Longitudinal variations in the hydroxyl emission: 1. Temperature

Data on longitudinal variations in the hydroxyl emission have been obtained based on long-term studies of the mesopause temperature and hydroxyl (OH) emission at different ground stations in the Northern Hemisphere and based on temperature measurements on the UARS WINDII satellite. Maximums at longitudes of Eurasia and North America and minimums over the Pacific and Atlantic oceans have been revealed in the global longitudinal temperature distribution. The average longitudinal temperature values show distinct seasonal variations. Local nonstationary large-scale inhomogeneities in the form of temperature maximums and minimums up to 30 K relative to the average temperature, correlating with the variations in the irregularity dimensions reaching several tens of degrees in longitude and latitude (which corresponds to several thousand kilometers), exist against a background of the average global temperature variation, reflecting the surface topography.     

Seasonal temperature variations near the mesopause according to the hydroxyl emission measurements in Zvenigorod

The rotational temperatures of hydroxyl molecules with different vibrational excitation, which were used to determine the seasonal variations in the vertical temperature distribution near the mesopause at altitudes of 85–90 km, have been obtained based on the spectral measurements of the atmospheric nightglow at IFA RAN observatory in Zvenigorod. The obtained characteristics of the annual and semiannual harmonics have been compared with their lidar and satellite measurements and model representations.     

On rotational temperature of the hydroxyl emission

The method for determining the rotational temperature of the hydroxyl emission of the upper atmosphere is analyzed. It is shown that a discrepancy of up to 14 K appears in the temperature values determined for the region of OH emission (～87 km) since different researchers use the intensity factors (line strengths) of the lines of the rotational structure of hydroxyl bands based on various theoretical calculations. This discrepancy considerably exceeds the error (2–3 K) of direct temperature measurements. The use of the set of such data in the analysis of the time and spatial temperature regime can lead to a distortion of the character of the long-term changes in the mesopause temperature. Analytical expressions are obtained making it possible to calculate a systematic correction for the temperatures determined with the use of various intensity factors. One should also take into account considerable seasonal variations in the dependence of rotational temperature values on the level of the hydroxyl vibrational excitation.     

Orography-caused variations in the 557.7 nm atomic oxygen emission intensity

For the first time, the spatial variations caused by the IGW generated in the troposphere when the air flow around the Kopet-Dag mountain ridge are detected based on the measurements of the spatial distribution of the 557.7 nm atomic oxygen emission intensity. The measurements were carried out at Vannovskii station, the Physicotechnical Institute, Academy of Sciences of the Turkmen SSR.     

Empirical model of the OI 630 nm emission variations. 3. Emitting layer height

The empirical model of variations in the emitting layer height and parameters has been developed based on an analysis of the rocket measurements of the vertical distributions in the 630 nm intensity. The dependences on the solar zenith angle during a day are most substantial. This dependence is responsible for the character of seasonal variations at different latitudes. The height of the emitting layer increases with increasing solar activity, reflecting a temperature rise in the upper atmosphere. The negative trend—0.35 km yr^?1 in the interval 1964–1990—has been revealed.     

Behavior of parameters of the ionospheric F2 layer at the edge of the centuries: 2. Height of the layer

The trends in the height of the ionospheric F2 layer, hmF2, for the period from the end of the 1990s to the beginning of the 2010s are considered. It is shown that for a majority of the considered situations (time of the day plus season) negative trends are obtained for all stations for which series of initial data satisfying the requirements were found. They vary from ?1.2 to ?3.1 km per year. The trends in the daytime are slightly higher than in the postsunset period which apparently manifests the influence of the contraction of the upper atmosphere on changes in the hmF2 value.     

Hydroxyl (6/2) airglow emission intensity ratios for rotational temperature determination

OH(6/2) Q1/P1 and R₁/P₁ airglow emission intensity ratios, for rotational states up to j = 4.5, are measured to be lower than implied by transition probabilities published by various authors including Mies, Langhoff et al. and Turnbull and Lowe. Experimentally determined relative values of j transitions yield OH(6/2) rotational temperatures 2 K lower than Langhoff et al., 7 K lower than Mies and 13 K lower than Turnbull and Lowe.     

Empirical model of variations in the helium 1083 nm emission. 2. Temperature

Based on the measurements of the ortho helium 1083 nm emission intensity during twilights and on the calculation of its variations depending on the solar zenith angle, the method for determining the atmospheric temperature at heights of 300–1000 km during the nighttime period of day has been developed, taking into account the diurnal and seasonal conditions.     

Empirical model of variations in the 630 nm atomic oxygen emission. 2. Temperature

A model of the temperature variations of the atomic oxygen 630 nm emission for the nighttime conditions is created on the basis of the ground-based interferometer measurements of the Doppler temperature by Fabry-Pérot interferometers. On the basis of these measurements, various regular variations and their approximations for temperature evaluations for the given solar and geophysical conditions in the nighttime period of the day are obtained.     

Empirical model of variations in the emission of the molecular oxygen Atmospheric system. 2. Temperature

The empirical approximations of variations in the rotational temperature of the emission of the molecular oxygen Atmospheric system, obtained based on the systematization of the long-term ground-based observations under different heliogeophysical conditions, are presented.     

Seasonal features in the response of the mesopause temperature and emission intensities to solar activity variations

The seasonal dependences of the response of the hydroxyl ((6–2) band) and molecular oxygen O₂(b ¹Σ _g ⁺ ) ((0–1) band) emission intensities, temperature, and density indicator in the region of the hydroxyl emission maximum (87 km) to solar activity have been obtained based on the spectral observations of the mesopause emissions at Zvenigorod observatory during 2000–2007. The ratio of the OH (7–3) and (9–4) band intensities, characterizing the behavior of the vibrational temperature, has been used as an indicator of density. It has been established that the response of the studied mesopause characteristics to solar activity is positive in all seasons. In winter the response is maximal in the intensities and temperature and is minimal in the density indicator. The main mechanisms by which solar activity affects the mesopause characteristics have been considered. The behavior of the internal gravity waves with periods of 0.33–7 h depending on solar activity has been studied. It has been noted that these waves become more active at a minimum of the 11-year solar cycle.     

Fabry-Perot interferometer measurements of neutral winds and F2 layer variations at the magnetic equator

This letter presents some night-time observations of neutral wind variations at F2 layer levels near the dip equator, measured by the Fabry-Perot interferometer set up in 1994 at Korhogo (Ivory Coast, geographic latitude 9.25°N, longitude 355°E, dip latitude -2.5°). Our instrument uses the 630 nm (O¹D) line to determine radial Doppler velocities of the oxygen atoms between 200 and 400 km altitude. First results for November 1994 to March 1995 reveal persistent eastward flows, and frequent intervals of southward winds of larger than 50 ms^–1 velocity. Compared with the simultaneous ionospheric patterns deduced from the three West African equatorial ionosondes at Korhogo, Ouagadougou (Burkina-Faso, dip latitude +1.5°) and Dakar (Sénégal, dip latitude + 5°), they illustrate various impacts of the thermospheric winds on F2 layer density: (1) on the mesoscale evolution (a few 10³ km and a few 100 minutes scales) and (2) on local fluctuations (hundreds of km and tens of minutes characteristic times). We report on these fluctuations and discuss the opportunity to improve the time-resolution of the Fabry-Perot interferometer at Korhogo.     

Empirical model of variations in the IR Atmospheric system of molecular oxygen: 2. Emitting layer height

The empirical regularities in the variations in the emitting layer parameters depending on the solar zenith angle have been obtained by analyzing and systematizing the data published on the vertical distribution of the volume emission rate of the 1.27 μm molecular oxygen Infrared Atmospheric system measured on rockets and satellites.     

Empirical model of variations in the OI 630 nm emission. 1. Intensity

The empirical model of variations in the atomic oxygen emission intensity depending on different heliogeophysical conditions such as nighttime, lunar time, lunar phase age, season, year, and solar activity level during the 11-year cycle, as well as on cyclic aperiodic activity variations, level of geomagnetic disturbances, and their manifestations in the form of midlatitude subauroral red arcs, has been developed based on the long-term measurements of this emission intensity.     

Empirical model of variations in the helium 1083 nm emission. 1. Intensity

The model of variations in the orthohelium 1083 nm emission intensity has been constructed based on the measurements at different stations. The analytical approximations of the nighttime intensity variations depending on the phase age of the Moon, season, solar activity during the 11-year cycle, and geomagnetic disturbances are presented.     

Time and spatial variations in the ratio of nighttime and daytime critical frequencies of the F 2 layer

The ratio of daytime and nighttime values of the foF2 critical frequency is analyzed on the basis of the data of 28 ionospheric stations in the Eastern Hemisphere. It is found that three types of time variations in this ratio are observed after 1980: an increase with time (a positive trend), a decrease with time (a negative trend), and the absence of pronounced changes (a zero trend). The sign of this trend is shown to be governed by the signs of the magnetic declination D and magnetic inclination I at the given ionospheric station. This fact makes it possible to assume that the above trend is caused by long-term variations in the zonal component V _ny of the horizontal wind in the thermosphere, the latter component contributing into the vertical drift velocity W. The causes of the systematic changes in the thermospheric circulation regime after 1980 are still unknown; however, it is quite probable that they are related to anthropogenic changes in the atmosphere.     

Empirical model of variations in the continuum emission in the upper atmosphere. 1. Intensity

The ground-based and satellite measurements of the upper-atmosphere continuum (continuous emission) intensity in the visible and near IR spectral regions have been analyzed. The data were obtained at the geophysical stations, located in different regions of the globe, and at Mir Space Station. The regularities in the spectral distribution of the continuum emission intensity and emission variations have been revealed for different heliogeophysical conditions.     

A model study of the temporal behaviour of the emission intensity and rotational temperature of the OH Meinel bands for high-latitude summer conditions

The temporal variation of OH* emission and weighted rotational temperature has been studied for high-latitude summer conditions. Observations for 60°N latitude show OH weighted temperatures that always exceed 145 K even during periods of noctilucent clouds. Using a one-dimensional model the effects in excited OH concentration produced by changes in temperature, eddy diffusion, and water concentration have been analysed. We are forced to conclude that there remains a discrepancy between the OH temperatures predicted by the model and that obtained from OH^* measurements. An increase in OH^* concentration from June to the beginning of August, followed by a slow decrease during August has been obtained in agreement with the measurements. The 16-day modulation present in the measurements was simulated in a simple manner by varying the temperature in the mesopause region. This variation produces periodic modulations in both OH^* concentration and weighted temperature of 16 days. The results show the temperature leading the OH^* column concentration by three days. This phase shift is also present in the observations.     

Empirical model of variations in the emission of the molecular oxygen atmospheric system. 1. Intensity

The data on regular variations in the emission intensity of the molecular oxygen Atmospheric system excited in the region of the lower thermosphere have been systematized based on the long-term studies. The empirical approximations of the emission behavior are presented.