2 FACs can be confirmed and multi-spacecraft analysis can also access perpendicular currents associated with the FAC signatures at the Swarm locations. Using the Swarm configuration, statistical correlation analysis of the local time variation of R1/R2 FACs can also be shown and compared to standard MVA analysis. The sensitivity of the analysis to the data cadence, and hence the time dependencies of the signals, is also investigated. For context, we identify the associated auroral boundaries through application of a method to determine the FAC intensity gradients in order to interpret and resolve the R1 and R2 FACs. We also show preliminary results of an extended survey of the ring current crossings for different years, estimating the local current density, field curvature and total current and analysing the spatial extent of the ring current region.
Energy Input to the Ionosphere-Thermosphere Due to Inductive Coupling with the Magnetosphere
1Jet Propulsion Laboratory, California Institute of Technology, United States of America; 2Department of Physics and Astronomy, Dartmouth College, United States of America
Uncertainty in mechanisms and in the amount of energy being transferred from the solar environment to the Earth’s magnetosphere-ionosphere-thermosphere (M-I-T) constitutes one of the core space weather problems. A reliable estimate of the IT energy budget is an important condition for improving forecasting capabilities of the IT system. Itis generally considered that the IT response to solar wind driving can be represented by an evolving set of quasi-steady-state electrostatic processes. This approach is applicable to describe physical processes with temporal scales larger than ~1000s (16 min) and spatial scales larger than ~1000 km (Richmond, 2010). These scales are too conservative for intense storms or strong substorms which feature high-latitude inductive ionospheric electric fields (reaching up to ~ 20% - 50% of a potential field) and inductive field-aligned currents (Vanhamäki, Amm and Viljanen, 2007).
We discuss theoretical foundations of inductive magnetosphere-ionosphere coupling due to ULF waves. Our focus will be on waves which provide the most efficient energy transport and M-I-T coupling. Based on inductive mechanisms we suggest modifications to IT energy budget estimates and definitions of Joule heating. We will also analyze the capabilities of satellite measurements of electric and magnetic wave fields to estimate energy transport and dissipation in the ionosphere.
Richmond, A. D. (2010), On the ionospheric application of Poynting’s theorem, J. Geophys. Res., 115, A10311, doi:10.1029/2010JA015768.
Vanhamäki, H., O. Amm and A. Viljanen (2007), Role of inductive electric fields and currents in dynamical ionospheric situations, Ann. Geophys., 25, 437–455.
Dynamics of CME and HSS Storms Revealed from Auroral Imaging and Field aligned Currents
1UCLA, United States of America; 2Boston University, United States of America; 3University of Calgary, Canada
Auroral imaging can reveal important spatial and temporal features of magnetic storms that are difficult to reveal otherwise. For CME storms, we find that shock impact with southward IMF quickly drives rapid auroral-oval poleward expansion (implying strong nightside reconnection), strong auroral activity, and rapid filling of newly closed field lines with new plasma. Another important CME storm feature is a strong dominance of auroral streamer activity relative to substorm activity during strongly southward IMF, suggesting that plasma sheet flow bursts are common but the plasma sheet is more stable to substorm onset than often expected for strong driving. Episodes of significant equatorward penetration of the auroral oval during CME storms appear to occur in association with auroral streamers, and thus with plasma sheet flow bursts. Evidence suggests that these flow bursts are accompanied by other major stormtime phenomena such as enhancement and equatorward motion of ionospheric and field-aligned currents, equatorward motion of the ionospheric trough, earthward injection of particles into the ring current, and transport of high TEC features into the auroral oval from the polar cap. Unlike CME storms, high-speed stream (HSS), with their fluctuating IMF, show many substorms as well as streamers. Also, major episodes of equatorward penetration of the auroral oval appear to occur in a steady, classical manner as well as via Streamers. The structure of field aligned currents appears to be reflect this difference. Common to all storms, are frequent intense auroral omega bands on the morning side, though their cause and effects on storm dynamics remain unknown. Another common feature is very clear streamer triggering of substorms and of omega bands, the triggering streamers appearing to be associated with flow bursts bringing new plasma into the evening convection and morning convection cell, respectively.
Magnetopause Erosion During the March 17, 2015, Magnetic Storm: Combined Field-Aligned Currents, Auroral Oval, and Magnetopause Observations
1NASA Goddard Space Flight Center, Greenbelt, MD, USA, United States of America; 2GFZ German Research Centre for Geosciences, Potsdam, Germany; 3The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA; 44. University of California, Los Angeles, CA, USA; 55. NOAA Space Weather Prediction Center, Boulder, CO, USA; 66. University of Michigan, Ann Arbor, MI, USA; 77. High Altitude Observatory, UCAR, Boulder, CO, USA; 88. Space Research Institute, Austrian Academy of Sciences, Graz, Austria; 99. Korea Astronomy and Space Science Institute, Daejeon, Korea; 1010. University of New Hampshire, Durham, NH, USA
We present multi-mission observations of field-aligned currents, auroral oval, and magnetopause crossings during the March 17, 2015 magnetic storm. Dayside reconnection is expected to transport magnetic flux, strengthen field-aligned currents, lead to polar cap expansion and magnetopause erosion. Our multi-mission observations assemble evidence for all these manifestations. After a prolonged period of strongly southward interplaneta ry magnetic field, Swarm and AMPERE observe significant intensification of field-aligned currents. The dayside auroral oval, as seen by DMSP, appears as a thin arc associated with ongoing dayside reconnection. Both the field-aligned currents and the auroral arc move equatorward reaching as low as ~60° MLat. Strong magnetopause erosion is evident in the in-situ measurements of the magnetopause crossings by GOES-13/15 and MMS. The coordinated Swarm, APMERE, DMSP, MMS and GOES observations, with both global and in-situ coverage of the key regions, provide a clear demonstration of the effects of dayside reconnection on the entire magnetosphere.