I. V. Medvedeva

Removal of Cr(VI) from aqueous solutions by magnetite nanoparticles with different sizes and crystal structure

AbstractIn this work a few nanopowders of magnetite (Fe3O4) produced by different methods were used as a sorbents. Three techniques were applied to make the nanopowders: (1) gas-phase synthesis, (2) chemical precipitation from water solution, and (3) laser atomization. Using these methods, the particles with different sizes and crystal structure have been produced. The effects of the particles size and structure of nanopowders on the removal of toxic Cr(VI) from an aqueous solution imitating ground waters and wastewaters with pH = 7.4–7.8 were studied at different solution temperatures. It is shown that magnetite is effective sorbent for the removal of Cr(VI) from polluted natural waters and sewage. It is found that sorption of Cr(VI) by magnetite is irreversible and has chemisorption character, and even small rise in temperature of the solution during the sorption process sharply increases efficiency of the sorption.

Temperature variations in the mesopause region according to the hydroxyl-emission observations at midlatitudes

The seasonal temperature variations in the mesopause region and the inter-day and nighttime temperature variability, the measure of which is standard deviations, have been studied based on the hydroxyl emission spectral observations at the Zvenigorod station of the Obukhov Institute of Atmospheric Physics in 2000–2011 and Institute of Solar Terrestrial Physics geophysical station (Tory) in 2008–2011. The long-term variations in all temperature variability parameters have been analyzed.

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.

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.

Studying atmospheric and ionospheric variabilities from long‐term spectrometric and radio sounding measurements

We investigated the variability in the neutral upper atmosphere and ionosphere parameters over East Siberia. The analysis is based on 2008–2014 data set of mesopause temperature (Tm) obtained from spectrometric measurements of the OH emission (834.0 nm, band (6–2)) at the Institute of Solar-Terrestrial Physics Geophysical Observatory (51.8°N, 103.1°E), and the data of F2 peak electron density (NmF2) from Irkutsk DPS-4 Digisonde (52.3°N, 104.3°E). The seasonal patterns of the NmF2 and Tm variability in different period ranges were analyzed and compared. The period range included day-to-day (periods T > 24 h) and tidal (8 h ≤ T ≤ 24 h) variations as well as variations in the internal gravity wave period range (T < 8 h). The comparison revealed both common features and distinctions in the seasonal patterns of the ionospheric and atmospheric variabilities. The main common feature is that the winter variability exceeds the summer one. In both atmospheric and ionospheric day-to-day variability seasonal variations, there are maxima in winter months and an additional maximum around the autumn equinox. The main distinction is that the equinox peaks observed in the seasonal variations of the diurnal atmospheric variability are not seen in the ionospheric seasonal pattern. The physical reasons of the obtained features are discussed. The revealed similarities in the seasonal behaviors may indicate that planetary waves propagating from the lower atmosphere layers have a significant impact on the mesopause temperature regime and ionospheric day-to-day variations.

Comparison of ground-based OH temperature data measured at Irkutsk (52°N, 103°E) and Zvenigorod (56°N, 37°E) stations with Aura MLS v3.3

Data about the variations of mesopause temperature (∼87 km) obtained from ground-based spectrographic measurements of the OH emission (834.0 nm, band (6-2)) at Irkutsk and Zvenigorod observatories were compared with satellite data on vertical temperature distribution in the atmosphere from Aura MLS v3.3. We analyzed MLS data for two geopotential height levels: 0.005 hPa (∼84 km) and 0.002 hPa (∼88 km) as the closest to OH height (∼87 km).We revealed that Aura MLS temperature data have lower values than ground-based (cold bias). In summer periods, that difference increases. Aura cold biases compared with OH(6-2) at Irkutsk and Zvenigorod were calculated. For the 0.002 hPa height level, the biases are 10.1 and 9.4 K, and for 0.005 hPa they are 10.5 and 10.2 K at Irkutsk and Zvenigorod, respectively. When the bias is accounted for, an agreement between Aura MLS and OH(6-2) data obtained at both Irkutsk and Zvenigorod is remarkable.

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.

Features of longitudinal variations in atmospheric temperature at heights of the radiating layer of 557.7-nm emission of atomic oxygen

On the basis of correlations between seasonal variations in the intensity and temperature of 557.7-nm emission, the mean monthly longitudinal variations in temperature are drawn. A comparison is performed with the data of interferometer and lidar measurements of temperature performed at various stations, as well as with the results of satellite studies. The dependences of the amplitudes of seasonal variations in temperature on latitude are obtained.

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.

Seasonal variation of upper-atmospheric emission in the atomic oxygen 558 nm line over east Siberia

Abstract Upper-atmospheric airglow observations were used to investigate the seasonal variation of upper-atmospheric emission in the atomic oxygen 558 nm [OI] line over the region of East Siberia (52° N, 103° E). There is qualitative agreement with the seasonal variations of 558 nm emission obtained in preceding decades at other mid-latitude stations, as well as with model approximations. Quantitative differences of the seasonal variation of 558 nm emission for the region of East Siberia are considered, which imply a more pronounced autumn maximum and larger values of monthly mean 558 nm emission intensities in the winter months (December–January). An analysis of the factors and phenomena that are responsible for the seasonal variation of 558 nm emission, and a comparison with the wind regime dynamics of the upper mesosphere - lower thermosphere as well as with stratospheric warmings in the region of East Siberia suggests the existence of regional (longitudinal) features in the seasonal variation of 558 nm emission.