The N I 8680- and 8629-Angstrom multiplets have been observed in the midlatitude dayglow during moderate-to-high solar activity. A rocket-borne near-infrared spectrometer of 13.4-Angstrom resolution recorded spectra between 120 and 219 km. Analysis yielded altitude profiles of emissions including the N-2 first positive (1 PG) (2,1) band, the O-2 atmospheric (0,1) and (1,2) bands, and the N I 8680- and 8629-Angstrom multiplets. Photoelectron impact models adequately described the measured 1 PG profile but significantly underestimated the N I multiplet emission rates. It is suggested that the primary source of the multiplets is photodissociation of N-2. The contribution of this process was estimated from a model based on the shape of the N I 1200-Angstrom line's photoexcitation cross section. If the proposed excitation mechanism is correct, peak cross-section values for the 8680- and 8629-Angstrom multiplets would have to be 7.2 +/- 5.2 x 10(-20) and 5.7 +/- 3.2 X 10-(20) cm(2), respectively.

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 modelling 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. We 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-1 s-1, where R represents rayleighs. The imager design is discussed and we present the results of some laboratory tests performed by means of an artificial source of the oxygen night-glow emission.

We have investigated the relationship between the oxygen nightglow and the atomic oxygen density in the lower thermosphere. This was done using data from two sounding rocket experiments conducted over White Sands Missile Range (32°N, 106°W). The first flight was launched on 2 November 1978 while the second was launched on 7 December 1981. Both flights contained resonance lamps to measure the atomic oxygen density. The peak density in both cases was near 1.9 × 1011 cm−3. In addition, the 1978 flight contained a photometer to measure the 5577 Å green line while the 1981 flight contained photometers to measure the green line, the u.v. nightglow, and the 7620 Å (0,0) atmospheric band. We have used empirical models of these airglow features to compare with the O density measurements. In the case of the atmospheric band, excellent agreement is seen concerning the shape of the atomic oxygen profile, while some discrepancies were seen with the Herzberg band and the green line. In all cases, the absolute value of our peak O density appeared to be about 2.5 times lower, for a given airglow intensity, than previous measurements.

A discussion of the laboratory calibration, calibration simulation, and accuracy of a resonance fluorescence instrument for measuring oxygen atoms is given. The discussion demonstrates that a sensor can be calibrated with good accuracy to obtain in situ measurements of the oxygen density in the mesosphere/lower thermosphere. Oxygen data are reported from six rocket flights. These data represent four midlatitude flights and two auroral flights. There are two night and two day profiles for the midlatitude experiments. The maximum densities found from these sets of data in the 90–100 km regions are between 1.5 × 1011 cm−3 and 3.5 × 1011 cm−3. Agreement with the MSIS-86 model predictions is obtained for altitudes above 120 km for midlatitude flights. The auroral data are less than the model prediction by about a factor of 2. The data show structure that is probably indicative of gravity wave effects of a nominal 5 km vertical wavelength.

The HARP instrument is a hyperbolic electrostatic analyzer working in the retarding potential mode. It is the lowest-energy member of the ESTER particle detector family. The energy range extends from 0.25 eV to 850 eV for both electrons and ions. The eight viewing sectors are arranged in a fan-shaped geometry in the antisolar hemisphere. They are simultaneously sampled while energy is stepped over a maximum number of 75 logarithmically spaced channels. The instrument is intended for thermal and superthermal solar-wind electron observations during the cruise phase and — more importantly — for electron and ion observations in the Mars environment.

An observation of the u.v. nightglow between 2670 and 3040 Å was conducted over White Sands Missile Range on 22 October 1984. A 1 4 m spectrometer operating at 3.5 Å resolution viewed the Earth's limb at tangent heights between 90 and 110 km for 120 s. A total of 41 spectral scans of the nightglow were obtained with the brightest feature being the O 2 ( A 3 Σ u + − X 3 Σ g − ) Herzberg I bands. The data were sorted into two groups, one from the top side of the layer and one containing the emission peak, and compared with synthetic spectra. The deduced O 2 ( A 3 Σ u + ) vibrational distributions indicate that at low altitudes, the higher vibrational levels ( v ́ > 6) were relatively depleted; however, the magnitude of the vibrational shift is much less than that predicted from theories of vibrational relaxation. It is shown that increasing the electronic quenching of O 2 ( A 3 Σ g + ) with respect to the vibrational quenching can reduce the vibrational shift in the model and qualitatively explain the observations; however, several details of the vibrational distribution are not well reproduced.

THE highly elliptical orbits of the Phobos 2 spacecraft, early in February 1989, proved particularly useful for plasma and field investigations of the martian environment. The low-altitude (∼ 860 km) pericentres and the deep penetration into the magnetotail provided excellent opportunities to explore new and important regions. Here we present preliminary results of electron and ion measurements in the vicinity of Mars with the hyperbolic analyser in the retarding potential mode (HARP). HARP is a differential electrostatic analyser, simultaneously covering eight directions arranged in a fan-shaped geometry, in the anti-solar hemisphere. The angular resolution is ˜20°, the energy resolution ˜10%. During the first two elliptical orbits, to be discussed here, electrons from 3.4 to 550 eV and ions from 0.25 to 550 eV were measured in 25 and 50 logarithmic energy steps, respectively. The energy distribution of electrons in the magnetosheath was found to be generally characterized by two distinct peaks. A fairly hot electron component was discovered in the plasma sheet of the areo-magnetic tail.

An observation of the ultraviolet nightglow between 2670 Å and 3040 Å was conducted over White Sands Missile Range on October 22, 1984, at 0020 hours LST during the Orionids meteor shower. A 1/4‐meter uv spectrometer operating at 3.5 Å resolution viewed the Earth's limb at tangent heights between 90 km and 110 km for 120 seconds. By inverting the observed limb intensities, a total zenith intensity of 1.4 kR is inferred for the Herzberg I system. Excess emission above the Herzberg I (7,3) band at 2852 Å is identified as the Mg I resonance line. The intensity ratio of the Herzberg I band system to the 2972 Å line from O(¹S) was less than that predicted from the accepted O(¹S) branching ratio and acceptable ratios of Herzberg I to 5577Å emissions. Arguments supporting the identification of the Herzberg III band system are also advanced.

The doublet emission from N II at 2139.7 Å and 2143.6 Å was observed by a 1/4‐m scanning spectrometer with 3.1 Å resolution in the daytime, high‐altitude thermosphere during moderate levels of solar activity. The spectrometer viewed the Earth's limb 5° below the local horizontal to give a nominal tangent height of 152 km. Both sub band heads of the nitric oxide gamma band system were resolved in the data at the resolution used. The emission features from N II are clearly evident on the short wavelength shoulder of the (1, 0) band. Synthetic profiles of the (1, 0) gamma band and the (0, 3) delta band of nitric oxide were fitted to the data using a chi‐square analysis. These contributions were removed from the data leaving a residual emission, considered to be the N II doublet. A chi‐square minimization of the data relative to a synthetic intensity profile was done. The minimum was for a line strength ratio between the 2139 Å and 2143 Å lines of 0.58±0.08. The mean solar EUV flux deduced from the intensity of the N II emission in this experiment is lower than other reported observations, consistent with a lower solar activity level.

In situ measurements of [H] between 73 and 93 km are reported for conditions of winter solstice, magnetic quiet, and a solar depression angle of 12°. The data were obtained by a rocket‐borne instrument using the resonance fluorescence technique. A discharge source emitting photons at 1216 Å was an integral part of the instrument. The instrument was radially deployed 80 cm by a boom from the front of the payload in order to avoid the shock created by the gas flow over the front of the payload. An attitude control system oriented the payload so that the gas flow was nearly perpendicular to the plane containing the incident and scattered photons, thus minimizing any correction for Doppler shift. The resonance radiation detector viewed a black backstop in order to minimize background radiation from the hydrogen geocorona; however, the background was not entirely eliminated. The signal‐to‐noise ratio was improved by summing the data in 1.8‐s bins. The observed hydrogen concentration maximized at 85 km at 1.5±1.1×108 atoms cm−3.

Ultraviolet emissions from Earth's aurora were observed at wavelengths between 1675 and 2075 Å by a sounding rocket payload launched at Churchill, Canada, on March 28, 1980. The emissions from the Lyman‐Birge‐Hopfield (LBH) and Vegard‐Kaplan (VK) bands of N2 were observed and analyzed to determine the relative populations of the υ′ = 0–6 levels of the a¹πg state and the υ′ = 4, 6, 7, and 8 levels of the A³Σg+ state respectively. The relative population of higher vibrational levels of the A³Σg+ state are consistant with direct excitation and cascade. The relative populations of the vibrational levels of the a¹πg state peak at υ′ = 2. Such a distribution has not been observed previously in the aurora.

The sources and sinks of the emission features from the atoms and molecules of the atmosphere are reviewed. The thermo-spheric emissions between 2000 and 8000 Å are reviewed specifically. There is much work that remains to be done with the visible emissions.

Absolute differential excitation cross sections of atomic oxygen (³P‐¹S transition) by electron impact have been measured by a crossed‐beam method. A thermal dissociation method was used for generating atomic oxygen. The energy and angular range measured were from 10 to 30 eV and from 30° to 150°, respectively. A several theoretical results were compared with the present measurements. It is found that the present results do not agree with the theoretical predictions in angular distribution as well as magnitude of total cross sections. The theoretical values are generally smaller than the measurements by a factor of two.

The Raman backscatter cross sections for a 355 nm light source for the three fine-structure components are calculated. The signal-to-noise considerations show that the determination of the densities of the three fine-structure components separately is a feasible experiment. Since these fine-structure components are calculated to be in local thermodynamic equilibrium up to at least 350 km altitude, this experiment also gives atmospheric temperature. It is pointed out that this experiment does not suffer from the drawbacks of the previous efforts to determine atomic oxygen density and should yield reliable results for this density as well as temperature.

The differential excitation cross section of O(¹D) from the ground state has been measured at 20 eV electron impact by a crossed‐beam method. The angular range covered was from 30 to 150 degrees. Atomic oxygen was generated by a thermal dissociation method (iridium oven). The measured total excitation cross section is (1.5±0.7)×10−17 cm² which agrees, within the accuracy of the measurement, with the theoretical value (1.7 × 10−17 cm²) calculated by Henry et al. (1969).

Experiments conducted with a low energy plasma lens, HARP, in the electron beam of the large vacuum chamber at Johnson Space Center indicate that an enhanced population of 50 to 300 volt electrons appear when the beam goes into the Beam‐Plasma Discharge (BPD) mode. Below the BPD instability the electron distribution appears to be characterized as non‐energized single particle scattering and energy loss. At 100 cm from the beam core in the BPD mode the fluxes parallel to the beam are reduced by a factor of 20 with respect to the fluxes at 25 cm. Some evidence for isotropy near the beam core is presented.

A determination of the plasma potential using an electrostatic analyzer is described in which the potential difference between the instrument slit system and surrounding plasma is minimized. Data obtained from rocket-borne instrumentation demonstrate the viability of this technique for electron fluxes between thermal energies (∼0.5 V) and suprathermal energies (many volts).

Doubly differential cross sections of secondary electrons ejected from ${\mathrm{H}}_{2}$ by electron impact have been measured by a crossed-beam method. The incident energies used were 25, 40, 60, 100, 150, and 250 eV. The energy and angular range of secondary electrons measured were from one half of the difference between incident energy and ionization potential to 1.0 eV and from 12\ifmmode^\circ\else\textdegree\fi{} to 156\ifmmode^\circ\else\textdegree\fi{}, respectively. The present results do not agree with those of DuBois and Rudd for slow secondary electrons (20 eV) ejected by 100-eV primary electrons. The present data lead to total ionization cross sections within 10% of other measurements.

Auroral optical emission rates, thermal ion and electron densities, and low‐energy electron fluxes were measured in an IBC I aurora by a rocket‐borne payload, simultaneously with the overpass of the Atmosphere Explorer C satellite. Auroral ionization rates deduced from the rocket payload and neutral gas densities measured by an instrument on the satellite are used in a model calculation of the thermospheric manifestation of the aurora. The internal consistency of the electron and photometric measurements is demonstrated for the particle‐induced emission of 3371‐Å. A quenching rate of the N2(A³Σu+) state is deduced, by using the measured oxygen densities, and found to be 1.2−.2+.7 × 10−10 cm³ s−1. A discrepancy between the calculated and measured ionospheric densities is discussed in terms of the abundance of nitric oxide. A discrepancy between calculated and measured low‐energy electron fluxes (E <100 eV) is attributed to local plasma processes. The major source of 5577‐Å emission is found to be energy transfer from the N2(A³Σu+) state. The 6300‐Å is found to be unexplained by both electron impact on atomic oxygen and dissociative recombination of O2+.