R. L. Gattinger

Validation of O(1S) wind measurements by WINDII: the WIND Imaging Interferometer on UARS

This paper describes the current state of the validation of wind measurements by the wind imaging interferometer (WINDII) in the O(1S) emission. Most data refer to the 90-to-110-km region. Measurements from orbit are compared with winds derived from ground-based observations using optical interferometers, MF radars and the European Incoherent-Scatter radar (EISCAT) during overpasses of the WINDII fields of view. Although the data from individual passes do not always agree well, the averages indicate good agreement for the zero reference between the winds measured on the ground and those obtained from orbit. A comparison with winds measured by the high resolution Doppler imager (HRDI) instrument on UARS has also been made, with excellent results. With one exception the WINDII zero wind reference agrees with all external measurement methods to within 10 m s−1 at the present time. The exception is the MF radar winds, which show large station-to-station differences. The subject of WINDII comparisons with MF radar winds requires further study. The thermospheric O(1S) emission region is less amenable to validation, but comparisons with EISCAT radar data give excellent agreement at 170 km. A zero wind calibration has been obtained for the O(1D) emission by comparing its averaged phase with that for O(1S) on several days when alternating 1D/1S measurements were made. Several other aspects of the WINDII performance have been studied using data from on-orbit measurements. These concern the instruments phase stability, its pointing, its responsivity, the phase distribution in the fields of view, and the behavior of two of the interference filters. In some cases, small adjustments have been made to the characterization database used to analyze the atmospheric data. In general, the WINDII characteristics have remained very stable during the mission to date. A discussion of measurement errors is included in the paper. Further study of the instrument performance may bring improvement, but the utimate limitation for wind validation appears to be atmospheric variability and this needs to be better understood.

Longitudinal structure in atomic oxygen concentrations observed with WINDII on UARS

WINDII, the Wind Imaging Interferometer on the Upper Atmosphere Research Satellite, began atmospheric observations on September 28, 1991 and since then has been collecting data on winds, temperatures and emissions rates from atomic, molecular and ionized oxygen species, as well as hydroxyl. The validation of winds and temperatures is not yet complete, and scientific interpretation has barely begun, but the dominant characteristic of these data so far is the remarkable structure in the emission rate from the excited species produced by the recombination of atomic oxygen. The latitudinal and temporal variability has been noted before by many others. In this preliminary report on WINDII results we draw attention to the dramatic longitudinal variations of planetary wave character in atomic oxygen concentration, as reflected in the OI 557.7 nm emission, and to similar variations seen in the Meinel hydroxyl band emission.

Comparison of ground-based optical observations of N2 second positive to N2 + first negative emission ratios with electron precipitation energies inferred from the Sondre Stromfjord radar

Optical emission ratios of the N2 Second Positive Group 0,0 band to N2+ First Negative Group 0,0 band were observed in the magnetic zenith at Sondre Stromfjord in parallel with radar observations of the electron density height profile. The dependence of the optical ratios on the inferred incident electron energies was investigated to assess whether the ratios could be used as an electron energy monitor. Analysis procedures were developed to minimize the effects of atmospheric scattering as well as spectral blending with other emission features. Two independent computational techniques for inferring the electron energies from the electron density profiles were compared and found to agree sufficiently well for the current study. The observed optical emission ratios were found to vary by less than 15% over the incident electron energy range from 2 to 12 keV. Comparisons were made with the ratios predicted by several auroral electron deposition models.

A comparison between auroral particle characteristics and atmospheric composition inferred from analyzing optical emission measurements alone and in combination with incoherent scatter radar measurements

On day 59 of 1987 a well calibrated set of photometric observations of auroral emissions (427.8, 630.0, 844.6, and 871.0 nm) was obtained at Sondre Stromfjord, Greenland coincident with incoherent scatter radar measurements of electron density. Ratios of these optical emissions were used to correct for atmospheric extinction and to infer the average energy of the precipitating electrons and the deviations in the atmospheric composition induced by auroral heating. Previously, the radar data taken alone had been used to infer the average energy of the auroral particles. For the first time a comparison is made of the results from this optical ratio technique with those obtained by combining the optical data with the radar data and with results obtained using the radar data alone. Specifically, we compare the average energy inferred by these techniques as well as the changes in the atomic oxygen to molecular nitrogen ratio in the lower thermosphere. This study shows the critical importance of characterizing the atmospheric scattering if reliable results are to be derived. In particular, it is shown that on occasion the optical technique may be even more reliable than using radar and optics together since, because of light scattering, the radar and the optics are sometimes observing different parts of the aurora. Magnetometer data are used to estimate local Joule heating. The combined data are also used to address the question of whether observed composition changes were produced locally.

Indirect Excitation Processes in Aurora

Indirect excitation processes for auroral emissions are briefly reviewed. New ground based measurements of height effects for the 1, 1 O2 Atmospheric band in auroral arcs are presented. These measurements are shown to be in quantitative agreement with the hypothesis of Wallace and Chamberlain (1959) that the v′ = 1 level of O2 (b1Σ) is excited primarily by energy transfer from O(1D) and deactivated vibrationally in collisions with O2.

Comments on the paper: diurnal, annual, and solar cycle variations of hydroxyl and sodium nightglow intensities in the Europe--Africa sector

Abstract Night-time variations of the OH nightglow intensity reported by Wiens and Weill are compared with the theoretical predictions of a number of models. The behaviour of this emission agrees better with the theoretical one for locations in the equatorial zone but becomes more variable and less predictable for mid-latitude stations. It is calculated that, as a result of an increase of the eddy diffusion coefficient K, the OH emission can deviate from the typical night-time variation and increase by a factor as high as 2 if K is multiplied by 10. It is suggested that the eddy diffusion coefficient in the upper atmosphere is lower and undergoes lower amplitude variations in the equatorial zone than in the mid-latitude regions.

Observation and Interpretation of Hydroxyl Airglow Emissions

The observation and interpretation of a number of interesting features associated with the OH airglow emissions are discussed. Correlations between magnetic activity and OH emission brightness as well as O2 1.27 μm band brightness are considered. Correlations between the brightness of the O2 1.27 μm band and the brightness of the OH and OI(5577 A) airglow emissions are also considered with references made to possible excitation mechanisms. Observational evidence which tends to confirm the possible existence of a nonequilibrium distribution in the population of the rotational levels of excited OH molecules in the atmosphere is presented.

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.

Observed Intensity Ratios of the N2 1PG Bands in Aurora

In evaluating the relative importance of direct electron impact vs. cascading in the excitation of the N2 first positive (1PG) system it is necessary to measure accurately the relative intensities of bands from as many different v′ levels as possible to establish the relative populations. Gattinger and Vallance Jones (1974) have obtained measurements of the vibrational development of the system in medium intensity aurora, and have compared their results with various theoretical distributions. Vallance Jones and Gattinger (1972) made similar but less comprehensive measurements on bright aurora and arrived at ratios for I(1,0):I(2,1):I(3,2) which were quite different from those determined in the later paper (Table I).

Near-ultraviolet limb imaging spectrograph for sounding rockets

As part of an ongoing investigation of airglow emissions of the upper atmosphere, an intensified CCD imaging spectrograph has been developed for a sounding rocket project called GEMINI (general excitation mechanisms in nightglow). The instrument, known as LISA (limb-imaging spectrograph for airglow), will be used to measure the limb profiles of some important nighttime airglow emission features. The observed limb profiles will be analyzed to provide atmospheric temperatures and density profiles of excited atomic and molecular species of interest to specific modeling problems in the mesopause and lower thermosphere. The GEMINI rocket is to be launched from White Sands Missile Range, New Mexico, in late 1993 or early 1994. The payload will be three-axis stabilized and absolute pointing will be derived from a star video camera. The authors describe the design capabilities of the LISA instrument, which include a spectral range of 310 to 390 nm, a wavelength resolution of [approximately]0.3 nm, a height resolution of 1 km, and a theoretical count rate of 0.04 count R[sub [minus]1] s[sub [minus]1], where R represents rayleighs. The imager design is discussed and they present the results of some laboratory test performed by means of an artificial source of the oxygen nightglow emission.