The atmospheric response in the aurora (ARIA) rocket was launched at 1406 UT on March 3, 1992, from Poker Flat, Alaska, into a pulsating diffuse aurora; rocket-borne instruments included an eight-channel photometer, a far ultraviolet spectrometer, a 130.4-nm atomic oxygen resonance lamp, and two particle spectrometers covering the energy range of 1-400 eV and 10 eV to 20 keV. The photometer channels were isolated using narrow-band interference filters and included measurements of the strong permitted auroral emissions N2 (337.1 nm), N•-(391.4 nm), and O I (844.6 nm). A ground-based photometer measured the permitted N•-(427.8 nm), the forbidden O I (630.0 nm), and the permitted O I (844.6 nm) emissions.The ground-based instrument was pointed in the magnetic zenith. Also, the rocket payload was pointed in the magnetic zenith from 100 to 200 km on the upleg. The data were analyzed using the Strickland electron transport code, and the rocket and groundbased results were found to be in good agreement regarding the inferred characteristic energy (E0 • 3 keV) of the precipitating auroral flux and the composition of the neutral atmosphere during the rocket flight. In particular, it was found that the O/N2 density ratio in the neutral atmosphere diminished during the auroral substorm, which started about 2 hours before the ARIA rocket flight. The data showed that there was about a 10-min delay between the onset of the substorm and the decrease of the O/N2 density ratio. At the time of the ARIA flight this ratio had nearly returned to its presubstorm value. However, the data also showed that the O/N2 density ratio did not recover to its presubstorm value until nearly 30 min after the particle and joule heating had subsided. Both the photometer and oxygen resonance lamp data showed the presence of structure in the atomic oxygen densities in the region above 130 km. The observed auroral brightness ratio B337.1/B391. 4 equaled 0.29 and was in agreement with other recent measurements. This ratio was also consistent with the greater than expected flux of secondary electrons measured by the onboard particle spectrometer between 40 and 10 eV.

The Atmospheric Response in Aurora (ARIA) I rocket experiment was designed to measure the energy and momentum forcing of the atmosphere during auroral disturbances and the resultant compositional and dynamical changes. It consisted of one instrumented rocket, three trimethyl aluminum chemical release rockets, and various ground-based optical instruments. The rockets were launched from Poker Flat Research Range, Alaska, in March 1992. The instrumented payload included a set of eight instruments for measuring various atmospheric and ionospheric quantities. This paper describes the contents of the program and the results of electrodynamic modeling and measurements. A substorm onset occurred approximately 4 hours before launch of the instrumented payload, giving rise to both particle and Joule heating in the vicinity of Poker Flat. By launch time, the substorm was well into recovery. We used optical measurements, electron density measurements from the Langmuir probe instrument, and model results from the Strickland electron transport code to specify latitudinal profiles of the height-integrated Pedersen conductivity. Comparison with assimilated mapping of ionospheric electrodynamics (AMIE) calculations of the Pedersen conductivities for this event indicated that AMIE located the enhanced auroral conductivity region Well. However, the magnitudes of the AMIE conductivities in the enhanced region were considerably less than the measurements due to localized substorm-related particle precipitation enhancements not accounted for by AMIE. Our conductivity profiles were used in conjunction with electric field values produced by the AMIE routine to examine the atmospheric heating rates associated with the substorm. The latitudinally integrated Joule heating rate was initially less than the particle heating rate, but rapidly increased to its maximum value at the time of the substorm maximum while the particle heating rate peaked prior to substorm maximum. The particle and Joule heating were collocated during the expansion and maximum phase, but as the substorm recovered, the Joule heating moved to higher latitudes, so that by the time of launch, the two heating regions were completely separated by several degrees. The analysis indicates that the rocket was launched directly into the atmospheric region where the maximum heating had occurred.Paper number 95JA00330. 0148-0227/95/95JA-00330505.00 getic particle fluxes and electric fields. Very intense electrodynamical forcing of the neutral atmosphere occurs during substorms in the diffuse aurora where large electric fields and high conductivities can coexist for several hours of local time [Frank and Ackerson, 1972; Hoffman and Burch, 1973; Rostoker et al., 1985]. Model simulations predict very strong E region zonal wind jets, strong heating, and large compositional changes [Hays et al., 1973; Fuller-Rowell, 1985; Mikkelsen and Larsen, 1991; Walterscheid and Lyons, 1989] which have not been adequately investigated and verified through experiment and Observations. The Atmospheric...

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Abstract. Results are presented for zenith observations of a noctilucent cloud (NLC) display over the Sondrestrom atmospheric research facility near Kangerlussuaq, Greenland, on July 30/31, 1995. The observations were made with a Rayleigh lidar, which measured the NLC particle volume backscatter coefficient, and with a UV spectrograph, which measured the intensity and degree of linear polarization of solar light scattered from the NLC. The intensity and polarization measurements were made at solar depression angles of -1.8 ø to -4.6 ø . These data allowed the first simultaneous observation from the ground of the altitude and thickness of the NLC and of the radius of the NLC particles. The NLC was found to be between 86 and 84 km in altitude with a thickness of 1 to 2 km and the NLC particles had a radius at or below 0.07/zm. We also report the first observation of an NLC sublimating due to the passage of an AGW through the 85-km altitude region. These observations are generally in agreement with models of noctilucent clouds. IntroductionWhile noctilucent clouds (NLCs) have been known for over 100 years, it has been difficult to make quantitative groundbased measurements of many of the NLC characteristics. the NLC particles more accurately than the backscatter ratio. We therefore will present the volume backscatter coefficient in describing details of the NLC and its evolution. As the volume backscatter coefficient is equal to the product of the particle number density and the particle backscatter cross section, some assumption about the particle size, composition, and shape is required to determine the density of NLC particles using lidar data. Even multiwavelength lidar observations of an NLC may have difficulty due to the unknown shape of the particles.Recently, Hecht et al. [1994] have reported on a newly developed prism-based UV spectrograph, the high-resolution ozone imager (HIROIG), which is capable of simultaneously measuring the sky spectrum from 270 to 370 nm at any particular polarization angle. By rotating a half-wave plate, the polarization angle can be changed, so that depending on the sky brightness, three of the four Stokes parameters can be obtained in approximately 30 s or less. This instrument can therefore be used to measure both the wavelength dependence of light scattered by NLC particles and the degree of linear polarization of light scattered by those particles. According to Gadsden and SchrOder [1989] both methods can be used to put limits on NLC particle size.The UV spectrograph was deployed at the Sondrestrom research facility from July 30 to August 10, 1995, and was run in conjunction with the Rayleigh lidar to make the first zenith measurements of an NLC using the two complementary techniques. By combining the data sets, additional features of the NLC can be derived such as particle number density and estimates of the NLC sublimation rate.

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