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1.
Flux-energy spectra of precipitating electrons are derived from electron density profiles measured by the EISCAT radar during auroral absorption events in the morning/noon local-time sector. The inversion technique uses effective recombination coefficient profiles computed on the basis of a previously validated theoretical model of the lower ionosphere. It is shown that flux-energy spectra for the energy range 30–200 keV are in reasonable agreement with those derived for the same events using trapped flux-energy spectra from geosynchronous satellite data and a model for diffusion of trapped electrons into the loss cone by scattering on whistler waves. During individual events, strongly varying precipitating fluxes are found to be due primarily to varying pitch-angle diffusion. 相似文献
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A. R. Breen P. J. Moran C. A. Varley W. P. Wilkinson P. J. S. Williams W. A. Coles A. Lecinski J. Markkanen 《Annales Geophysicae》1998,16(10):1265-1282
Co-rotating interaction regions (CIRs) between fast and slow streams of plasma are a prominent feature of the solar wind. Measurements of interplanetary scintillation (IPS) using the three widely separated antennas of the EISCAT facility have been used to detect the compression regions at the leading edges of interaction regions and to determine the location and velocity of the structure. Observations show that interaction regions have developed as close to the Sun as 25–30 solar radii, a result supported by theoretical modelling which shows that the conditions needed for CIRs to develop exist inside 30 solar radii. 相似文献
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Mesospheric observations were obtained by the EISCAT UHF and VHF radars during the solar proton event of March 1990. We present the first comparison of incoherent-scatter spectral measurements from the middle mesosphere using simultaneous, co-located observations by the two radars. VHF spectra observed with a vertical antenna were found to be significantly narrower than model predictions, in agreement with earlier UHF results. For antenna pointing directions that were significantly away from the vertical, the wider VHF radar beam gave rise to broadening of the observed spectra due to vertical shears in the horizontal wind. In this configuration, UHF spectral measurements were found to be more suitable for aeronomical applications. Both radar systems provide consistent and reliable estimates of the neutral wind. Spectral results using both the multipulse and pulse-to-pulse schemes were intercompared and their suitability for application to combined mesosphere - lower thermosphere studies investigated. 相似文献
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Tomographic reconstruction of the three-dimensional auroral are emission is used to obtain vertical and horizontal distributions of the optical auroral emission. Under the given experimental conditions with a very limited angular range and a small number of observers, algebraic reconstruction methods generally yield better results than transform techniques. Different algebraic reconstruction methods are tested with an auroral are model and the best results are obtained with an iterative least-square method adapted from emission-computed tomography. The observation geometry used during a campaign in Norway in 1995 is tested with the are model and root-mean-square errors, to be expected under the given geometrical conditions, are calculated. Although optimum geometry was not used, root-mean-square errors of less than 2% for the images and of the order of 30% for the distribution could be obtained. The method is applied to images from real observations. The correspondence of original pictures and projections of the reconstructed volume is discussed, and emission profiles along magnetic field lines through the three-dimensionally reconstructed arc are calibrated into electron density profiles with additional EISCAT measurements. Including a background profile and the temporal changes of the electron density due to recombination, good agreement can be obtained between measured profiles and the time-sequence of calculated profiles. These profiles are used to estimate the conductivity distribution in the vicinity of the EISCAT site. While the radar can only probe the ionosphere along the radar beam, the three-dimensional tomography enables conductivity estimates in a large area around the radar site.Former address: MPE Garching 相似文献
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Prikner K. Mursula K. Kangas J. Feygin F. Z. Kerttula R. 《Studia Geophysica et Geodaetica》2002,46(3):507-526
The ionospheric Alfvén resonator (IAR) was numerically simulated under non-stationary ionospheric and magnetospheric conditions of the IPDP event of December 4, 1986. The full numerical wave method was applied using height profiles of the ionospheric plasma parameters obtained from the Scandinavian EISCAT radar measurements close to the Ivalo latitude. An attempt to model the inverse problem of numerical simulation—prolongation of the electron density profiles at altitudes above the ionospheric F layer—was made on the basis of the IAR simulation in correlation with the IPDP frequency increase. The change of the IAR wave characteristics during the substorm was illustrated by height profiles of the total wave amplitude and various polarization characteristics, taking into consideration the ordinary L-mode and the extraordinary R-mode waves for parallel and non-parallel incidence with respect to the magnetic field line. 相似文献
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Csilla Szasz Johan Kero Asta Pellinen-Wannberg David D. Meisel Gudmund Wannberg Assar Westman 《Earth, Moon, and Planets》2008,102(1-4):373-378
We have investigated the conditions for simultaneous meteor observations with the EISCAT UHF radar system and telescopic optical
devices. The observed characteristics of 410 meteors detected by all three UHF receivers are compared with model simulations
and their luminosity is calculated as a part of a meteoroid ablation model using a fifth order Runge–Kutta numerical integration
technique. The estimated absolute visual magnitudes are in the range of +9 to +5. The meteors should therefore be observable
using intensified CCD or EMCCD (Electron Multiplying CCD) cameras with telephoto lenses. A possible setup of a coordinated
radar and optical campaign is suggested. 相似文献
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本文利用欧洲非相干散射雷达数据,分析研究了极光带静日电离层行扰,得到较高F区中非线性波-波相互作用的实验证据.TID动态频谱与一维波数谱显示等离子体参量起伏（不规则性）时空尺度由长周期向短周期、由小波数向大波数演化;双谱与作用密度时变率表明有一系列连锁式非线性三波共振相互作用发生.重力波波数随高度的变化说明在较高F区出现了重力波的过反射（over-reflection）.简要讨论了引起过反射的波-流相互作用.重力波的反射及其波数的弱频散性有可能使非线性三波相互作用共振条件得以满足. 相似文献
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Anja Strφmme 《极地研究(英文版)》2002,13(1)
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Ion composition measurements and modelling at altitudes from 140 to 350 km using EISCAT measurements
This work aims at processing the data of CP1 and CP2 programs of EISCAT ionospheric radar from 1987 to 1994 using the –full profile method which allows to solve the –temperature-composition ambiguity problem in the lower F region. The program of data analysis was developed in the CEPHAG in 1995–1996. To improve this program, we implemented another analytical function to model the ion composition profile. This new function better reflects the real profile of the composition. Secondly, we chose the best method to select the initial conditions for the –full profile procedure. A statistical analysis of the results was made to obtain the averages of various parameters: electron concentration and temperature, ion temperature, composition and bulk velocity. The aim is to obtain models of the parameter behaviour defining the ion composition profiles: z50 (transition altitude between atomic and molecular ions) and dz (width of the profile), for various seasons and for high and low solar activities. These models are then compared to other models. To explain the principal features of parameters z50 and dz, we made an analysis of the processes leading to composition changes and related them to production and electron density profile. A new experimental model of ion composition is now available. 相似文献