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 pulsating aurora energy content. We analyzed the inverted energy content from 53 events using the Poker Flat Incoherent Scatter Radar. We compared this 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 present new results using data collected by the Poker Flat Incoherent Scatter Radar (PFISR) of energy transfer rates which include the effects from neutral winds in the high latitude E-region ionosphere-thermosphere (IT) during Fall 2015. The purpose of our investigation is to understand the magnetic local time (MLT) dependence of the peak energy transfer, which occurs asymmetrically in the morning-evening (dawn-dusk) MLT sector. The statistical characteristics of both altitude-resolved and altitude-integrated energy transfer rates in the auroral E region local to PFISR during different geomagnetic conditions are quantified. Our analysis shows that the geomagnetic activity level has a large impact on the energy transfer rates. In contrast with previous investigations, we find both the altitude integrated electromagnetic (EM) energy transfer rate and Joule heating rate are larger in the evening sector than in the morning sector during all geomagnetic activity conditions. We also observe non-negligible negative EM energy transfer rates below 110 km in the morning sector during active conditions, which is associated with neutral winds during this MLT interval. The statistical results show that the neutral winds tend to increase the Joule heating rate in a narrow altitude range in the morning sector and impact a broader region with respect to altitude and time in the evening sector in the E region under moderate and active conditions. We find that during quiet conditions that the neutral winds have a significant contribution to the Joule heating and contribute up to 75% of the Joule heating. However, during active conditions, the enhanced fields are a dominant driver of Joule heating, while the neutral wind effects can reduce the Joule heating rates by 25% or more relative to the passive heating rates.

We demonstrate a novel method for observing Large Scale Traveling Ionospheric Disturbances (LSTIDs) using high frequency (HF) amateur radio reporting networks, including the Reverse Beacon Network (RBN), Weak Signal Propagation Reporter Network (WSPRNet), and PSKReporter. LSTIDs are quasi-periodic variations in ionospheric densities with horizontal wavelengths > 1000 km and periods between 30 to 180 min. On 3 Nov 2017, LSTID signatures were observed simultaneously over the continental United States in amateur radio, SuperDARN HF radar, and GNSS Total Electron Content with a period of ~2.5 hr, propagation azimuth of ~163°, horizontal wavelength of ~1680 km, and phase speed of ~1200 km/hr. SuperMAG SME index enhancements and Poker Flat Incoherent Scatter Radar measurements suggest the LSTIDs were driven by auroral electrojet intensifications and Joule heating. This novel measurement technique has applications in future scientific studies and for assessing the impact of LSTIDs on HF communications.

Sporadic-E (Es) layers are characterized as thin layers (1-5 km) of enhanced electron density that occur between 90-120 km in altitude. Sporadic E at mid- and low-latitudes has a reasonably well established climatology, while at high latitudes there have been fewer investigations that have characterized the climatology of sporadic E occurrence using altitude resolved measurements. Incoherent scatter radar provides direct altitude resolved measurements of the E-region ionosphere with relatively high altitude resolution. Since 2008, the Poker Flat Incoherent Scatter Radar (PFISR) has been operating in nearly continuous operations through a low duty cycle mode, thus enabling observations of sporadic E. The distinction between Es and auroral precipitation is detectable and is generally associated with the differences in structure height with Es being on average smaller in altitudinal range and shorter time duration. The purpose of this investigation is to present observations of sporadic E derived from this nearly continuous database of alternating code and Barker code PFISR data spanning the years from 2007-2021. We visually identified the sporadic E layers and have found approximately 300 events. We present statistical results of the occurrence, duration, and characteristics of high latitude sporadic E derived from these events. The preponderance of events manifested within 95 to 120 km, typically lasted 1 to 3 hours, and mostly occurred during May through September with observance peaking in July. In addition, the trends indicated a potential disconnect between sporadic-E events and auroral activity, which was previously considered the primary driving force behind high latitude sporadic-E events. The climatology of high latitude sporadic E is an important contribution that must be considered in future high latitude models of the ionosphere.

The Pedersen component of the Lorentz force produces an acceleration that is generally in the zonal direction in much of the dawn and dusk sectors in the auroral oval. During disturbed conditions, as the neutral flow begins to accelerate and the flow speeds increase, a balance develops in the meridional direction between the Coriolis, curvature, and pressure gradient forces, which are dominant in the lower thermosphere. The gradient wind equation that describes this balance predicts that the cyclonic flow on the dawn side is limited to the so-called regular solution, which has a maximum value of twice the geostrophic wind speed. The anticyclonic flow on the dusk side, on the other hand, can satisfy either the regular or anomalous solution with a transition at twice the geostrophic wind speed. The anomalous flow solutions have wind speeds significantly greater than the transition value, but are limited by the inertial wind value, i.e., the value that corresponds to a balance between the curvature and Coriolis forces. The analysis is carried out to show this result, which indicates that a significant quantitative asymmetry is expected between the dawn- and dusk-side flow, as is observed and has been shown in both observations and a number of numerical modeling studies. Implications for the wind distribution of perturbed pressure gradients and inertial instability are discussed.

In this presentation, we seek to understand the altitudinal response of the auroral E-region neutral wind to substorms using observations from the Poker Flat Incoherent Scatter Radar (PFISR). Zou et al. (2009) presented different nighttime ion drift pattern associated with three different types of substorm events whose onset locations were at, to the east and to the west of PFISR. In addition, Zou et al. (2021) presented different types of latitudinal responses of the F-region neutral wind to substorm events and suggested that the response is highly local time dependent. While these two studies give much insight on the F region ion and neutral responses during substorm events, the E region neutral wind response is not well-understood. Previous studies showed that during disturbed conditions E-region winds, in particular below 110 km, are larger than what tidal theory predicts, while the winds in the upper E-region shows strong impacts from the convection flow. We select events whose onset locations are over the PFISR radar site, but in different MLT sectors using the SuperMag data product during 2010-2019. We present a superimposed epoch analysis of three different types of events after subtracting the quiet background neutral winds. This study will further our understanding of the contribution in a statistical view from forces that are associated with the E-region wind variation during substorm events during different MLT sectors and spanning the altitude range from 90-130 km.

Quantification of energetic electron precipitation caused by wave-particle interactions is fundamentally important to understand the cycle of particle energization and loss of the radiation belts. One important way to determine how well the wave-particle interaction models predict losses through pitch-angle scattering into the atmospheric loss cone is the direct comparison between the ionization altitude profiles expected in the atmosphere due to the precipitating fluxes and the ionization profiles actually measured with incoherent scatter radars. This paper reports such a comparison using a forward propagation of loss-cone electron fluxes, calculated with the electron pitch angle diffusion model applied to Van Allen Probes measurements, coupled with the Boulder Electron Radiation to Ionization (BERI) model, which propagates the fluxes into the atmosphere. The density profiles measured with the Poker Flat Incoherent Scatter Radar operating in modes especially designed to optimize measurements in the D-region, show multiple instances of quantitative agreement with predicted density profiles from precipitation of electrons caused by wave-particle interactions in the inner magnetosphere. There are two several-minute long intervals of close prediction-observation approximation in the 65-93 km altitude range. These results indicate that the whistler wave-electron interactions models are realistic and produce precipitation fluxes of electrons with energies between 10 keV to >100 keV that are consistent with observations.

We report one of the first comprehensive ground-based investigations of energy transfer rates in the E-region ionosphere compared relative to geomagnetic activity, seasonal effects, and solar activity level using nearly continuously sampled data collected with the Poker Flat Incoherent Scatter Radar (PFISR) between 2010-2019. We quantified the integrated electromagnetic (EM) energy transfer rate and the integrated Joule heating rate in the E-region between 90-130 km, which includes the contributions from the neutral winds. We find that (1) the median Joule heating rate and electromagnetic (EM) energy transfer rate in the evening sector is larger in the winter versus the summer and have similar magnitudes in the spring and fall for the same solar activity and geomagnetic conditions. (2) The seasonal dependence of the energy transfer rates is closely associated with the seasonal variations of the electric fields. Our analysis shows that the larger EM energy transfer and Joule heating rates in disturbed conditions in the winter versus the summer are associated with the combined effects of both the electric field and Pedersen conductance with the electric field playing a dominant role. Given that the Pedersen conductance in the evening sector is closely related to the particle precipitation and field-aligned currents in the auroral region, this study provides complementary ionospheric evidence of the winter-summer asymmetry of the intensity and density of field-aligned currents (e.g. Ohtani et al., 2009). (3) The geomagnetic activity level has the most significant impacts on the magnitude of the energy transfer rates, followed by seasonal variations, and last the solar activity level.