Electromagnetic ULF Wave Energy Leakage through the Ionosphere as Observed by Low-Orbiting Satellites SWARM and Ground AMBER Array
11. Space Research Institute, Russian Federation; 22. Institute of the Earth Physics. Russian Federation
We study the transmission of ULF waves in the band Pc2-3/Pi2 through the ionosphere to the ground. For that the synchronous data from the low-orbiting satellites SWARM and ground magnetometer AMBER array have been used. The analysis of combined satellite/ground observations gives a possibility to reveal a physical nature of Pc2-3 and Pi2 waves in the upper ionosphere.
Strong Ambipolar-driven Ion Upflow Within the Cleft Ion Fountain During Low Geomagnetic Activity
1University of Calgary, Canada; 2National Centers for Environmental Information,USA; 3University of Alberta, Canada; 4SRI international, USA
We investigate low-energy (<10 eV) ion upflows (mainly O+) within the cleft ion fountain (CIF) using conjunctions of the Enhanced Polar Outflow Probe (e-POP) satellite, the DMSP F16 satellite, the SuperDARN radar, and the Resolute Bay Incoherent Scatter Radar North (RISR-N). The SEI instrument onboard e-POP enables us to derive ion upflow velocities from the 2-D images of ion distribution functions with a frame rate of 100 images per second, and with a velocity resolution of the order of 25 m/s. We identify three cleft ion fountain events with very intense (>1.6 km/s) ion upflow velocities near 1000 km altitude during quiet geomagnetic activity (Kp < 3). Such large ion upflow velocities have been reported previously at or below 1000 km, but only during active periods. Analysis of the core ion distribution images allows us to demonstrate that the ion temperature within the CIF does not rise by more than 0.3 eV relative to background values, which is consistent with RISR-N observations in the F region. The presence of soft electron precipitation seen by DMSP and lack of significant ion heating indicate that the ion upflows we observe near 1000 km altitude are primarily driven by ambipolar electric fields.
Diagnosing the Topside Ionosphere Using Synchronous E- and B-field Measurements from the Swarm Satellite Constellation
1University of Alberta, Canada; 2University of Calgary, Calgary, Alberta, Canada; 3John Hopkins University Applied Physics Laboratory, Laurel, MD, USA; 4Mullard Space Science Laboratory, University College London, London, UK; 5NASA Goddard Space Flight Center, Greenbelt, MD, USA; 6National Observatory of Athens, Athens, Greece; 7National and Kapodistrian University of Athens, Athens, Greece
This study explores the potential for using the synchronous E-field and B-field measurements from the Swarm satellite constellation for diagnosing the topside ionosphere. Within the framework of reflected and interfering Alfven waves interacting with a reflecting boundary, we examine the use of the spectral properties of these fields to infer key local ionospheric parameters such as Pedersen conductivity, Alfven speed and distance from the reflective layer. These techniques have the potential to present more accurate estimates of the potential dynamical and spatial variation of these important quantities than relying on empirical or statistical models such as International Reference Ionosphere. A methodology to infer the Alfven speed and density from multi-spacecraft Alfven wave observations is also discussed, which could allow the validity of the Langmuir probe measurements to be tested.
Validation of a Comprehensive Numerical Model of Ionosphere by Comparison with EISCAT Observations
University of Alberta, Canada
The authors developed a numerical model of coupled ionosphere and magnetosphere. The model was applied to simulate ionospheric dynamics in the post-midnight pre-dawn sector observed by EISCAT radar in Tromso during periods of low magnetospheric activity. The model demonstrated good quantitative agreement with the observations of electron density and temperature and ion temperature for altitudes between 100 km and 450 km during a 2 hour time interval. This was achieved after adding the following physics: (i) Chemistry model distinguishes metastable oxygen ion states (4S, 2D, 2P). (ii) EUV flux changes according to the Earth rotation. (iii) Photoelectrons produce ionization and are a source of electron heating (a transport code for the photoelectrons was developed accounting for ionization by secondary electrons). (iv) Production of O+ by photoelectrons is split between the three metastable ion states. (v) High-altitude boundary condition for the electron and ion temperatures corresponds to a zero heat flux. (vi) The electric field has both meridional and azimuthal components producing both Pedersen and Hall currents. (vii) Azimuthal plasma density variation associated with the Earth rotation contributes to plasma density modification by the global convection (a method has been found to include this effect in a model which is essentially 1D). With the updated model, significant modification of the ion composition was found: densities of molecular ions N2+ and NO+ are a few times higher while the density of the dominant ion species O+ is a few times lower than values predicted by the model before the aforementioned changes. This study demonstrated that the model can be a valuable tool for analysis of ground based and spacecraft observations.
Pc1 Wave Observations in the Topside Ionosphere with Swarm Satellites
1National Observatory of Athens, Greece; 2University of Alberta, Canada; 3University of Athens, Greece; 4ESTEC, Netherlands
The ongoing Swarm satellite mission provides an opportunity to a better knowledge of the near-Earth electromagnetic environment. Herein, we study the occurrence of ultra low frequency (ULF) wave events in the Pc1 frequency range (0.2-5 Hz) observed by the Swarm satellite mission for a period spanning two years after the constellation's final configuration. We present maps of the dependence of Pc1 wave power with magnetic latitude and magnetic local time as well as geographic latitude and longitude from the three satellites at their different locations in the topside ionosphere. The observed wave events are disturbances in the Pc1 band in the Swarm frame - which could be Pc1 proper at low L-shell value but likely are related to magnetosphere-ionosphere coupling at higher latitudes. Our initial results emphasize the fact that the Pc1 power distribution at low-Earth orbit as provided by the Swarm spacecraft is better organized in geographic than geomagnetic coordinates.
Modelling Anisotropic Temperature Ratios in the Weakly Collisional Altitude Region Observed by Swarm
University of Saskatchewan, Canada
Using the Swarm EFI detector, Archer et al. [Geophys. Res. Lett., 42, 981, 2015.] obtained large and unexpected ratios of the ion temperatures perpendicular to the magnetic field to the ion temperatures parallel to the magnetic field at 550 km. In these measurements, both the ion temperatures parallel and perpendicular to the magnetic field were large, the electric fields were strong and highly localized, and strong ion upflows were observed. These new findings have prompted further study into previous work on the effect frictional heating has on the ion velocity distribution. In a first set of studies, we have revisited previously proposed cross-sections for resonant charge exchange collisions between O+ and atomic oxygen. In a second set of studies, given the 550 km altitude of the Swarm observations, we have advanced the previous studies made by Loranc and St.-Maurice [J. Geophys. Res., 99, 17429, 1994.], who studied the effect of the altitude transition from highly collisional regions below 400 km to weakly collisional regions higher up. In our study, the ions are taken to be collisionless above a given boundary altitude, and the velocity distribution evolves as a result of the vertical transport of newly heated ions, with the fastest ions being the first to reach a particular altitude above the prescribed boundary altitude. Below that boundary, frictional heating is occurring and producing velocity distributions of the kind found with the Monte Carlo analysis of Winkler et al. [J. Geophys. Res., 97, 8399, 1992]. In our upgraded model of the weakly collisional altitude region, we have studied the effects of changing velocity distributions at the collisional boundary. This model includes the effect of temporal electric field changes on a convecting magnetic field line, as well as the effect of changing densities at the boundary owing to chemistry that accompany the strong electric fields. In addition, the effect of the evolving densities on the polarization electric field above the collisional boundary has also been incorporated. From this analysis we have obtained anisotropic temperature ratios, plasma densities, ion heat flows, and ion upflows as a function of time and altitude for a variety of trigger conditions and a variety of possible ion-neutral cross-sections. The goal of this work is to match the conditions of the Swarm observations through modeling and compare our calculations to what is observed.