Data from the Midcourse Space Experiment Tilere is evidence (R. H. Picard, J,'unes H. Brown (MSX) has provided the first observations of thunderstorm-personal communications, 1997) that gravity wave generated gravity waves imaged from space. Gravity wave structures are present in a number of MSX MWIR images. theory predicts that isolated, sufficiently convective This evidence is based on morphology, length scales, thunderstorms can launch waves mid create a unique power specUa and MWIR mdimive properties. The present intensity pattern of concentric circles on a radiating sinface paper shows that in particular cases the sources of these of constant altitude above such a storm. banong the MSX waves can be established as thunderstorms. This source constant-nadir-angle mid-wave hlfmred (MWIR) identification was prompted by the work of Taylor anti observations, two instances of such patterns have been Hapgood [1988] who showed that a pattern of concentric identified. It was conf'mned frown •neteorological satellite circles in ground-based observations of nightglow images that highly convective isolated thunderstorms emissions in the mesopause region was caused by va• occurred at the locations and ti•nes expected. isolated thunderstorm that occurred six hours prior to the nightglow observation.

The spectral characteristics and fluorescent efficiencies for electron excitation of nitrogen and air at 600 Torr have been determined. Results are presented for the efficiency of conversion of electron energy to optical radiation in approximately one hundred resolved spectral components of air and nitrogen between 3200 and 10 800 Å when bombarded by 50-keV electrons. The total fluorescent efficiency under these conditions is (0.14±0.02)% for nitrogen and (6.7±1.0)×10—3% for air. In nitrogen the first positive (B 3Πg→A 3Σu+), second positive (C 3Πu→B 3Πg), Gaydon green, Herman infrared, and Goldstein—Kaplan (C′ 3Πu→B 3Πg) band systems of N2 and the first negative (B 2Σu+→X 2Σg+) band system of N2+ were observed. The (0–2) and (0–3) transitions of the Herman infrared system and [N I]32(2D—2P) forbidden doublet at 1.04 μ, previously unreported in the laboratory, were observed. In air the first positive and second positive band systems of N2 and the first negative band system of N2+ were observed as well as atomic spectra of nitrogen, oxygen, and argon.

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Abstract.Distinctive structure in the 4.3-/•m spectral region has been imaged by the SPIRIT 3 radiometer on the MSX satellite observing the cloud-free atmosphere. We show nadir, high-nadir-angle (NA) sublimb, and limb images which, coupled with radiative transfer analysis, indicate that this structure originates from internal gravity waves (GWs). Such structure occurs in a significant fraction of both below-the-horizon (BTH), or sublimb, and above-the-horizon (ATH), or limb, obser-

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Time‐resolved spectra of the decay of the O2 infrared atmospheric ( a¹Δg → X³Σg−) ( 0,0) band emission in the evening twilight at 41.7°N have been obtained using the Fourier transform infrared (FTIR) technique. The measurements were made during a two‐month summer‐fall period which included the autumnal equinox. The late twilight variations were well described by single exponentials with decay time constants which ranged from (44.4±1.6) min in early August to (61.1±2.1) min near the equinox. In this connection, a strong positive trend in the time constant was observed during late August and early September. When combined with available data for collisional quenching and for fall‐winter, upper‐mesospheric altitude distributions of O2 (a¹Δg, ν=0) in the late twilight, these observations support a radiative lifetime of about one hour.

A 2‐kW electron accelerator was launched in October 1974 from the White Sands Missile Range, New Mexico, as the initial launch in the Excede series of artificial auroral experiments. The launch, designated Precede, was supported by a number of ground‐based optical systems to record the electron‐induced atmospheric emissions as a remote diagnostic technique of accelerator performance in addition to recording emissions of aeronomic interest in a controlled artificial aurora. The electron source, square wave modulated at 0.5 Hz, was initiated at 95 km on payload ascent and continued through apogee (120 km) to a descent altitude of approximately 80 km, providing a total of 90 pulses of the 2.5‐kV 0.8‐A electron beam over a period of 180 s. A rocket‐borne retarding potential analyzer provided a measure of the energy distribution of electrons returning to the vehicle skin. The energy distribution of the return current electrons has been compared with laboratory measurements of the energy distribution of secondary electrons as a function of scattering angle to infer a vehicle potential due to a net positive charge buildup on the electron‐emitting payload. The steady state vehicle potential at apogee is less than 30 V, with substantially smaller values determined at lower altitudes. Langmuir probe theory is shown to model accurately the altitude dependent steady state vehicle potential. Ground‐based optical systems included an image‐intensified spectrograph and a dual channel telephotometer recording the time dependent emission profile of the N2+ (B²Σu+ → X²Σg+) first negative (0‐0) band at 3914 Å and the O(¹S → ¹D) transition at 5577 Å. The spectrograph recorded emissions in the 4200‐ to 8500‐Å wavelength range including the prominent transitions of the N2+ first negative, N2(B³Πg → A³Σu+) first positive and N2+ (A²Πu → X²Σg+) Meinel systems as well as the O(¹S) 5577‐Å line. With the exception of the N2+ first negative system the image‐intensified spectrograph indicated that these emissions are collisionally deactivated in the 80‐ to 110‐km altitude range. The ground‐based telephotometer measurements were corrected for the effects of atmospheric extinction by monitoring the apparent photon emission rates of several bright stars. An electron‐induced luminous efficiency of (4.5 ± 0.4) × 10−3 was determined for the N2+ 1 N (0‐0) transition at 3914 Å in the 80‐ to 100‐km altitude range.

The vibrational temperature and molecular density of thermospheric nitrogen were probed in situ above Fort Churchill, Manitoba, Canada, on March 13, 1970. The rocket‐borne system utilized electron beam induced luminescence of the atmosphere as a diagnostic technique in effecting the measurements. The vibrational populations of N2+ ions in the B²Σu+ state were inferred from the intensities of selected transitions of the N2+ first negative (1N) band system (B²Σu+−X²Σg+) induced by a 2.5‐keV electron impact. Four narrow band photometers were used to measure the radiant intensity of the (0–1), (0–2), (1–2), and (2–4) N2+ 1N transitions. In the technique employed the vibrational population of N2(X¹Σg+) is derived from the N2+(B²Σu+, υ′ = 0 and 1) populations if it is assumed that the relative cross sections for production of the excited N2+ ions by simultaneous ionization and excitation of the neutral molecule are proportional to the appropriate Franck‐Condon factors. The inferred population of N2+(B²Σu+, υ′ = 2) is not consistent with this simple model, appearing anomalously large at low vibrational temperatures. Within the limits of uncertainty imposed by the nature of the experimental technique and by the precision realized in the measurements the inferred vibrational population ratio, [N2(υ = 1)]/[N2(υ = 0)], was not recognizably greater than that based on model atmospheric kinetic temperatures appropriate for the time of the flight (950°K exospheric temperature). An upper limit for the N2 vibrational temperature is given in the altitude range 80–175 km (1500°K at 175 km, 1200°K at 155 km, 1000°K at 135 km, and 800°K for altitudes less than 115 km). Measured N2 molecular densities are in substantial agreement (<±10% disparity) with the Jacchia (1971) model atmosphere in the 145‐ to 175‐km altitude range. At lower altitudes the measured concentrations are significantly less than the model values. For example, the measured molecular density at 120 km [2.3 × 1011 cm−3] is approximately 61% of the model value. Further departure of the results from the model at altitudes less than 120 km is attributed in part to the effects of supersonic flow about the vehicle.