Marina A. Chernigovskaya

Modeling of response of the thermosphere-ionosphere system to sudden stratospheric warmings of years 2008 and 2009

A study of the response of the thermosphere and ionosphere to sudden stratospheric warmings (SSWs) which occurred in January of 2008 and 2009 is presented. The Global Self-consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP) developed in the West Department of IZMIRAN was a theoretical basis for this study. A comparison of the simulation results of the thermosphere-ionosphere response to SSW events with the observational data over Irkutsk and also with theoretical and experimental studies carried out during the recent years is performed. SSW events were modeled by setting disturbances in the neutral temperature and density at the lower boundary of the GSM TIP model (80 km above the Earth’s surface). It is shown that the disturbances related to SSW lead to substantial global effects in the thermosphere and ionosphere. The analysis of the experimental data showed that, in spite of very similar solar and geophysical conditions on the background of which two considered stratospheric warming events happened, the occurring disturbances in temperature at heights of the mesosphere and lower thermosphere differ substantially from each other, although some common regularities still take place especially at heights of the ionospheric F region.

Influence of stratospheric warming on 557.7 nm airglow variations

We investigate the influence of stratospheric warming on 557.7 nm airglow variations on the basis of the experimental data received at the ISTP SB RAS Geophysical observatory (52°N, 103°E) in 1998-2005. In the researched period some cases of abnormal behavior of 557.7 nm airglow intensity in absence of strong geomagnetic disturbances have been found out. We revealed, that these significant increasing of 557.7 nm airglow intensity concerning to mesosphere-low thermosphere heights, are caused by strong stratospheric warming when disturbances cover the big range of atmosphere heights. It is emphasized, that for the Asian region, and, in particular, for the region of Eastern Siberia, there is a big concentration of stratospheric warming centers that can result in occurring regional features in airglow characteristics.

Erythemal ultraviolet radiation as deduced from data of ground-based and satellite measurements

A comparative analysis of midday values of direct erythemal radiation (ER) from ground-based measurements at Irkutsk and of values of total ER from satellite data for the period 1999-2001 is carried out. A correlation analysis is made of the ground-based of total ER from satellite data for the period 1999-2001 is carried out. A correlation analysis is made of the ground-based and satellite data for separate months and years, and for the input data set for the entire three-year period. In the analysis of the day-to-day variations we identified periods with a high degree of correlation (0.86-0.99) between ground-based and satellite data, as well as periods with distrubances in the consistency of the variations. We discuss the possible reasons behind the features identified and the differences observed in the ER variations of ground-based measurements and satellite data. In the ground-based measurements we identified an asymmetry of the seasonal ER behavior with respect to the summer solstice, implying an increase of ER-values in the second half-year when compared with the first half-year for the same angular altitudes of the Sun. This feature is more poorly pronounced in the satellite data and is distinguished when only days with clear weather are taken into account. A pronounced seasonal behavior of the ER variation coefficients with large values in the second half-year is pointed out.

Irregular variations of ground-level ultraviolet radiation

We present and analyze the data of daily observations of ground-level near-noon ultraviolet (UV) radiation of the Sun in the wavelength range 295 - 345 nm at Irkutsk (East Siberia, 52 degree(s)N, 104 degree(s)E) for 1998 - 2000. The study revealed an asymmetry of the seasonal variation of UV radiation with respect to the summer solstice, and its dependence on the wavelength in the spectral range under consideration. Irregular variations of ground-level UV radiation, typical of the region, were identified, which depend on the season, and on the selected spectral range. The detected features of the irregular variations are interpreted in terms of the existence of a pronounced annual variation in total ozone content, the variation (during different seasons) of the proportion of the contribution to the attenuation of UV radiation from the Rayleigh and aerosol scattering, the absorption by ozone, and of the specific climatic weather regime in East Siberia.

Variations of the ground-level ultraviolet radiation in East Siberia

Abstract Daily measurements of the ground-level ultraviolet radiation (UVR) for the years 1998–2000 were used to investigate the seasonal UVR variation in the East Siberian region. The study revealed the asymmetry of the seasonal UVR variation with respect to the angular altitudes of the Sun, caused by the seasonal variation of the total ozone content (TOC), and possibly by the presence of the snow cover. Characteristics of the occurrence of short-lasting increases in UVR are considered, which are associated with TOC anomalies and with high atmospheric transparency. Fluctuations of the ground-level UVR with periods of 2.8, 6–13 and 26 days are identified. A study is made of the dependence of the ground-level UVR on solar activity. Statistically significant correlation coefficients with solar activity indices are obtained.

Long-term variations of erythemal ultraviolet radiation in Irkutsk as deduced from satellite measurements

The analysis of temporal variations of erythemal ultraviolet radiation (EUVR) in Irkutsk is given on the basis the data of satellite measurements of solar EUVR by TOMS (Nimbus-7, Earth Probe) processed with the help of special complex of programs for the periods 1979-1992 and 1996-2003. The results of the long-term homogeneous measurement analysis carried out and processed by unified techniques allow establishing climatic norms of different temporal variation scales (inter-seasonal, inter-annual, within the cycle of solar activity). The possible reasons of the observing temporal variations of ground-level EUR in Irkutsk are being discussed.