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Pulsating aurora are common diffuse-like aurora. Studies have suggested that they contain higher energy particles than other types and are possibly linked to substorm activity. There has yet to be a quantitative statistical study of the variation in pulsating aurora energy content related to substorms. We analyzed the inverted energy content from 53 events using the Poker Flat Incoherent Scatter Radar. To reduce the uncertainty, we split the differential energy flux into low and high energy using the limit of 30 keV. We also analyzed the lower altitude boundary of the electron density profile, characterized by a number density of > 1 0 10 m −3 , and used this as a proxy for high energy. We compared both of these to magnetic local time (MLT), AE index, and temporal proximity to substorm onset. There was a slight trend in MLT, but a much stronger one in relation to both substorm onset and AE index. For higher AE and closer to onset the total energy flux and flux above 30 keV increased. In addition, this higher energy remained enhanced for an hour after substorm onset. Our results confirm the high energy nature of pulsating aurora, demonstrate the connection to substorms, and imply their importance to coupling between the magnetosphere and atmosphere. 

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. 

In the D‐region, the ionization rate cannot be detected directly with any known measurement technique, therefore it must be estimated. Starting from space‐based measurements of precipitating particle flux, we estimate the ionization rate in the atmosphere using the Electron Precipitation Monte Carlo transport method. This ionization rate is used to calculate the expected electron density in the D‐region with the Glukhov‐Pasko‐Inan five species (GPI5) atmospheric chemistry model. We then compare the simulated electron density with that measured by the Poker Flat Incoherent Scatter Radar (PFISR). From ground‐based radar measurements of electron density enhancements due to sub‐relativistic and relativistic electron precipitation, we present a method to extract the ionization rate altitude profiles using inverse theory. We use this estimation of ionization rate to find the energy distribution of the precipitating particles. With this inverse method, we are able to link ground measurements of electron density to the precipitating flux in a time dependent manner and with uncertainty in the inverted parameters. The method was tested on synthetic data and applied to specific PFISR data sets. The method is able to retrieve the ionization rate altitude profiles that, when forward modeled, return the expected electron densities within ∼7% error as compared to the PFISR data. For the case presented here, the arbitrary energy distribution inversion results are comparable in magnitude and shape to those presented in Turunen et al. (2016,https://doi.org/10.1002/2016jd025015) for the inversion of a single event of pulsating aurora observed by EISCAT.

 

Joule heating deposits a significant amount of energy into the high‐latitude ionosphere and is an important factor in many magnetosphere‐ionosphere‐thermosphere coupling processes. We consider the relationship between localized temperature enhancements in polar cap measured with the Resolute Bay Incoherent Scatter Radar‐North (RISR‐N) and the orientation of the interplanetary magnetic field (IMF). Based on analysis of 10 years of data, RISR‐N most commonly observes ion heating in the noon sector under northwards IMF. We interpret heating events in that sector as being primarily driven by sunwards plasma convection associated with lobe reconnection. We attempt to model two of the observed temperature enhancements with a data‐driven first principles model of ionospheric plasma transport and dynamics, but fail to fully reproduce the ion temperature enhancements. However, evaluating the ion energy equation using the locally measured ion velocities reproduces the observed ion temperature enhancements. This result indicates that current techniques for estimating global plasma convection pattern are not adequately capturing mesoscale flows in the polar cap, and this can result in underestimation of the energy deposition into the ionosphere and thermosphere.

 

Mesoscale high‐latitude electric fields are known to deposit energy into the ionospheric and thermospheric system, yet the energy deposition process is not fully understood. We conduct a case study to quantify the energy deposition from mesoscale high‐latitude electric fields to the thermosphere. For the investigation, we obtain the high‐latitude electric field with mesoscale variabilities from Poker Flat Incoherent Scatter Radar measurements during a moderate geomagnetic storm, providing the driver for the Global Ionosphere and Thermosphere Model (GITM) via the High‐latitude Input for Mesoscale Electrodynamics framework. The HIME‐GITM simulation is compared with GITM simulations driven by the large‐scale electric field from the Weimer model. Our modeling results indicate that the mesoscale electric field modifies the thermospheric energy budget primarily through enhancing the Joule heating. Specifically, in the local high‐latitude region of interest, the mesoscale electric field enhances the Joule heating by up to five times. The resulting neutral temperature enhancement can reach up to 50 K above 200 km altitude. Significant increase in the neutral density above 250 km altitude and in the neutral wind speed are found in the local region as well, lagging a few minutes after the Joule heating enhancement. We demonstrate that the energy deposited by the mesoscale electric field transfers primarily to the gravitational potential energy in the thermosphere.

 

Scintillation in the polar cap ionosphere is observed with a Coherent Electromagnetic Radio Tomography (CERTO) receiver while the Resolute Bay Incoherent Scatter Radars (RISR) provide background plasma conditions in a 3D volume. We interpret fluctuations in the very high frequency (VHF) and ultrahigh frequency (UHF) signal associated with mid‐scale ionospheric structuring using 3D density gradients and plasma drift velocity vectors and calculate the maximum gradient drift instability growth rate. Plasma structuring is evident for any plasma density gradient, but sub‐kilometer structures are less likely on the leading edge of polar patches, possibly due to a much faster diffusion rate for small‐scale structures. Structures are much more uniformly distributed around density enhancements that do not have clear leading and trailing edges. Although the gradient drift instability is an important factor in polar cap structuring, linear growth rates are most successful at predicting structuring around isolated density enhancements in consistent plasma flows. For more general density gradients, the time history of a plasma parcel and local diffusion rates must also be considered.

 

Measurements of plasma lines by the Arecibo incoherent scatter radar are known to have sharp striations in power, varying with the plasma frequency and magnetic aspect angle of the radar beam. We explain these power striations as the manifestation of a suprathermal electron population with peaks in energy at approximately 15, 25, and 45 eV. These energies correspond to sharp features in the photoelectron energy spectra measured by rockets and spacecraft. A new theory is developed to predict the plasma line power for an arbitrary, magnetized suprathermal distribution. The magnetization terms in this theory are shown to contribute substantially to the enhancement of plasma line power through inverse Landau and cyclotron damping of the suprathermal peaks. The theory is applied as a forward model to measurements obtained at Arecibo for different magnetic field aspect angles, showing general agreement with the data. At large magnetic aspect angles the theory reproduces the upper‐hybrid instability which can cause 150 km echoes. The developed theory allows for the suprathermal distribution at a given altitude to be probed across a wide range of energies and pitch angles.