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We use simultaneous auroral imaging, radar flows, and total electron content (TEC) measurements over Alaska to examine whether there is a direct connection of large-scale traveling ionospheric disturbances (LSTIDs) to auroral streamers and associated flow channels having significant ground magnetic decreases. Observations from seven nights with clearly observable flow channels and/or auroral streamers were selected for analysis. Auroral observations allow identification of streamers, and TEC observations detect ionization enhancements associated with streamer electron precipitation. Radar observations allow direct detection of flow channels. The TEC observations show direct connection of streamers to TIDs propagating equatorward from the equatorward boundary of the auroral oval. The TIDs are also distinguished from the streamers to which they connect by their wave-like TEC fluctuations moving more slowly equatorward than the TEC enhancements from streamer electron precipitation. TIDs previously observed propagating equatorward from the auroral oval have been identified as LSTIDs. Thus, the TIDs here are likely LSTIDs, but we lack sufficient TEC coverage necessary to demonstrate that they are indeed large scale. Furthermore, each of our events shows TID’s connection to groups of a few streamers and flow channels over a period in the order of 15 min and a longitude range of ∼15–20°, and not to single streamers. (Groups of streamers are common during substorms. However, it is not currently known if streamers and associated flow channels typically occur in such groups.) We also find evidence that a flow channel must lead to a sufficiently large ionospheric current for it to lead to a detectable LSTID, with a few tens of nT ground magnetic field decreases not being sufficient.

Key Points: 8 • E region energy transfer rates are estimated from PFISR measurements for the 9 first time. 10 • The electromagnetic energy transfer rate and the Joule heating rate are larger in 11 ...

Sudden commencement (SC) induced by solar wind pressure enhancement can produce significant global impact on the coupled magnetosphere-ionosphere (MI) system, and its effects have been studied extensively using ground magnetometers and coherent scatter radars. However, very limited observations have been reported about the effects of SC on the ionospheric plasma. Here we report detailed Poker Flat Incoherent Scatter Radar (PFISR) observations of the ionospheric response to SC during the 17 March 2015 storm. PFISR observed lifting of the F region ionosphere, transient field-aligned ion upflow, prompt but short-lived ion temperature increase, subsequent F region density decrease, and persistent electron temperature increase. A global magnetohydrodynamic (MHD) simulation has been carried out to characterize the SC-induced current, convection, and magnetic perturbations. Simulated magnetic perturbations at Poker Flat show a satisfactory agreement with observations. The simulation provides a global context for linking localized PFISR observations to large-scale dynamic processes in the MI system.

Plasma density cavities are correlated with heavy ion outflow where ions are heated transversely by wave particle interactions (WPIs). This paper presents the first result of a 3D ionospheric fluid model that incorporates plasma temperature anisotropies and a phenomenological treatment of WPIs, leading to transversely accelerated ions (TAIs). It is demonstrated that O+ outflow can generate density cavities in the topside ionosphere. With the empirical heating rate applied in a designated heating region on the dayside, the O+ species in the heating region is accelerated upward by the mirror force. The O+ species below the heating region upflows under the parallel pressure gradient force and the parallel electric force. As the O+ species flows upward, the plasma is eroded both below and inside the heating region. Parametric modeling studies show that the depth of density cavities in the upper ionosphere increases as the heating rate increases. The percent change in the density of the cavity relative to the local background density is practically independent of the low-altitude cutoff of the heating region, but the altitude of the relative density minimum moves upward with the increasing altitude of cutoff. The O+ flux is insensitive to the change of the heating rate, while depends strongly on the altitude of cutoff. Using empirical values of the initial heating rate and the height of the low-altitude boundary as input, the ranges of the modeled electron density and the O+ outflow moments are in reasonable agreement with observations of a storm-time density cavity observed by the FAST satellite. The 3D ionospheric model has the potential to be coupled to magnetospheric models for magnetosphere-ionosphere (MI) coupling.

We present the first simulations of magnetospheric sawtooth oscillations under steady solar wind conditions that are driven internally by heavy ion outflow from a physics-based model. The simulations presented use the multifluid Lyon-Fedder-Mobarry magnetohydrodynamics model two-way coupled to the ionosphere/polar wind model (IPWM). Depending on the type of wave-particle interactions utilized within IPWM, the coupled simulations exhibit either sawtooth oscillations or steady magnetospheric convection. Contrasting the simulations that do and do not develop sawtooth oscillations yields insights into the relationship between outflow and sawtooth oscillations. The total outflow rate is not an adequate predictor of the convection mode that will emerge. The simulations that develop sawtooth oscillations are characterized by intense outflow concentrated in the midnight auroral region. This outflow distribution mass loads the tail reconnection region without excessively mass loading the dayside reconnection region and leads to an imbalance between the dayside and nightside reconnection rates.

Thermal ion retarding potential analyzers (RPAs) are used to measure in situ auroral ionospheric plasma parameters. This article analyzes data from a low-resource RPA in order to quantify the capability of the sensor. The RPA collects a sigmoidal current-voltage (I-V) curve, which depends on a non-linear combination of Maxwellian plasma parameters, so a forward-modeling procedure is used to match the best choice plasma parameters for each I-V curve. First, the procedure is used, given constraining information about the flow moment, to find scalar plasma parameters-ion temperature, ion density, and spacecraft sheath potential-for a single I-V curve interpreted in the context of a Maxwellian plasma distribution. Second, two azimuthally separated I-V curves from a single sensor on the spinning spacecraft are matched, given constraining information on density and sheath potential, to determine the bulk plasma flow components. These flows are compared to a high-fidelity, high-resource flow diagnostic. In both cases, the procedure's sensitivity to variations in constraining diagnostics is tested to ensure that the matching procedure is robust. Finally, a standalone analysis is shown, providing plasma scalar and flow parameters using known payload velocity and International Reference Ionosphere density as input information. The results show that the sensor can determine scalar plasma measurements as designed, as well as determine plasma DC flows to within hundreds of m/s error compared to a high-fidelity metric, thus showing their capability to replace higher-resource methods for determining DC plasma flows when coarse-resolution measurements at in situ spatial scales are suitable.

Motivated by rocket observations showing a variety of different ionospheric responses to precipitation, this paper explores the influence of the background ionospheric density on upflow resulting from auroral precipitation. Simulations of upflow driven by auroral precipitation were conducted using a version of the Varney et al. (2014) model driven by precipitation characterized by observations made during the 2012 Magnetosphere-Ionosphere Coupling in the Alfven resonator rocket mission and using a variety of different initial electron density profiles. The simulation results show that increased initial density before the onset of precipitation leads to smaller electron temperature increases, longer ionospheric heating timescales, weaker ambipolar electric fields, lower upflow speeds, and longer upflow timescales but larger upflow fluxes. The upflow flux can increase even when the ambipolar electric field strength decreases due to the larger number of ions that are accelerated. Long-term observations from the European Incoherent Scatter (EISCAT) Svalbard radar taken during the International Polar Year support the effects seen in the simulations. This correlation between ionospheric density and ion upflows emphasizes the important role of photoionization from solar ultraviolet radiation, which the EISCAT observations show can increase ionospheric density by as much as an order of magnitude during the summer months.

The efficiencies of pathways of thermospheric heating via soft electron precipitation in the dayside cusp region are investigated using the coupled magnetosphere-ionosphere-thermosphere model (CMIT). Event-based data-model comparisons show that the CMIT model is capable of reproducing the thermospheric mass density variations measured by the CHAMP satellite during both quite and active periods. During the 24 August 2005 storm event (Kp = 6−) while intense Joule heating rate occurs in the polar cusp region, including soft electron precipitation is important for accurately modeling the F region thermospheric mass density distribution near the cusp region. During the 27 July 2007 event (Kp = 2−) while little Joule heating rate occurs in the polar cusp region, the controlled CMIT simulations suggest that the direct pathway through the energy exchange between soft electrons and thermospheric neutrals is the dominant process during this event, which only has a small effect on the neutral temperature and mass density at 400 km altitude. Comparisons between the two case studies show that the indirect pathway via increasing the F region Joule heating rate is a dominant process during the 24 August 2005 storm event, which is much more efficient than the direct heating process.

Initial demonstrations of an ionosphere/polar wind model including a phenomenological treatment of transverse heating by wave particle interactions (WPIs) are presented. Tests with fixed WPI parameters in a designated heating region on the dayside with time-varying convection show that the parameters of the resulting nonthermal ion outflow are strongly coupled to the convection. The hemispheric outflow rate is positively correlated with the convection speed with a time delay related to the travel time to the upper boundary. Increases in convection increase the thermal plasma access to the heating region, both by increasing the upflow associated with frictional heating and by increasing the horizontal transport. The average parallel velocities and energies of the escaping nonthermal ions are anticorrelated with the convection speed due to the finite dwell time in the heating region. The computationally efficient model can be readily coupled into global geospace modeling frameworks in the future.

Photoelectrons escape from the ionosphere on sunlit polar cap field lines. In order for those field lines to carry zero current without significant heavy ion outflow or cold electron inflow, field-aligned potential drops must form to reflect a portion of the escaping photoelectron population back to the ionosphere. Using a 1-D ionosphere-polar wind model and measurements from the Resolute Bay Incoherent Scatter Radar (RISR-N), this paper shows that these reflected photoelectrons are a significant source of heat for the sunlit polar cap ionosphere. The model includes a kinetic suprathermal electron transport solver, and it allows energy input from the upper boundary in three different ways: thermal conduction, soft precipitation, and potentials that reflect photoelectrons. The simulations confirm that reflection potentials of several tens of eV are required to prevent cold electron inflow and demonstrate that the flux tube integrated change in electron heating rate (FTICEHR) associated with reflected photoelectrons can reach 109eV cm−2s−1. Soft precipitation can produce FTICEHR of comparable magnitudes, but this extra heating is divided among more electrons as a result of electron impact ionization. Simulations with no reflected photoelectrons and with downward field-aligned currents (FAC) primarily carried by the escaping photoelectrons have electron temperatures which are ∼250–500 K lower than the RISR-N measurements in the 300–600 km region; however, simulations with reflected photoelectrons, zero FAC, and no other form of heat flux through the upper boundary can satisfactorily reproduce the RISR-N data.

Spectrographic airglow measurements were made during an ionospheric modification experiment at High Frequency Active Auroral Research Program on 12 March 2013. Artificial airglow enhancements at 427.8, 557.7, 630.0, 777.4, and 844.6 nm were observed. On the basis of these emissions and using a methodology based on the method of Backus and Gilbert (1968, 1970), we estimate the suprathermal electron population and the subsequent equilibrium electron density profile, including contributions from electron impact ionization. We find that the airglow is consistent with heater-induced ionization in view of the spatial intermittency of the airglow.

Jicamarca measurements of electron temperatures at high altitudes (500–1500 km) from the last solar minimum routinely show variations of hundreds of Kelvin from day-to-day. Possible sources of these variations are explored using the SAMI2-PE is another model of the ionosphere including photoelectron transport (SAMI2-PE) model, which includes a multistream photoelectron transport model. Changes to the electric fields, meridional winds, and thermospheric densities can all change the electron densities and temperatures at high altitudes. The high altitude electron temperatures are primarily determined by a balance between heating from photoelectrons which travel up the field lines and thermal diffusion which carries heat back down the field lines. The winds and electric fields will change the altitude and densities of the off-equatorial F -region peaks, especially on the field lines connected to the equatorial arcs. The densities and temperatures in the plasmasphere will self consistently adjust themselves to achieve diffusive equilibrium with the off-equatorial F -regions. Furthermore, decreases in the density and/or altitude of the F -region makes it easier for photoelectrons to escape to high altitudes. These connections between the equatorial plasmasphere, the off-equatorial F -regions, and the neutral thermosphere suggest that high altitude measurements at Jicamarca could be used to study thermospheric variability.

On-orbit firings of both liquid and solid rocket motors provide localized disturbances to the plasma in the upper atmosphere. Large amounts of energy are deposited to ionosphere in the form of expanding exhaust vapors which change the composition and flow velocity. Charge exchange between the neutral exhaust molecules and the background ions (mainly O+) yields energetic ion beams. The rapidly moving pickup ions excite plasma instabilities and yield optical emissions after dissociative recombination with ambient electrons. Line-of-sight techniques for remote measurements rocket burn effects include direct observation of plume optical emissions with ground and satellite cameras, and plume scatter with UHF and higher frequency radars. Long range detection with HF radars is possible if the burns occur in the dense part of the ionosphere. The exhaust vapors initiate plasma turbulence in the ionosphere that can scatter HF radar waves launched from ground transmitters. Solid rocket motors provide particulates that become charged in the ionosphere and may excite dusty plasma instabilities. Hypersonic exhaust flow impacting the ionospheric plasma launches a low-frequency, electromagnetic pulse that is detectable using satellites with electric field booms. If the exhaust cloud itself passes over a satellite, in situ detectors measure increased ion-acoustic wave turbulence, enhanced neutral and plasma densities, elevated ion temperatures, and magnetic field perturbations. All of these techniques can be used for long range observations of plumes in the ionosphere. To demonstrate such long range measurements, several experiments were conducted by the Naval Research Laboratory including the Charged Aerosol Release Experiment, the Shuttle Ionospheric Modification with Pulsed Localized Exhaust experiments, and the Shuttle Exhaust Ionospheric Turbulence Experiments.

It is generally assumed that negatively charged icy dust particles in the mesosphere are charged by the collection of thermal plasma particles. However, there are some indications that there may be a population of hyperthermal electrons in the D-region under auroral activity under certain conditions (e.g. Margot-Chaker and McNamara, Planetary and Space Science 32, 391, 1984). In this brief communication, we speculate on the effect of a hyperthermal distribution of electrons on dust charging, and how this might affect prevailing turbulence scattering theory for polar summer mesophere echoes.

Many of the expressions for the reflectivity of polar mesospheric summer echoes (PMSE) predict that the echo strength is controlled by the electron density. We present several observations made using the Poker Flat Incoherent Scatter Radar which are difficult to explain based on those expressions, including observations at night with no detectable incoherent scatter below 90 km and during aurora where the reflectivity shows no response to abrupt changes in ionization. We derive a new expression for the reflectivity and are still able to explain all of these observations as scatter from free electrons. When the electron density is much smaller than the ice density the reflectivity is a strong function of electron density. In the opposite limit the reflectivity is solely controlled by the ice density because only a fraction of the electron density variance generated at the largest scales can get convected to sufficiently small scales.

In this paper, we report on multi-beam spectral observations of polar mesospheric summer echoes (PMSE) at 450 MHz (Bragg scattering wavelength of ∼ 33 cm ) carried out with the Poker Flat Incoherent Scatter Radar (PFISR) located near Fairbanks, Alaska. The observations presented in this paper occurred with auroral particle precipitation, which enhanced the otherwise low nighttime D-region ionization. The observations indicate two classes of spectra associated with PMSE at this frequency: a relatively rare, “broad” class of spectra that seems to be particularly turbulent with spectral widths (root mean square velocity fluctuations) of 6–7 m/s, and the more common “narrow” spectra, with spectral widths close to 1 m/s. The results are discussed in terms of the turbulence scattering theory of PMSE. Using the theories of Rapp and Lubken [2003. On the nature of PMSE: electron diffusion in the vicinity of charged particles revisited. Journal of Geophysical Research 108, 8437, doi: 10.1029/2002JD002857 ], we find that neutral turbulence together with enhancement of the Schmidt number by the presence of charged ice can indeed explain the observations, even at these small scales. The echoes are likely associated with large charged ice particles (a few 10 s of nanometers in radius). The narrowest echoes, while seemingly resulting from relatively modest neutral turbulence, thus acquire long diffusion times which allow them to drift with the background winds for tens of seconds, possibly explaining the predominance of these narrow-width echoes.

[1] The electron energy distribution during an Fregion ionospheric modification experiment at the HAARP facility near Gakona, Alaska, is inferred from spectrographic airglow emission data. Emission lines at 630.0, 557.7, and 844.6 nm are considered along with the absence of detectable emissions at 427.8 nm. Estimating the electron energy distribution function from the airglow data is a problem in classical linear inverse theory. We describe an augmented version of the method of Backus and Gilbert which we use to invert the data. The method optimizes the model resolution, the precision of the mapping between the actual electron energy distribution and its estimate. Here, the method has also been augmented so as to limit the model prediction error. Model estimates of the suprathermal electron energy distribution versus energy and altitude are incorporated in the inverse problem formulation as representer functions. Our methodology indicates a heater-induced electron energy distribution with a broad peak near 5 eV that decreases approximately exponentially by 30 dB between 5–50 eV.

[1] A case study of mesospheric winds and waves observed by the Poker Flat Incoherent Scatter Radar (PFISR) on 23 April 2008 is presented. Active auroral precipitation created sufficient ionization for nearly 12 h of continuous incoherent scatter measurements of the D region ionosphere from ∼60 to 90 km altitude. PFISR utilized a multilook-direction mode which permitted measurements of vector winds, in addition to high precision vertical velocities, at high temporal resolution. A large-amplitude coherent wave packet (appearing superficially to be a single wave) with a downward phase velocity and a long period (τ ∼ 10.5 h) was observed. Vertical wavelengths were measured directly to be λz ≃ 4–10 km, increasing with altitude. The proximity of τ to the local inertial period in addition to its large horizontal wavelength are suggestive of a coherent inertia-gravity wave (IGW) packet. Using polarization analyses, we find that the IGWs are propagating mainly southward. The waves were observed to saturate at z ∼ 70–85 km, and have their largest amplitudes in the first 8 h of the measurements (before 2000 UT). A stability analysis confirms that the waves were likely dynamically unstable at these altitudes and times. In conjunction with this observation, the background wind is found to be southward of HWM winds by 10–20 m/s until ∼2000 UT, consistent with the horizontal background wind acceleration created by the saturation of these IGWs. After 2000 UT, the background wind relaxes to the north by 10–20 m/s, consistent with a significant decrease of the IGW amplitudes. The IGWs may have originated from a jet stream adjustment at z ∼ 10 km in northern Russia about 5 days prior to the observation in Alaska.