We present an overview of the capabilities of LeoLabs’ Kiwi Space Radar (KSR), our recently completed S-band radar located in New Zealand. KSR provides high precision range and doppler velocity measurements of Resident Space Objects in Low-Earth Orbit down to radar cross-sections of -34dBsm. We perform a quantitative analysis of the measurement precision of the radar, its impact on our orbital tracking of LEO objects, and its ability to measure previously untracked RSOs. KSR is the first of several S-band radars that LeoLabs is building, and we present the anticipated performance of our world-wide network of radars when completed.

The Sun's connection with the Earth's magnetic field and atmosphere is carried out through the exchange of electromagnetic and mass flux and is regulated by a complex interconnection of processes. During space weather events, solar flares, or fast streams of solar atmosphere strongly disturb the Earth's environment. Often the electric currents that connect the different parts of the Sun-Earth system become unstable and explosively release the stored electromagnetic energy in one of the more dramatic expressions of space weather-the geomagnetic storm and substorm. Some aspects of the magnetosphere-ionosphere connection that generates auroral arcs during space weather events are well-known. However, several fundamental problems remain unsolved because of the lack of unambiguous identification of the magnetic field connection between the magnetosphere and the ionosphere. The correct mapping between different regions of the magnetosphere and their foot-points in the ionosphere, coupled with appropriate distributed measurements of plasma and fields in focused regions of the magnetosphere, is necessary to establish unambiguously that a given magnetospheric process is the generator of an observed arc. We present a new paradigm that should enable the resolution of the mapping ambiguities. The paradigm calls for the application of energetic electron beams as magnetic field tracers. The three most important problems for which the correct magnetic field mapping would provide closure to are the substorm growth phase arcs, the expansion phase onset arcs and the system of arcs that emerge from the magnetosphere-ionosphere connection during the development of the early substorm expansion phase phenomenon known as substorm current wedge (SCW). In this communication we describe how beam tracers, in combination with distributed measurements in the magnetosphere, can be used to disentangle the mechanisms that generate these critical substorm phenomena. Since the application of beams as tracers require demonstration that the beams can be injected into the loss cone, that the spacecraft potentials induced by the beam emission are manageable, and that sufficient electron flux reaches the atmosphere to be detectable by optical or radio means after the beam has propagated thousands of kilometers under competing effects of beam spread and constriction as well as effects of beam-induced instabilities, in this communication we review how these challenges are currently being addressed and discuss the next steps toward the realization of active experiments in space using relativistic electron beams.

Near-continuous electron density measurements obtained over a similar to 3 year period, 2010-2013, using the Poker Flat Incoherent Scatter Radar (PFISR) in central Alaska (69 degrees N, 147 degrees W) have been analyzed to quantify the properties of over 650 high-latitude medium-scale traveling ionospheric disturbances (MSTIDs). Our analysis focused on the altitude range 100-300 km encompassing the lower ionosphere/thermosphere and yielded first full seasonal day/night distributions of MSTIDs at high northern latitudes with mean values: horizontal wavelength 446 km, horizontal phase speed 187 m/s, and period 41 min. These year-round measurements fill an important summertime gap in existing MSTID measurements revealing predominantly eastward wave propagation during the summer, while continued winter season observations agree well with previous reports of near southward propagating MSTIDs. Our 3 years of results suggest a cyclic change in the seasonal horizontal propagation directions that was found to be quantitatively consistent with critical level wind and dissipative filtering. Concurrent measurements of the vertical wavelength spectrum as a function of altitude also compared favorably in shape with that calculated using a theoretical dispersion relation (Vadas & Fritts, 2005, https://doi.org/10.1029/2004JD005574) for the thermosphere, but with a higher mean value. Evidence supporting the systematic broadening and shrinking in the azimuthal distributions of the MSTIDs during the course of the year was also found, as well as an unexpected correlation between the MSTID propagation directions and the AE index, both of which are under further investigation.

The Earth's ionosphere plays an important role in supplying plasma into the magnetosphere through ion upflow/outflow, particularly during periods of strong solar wind driving. An intense ion upflow flux event during the 1 June 2013 storm has been studied using observations from multiple instruments. When the open-closed field line boundary (OCB) moved into the Poker Flat incoherent scatter radar (PFISR) field of view, divergent ion fluxes were observed by PFISR with intense upflow fluxes reaching similar to 1.9 x 10(14)m(-2) s(-1) at similar to 600 km altitude. Both ion and electron temperatures increased significantly within the ion upflow, and thus, this event has been classified as a type 2 upflow. We discuss factors contributing to the high electron density and intense ion upflow fluxes, including plasma temperature effect and preconditioning by storm-enhanced density (SED). Our analysis shows that the significantly enhanced electron temperature due to soft electron precipitation in the cusp can reduce the dissociative recombination rate of molecular ions above similar to 400 km and contributed to the density increase. In addition, this intense ion upflow flux event is preconditioned by the lifted F region ionosphere due to northwestward convection flows in the SED plume. During this event, the OCB and cusp were detected by DMSP between 15 and 16 magnetic local times, unusually duskward. Results from a global magnetohydrodynamics simulation using the Space Weather Modeling Framework have been used to provide a global context for this event. This case study provides a more comprehensive mechanism for the generation of intense ion upflow fluxes observed in association with SEDs.

For companies with multiple orbital assets, managing the risk of collision with other low-Earth orbit (LEO) Resident Space Objects (RSOs) can amount to a significant operational burden. LeoLabs and Planet investigate the impact of a workflow that integrates commercial Space Situational Awareness (SSA) data into conjunction assessments for large satellite constellations. Radar measurements from LeoLabs are validated against truth orbits provided by the International Laser Ranging Service (ILRS) and to measurements from Planet’s on-board GPS instrumentation. The radar data is then used as input for orbit fits in order to form the basis of a conjunction assessment. To confirm the reliability of the orbit determination (OD), the generated ephemerides are validated against ILRS and GPS-derived orbits. In addition, a covariance realism assessment is performed in order to check for self-consistency by comparing the propagated orbit and the associated covariance against later measurements. Several cases are investigated to assess the benefits of integrating radar-derived products with Conjunction Data Messages (CDMs) received on Planet spacecraft. Conjunction assessment is refined using onboard GPS measurements from Planet satellites along with tracking measurements of the secondary RSO by LeoLabs. This study demonstrates that commercial data provided by LeoLabs is reliable, accurate, and timely, and that ephemeris generated from LeoLabs data provides solutions and insights which are consistent with those provided in CDMs. For the cases analyzed, the addition of commercial SSA data from LeoLabs has a positive impact on operations due to the additional information on the state of the secondary RSO which can lead to increased confidence in any maneuver-related decisions. Measurements from LeoLabs can also be used to improve conjunction assessment for commercial satellites that do not have any operator OD.

We have combined radar observations and auroral images obtained during the Poker Flat Incoherent Scatter Radar Ion Neutral Observations in the Thermosphere campaign to show the common occurrence of westward moving, localized auroral brightenings near the auroral equatorward boundary and to show their association with azimuthally moving flow bursts near or within the subauroral polarization stream (SAPS) region. These results indicate that the SAPS region, rather than consisting of relatively stable proton precipitation and westward flows, can have rapidly varying flows, with speeds varying from similar to 100m/s to similar to 1km/s in just a few minutes. The auroral brightenings are associated with bursts of weak electron precipitation that move westward with the westward flow bursts and extend into the SAPS region. Additionally, our observations show evidence that the azimuthally moving flow bursts often connect to earthward (equatorward in the ionosphere) plasma sheet flow bursts. This indicates that rather than stopping or bouncing, some flow bursts turn azimuthally after reaching the inner plasma sheet and lead to the bursts of strong azimuthal flow. Evidence is also seen for a general guiding of the flow bursts by the large-scale convection pattern, flow bursts within the duskside convection being azimuthally turned to the west, and those within the dawn cell being turned toward the east. The possibility that the SAPS region flow structures considered here may be connected to localized flow enhancements from the polar cap that cross the nightside auroral poleward boundary and lead to flow bursts within the plasma sheet warrants further consideration.

The sensitivity of radar systems to detect different velocity populations of the incoming micrometeoroid flux is often the first argument considered to explain disagreements between models of the Near-Earth dust environment and observations. Recently, this was argued by Nesvorný et al. to support the main conclusions of a Zodiacal Dust Cloud (ZDC) model which predicts a flux of meteoric material into the Earth's upper atmosphere mostly composed of small and very slow particles. In this paper, we expand on a new methodology developed by Janches et al. to test the ability of powerful radars to detect the meteoroid populations in question. In our previous work, we focused on Arecibo 430 MHz observations since it is the most sensitive radar that has been used for this type of observation to date. In this paper, we apply our methodology to two other systems, the 440 MHz Poker Flat Incoherent Scatter Radar and the 46.5 Middle and Upper Atmosphere radar. We show that even with the less sensitive radars, the current ZDC model over-predicts radar observations. We discuss our results in light of new measurements by the Planck satellite which suggest that the ZDC particle population may be characterized by smaller sizes than previously believed. We conclude that the solution to finding agreement between the ZDC model and sensitive high power and large aperture meteor observations must be a combination of a re-examination not only of our knowledge of radar detection biases, but also the physical assumptions of the ZDC model itself.

Anomalous incoherent scatter radar (ISR) spectra confined to narrow altitude ranges near the F region peak and correlated with dynamic auroral precipitation have previously been identified and explained in terms of the cavitating beam-driven Langmuir turbulence. In this work we used a one-dimensional Zakharov simulation to constrain the range of physical mechanisms underlying these observational features. We find that although Langmuir wave collapse and caviton formation generated by electron beams with energies of 1keV can give rise to similar radar echoes, the predicted spectral features and intensities of such echoes are inconsistent with experimental data acquired by various ISRs. Our results suggest that the free energy for the turbulence must be provided by unstable low-energy (5-20eV) electron populations and that such populations must be produced locally in the F region ionosphere.

Common volume measurements by the Resolute Bay Incoherent Scatter Radar‐North (RISR‐N) and Optical Mesosphere and Thermosphere Imagers (OMTI) have been used to clarify the electrodynamic structure of a Sun‐aligned arc in the polar cap. The plasma parameters of the dusk‐to‐dawn drifting arc and surrounding ionosphere are extracted using the volumetric imaging capabilities of RISR‐N. Multipoint line‐of‐sight RISR‐N measurements of the plasma drift are inverted to construct a time sequence of the electric field and field‐aligned current system of the arc. Evidence of dramatic electrodynamic and plasma structuring of the polar cap ionosphere due to the arc is described. One notable feature of the arc is a meridionally extended plasma density depletion on its leading edge, located partially within a downward field‐aligned current region. The depletion is determined to be a by‐product of enhanced chemical recombination operating on a time scale of 15 min. A similarly shaped electric field structure of over 100 mV/m and line‐of‐sight ion temperatures nearing 3000 K were collocated with the depletion.

A new, 14-panel Advanced Modular Incoherent Scatter Radar (AMISR-14) system was recently deployed at the Jicamarca Radio Observatory. We present results of the first coherent backscatter radar observations of equatorial spread F(ESF) irregularities made with the system. Colocation with the 50MHz Jicamarca Unattended Long-term studies of the Ionosphere and Atmosphere (JULIA) radar allowed unique simultaneous observations of meter and submeter irregularities. Observations from both systems produced similar Range-Time-Intensity maps during bottom-type and bottomside ESF events. We were also able to use the electronic beam steering capability of AMISR-14 to image scattering structures in the magnetic equatorial plane and track their appearance, evolution, and decay with a much larger field of view than previously possible at Jicamarca. The results suggest zonal variations in the instability conditions leading to irregularities and demonstrate the dynamic behavior of F region scattering structures as they evolve and drift across the radar beams.

We present three case studies that examine optical and radar methods for specifying precipitating auroral flux parameters and conductances. Three events were chosen corresponding to moderate nonsubstorm auroral activity with 557.7 nm intensities greater than 1kR. A technique that directly fits the electron number density from a forward electron transport model to alternating code incoherent scatter radar data is presented. A method for determining characteristic energy using neutral temperature observations is compared against estimates from the incoherent scatter radar. These techniques are focused on line‐of‐sight observations that are aligned with the local geomagnetic field. Good agreement is found between the optical and incoherent scatter radar methods for estimates of the average energy, energy flux, and conductances. The Pedersen conductance predicted by Robinson et al. (1987) is in very good agreement with estimates calculated from the incoherent scatter radar observations. However, we present an updated form of the relation by Robinson et al. (1987), ΣH/ΣP=0.57〈E〉0.53, which was found to be more consistent with the incoherent scatter radar observations. These results are limited to similar auroral configurations as in these case studies. Case studies are presented that quantify auroral electron flux parameters and conductance estimates which can be used to specify the magnitude of energy dissipated within the ionosphere resulting from magnetospheric driving.

The Resolute Bay Incoherent Scatter Radar North (RISR-N) data collected between January 2012 and June 2013 are employed to identify and analyze 14 events with significant plasma density depressions (N-e<4 x 10(10) m(-3)) in the winter polar cap ionosphere. The RISR-N observations near a magnetic latitude (MLAT) of 85 degrees N refer to the region poleward of the previously identified polar hole-auroral cavity region 70 degrees-80 degrees MLAT where extremely low densities (down to 2 x 10(8) m(-3) near 300 km in altitude) are found at times. Multipoint observations by RISR-N are also characterized by multiple series of propagating local density enhancements (plasma structures) both well outside and in the vicinity of polar holes. A superposed epoch analysis of plasma density and convection reveals that the density depressions tend to reach their minimum near the reversal of the meridional convection component. The wavelet analysis of plasma density time series shows that the wave power is enhanced within the depressions and tends to peak near the density minimum. The plasma structures are more elongated at mesoscales (>150 km), with no apparent differences between structure shapes outside and inside low-density regions. The structure propagation velocity is perpendicular to its elongation direction and consistent with that of the large-scale plasma convection. The observations indicate that large-scale density depressions can form under a variety of convection conditions and that plasma structuring processes outside the depressions may be responsible for their partial filling.

The second Radio Aurora Explorer (RAX‐2) satellite has completed more than 30 conjunction experiments with the Advanced Modular Incoherent Scatter Radar chain of incoherent scatter radars in Alaska and Resolute Bay, Canada. Coherent radar echoing occurred during four of the passes: three when E region electron drifts exceeded the ion acoustic speed threshold and one during HF heating of the ionosphere by the High Frequency Active Auroral Research Program heater. In this paper, we present the results for the first three passes associated with backscatter from natural irregularities. We analyze, in detail, the largest drift case because the plasma turbulence was the most intense and because the corresponding ground‐to‐space bistatic scattering geometry was the most favorable for magnetic aspect sensitivity analysis. A set of data analysis procedures including interference removal, autocorrelation analysis, and the application of a radar beam deconvolution algorithm mapped the distribution of E region backscatter with 3 km resolution in altitude and ∼0.1° in magnetic aspect angle. To our knowledge, these are the highest resolution altitude‐resolved magnetic aspect sensitivity measurements made at UHF frequencies in the auroral region. In this paper, we show that despite the large electron drift speed of ∼1500 m/s, the magnetic aspect sensitivity of submeter scale irregularities is much higher than previously reported. The root‐mean‐square of the aspect angle distribution varied monotonically between 0.5° and 0.1° for the altitude range 100–110 km. Findings from this single but compelling event suggest that submeter scale waves propagating at larger angles from the main E×B flow direction (secondary waves) have parallel electric fields that are too small to contribute to E region electron heating. It is possible that anomalous electron heating in the auroral electrojet can be explained by (a) the dynamics of those submeter scale waves propagating in the E×B direction (primary waves) or (b) the dynamics of longer wavelengths.

Recent model development of the Zodiacal Dust Cloud (ZDC) model (Nesvorný et al. 2010, 2011b) argue that the incoming flux of meteoric material into the Earth's upper atmosphere is mostly undetected by radars because they cannot detect small extraterrestrial particles entering the atmosphere at low velocities due to the relatively small production of electrons. In this paper we present a new methodology utilizing meteor head echo radar observations that aims to constrain the ZDC physical model by ground-based measurements. In particular, for this work, we focus on Arecibo 430 MHz observations since this is the most sensitive radar utilized for this type of observations to date. For this, we integrate and employ existing comprehensive models of meteoroid ablation, ionization and radar detection to enable accurate interpretation of radar observations and show that reasonable agreement in the hourly rates is found between model predictions and Arecibo observations when: 1) we invoke the lower limit of the model predicted flux (~16 t/d) and 2) we estimate the ionization probability of ablating metal atoms using laboratory measurements of the ionization cross sections of high speed metal atom beams, resulting in values up to two orders of magnitude lower than the extensively utilized figure reported by Jones (1997) for low speeds meteors. However, even at this lower limit the model over predicts the slow portion of the Arecibo radial velocity distributions by a factor of 3, suggesting the model requires some revision.

Winds in the thermosphere are highly important for transporting mass, momentum, and energy over the globe. In the high-latitude region, observations show that ion and neutral motions are strongly coupled when the aurora is present but the coupling is less evident when there is no aurora. In this study, we investigate the ability of the Global Ionosphere-Thermosphere Model (GITM) to simulate the mesoscale wind structure over Alaska during a substorm. Thirteen distinct numerical simulations of a substorm event that occurred between 02:00 and 17:00 Universal Time on 24 November 2012 have been performed. Distinct drivers considered include the Weimer and SuperDARN potential patterns and the OVATION Prime and OVATION-SME auroral models. The effects of the boundary between the neutral wind dynamo calculation and the high-latitude imposed electric potential were also considered. Neutral wind velocities and thermospheric temperatures measured by the Scanning Doppler Imager instruments located at three locations in Alaska were compared to GITM simulation results, and electron densities within GITM were compared to data from the Poker Flat Incoherent Scatter Radar. It was found that the different drivers used between multiple simulations lead to various amounts of momentum coupling within the simulation, affecting the accuracy of the modeled neutral and ion flow patterns and the strength of electron precipitation at high latitudes. This affirms that better observations of auroral precipitation and electric fields are required to accurately understand and consistently reproduce the mesoscale neutral wind flow patterns and temperature structure in the high-latitude thermosphere.

Precipitating auroral electrons can produce discrete auroral arcs that contain signatures of the magnetospheric auroral source region. Differential number flux observations over two discrete aurorae were obtained by the Auroral Currents and Electrodynamics Structure sounding rocket mission, which successfully launched in 2009. These observations were made at E region altitudes of approximately 130 km. A model of precipitating auroral electrons as described by Evans (1974) was fit to the electron differential number flux obtained by the payloads, and parameters from the model were used to infer properties of the auroral source region. It is shown that the field‐aligned precipitating electrons were better fit by a kappa distribution function versus a Maxwellian distribution function for the equatorward side of the first, quasi‐stable, auroral arc crossing. The latter half of the first auroral arc crossing and second auroral crossing show that the precipitating electrons were better fit by a Maxwellian distribution function, which provides additional observational confirmation of previous studies. The low‐energy electron population determined by the Evans (1974) model was within a factor of 2 of the observed differential number flux. The source region parameters determined from fitting the model to the data were compared with relevant studies from sounding rockets and satellites. Our observations are consistent with the results of Kletzing et al. (2003) that the plasma sheet electrons mapping to auroral zone invariant latitudes are characterized by kappa distribution functions.