A large body of experimental evidence lends credit to the existence of a close relationship between ionospheric parameters and the underlying atmosphere. Vertical-incidence ionospheric sounding data and temperature measurements at stratospheric (30 km) and mesospheric (80 km) heights have been used in investigating the interrelation between the occurrence of fluctuations with periods of planetary waves in temperature variations at different heights and in F2 layer critical frequency variations (foF2) under low solar activity conditions for the time interval 2006-2007. The distinctive characteristics of the manifestation of common periodicities of the wave structures under consideration are discussed. The statistically significant periods of stratospheric and mesospheric temperature fluctuations vary from 11 to 49 days, whereas foF2 periodograms show higher-frequency fluctuations with periods of 5, 8, 9, and 10 days. The study revealed a similarity between periodic structures for the variations in the parameters involved.

Regular measurements of the velocity and direction of the horizontal wind in the mesosphere/lower thermosphere (MLT) region at a height of ∼95 km have been conducted since 1975 over Eastern Siberia (Badary observatory near Irkutsk), using the spaced-diversity reception method in the LF range. The accumulated database of measurement results (for more than 20 years, from 1974 to 1996) makes it possible to get information on the impact on wind in the MLT region from both below (stratospheric warmings) and above (geomagnetic storms as a consequence of magnetospheric disturbances) with sufficient statistical reliability. Effects of stratospheric warmings and strong geomagnetic storms in the prevailing wind and amplitude of the semidiurnal tide are evaluated by the superposed epoch method. It is shown that the effects of stratospheric warmings depend on the type (intensity) of stratospheric warming and on the phase of quasi-biennial oscillations of the wind in the equatorial stratosphere at the 30 hPa level. The response of MLT winds to external impacts is different for the 21st and 22nd cycles of solar activity. Effects of geomagnetic storms (A p > 100) are manifested in the decrease in the eastward prevailing wind and increase in the semidiurnal tide amplitude.

The occurrence frequency of extremely large and extremely small values of the total ozone content (TOC) for Irkutsk, Berlin, and Saskatoon midlatitude stations (located near 52°N but in different climatic zones) are calculated based on the daily satellite measurements in the 1978–2005 period. The data for various seasons are presented. The interannual variability and regional differences are demonstrated. The results indicate that the TOC variability is mainly caused by natural atmospheric processes.

The results of a periodogramanalysis of the variations in the ionospheric parameters, measured using the vertical radio sounding method at midlatitude Irkutsk observatory (Eastern Siberia), are presented. The 1984–1986 period of observations was used. It has been indicated that the statistically significant oscillations with periods typical of planetary waves are present in the variations in f 0 E s , f b E s , h ′E s , f min , f 0 F2, and h ′F.

A review is presented on some of the most important experimental results and models obtained by international scientific community during last decade for the mesospheric and lower thermospheric dynamics (mean winds, planetary waves, tides and internal gravity waves). In addition to climatological features, the external forcing - the coupling from below (stratosphere) and possible influence of solar and geomagnetic activity on the dynamical processes at this region are presented.

The climatological characteristics of the total ozone content (TOC) in the 100°–110° E longitudinal zone have been studied. The results of the TOC measurements, using the TOMS spectrometer installed on board the Earth Probe satellite from July 1996 to January 2003, have been used. Substantial latitudinal differences in the TOC variations have been found. The “latitudinal effect” is especially distinct in the annual behavior. The annual wave amplitude substantially increases from the equator to the pole in the Northern Hemisphere. The dispersion also substantially varies along latitude: the TOC variability is minimal at the equatorial stations. It has been noted that the total ozone content increased in 2002, and this increase was most substantial (by 110 DU) in the Antarctic Regions (at Vostok station). The quasi-biennial oscillations with the amplitude maximum at the equatorial stations have been revealed.

The correlation between total ozone content lower thermosphere horizontal wind parameters, and standard indices of solar activity and geomagnetic activity has been studied. The satellite measurements of TOC for five observatories in Central Europe and the lower thermosphere wind measurements for Collm observatory (Germany) were used for 1996–2003. The quasi-periodic structure of these variations and the correlation between the corresponding periodograms were also studied. The quantitative evaluation of the statistically significant correlations and common periodicities were revealed.

The relation of the long-period variations in the midnight and noon values of the critical frequency of the ionospheric F 2 layer at three midlatitude stations (Irkutsk, Moscow, and Boulder) to the daily mean index of geomagnetic activity in years of different solar activity has been studied. It has been found that the correlation coefficients between the above parameters depend on time of day, season, and solar activity level. The correlation coefficients are higher at night than in the daytime, especially at low solar activity. The highest absolute values of the correlation coefficient most often appear during equinoxes: April–May and September–October. It has been shown that the variability of the critical frequencies of the midlatitude ionospheric F 2 layer depends not only on geomagnetic activity but also (to a considerable degree) on the effect of the lower atmosphere.

On a database of vertical sounding of the ionosphere, received on middle-latitude stations Irkutsk (52.5 degrees N, 103 degrees E), Moscow (55.5 degrees N, 37.3 degrees E), and Boulder (40.0 degrees N, 254.7 degrees E) we investigated features of display of the long-period fluctuations (with the periods of internal atmospheric planetary waves) in variations of critical frequency of a F2-layer for a maximum and a minimum of solar activity. Existence of fluctuations with the periods similar to 7, similar to 10, similar to 16, similar to 22 and similar to 27 days has been revealed. Their amplitude and time of existence essentially depend on a level of solar activity, a season and regional features. It is shown, that in a minimum of solar activity fluctuations with the shorter periods (<15 days), and within a maximum - with longer (> 20 days) were more often observed. Fluctuations with the periods similar to 16 days are most on a regular basis shown, in the summer they can be present during two months. It is established, that fluctuations such as planetary waves in Eastern Siberia are observed approximately in 2 times more often, than in Northern America.

For the first time, using many years of measurements of lower-thermospheric parameters (the horizontal wind velocity for 1976–1995, and minimum reflection frequency for 1983–1991) over Irkutsk (52°N, 105°E), the dynamics of their large-scale variations was investigated. The study used a sliding multiple correlation periodogram analysis. Regular seasonal, semi-annual and annual variations were detected. Quasi-biennial variations are regarded as irregular variations with a constantly changing over a rather wide range period. Variations with similar periods were also detected in the planetary index of geomagnetic activity Ap, and in the solar radio flux index F10.7. Our correlation analysis indicates that large-scale variations of the wind velocity and fmin in the lower thermosphere are correlated with those in the geomagnetic field. The large-scale variations under investigation characterize a regular long-term variability of lower-thermospheric parameters and can serve as climatic characteristics for the description of the climate of this atmospheric region.

The challenge of climate is treated as a problem not only of statistical dynamics of the ground-level atmosphere but also of electrodynamics, with due regard for all atmospheric regions—from the troposphere to the boundary with the Earth’s magnetosphere. Long-term series of uniform measurements of the parameters of the thermosphere/ionosphere system make possible suggesting some climatic characteristics for the upper atmosphere. We present the results derived from analyzing the data of vertical-incidence ionospheric radio sounding (1948–1996) and the horizontal wind velocity measurements in the lower thermosphere/ionosphere (1976–1996) from observatory Irkutsk, East Siberia (52°N, 105°E). The analysis revealed long-term variations of such parameters as the minimum reflection frequency (fmin), the F-region virtual height (h′F), the critical frequency (foF2), the electron density dispersion (N) (spread-F parameter), the occurrence frequency of different types of sporadic ionospheric features, the virtual height of these sporadic layers, and the prevailing wind velocity in the height range 80–100km. The association of climatic characteristics of the upper atmosphere with solar and geomagnetic activity, and the evolution of large-scale variations of the parameters under investigation are discussed.

The main features of upper atmosphere dynamics as an important part of upper atmosphere climatology are presented. The dynamics of the mesosphere and lower thermosphere (MLT) are of special interest. The results are based on the long series of investigations in East Siberia and data from a world-wide network of observatories. We present the regional climatic norms for the prevailing wind and semi-diurnal tide and the main features of the quasi-periodic structure of the wind field. The non-zonality of MLT dynamics is demonstrated as well as regional differences in the response of the wind field to stratospheric disturbances, solar activity variations and geomagnetic storms.

[1] To take a new approach to the lower thermosphere (80‐100 km) long-term behavior, the variations of the dates of the equinoctial rearrangements of the zonal wind circulation were considered. We have evaluated the duration of unstable equinoctial rearrangements periods and duration of rather stable summer and winter circulation periods as well. The identical multiyear radio measurements of the horizontal winds in the lower thermosphere/ionosphere at two midlatitude (52 N) observatories (Irkutsk (Badary Observatory), East Siberia, and Collm, central Europe) during 1981‐1996 were used. It is shown that there are significant nonzonality and regional dierences in the character of the circulation rearrangements. The duration of the winter circulation in East Siberia is systematically longer than in central Europe. However, the tendency to a decrease of the summer circulation duration for the years under consideration is observed for both regions. INDEX TERMS: 0341 Atmospheric Composition and Structure: Middle atmosphere: constituent transport and chemistry; 2437 Ionosphere: Ionospheric dynamics; 2427 Ionosphere: Ionosphere/atmosphere interactions; KEYWORDS: Lower thermosphere/ionosphere; Prevailing wind; Long-term changes.

The main mechanism of interaction between lower neutral atmosphere and ionosphere are the upward propagating atmospheric planetary waves. In the Institute of Solar-Terrestrial Physics RAS the experimental investigations of the interaction between different atmospheric layers from the stratosphere up to ionospheric E- and F-regions were carried out. The long-term database of some midlatitude upper atmosphere parameters was used (the horizontal thermosphere/ionosphere wind, the minimal vertically reflected from the ionosphere radio-frequency fmin, total ozone content, stratospheric temperature). The seasonal variations and significant non-zonality (longitudinal dependence) of the quasi-periodical structure were revealed. The influence of solar and geomagnetic activity periodicities from above and stratospheric thermo-baric field from below on the upper atmosphere processes are evaluated. In spite of significant changeability of planetary waves in the atmosphere- ionosphere system (from day to day, seasonal, from year to year, with solar cycle etc.) there are some similarities for the different atmospheric layers. The empirical model for the lower thermosphere wind field quasi-periodical structure was constructed. It is shown that increasing of planetary waves (wave-numbers 1 and 2) activity leads to the decreasing of the prevailing zonal wind velocity. We consider the atmosphere- ionosphere planetary waves as indicators of the complex disturbances in the Sun-Earth system and important element of upper atmosphere climate.

The time variations of daily values of the Total Ozone Content (TOC) during 1978-1992 at stations Irkutsk, Collm, Madrid and Saskatoon were investigated. These stations are located in the middle latitudes but have essentially different longitudes. The TOMS-database (satellite Nimbus-7) was used. The multi-correlation periodogramanalysis with sliding step 1 month was applied. The fluctuations with the periods lying in rater wide band including 27-day variations (21-39) days were revealed. Amplitudes of these fluctuations have a well-defined annual course with a maximum in the winter and a minimum in the summer. The variations of amplitudes of 27-day fluctuations contain an annual wave and quasibiennial oscillations with periods 20-28 months. At Saskatoon and Irkutsk, during years close to maxima of solar activity (1980 and 1990) the amplitudes of 27-day TOC fluctuations are the greatest. The significant correlation between amplitudes of fluctuations at considered middle-latitude stations practically without of phase lag is found out. Correlation functions are quasiperiodical with maxima of correlation coefficients each two years. It is possible to explain the results by joint influence of 27-day variations of solar activity connected with rotation of the sun and planetary atmospheric waves activity. The regular 27-day TOC fluctuations can be considered as climatic parameters of TOC variability in the Earth’s atmosphere.

The daily values of the prevailing zonal wind V-0x obtained at Irkutsk (Badary, Russia, East Siberia), Collm (Central Europe, Germany), and Saskatoon (Canada) stations, located at approximately the same latitude (similar to52degrees N) but at considerably different longitudes, have been used. The seasonal variations in the wind and their variability during the period of synchronous continuous observations (from January 1984 to October 1990) are studied. The climatic characteristics of the wind (the mean values of V-0x for a decade) suitable for describing its seasonal variations are calculated. An substantial feature in the manifestation of the seasonal variations in the prevailing zonal wind in the lower thermosphere over Irkutsk-the absence of traditional 3-month seasonal oscillations-has been found out. Two types of the seasonal oscillations with periods of 2.3 and 3.7 months have been revealed for Irkutsk.

For the first time, using long-term f(min) measurements acquired by the method of standard vertical-incidence radio incidence at st. Irkutsk (52degrees N, 105degrees E) for the time interval 1983-1991, we investigated the dynamics of large-scale variations of the minimum reflection frequency (f(min)) of radio waves from the ionosphere. Sliding multiple correloperiodogram analysis was used. We detected regular seasonal (91 days) and 27-day oscillations with almost constant periods, the semi-annual wave characterized by a period fluctuating over a rather wide range (176-221 days), and the annual wave with the mean period of 365 days. A clearly pronounced annual trend of seasonal df(min) fluctuations was observed. Quasi-biennial variations may be classed as irregular fluctuations with a constantly varying period over a rather wide range (588-886 days). The large-scale variations of f(min) under investigation which characterize its long-term variability, may serve as climatic characteristics for the description of this atmospheric region.