Journal of Atmospheric and Terrestrial Physics最新文献

Measurements are presented of the height profile of the volume emission rate of the P₁(3) line of the (8-3) band of the hydroxyl airglow at latitudes of 40° N and 40° S as observed with the WINDII instrument on board the UARS satellite during the northern spring equinox in 1993. The emission layer peaks near 88 km during most of the night, with a half width of 6–8 km. The profile is slightly asymmetric with a more rapid decrease on the bottom side. During the early hours after sunset, the volume emission rate on the bottom side of the layer appears to decay exponentially with a time constant which varies from 1.1 h at 78 km to 2.9 h at 82 km. These decay rates are faster by a factor of three or four than those expected on the basis of the removal of atomic oxygen by three-body recombination. As a result it is concluded that the observed decay results from a combination of tidal modulation of the emission rate along with chemical removal of atomic oxygen.

On top of the 379 m high Ramnan mountain on the island of Andøya (69°30′N, 16°01′E) in Northern Norway, the ALOMAR (The Arctic Lidar Observatory for Middle Atmospheric Research) will soon be in operation. Through measurements of different atmospheric parameters, ALOMAR will provide information on the dynamics of the middle and upper atmosphere using ground-based instrumentation. Routine measurements, including ozone observations, can be carried out more efficiently than currently possible. The observatory is currently using three LIDAR instruments, one radar and several ground-based instruments to measure density, temperature, wind profiles and aerosol densities over a height range of approximately 10 to 100 km. ALOMAR will provide scientists worldwide with the opportunity for year-round, in-depth studies of the polar middle atmosphere, concentrating on physics, chemistry and meteorology. The observatory will offer unique research opportunities, and its activities can be correlated using the Andøya Rocket Range (ARR), who operate the facility, and with other important research facilities such as the EISCAT radar, and the University of Tromsø observatories which are located nearby. There are many opportunities for additional cooperative scientific experiments using ground-based measurements and instruments carried by aircraft, balloons and sounding rockets.

Beginning from 1961, data from a number of Soviet and Dobson ground-based spectrophotometric stations located in the latitude range from 43°N to 60°N (more or less equally spaced in longitude, at 43°N, 53°N and 60°N) are analysed. It is shown that there is a certain correlation between the total ozone amount and the 11-year solar cycle for some stations. In addition, when averaging annual deviations of the total. ozone content from the long-term mean values for each station and then for all the stations, the final curve of the ozone trend shows agreement with the long-term variation of the solar constant (over the period from 1961–1992) which may be part of the 80–90 year Gleissberg cycle. We therefore suppose that the main reason for the ozone trend found is the variation in solar activity.

We analyze 375 h of Na Wind/Temperature lidar measurements of the mesopause region (≈ 80–105 km) Na density and temperature profiles on 57 nights distributed over 2 yr at Urbana, Illinois. These observations yield a high-resolution seasonal data set of gravity wave activity in the upper mesosphere. From this data, we present measurements of the Brunt-Väisälä period, the relative atmospheric density perturbations and their spectra, and the parameters of 143 quasi-monochromatic gravity waves. The direct measurement of the Brunt-Väisälä period allows accurate calculation of the horizontal velocity perturbations and vertical displacement perturbations from the density measurements. The horizontal velocity and vertical displacement vertical wave number spectrum magnitudes and indices show considerable seasonal and nightly variability. The gravity wave amplitudes, wavelengths, and observed periods exhibit systematic relationships similar to those found in previous studies, and are consistent with the MU radar measurements of intrinsic gravity wave parameters. Here, we present a detailed analysis of the observations in terms of Diffusive-Filtering Theory models of gravity wave propagation. The magnitudes of the vertical wave number spectrum, the form of the joint vertical wave number and frequency spectrum, and the systematic relationships between the monochromatic gravity wave parameters are consistent with the Diffusive-Filtering model. We compare these results with a variety of radar, lidar, and airglow observations from other sites. This observational study suggests that the complex nonlinear interactions of the gravity wave field may be modeled successfully as a diffusive damping process, where the effective diffusivity is a function of the total wave variance.

The MULTIFOT airglow photometer payload was launched from Alcântara (2.5°S, 44.4°W) on a SONDA III rocket at 23:52 hrs local time on 31 May 1992. A total of ten photometers, six forward-looking and four side-looking, measured the height profiles of the airglow emissions O₂ Herzberg band system, 01557.7 run, NaD 589.3 nm, 01630.0 nm, OH(8,3) band R branch at 724.0 nm, O₂ Atmospheric (0,0) band at 762.0 nm and the sky background at 578 nm and 710 nm. At the time of launch, a ground-based airglow photometer observed the intensity variations of these emissions, together with the rotational temperature of the OH(9,4) band, and a sodium lidar measured atomic sodium concentration from 80 to 110 km.

Night-time thermospheric temperatures, T63o, and mesospheric rotational temperatures, T(OH) and T(O₂), have been measured at Cachoeira Paulista (23°S, 45°W, 16°S dip latitude), located in both the equatorial ionospheric anomaly and the South Atlantic Geomagnetic Anomaly, with a Fabry-Perot interferometer and a multi-channel tilting filter-type photometer, respectively. The thermospheric temperatures are obtained from the Doppler line broadening of the OI 630.0 nm emission and the mesospheric rotational temperatures from the OH(9,4) and O₂A(0,1) band emissions. Measurements made during three geomagnetic storms showed that the nocturnal mean values of T₆₃₀ during the recovery phase of the storms were lower than those observed during quiet time and from model predictions. Also, the nocturnal mean value of the T₆₃₀ soon after the SSC event on 27 June 1992 was higher than the quiet time and model predictions. The observed mesospheric nocturnal mean rotational temperatures, T(O₂) and T(O₂), were unaffected by the storms. A comparison of the night-time observed temperatures T₆₃₀, T(OH) and T(O₂) with those calculated using the MSIS-86 model is also presented.

A rocket payload designed to measure mesospheric sodium, hydroxyl and oxygen nightglow emissions, in addition to electron density and temperature, was launched from the Alcantara Launch Center (2°S, 44°W), Brazil, at 23:52 LST on 31 May 1992. The height profiles of the atomic oxygen OI557.7 nm and molecular oxygen Atmospheric (0-0) band emissions showed maxima at 100±3 km and 98±3 km, respectively. The emission data are used to calculate the atomic oxygen concentration profiles. The results show the validity for the equatorial region of the empirical parameters proposed by McDade et al. (1986).

Zenith observations of the oxygen λ1630 nm auroral/airglow emission (produced at an altitude of ∼220 to ∼250 km) were obtained with the Mawson Fabry-Perot Spectrometer (FPS) during three ‘zenith direction only’ observing campaigns in 1993. The data show many instances of strong (50 to 100 m s⁻¹) upwellings in the vertical wind, when the auroral oval is located equatorward of the zenith. Our data appear consistent with the existence of a region of upwelling up to ∼ 4° poleward of the poleward boundary of the visible auroral oval, rather than short duration, explosive heating events. The upwellings are probably the vertical component of wind shear produced by reversal of the zonal thermospheric winds, which occurs near the poleward boundary of the visible auroral oval. Zenith temperature was also seen to increase when the oval was equatorward of Mawson, showing rises of up to 300 K or more. However, this increase is at times unrelated to the upwellings, and seems to be caused by the expansion of the warm polar cap over the observing site.

On a number of nights the boundary between the polar cap and the auroral oval was observed to pass over our site several times, occasionally showing a quasi-periodic expansion and contraction. We speculate that this quasi-periodic movement may be related to periodic auroral activity that is known to generate large-scale gravity waves.

The optical peculiarities of the initial ion cloud dynamics in the CRRES G-9 Caribbean barium release are studied. Comparison of simulation results and optical data of ‘skidding’ of the ion barium cloud observed by low-light-level TV-images indicates good agreement. The simulation is based on a modified 2D electrostatic code. The background electric field and a model of the inhomogeneous ionization of the neutral cloud were included. The fragmentation of the back of the cloud during the ion ‘skidding’ process is explained by the results of the simulation.