E.S. Kazimirovsky

EFFECTS ON THE IONOSPHERE DUE TO PHENOMENA OCCURRING BELOW IT

The terrestrial thermosphere and ionosphere form the most variable part of theEarths atmosphere. Because our society depends on technological systems thatcan be affected by thermospheric and ionospheric phenomena, understanding,monitoring and ultimately forecasting the changes of the thermosphere–ionosphere system are of crucial importance to communications, navigation and the exploration of near-Earth space. The reason for the extreme variability of the thermosphere–ionosphere system isits rapid response to external forcing from various sources, i.e., thesolar ionizing flux, energetic charged particles and electric fields imposed via the interaction between the solar wind, magnetosphere and ionosphere, as well as coupling from below (“meteorological influences”) by the upward propagating, broad spectrum,internal atmospheric waves (planetary waves, tides, gravity waves) generated in thestratosphere and troposphere. Thunderstorms, typhoons, hurricanes, tornadoes andeven seismological events may also have observable consequences in the ionosphere.The release of trace gases due to human activity have the potential to cause changes inthe lower and the upper atmosphere.A brief overview is presented concerning the discoveries and experimentalresults that have confirmed that the ionosphere is subject to meteorologicalcontrol (especially for geomagnetic quiet conditions and for middle latitudes).D-region aeronomy, the winter anomaly of radiowave absorption, wave-liketravelling ionospheric disturbances, the non-zonality and regional peculiaritiesof lower thermospheric winds, sporadic-E occurrence and structure, spread-Fevents, the variability of ionospheric electron density profiles and Total ElectronContent, the variability of foF2, etc., should all be considered in connection withtropospheric and stratospheric processes. “Ionospheric weather”, as a part of spaceweather, (i.e., hour-to-hour and day-to-day variability of the ionospheric parameters)awaits explanation and prediction within the framework of the climatological, seasonal,and solar-cycle variations.

Variations of the ground-measured solar ultraviolet radiation during the solar eclipse on March 9, 1997

Abstract Results of investigations of the solar ultraviolet radiation measured on the ground during the solar eclipse observed over Irkutsk on March 9, 1997 are presented. The spectral distribution variations (radiation 296–326 nm) are revealed and discussed in connection with proposed ozone-eclipse effect. It is suggested that variations in spectra observed at the time close to the maximum phase of eclipse can be caused by the multiple scattering effect of the ultraviolet radiation.

An investigation of the upper atmospheric optical radiation in the line of atomic oxygen 557.7 nm in East Siberia

Abstract The observed data of night sky emission in lines 557.7 and 630nm for the 1997–1999 seasons above the East-Siberian region are shown. The abnormal increase of intensity of emission 557.7nm in January–February 1998 is described. The possible connection of this phenomenon with a stratosphere warmings above Eastern-Siberia during this season is discussed.

The manifestation of seismic activity in 557.7 nm emission variations of the earth's upper atmosphere

Abstract For the Baikal seismic zone (East Siberia region, 52°N, 103°E) the Earths upper atmosphere radiation parameters were analysed for 557.7 nm emission line of atomic oxygen [OI] (de-excitation heights 85–115 km) during earthquakes. The analysis revealed an increase in mean night-time 557.7 nm emission intensities prior to earthquakes, with a decrease in intensities during post-earthquake days. Preliminary results of a spectral analysis suggest possible changes in spectra (from a few to tens of minutes) of 557.7 nm emission prior to and after earthquakes. The results are compared with those obtained for the earthquakes in the Central Asian region.

The upper mesosphere/lower thermosphere wind field nonzonality as possible sign of the external forcing from above and from below

Abstract The geographical nonzonality of the global wind field was investigated through a long-term study of upper mesopause/lower thermosphere horizontal winds (average altitude 95 km) near Irkutsk, East Siberia, Russia (52° N, 104° E) in comparison with similar wind measurements at the stations, which are well spaced along the 52° N latitude circle. The longitudinal/regional variations in the dynamics of the upper middle atmosphere are illustrated. This effect may significantly manifest itself in the different amplitudes of the prevailing zonal wind, in the different times of the winter-spring transition of the zonal circulation, in the different response to the sudden stratosphere warmings, and in the different response to the geomagnetic storms and Solar Proton Events. The reasons of the nonzonality could be planetary scale mesopause oscillations structure; the external forcing from below due to different conditions for the generation and propagation upward of the internal atmospheric waves; the real difference of the geomagnetic latitudes. The nonzonality of the mesopause wind field may be important when empirical and physical upper atmosphere models are being formed.

The total ozone content and orography

Abstract Systematical differences of the Total Ozone Content over high mountains (The Pamirs, Andes) and westward located plains are revealed. The changes in the total ozone over mountains are preliminary interpreted in terms of the upward propagation of atmospheric internal gravity waves generated when the horizontal wind iniciates upward motions when it meets an obstacle — the mountain ridge.

The peculiarities of wind field in the upper middle atmosphere in the East Siberia rRegion

Abstract The climatology of wind field in height range 85–95 km over East Siberia on the base of continuous measurements during 1975–1990 is described and compared with analogous data over Central Europe and Canada. The longitudinal effects and coupling to regions above and below are discussed.

Relative contribution of energy sources to quasiperiodic wind variations in the lower thermosphere

Abstract Based on zonal (Vox) and meridional (Voy) prevailing wind measurements from June 1982 to May 1986 at three stations: Irkutsk, Collm and Saskatoon, as well as the solar radio emission at 10.7 cm wavelength (F10.7) and the planetary index of geomagnetic activity (Ap), an analysis of their periodic structure is presented. The estimates of the relative contribution of the helio-geomagnetic activity quasiperiodic variation to prevailing wind fluctuations show that a key role in the formation of 27-day oscillations are played by variations of the solar radio emission index F10.7.

Modelling of ionospheric drifts in view of IRI

Abstract D/E region drift data, as worldwide obtained from 1957 to 1970 by methods D1 and D3, are statistically analyzed and a computer program describing the average variations in geomagnetic latitude and time is developed.

The non-zonal effect in the dynamical structure of the midlatitude MLT-region

Abstract Ionospheric drift measurements in the LF range, which refer to altitudes between 80 and 100 km, make it possible to permanently monitor the circulation in the upper mesosphere/lower thermosphere region (MLT-region). A long-term (1975–1996) study of the MLT region dynamical structure at stations, well-spaced along 52°N latitude circle has revealed the nonzonality in the MLT dynamical structure. This non-zonality in the nighttime prevailing wind, tidal variability and planetary wave activity is considered including results obtained during the MLTCS, DYANA and CRISTA/MAHRSI Campaigns. The longitudinal variations could be interpreted as sign of “coupling from below” and may be important when empirical and physical upper atmosphere models are being formed.