Measurements of neutral N2 density from mass spectrometers on five satellites (AE‐B, Ogo 6, San Marco 3, Aeros A, and AE‐C) and neutral temperatures inferred from incoherent scatter measurements at four ground stations (Arecibo, Jicamarca, Millstone Hill, and St. Santin) have been combined to produce a model of thermospheric neutral temperatures and N2 densities similar to the Ogo 6 empirical model. The satellite‐ and ground‐based measurements provide unique and complementary information on the structure of the thermosphere. Incoherent scatter data have good local time coverage at the station locations and provide data for studies of long‐term trends. Measurements from satellites provide information at different altitudes, latitudes, longitudes, solar activities, and seasons. The overall data set covers the time period from the end of 1965 to mid‐1975. The global average temperature from the new model for an F10.7 of 150 is 1041°K or 56°K lower than that from the Ogo 6 model. The annual temperature variation is about two‐thirds that of the Ogo 6 model, but variations in lower bound density (inferred from low‐altitude AE‐C data) and lower bound temperature (from incoherent scatter data) result in annual density variations at high altitude very similar to those in the Ogo 6 model. Diurnal and semidiurnal variations in lower bound density and temperature gradient parameters are also introduced. Model diurnal exospheric temperature variations reflect the observed changes with season seen in incoherent scatter measurements. Data used in the model cover a wide range of solar activities (mean F10.7 of 75–180), and the annual and diurnal temperature amplitudes are found to increase with solar activity at twice the rate of the mean temperature. The model fits moderate magnetic activity better than the Ogo 6 model but does not include observed longitude variations. The overall good agreement of the individual data sets with the model confirms the basic consistency of the various measurements taken in different time periods.
Several nights of optical and radar data were obtained from February 3 to 10, 1986 at Sondre Stromfjord, Greenland during a great geomagnetic storm when Ap reached 202. These data, excluding O I (630.0 nm), were used to monitor changes in O and O2 densities in the region from 100 to 200 km and are consistent with results of Hecht et al. (1989) wherein the O I (630.0 nm) emission was used. That is, there were large depletions of O in the E region during the peak of the storm. Using 24‐hour Ap values both MSIS‐83 and MSIS‐86 underestimated the depletion of O during the storm. MSIS‐86 did noticeably worse than did MSIS‐83, probably a result of the low exospheric temperature predicted by MSIS‐86. However, when 3‐hour ap values were used both models did better in predicting the measured O depletions, although MSIS‐86 again was less successful than was MSIS‐83. The data results also show that the enhancements in O2 were less than predicted by MSIS models in either mode. From 0200–0230 UT on February 9, 1986, a time just after the peak of geomagnetic activity as measured by Kp, the O mixing ratio near 135 km was found to increase by nearly a factor of 2. This increase is consistent with the passage of an atmospheric gravity wave through this altitude region providing that the scale height of O above 140 km is greater than predicted by the model.
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.
Measured E region neutral winds from the Atmospheric Response in Aurora (ARIA 1) rocket campaign are compared with winds predicted by a high-resolution nonhydrostatic dynamical thermosphere model. The ARIA 1 rockets were launched into the postmidnight diffuse aurora during the recovery phase of a substorm. Simulations have shown that electrodynamical coupling between the auroral ionosphere and the thermosphere was expected to be strong during active diffuse auroral conditions (Walterscheid and Lyons, 1989). This is the first time that simulations using the time history of detailed specifications of the magnitude and latitudinal variation of the auroral forcing based on measurements have been compared to simultaneous wind measurements. Model inputs included electron densities derived from ground-based airglow measurements, precipitating electron fluxes measured by the rocket, electron densities measured on the rocket, electric fields derived from magnetometer and satellite ion drift measurements, and large-scale background winds from a thermospheric general circulation model. Our model predicted a strong jet of eastward winds at E region heights. A comparison between model predicted and observed winds showed modest agreement. Above 135 km the model predicted zonal winds with the correct sense, the correct profile shape, and the correct altitude of the peak wind. However, it overpredicted the magnitude of the eastward winds by more than a factor or 2. For the meridional winds the model predicted the general sense of the winds but was unable to predict the structure or strength of the winds seen in the observations. Uncertainties in the magnitude and latitudinal structure of the electric field and in the magnitude of the background winds are the most likely sources of error contributing to the differences between model and observed winds. Between 110 and 135 km the agreement between the model and observations was poor because of a large unmodeled jetlike feature in the observed winds (140 m s-1). Agreement between the present simulation and the earlier simulations of Walterscheid andLyons (1989) is favorable, although the winds in the present simulation are considerably weaker for particle precipitation of similar characteristic energy and flux. The reasons for the difference were the smaller latitudinal extent of the model diffuse aurora and the weaker electric fields in our simulation. We have shown that the enhanced electron densities and electric fields associated with the postmidnight diffuse aurora provide the potential for a rapid acceleration of the zonal winds as shown by Walterscheid and Lyons (1989). However, the modeled response to the large-scale electric field is too great. This suggests that the assimilated mapping of ionospheric electrodynamics (AMIE) electric field is also too large. The actual electric field is most likely reduced locally in regions of enhanced ionization and conductivity within the diffuse aurora. In addition, we have shown that the "exotic" jetlike wind feature between 110 and 13...
Waves in the neutral upper atmosphere have been measured by the open source neutral mass spectrometer (Oss) during both the elliptical and the circular phases of the Atmosphere Explorer-C mission. Typical peak-to-peak wave amplitudes seen in [N•! are 30%, although amplitudes of 55% have been recorded. The amplitudes are mass dependent, Ar showing the largest perturbation. Helium is typically found to be out of phase with the heavier constituents. A survey of Oss data from 338 circular orbits shows that the highest wave amplitudes and the greatest number of occurrences are found in both the northern and the southern high-latitude regions. The near-simultaneous measurements of waves in both hemispheres at high latitudes also point toward a source related to conjugate phenomena. A possible second class of lower-amplitude waves peaks at high latitudes; however, a secondary peak near +--25 ø magnetic latitude may be due to waves generated near the equatorial region. A study of wave amplitudes and occurrences during a magnetic storm shows a possible transpolar propagation of waves from a magnetically active region near local midnight. The assumption of horizontal propagation would explain the observed high-latitude distribution of large-amplitude waves. The results of this study are compared with previous measurements of neutral wave structure. INTRO DU CTION In the last few years, in situ measurements of wave structure in the thermospheric neutral density have been made from earth-orbiting satellites. Early data obtained by means of ionization gages [Newton et al., 1969; Dyson et al., 1970! and accelerometers [Marcos and Champion, 1972; Forbes and Marcos, 1973! have indicated the existence of waves that appear to be propagating in the northsouth direction over a large range of latitudes. Recently, neutral mass spectrometers on the Atmosphere Explorer satellites have enabled high-resolution observations of wave structure in the individual neutral constituents to be made. Preliminary reports of the wave characteristics have been given by Reber et al. [1975! and Potter et al. [1975!. Mayr and Trinks [1975! also reported evidence of long-wavelength perturbations measured by a gas analyzer on the Esro 4 satellite. The unique elliptical and circular phases of the Atmosphere Explorer-C (AE-C) mission have provided the basis for a comprehensive wave study utilizing the large amount of data accumulated by the open source mass spectrometer (Oss) during the 2 years following launch. This paper discusses the phase relationships between the constituents and presents the results of a wave occurrence and amplitude survey covering 338 despun circular orbits in which the local time and latitude characteristics of the waves are presented. Conclusions based on this survey are then tested in a study of waves measured at high latitudes during a geomagnetic storm. INSTRUMENTATION The AE-C satellite was launched from the Western Test Range on December 16, 1973, into an elliptical orbit with 68.1 ø inclination. The initial perigee and apogee...
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