Richard Alexander Doe

Initial comparison of POLAR UVI and Sondrestrom IS radar estimates for auroral electron energy flux

Calibrated images from the POLAR satellite ultraviolet imager (UVI) in the 165.5 to 174.5 nm portion of the N2 Lyman-Birge-Hopfield band (LBH-long) can be used to estimate the energy flux (FE) of auroral electrons precipitating into the high-latitude ionosphere. Similarly, electron density profiles, as measured by ground-based incoherent-scatter radar, can be used to estimate FE and mean energy (Eo) by solving a system of linear equations relating the E-region ionization rate profile to a family of monoenergetic ion production profiles. A coordinated POLAR/Sondrestrom radar experiment, designed as an initial comparison of POLAR UVI and ground-based estimates of FE for a stable auroral arc, was executed during a POLAR apogee on May 20, 1996 at the Sondrestrom radar facility (lat. 66.99°N, long. 50.95°W). Reconstructed energy distributions, based on radar-measured Ne profiles, indicate an approximately 2 keV Maxwellian source with an energy flux of from 6.4 to 14 mW m−2. LBH-long images, binned over 0.5° of latitude and 1.0° of longitude, were used to derive energy flux as well. The UVI-derived FE time history agrees favorably with radar estimates both in absolute magnitude and in the trend for this period. This experiment suggests that reliable estimates for the precipitating electron source energy and its ionospheric response can be derived from either ground-based radar or POLAR UVI images during summertime conditions.

Observations of persistent dayside F region electron temperature enhancements associated with soft magnetosheathlike precipitation

A series of experiments with the Sondrestrom incoherent scatter (IS) radar (66.99°N latitude, 50.95°W longitude) were designed to examine F region structure in the dayside auroral oval in order to search for plasma signatures from magnetospheric regions such as the cusp, boundary plasma sheet, low-latitude boundary layer, and mantle. This IS radar mode, optimized to search for ionospheric features which remain fixed in local time, was coordinated with overflights of the DMSP F-10 satellite on 2 days in September 1992. For both study days, IS radar data show persistent (∼ 7 hour), enhanced T e regions at 300 to 500 km. These enhanced T e regions evolve during periods in which relatively unstructured, laminar N e densities are observed and thus are not merely the result of a structured suppression of electron cooling. The cores of these T e enhancements were observed at latitudes and magnetic local times corresponding to DMSP satellite measurement of soft (< 100 eV) cusplike precipitation. These T e hotspots move systematically equatorward with increasing geomagnetic activity and display a sharp field-aligned equatorward edge at the location of satellite cusp detection. Unlike prior IS radar/satellite cusp investigations, no significant N e enhancements were measured coincident with T e hotspots. A simple ionospheric model is invoked to confirm that such soft cusplike precipitation does not significantly alter the magnitude of the ambient plasma density, and we argue that cusp detection based on collocated N e and T e enhancements is seldom possible. The local time persistence of the T e enhancements, beyond the typical cusp widths, suggests an association with additional dayside magnetospheric regimes such as the low-latitude boundary layer. Both latitudinal and vertical T e gradients maximize at the location of satellite cusp detection, suggesting that the heat source is a divergence of magnetospheric heat flux on freshly reconnected geomagnetic field lines.

Tomographic reconstruction of 630.0 nm emission structure for a polar cap arc

Monochromatic imagers located at two sites in the Canadian Arctic were operated concurrently during the poleward transit of a duskside sun-aligned polar cap arc on 19 February 1996. The arc was observed by both stations in 630.0 nm images over a 5-min period. Profiles of 630.0 nm brightness versus elevation angle were extracted from pairs of images along a great circle defined by the two ground stations. These data were then supplied as inputs to a tomographic reconstruction for the arc-related 630.0 nm volume emission rate in a vertical (latitude vs. altitude) plane: η630 (lat,z). The time evolution of η630 (lat,z) structure for this polar cap arc indicates that a modification to the electron source energy distribution and not a thermospheric process (such as neutral heating and plasma diffusion/decay) controlled the arc-related 630.0 nm emission.

Ground‐based signatures for the nightside polar cap boundary

This work describes an application of incoherent scatter (IS) radar and all-sky imaging techniques to the identification of signatures for the nightside auroral zone/polar cap boundary. This identification is made by estimating the characteristic energy of precipitating electrons across all latitudes measured by the IS radar. The primary method used to discern the boundary is based on an algorithm wherein the detailed shape of E region ionization profiles is mapped to the required number flux from a library of monoenergetic ionization profiles. This procedure results in a reconstructed energy distribution for the precipitating electrons from which a characteristic energy is derived. The latitudinal gradient of the characteristic energy is subsequently used to identify the boundary. Monochromatic all-sky imagers are used to establish the time history of the boundary and estimate characteristic energy (at magnetic zenith). Additional plasma signatures such as auroral ionospheric cavities and localized F region Te enhancements are shown to provide contextual clues for the location of the boundary. Three in-depth case study periods are used to qualify the various boundary identification methods. A detailed study of 30 IS radar scans in the geomagnetic meridian is used to conclude that a latitudinal gradient in characteristic energy of −5 to −11 keV per degree, when measured adjacent to an extended region of low-energy precipitation, can locate the boundary with a latitudinal precision of 0.2°.

Energy transfer between the ionosphere and magnetosphere during the January 1997 CME event

This Letter shows that transient changes in convection and precipitation patterns can significantly influence the electromagnetic energy transfer between the magnetosphere and the ionosphere. At the times of the transient events during the 10 January 1997 storm that was produced by a Coronal Mass Ejection (CME)-related magnetic cloud, the Sondrestrom incoherent scatter radar measured the local electrodynamic response of the high-latitude ionosphere. Important discrepancies between the net electrodynamic energy flux and the electromagnetic energy flux estimated for a stationary atmosphere suggest that the assumption of the ionosphere as a purely resistive load is often inadequate during these transient events as neutral winds cannot conform to the new orientation of the electric field and thus impact the load/generator characteristics of the ionosphere.

Ionospheric electron heating by structured electric fields: Theory and experiment

Ionospheric electron heating due to structured electric fields is considered herein. In a survey of incoherent scatter (IS) radar data gathered with the Sondrestrom IS radar in Greenland (66.99°N, 50.95°W), we find that such heating takes place at F layer altitudes accompanying intense auroral events in the E layer. Because of competition with heating by precipitating particles this type of heated region can only be observed when it is shifted from the geomagnetic field line penetrating the associated E layer arc. We have detected regions of this sort in which we argue that the temperature is enhanced either by illumination of auroral ionospheric cavities by an Alfven wave source or by collocation with turbulent electrostatic fields. We have developed a model that predicts the observed Te enhancement in the F layer. We also present a consistent physical picture of auroral activity involving coupling between the magnetosphere and the ionosphere via electrostatic and wave- or turbulence-induced field-aligned currents. Both can be generated by the region surrounding the electron acceleration zone. Applying our model to the observations allows us to separate electron heating due to structured fields (with a pronounced maximum in the F layer), static field-aligned currents (with the electron temperature smoothly increasing with altitude from the F layer up to the magnetosphere), and electron impact in the E layer. In turn, the temperature observations give us information on the Alfven wave impinging on the auroral F layer and/or the turbulent electrostatic fields which map to the ionosphere.

Coordinated convection measurements in the vicinity of auroral cavities

Meridional radar scans of electron density from the Sondrestrom incoherent scatter radar (Greenland, 66.99°N, 50.95°W) have been used to identify latitudinally narrow, field-aligned depletions of the auroral F region ionosphere. Observations of these so-called auroral cavities have been reported in earlier case studies in close proximity to E layer arcs at the poleward edge of the nightside oval (Doe et al. 1993). These radar data indicated that the cavities and arcs remained as collocated pairs for periods as long as an hour, while coordinated imaging and satellite measurements indicated that the pairs were extended in magnetic local time

Nematic Fabry-Perot etalons for ground- and space-based atmospheric remote sensing

Birefringent, nematic liquid crystals (LC) have been laminated between the substrates of several Fabry-Perot etalons. The application of an electric field allows the effective index of refraction of the LC to be varied. A polymer alignment layer is used to align the crystals perpendicular to the optical axis of the Fabry-Perot etalon. An oscillating electric field is used to rotate the crystal around the optical axis of the etalon, effectively changing the index of refraction. This change in index is used to tune the Fabry-Perot etalon in a manner similar to traditional pressure and mechanical tuning systems. However, the approach described here has the advantage of producing a solid-state etalon that is tunable without needing a bulky pressure system or environmentally sensitive piezo-electric stacks. A two etalon spectrometer consisting of two Fabry- Perot etalons coupled to a CID detector has been developed. A suppression etalon with a gap of 10 micrometers , and a LC wit a refractive index of 1.63 are used in conjunction with a high resolution etalon to produce an instrument ideal for observing the atomic spectra of hot, light neutral species and the molecular bands in the atmosphere. Several other etalons have been constructed to further develop this technology. Clear apertures greater than 2 inches have been achieved, and a hybrid spacer technique has been developed to allow for etalons with spacings of up to 1 cm. Fabry- Perot partial reflective coatings capable of operation from the visible to the NIR will also be discussed.

Climate-monitoring CubeSat mission (CM2): a project for global mesopause temperature sensing

The goals of the Climate Monitoring CubeSat Mission (CM2) are to accelerate climate projection by obtaining global temperature, tidal and wave measurements with a simple CubeSat-based imaging spectrograph; and to demonstrate how a high-resolution imaging spectrograph can be deployed on a CubeSat satellite. In the middle atmosphere (50 - 100 km), beyond the reach of balloons or satellites, thermal signatures of CO2 radiation and wave activity have been largely missing from climate model inputs. This paper outlines an instrument to advance the state of the art in atmospheric climate projection by providing critical global measurements of middle-atmosphere temperatures and waves with a CubeSatscale imaging spectrograph. The CM2 will remotely sense middle-atmosphere temperatures and waves at ~90 km by analyzing spectra of intrinsically bright molecular oxygen emissions at near-infrared wavelengths in the O2 atmospheric band. The core instrument will be a miniaturized imaging spectrograph based on a monolithic spatial heterodyne spectrometer (SHS). This spectrograph will have sensitivity and spectral resolution to extract temperatures with 10° K precision and waves with 4 km scale resolution along a ~200 km cross-track swath. The SHS is significantly more robust than conventional interferometers, and thus better suited to space-based observation. Acquiring high-resolution middle-atmosphere temperature, tidal, and wave data on a daily, global basis will significantly improve climate models, and will help assess long-term greenhouse gas mitigation policy impact on upper-atmosphere thermal signatures. The CM2 program will also establish the efficacy of highresolution CubeSat-based broadband (near-IR to UV) spectroscopy for application to other atmospheric research missions.