Vincent B Wickwar

The 6300 Å O1D airglow and dissociative recombination

Measurements of night-time 6300 A airglow intensities at the Arecibo Observatory have been compared with dissociative recombination calculations based on electron densities derived from simultaneous incoherent backscatter measurements. The agreement indicates that the nightglow can be fully accounted for by dissociative recombination. The comparisons are examined to determine the importance of quenching, heavy ions, ionization above the F-layer peak, and the temperature parameter of the model atmosphere. Comparable fits between the observed and calculated intensities are found for several available model atmospheres. The least-squares fitting process, used to make the comparisons, produces comparable fits over a wide range of combinations of neutral densities and of reaction constants. Yet, the fitting places constraints upon the possible combinations; these constraints indicate that the latest laboratory chemical constants and densities extrapolated to a base altitude are mutually consistent.

Chatanika Radar Measurements

The auroral ionosphere often differs from the mid- and low-latitude ionosphere due to the influx of energetic particles (primarily electrons) and the mapping of convection electric fields down the magnetic field lines from the magnetosphere. The auroral ionosphere can significantly affect the neutral atmosphere above about 100 km. This paper presents Chatanika Radar measurements related to the physics and chemistry of the atmosphere.

High-Resolution Observations of Electric Fields andF-Region Plasma Parameters in the Cleft Ionosphere

Details of the high-latitude ionosphere in the vicinity of the noon sector cleft have been examined using the Sondrestrom radar on April 18, 1983. An experiment combining azimuth and elevation scans was used to reveal the patterns of convection and F region temperature and density over a region of 1000 km diameter centered on the radar at 75°Λ. High-resolution line-of-sight observations have been used to produce detailed maps of the convection pattern and plasma transport each 20 minutes as the radar rotated through the noon sector during the 8 hour experiment. Patterns of electrostatic potential across the radar field of view reveal strong poleward and eastward convection in the morning sector several hours pre-noon, a region of low speed convection associated with the velocity convergence region, and high speed poleward and westward plasma transport from the afternoon sector into the region of cleft precipitation and polar cap entry near noon. The divergence of plasma flow at polar latitudes away from the cleft is seen in both the convection velocity and F region density data (poleward flow through the ionospheric cleft populates the polar cap with enhanced plasma density). A topside density trough is associated with the poleward edge of the strong afternoon convection toward noon where flow velocities approach 2000 m/s and a potential drop of 50 kV is seen across a 500 km region. The region of high-speed plasma entry into the polar cap was characterized by predominently northwestward directed flow on this day on which the IMF was directed away from the sun and Bz was near 0. Plasma entered polar latitudes across a rotational convection reversal which spanned at least 3 hours of local time in the noon sector. Low energy particle precipitation and an enhancement in the ionospheric electron temperature and density were observed at this convection reversal. High-resolution redar data revealed a region of multiple soft arcs aligned with the reversal and polar cap boundary in the post-noon sector.

New generation topside sounder

Having ionospheric electron density distributions as a function of height, latitude, longitude, and time under different conditions is essential for scientific, technical, and operational purposes. A satellite-based, swept-frequency, HF sounder can obtain electron density profiles on a global scale. We are developing a new generation HF sounder that employs recent developments in technology, electronics, and processing capabilities. It will provide global-scale electron density distributions, contours of fixed densities, maps of ƒoF2, hmax, etc. It will allow us to map irregularities, estimate anomalous propagation and conditions for ducting, determine angles of arrival, etc. It will also be able to perform various plasma diagnostics and, because of new flexibility, will be programmable from the ground to perform a variety of experiments in space. Need for such a system exists through the Department of Defense and several civilian agencies. Some of the novel features of the system include software-based design, direction of arrival estimation and synthetic aperture radar-type operation, onboard processing, and reconfigurable and flexible architecture with multimission capabilities.

Mapping the wind in the polar thermosphere a case study within the CEDAR Program

The thermosphere is that region of neutral atmosphere in which atmospheric constituents are gravitationally bound to the Earth but are barometrically distributed according to their molecular or atomic weights. Unlike the lower atmosphere, mixing processes a reweak, which allows each constituent gas to behave independently. The thermosphere begins at about 100-km-altitude and extends up to 500 km or beyond. The temperature increases with height throughout the layer, which is a stabilizing influence.

An Auroral Enhancement of O2λ1.27-μm Emission

Abstract The ground-level zenith radiance of the atmospheric emission at λ 1.27 μm was radiometrically observed to increase by a factor of approximately two with the onset of an IBC III + auroral breakup above Chatanika, Alaska, on 10 March 1975. Time-resolved optical spectra clearly show that the slow component of the enhancement is associated with the (0,0) band of the infrared atmospheric system of O 2 . Photometric and incoherent scatter radar data are used to define the energy-deposition profile and the absolute energy flux for the event. The magnitude of the O 2 λ 1.27- μm enhancement compares favourably with the predictions of an auroral excitation model which includes only secondary-electron excitation of molecular oxygen in the O 2 ( a 1 Δ g ) source term.

Conjugate photoelectrons at L = 5·6 and the 6300 Å postsunset enhancement

Abstract A series of simultaneous incoherent-backscatter and 6300 A tilting-filter photometer observations were made in the winter and early spring of 1972 at Chatanika, Alaska. These observations have been combined for magnetically quiet nights to deduce the presence of excitation by two sources in addition to dissociative recombination. The first appears to be a source that is steady for at least three hours, centered about local midnight, but that varies from night to night, taking on values between 10 and 40 Rayleighs for the nights in question. It is suggested that this source may be a flux of low-energy electrons or protons. The second source is impact excitation by electrons from the magnetic conjugate point. The emission due to this source appears to be small immediately after local sunset, rises to a maximum at about 92° conjugate solar zenith angle (CSZA), and then decreases to zero in the vicinity of 105° CSZA. The deduced intensities for this source at 92° CSZA are in the region of 15–30 Rayleighs for local F -layer critical frequencies of 3−2 MHz, respectively.

Ground-based Observations of O2+ 1N Band Enhancements Relative to N2+ 1N Band Emission

Abstract Spectrometric measurements in normal aurora of O2+ first negative (1N) and N2+ first negative (1N) emissions over the wavelength range 5175–5325 A have been obtained with coincident incoherent scatter radar measurements with both instruments pointed in the same direction, the geomagnetic zenith. A comparison of the inferred mean energies derived from the radar observations for several normal aurora was made with the spectral ratio I(O 2 + 1N; 2, 0) I(N 2 + 1N; 0, 3) obtained from the optical observations. The intensity ratio was found to decrease by nearly 40% from aurora with mean energy ∼ 10 keV to aurora with mean energy ∼ 2 keV. The altitude of the peak E-region electron density co-varied with the spectral ratio from ∼ 105 km for the harder aurora to ∼ 130 km for the softer aurora. The inferred rotational temperature from the matching synthetic spectra co-varied from 250 to 500 K over the same energy limits. Model analysis based on both mono-energetic and Maxwellian precipitating electron fluxes show reasonable agreement with the observed I(O 2 + 1N; 2, 0) I(N 2 + 1N; 0, 3) ratio when MSIS n(O2) and n(N2) densities corresponding to the experimental dates are used.