| 1. |
- Barabash, Victoria, et al.
(author)
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Electron density profiles in the quiet lower ionosphere based on the results of modeling and experimental data
- 2012
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In: Annales Geophysicae. - : European Geosciences Union (EGU). - 0992-7689 .- 1432-0576. ; 30:9, s. 1345-1360
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Journal article (peer-reviewed)abstract
- The theoretical PGI (Polar Geophysical Institute) model for the quiet lower ionosphere has been applied for computing the ionization rate and electron density profiles in the summer and winter D-region at solar zenith angles less than 80° and larger than 99° under steady state conditions. In order to minimize possible errors in estimation of ionization rates provided by solar electromagnetic radiation and to obtain the most exact values of electron density, each wavelength range of the solar spectrum has been divided into several intervals and the relations between the solar radiation intensity at these wavelengths and the solar activity index F10.7 have been incorporated into the model. Influence of minor neutral species (NO, H2O, O, O3) concentrations on the electron number density at different altitudes of the sunlit quiet D-region has been examined. The results demonstrate that at altitudes above 70 km, the modeled electron density is most sensitive to variations of nitric oxide concentration. Changes of water vapor concentration in the whole altitude range of the mesosphere influence the electron density only in the narrow height interval 73–85 km. The effect of the change of atomic oxygen and ozone concentration is the least significant and takes place only below 70 km. Model responses to changes of the solar zenith angle, solar activity (low–high) and season (summer–winter) have been considered. Modeled electron density profiles have been evaluated by comparison with experimental profiles available from the rocket measurements for the same conditions. It is demonstrated that the theoretical model for the quiet lower ionosphere is quite effective in describing variations in ionization rate, electron number density and effective recombination coefficient as functions of solar zenith angle, solar activity and season. The model may be used for solving inverse tasks, in particular, for estimations of nitric oxide concentration in the mesosphere.
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| 2. |
- Belova, E., et al.
(author)
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The dynamical background of polar mesosphere winter echoes from simultaneous EISCAT and ESRAD observations
- 2005
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In: Annales Geophysicae. - : European Geosciences Union. - 0992-7689 .- 1432-0576. ; 23:4, s. 1239-1247
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Journal article (peer-reviewed)abstract
- On 30 October 2004 during a strong solar proton event, layers of enhanced backscatter from altitudes between 55 and 75km have been observed by both ESRAD (52MHz) and the EISCAT VHF (224MHz) radars. These echoes have earlier been termed Polar Mesosphere Winter Echoes, PMWE. After considering the morphology of the layers and their relation to observed atmospheric waves, we conclude that the radars have likely seen the same phenomenon even though the radars' scattering volumes are located about 220km apart and that the most long-lasting layer is likely associated with wind-shear in an inertio-gravity wave. An ion-chemistry model is used to determine parameters necessary to relate wind-shear induced turbulent energy dissipation rates to radar backscatter. The model is verified by comparison with electron density profiles measured by the EISCAT VHF radar. Observed radar signal strengths are found to be 2-3 orders of magnitude stronger than the maximum which can be expected from neutral turbulence alone, assuming that previously published results relating radar signal scatter to turbulence parameters, and turbulence parameters to wind shear, are correct. The possibility remains that some additional or alternative mechanism may be involved in producing PMWE, such as layers of charged dust/smoke particles or large cluster ions.
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| 3. |
- Dalin, Peter A., et al.
(author)
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Wave influence on polar mesosphere summer echoes above Wasa : experimental and model studies
- 2012
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In: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 30:8, s. 1143-1157
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Journal article (peer-reviewed)abstract
- Comprehensive analysis of the wave activity in the Antarctic summer mesopause is performed using polar mesospheric summer echoes (PMSE) measurements for December 2010–January 2011. The 2-day planetary wave is a statistically significant periodic oscillation in the power spectrum density of PMSE power. The strongest periodic oscillation in the power spectrum belongs to the diurnal solar tide; the semi-diurnal solar tide is found to be a highly significant harmonic oscillation as well. The inertial-gravity waves are extensively studied by means of PMSE power and wind components. The strongest gravity waves are observed at periods of about 1, 1.4, 2.5 and 4 h, with characteristic horizontal wavelengths of 28, 36, 157 and 252 km, respectively. The gravity waves propagate approximately in the west-east direction over Wasa (Antarctica). A detailed comparison between theoretical and experimental volume reflectivity of PMSE, measured at Wasa, is made. It is demonstrated that a new expression for PMSE reflectivity derived by Varney et al. (2011) is able to adequately describe PMSE profiles both in the magnitude and in height variations. The best agreement, within 30%, is achieved when mean values of neutral atmospheric parameters are utilized. The largest contribution to the formation and variability of the PMSE layer is explained by the ice number density and its height gradient, followed by wave-induced perturbations in buoyancy period and the turbulent energy dissipation rate
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| 4. |
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| 5. |
- Kirkwood, Stella, et al.
(author)
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Ionization and NO production in the polar mesosphere during high-speed solar wind streams: model validation and comparison with NO enhancements observed by Odin-SMR
- 2015
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In: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 33:5, s. 561-572
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Journal article (peer-reviewed)abstract
- Precipitation of high-energy electrons (EEP) intothe polar middle atmosphere is a potential source of signif-icant production of odd nitrogen, which may play a role instratospheric ozone destruction and in perturbing large-scaleatmospheric circulation patterns. High-speed streams of so-lar wind (HSS) are a major source of energization and pre-cipitation of electrons from the Earth’s radiation belts, butit remains to be determined whether these electrons makea significant contribution to the odd-nitrogen budget in themiddle atmosphere when compared to production by solarprotons or by lower-energy (auroral) electrons at higher al-titudes, with subsequent downward transport. Satellite ob-servations of EEP are available, but their accuracy is notwell established. Studies of the ionization of the atmospherein response to EEP, in terms of cosmic-noise absorption(CNA), have indicated an unexplained seasonal variation inHSS-related effects and have suggested possible order-of-magnitude underestimates of the EEP fluxes by the satelliteobservations in some circumstances. Here we use a model ofionization by EEP coupled with an ion chemistry model toshow that published average EEP fluxes, during HSS events,from satellite measurements (Meredith et al., 2011), are fullyconsistent with the published average CNA response (Ka-vanagh et al., 2012). The seasonal variation of CNA responsecan be explained by ion chemistry with no need for any sea-sonal variation in EEP. Average EEP fluxes are used to esti-mate production rate profiles of nitric oxide between 60 and100 km heights over Antarctica for a series of unusually wellseparated HSS events in austral winter 2010. These are com-pared to observations of changes in nitric oxide during theevents, made by the sub-millimetre microwave radiometer onthe Odin spacecraft. The observations show strong increasesof nitric oxide amounts between 75 and 90 km heights, at alllatitudes poleward of 60 ◦ S, about 10 days after the arrival ofthe HSS. These are of the same order of magnitude but gen-erally larger than would be expected from direct productionby HSS-associated EEP, indicating that downward transportlikely contributes in addition to direct production.
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| 6. |
- Kirkwood, S., et al.
(author)
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Polar mesosphere winter echoes by ESRAD, EISCAT and lidar
- 2002
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Book (other academic/artistic)abstract
- The ESRAD 52 MHz MST radar (67° 53 ‘ N, 21 ° 06 ‘ E) has observed thin layers of enhanced radar echoes in the winter mesosphere during several recent solar proton events. The detection of these polar mesosphere winter echoes (PMWE) is generally found to correlates well with low values of λ (the ratio of negative ion density to electron density). However PMWE are found to persist for values of λ up to ~100. Present knowledge of the nature of neutral turbulence in the winter mesosphere suggests that such turbulence cannot generate electron density fluctuations with scale-sizes as short as the 3 m needed to produce radar echoes at 52 MHz. This is particularly true as λ increases to ~100. Joint observations from ESRAD and the EISCAT 224 MHz radar suggest that PMWE is also detectable at 67 cm scale-sizes, further increasing the difficulty in explaining the echoes by neutral turbulence. Joint observations from ESRAD and lidar are also inconsistent with the expected behaviour of turbulence. Together with results concerning the thickness, echo aspect-sensitivity and echo spectral-width of the PMWE, these observation leads to the conclusion that the layers cannot be explained by turbulence alone. A role for charged aerosols in creating PMWE is proposed. The presence of aerosols is supported by the lidar observations.
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| 7. |
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