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The proposed model of particles transport in the solar atmosphere during flares consists in a low density plasmoid originating deep in the atmosphere and rising under magnetic and buoyancy forces. Confined particles are selectively released during the ascent and their interaction with the solar atmosphere produces X and γ bremsstrahlung. The characteristics of high energy particles released in the interplanetary medium are found to agree with observations.
During the MEDOC campaign #4 (October 1999), we observed an active region filament with the SUMER/SoHO spectrometer using the 584.33 Å HeI line. After a description of the HeI line profile in the filament, we present a Fourier analysis of SUMER long time observations. This analysis allows to detect oscillations in several ranges of periodicities: 6–20 min, 40–90 min. We discuss these periodicities in terms of Alfvén and magnetoacoustic waves obtained with a filament model developed by Joarder & Roberts (1993).
We present the results obtained from analyzing SUMER/SOHO observation data of a quiescent solar prominence. From the 1 hour data set, we derive via a wavelet transform, characteristic frequencies in terms of intensity and velocity oscillations, as measured in 4 transition region lines.
The aim of the present study is to confirm and enrich the results obtained so far on dynamics and diagnostics of solar prominences. A prominence observed on October 16/17, 1999 in the frame of the updated JOP09 was studied. A density diagnostics was made on the basis of the line intensity ratio O IV 1401/1404. The Doppler velocities were derived using SUMER Si IV, O IV and CDS O V 629.73 Å lines.
In the present work EUV spectra of quiet Sun regions, observed with the Coronal Diagnostic Spectrometer (CDS) on SOHO, are analysed in order to determine the Differential Emission Measure (DEM) of selected areas of the field of view. The purpose of the present work is to study the differences between the DEM curves of the quiet Sun cell centers areas, intermediate areas and network boundaries.
Solar Orbiter will provide, at very high spatial (35 km pixel size) and temporal resolution, novel observations of the solar atmosphere and unexplored inner heliosphere, which will be made in the heliosynchronous segments of the orbits at heliocentric distances near 45 solar radii and out of the ecliptic plane at high heliographic latitudes up to 38°. The Solar Orbiter will achieve its wide-ranging scientific aims with a suite of sophisticated instruments through an innovative orbit design.
This paper reviews the diagnostic techniques currently used to establish estimates of the physical properties of prominences. Most often the fine structure of prominences cannot be resolved. Because of this and the complex structures and the varied forms of prominences, it is difficult to establish definitive values for temperature, density, magnetic field, electric field, differential emission measure, mass flows, etc. Nevertheless, there are many useful techniques ranging from spectroscopic analysis to measurements of prominence oscillations. Most of the major techniques are reviewed in this paper, with examples of the results and an extensive bibliography. Special attention is paid to the potential diagnostic value of optically thick lines. Suggestions are made for further progress based on SOHO and other observations.
On September 21, 1996 a filament located in a region close to an enhanced network was observed with the SOHO SUMER and CDS instruments. Four Lyman lines have been detected (Lδ, Lϵ, L-6, L-7) by SUMER in the raster mode. We have corrected the spectral data for flatfield and destreching and made wavelength and absolute intensity calibrations. In all these lines we detect a central absorption and an asymmetry in the intensity of the two peaks. Preliminary NLTE computations indicate that these Lyman profiles and their absolute intensities can be reproduced with the existing models provided that we take into account a prominence-corona transition region (PCTR).
Simultaneous XUV and microwave (μ – ѡ) observations of a solar filament, performed by several instruments onboard SOHO and by the Very Large Array (VLA), are analyzed. The filament appears as a dark structure, very similar in shape to the optical Hα filament, in all images taken in the transition region (TR) lines observed by CDS, in the Ne VIII lines observed by SUMER at λ = 770Å and 780Å and at all radio wavelengths with 1.7 cm ≤ λ ≤ 6 cm. Contrary to that, in six TR lines observed by SUMER at λ > 1300Å no trace of the filament, either in absorption or in emission, is visible. Finally, at λ = 21 cm, as well as in all images taken in coronal lines by CDS and EIT, a dark feature is present at the filament position, although with less defined contours than in the first-mentioned TR images. The constraints imposed by all these observations are discussed and interpreted.
The possibility of multiple reflections generating standing surface wave modes carrying field-aligned current (FAC) in an arch-like prominence structure is studied. The conditions for enhancement of FAC leading to observable destabilising effects are specified.
Excellent review papers have been presented in this session by S. Solanki (Manifestations of solar magnetic fields), K. Dere (Coronal Mass Ejections and interplanetary ejecta) and W. Droege (Particle acceleration by waves and fields) and the relevant texts can be found in this volume.
The Joint Discussion benefited from three contributed papers: X-Ray/Radio network flares of the quiet Sun by A.O. Benz, S. Krucker, L.W. Acton, and T.S. Bastian (presented by A.O. Benz) Radio observations of coronal X-ray jets by M.R. Kundu
The distribution of the solar intensity in the Lyman α line has been measured close to the visible limb. It is compared to a computation including LTE departures (as evaluated by Y. Cuny). As far as the profile of the line and the intensity (integrated over the line) are concerned, the interspicular model of Coates is the only one which seems to agree with the observations.
For space weather applications, it is important to understand filaments evolution and especially their eruptions associated with coronal mass ejections. In view of the cadence and continuity of SDO observations, AIA and HMI offer a unique tool for such a program. Because of the data volume and the requirement of short latency, only an automated detection can be worked out. We present a new method for the automated detection and tracking of filaments, based on the analysis of AIA 30.4 nm He ii images, with the capability to use also the magnetic field measured by HMI.
Time resolved photoluminescence (PL) measurements are performed on oxidized and fresh porous silicon at room temperature. Comparing the evolution of the nanosecond time delayed PL in both cases, a new feature of the PL spectra is identified: the fast-red band, present as well in fresh or aged samples. The nonlinear excitation intensity dependence of this component is described by a simple model where, the Auger effect inside isolated silicon nanocrystallites plays the dominant role.
Carrier dynamics properties in swollen poly(octylthiophene) gels are investigated via their radiative and non-radiative recombination rates (Wr and Wnr respectively) as a function of their swelling ratio (Q). Photoluminescence decay time (τ, in the picosecond range) and luminescence quantum efficiency (QE) are found to strongly increase with Q. This implies that Wr increases and Wnr decreases as Q increases; such a result cannot be understood if one accounts only for the well-known dilution effect observed for organic dyes. Our interpretation is that the enhanced carrier transport due to the increase of interchain interactions observed upon deswelling induces a separation of carriers. Then, these latter present an increased probability to find non-radiative traps. Variation of the conductivity versus Q in doped gels is also discussed.
Highly porous silicon, well passivated via an anodic oxidation process, is a stable and efficient visible light emitter showing a 3% photoluminescence efficiency at room temperature. Luminescence decay times are on the order of 100 μs at room temperature and 10 ms at low temperature. Above room temperature the de-excitation is dominated by non-radiative processes well describe by a tunnelling escape of carriers from confined regions. The “anomalous” luminescence behaviour showing a dramatic increase of the lifetimes upon cooling associated with a decrease of the intensity is explained by the temperature dependence of the effective radiative recombination rates due to a population redistribution among two excited states with very different radiative relaxation rates.
It is shown that visible photoluminescence and electroluminescence can be obtained from porous silicon layers. Room temperature photoluminescence is readily obtained from as-formed high porosity samples. Light emission at wavelengths as short as 560 nm can be observed after further thinning of the silicon pore walls by dissolution in HF under illumination. Silicon walls can also be thinned by an electrochemical oxidation process, this method allowing to use layers of rather low porosities (65%) which thus gives good mechanical properties to the samples. The thinning of the already very small size crystallites of porous silicon leads to quantum size effects which are at the origin of the light emission far above the band gap of silicon. Photoluminescence decay characteristics suggest that a tunnelling effect could be involved in the recombination mechanism of photogenerated charge carriers. Bright electroluminescence during anodic oxidation of porous silicon has been also evidenced. The influence of the porosity, of the layer thickness and of the anodic current density on the integrated electroluminescence intensity are described in detail.
Bright visible electroluminescence has been evidenced during the anodic oxidation of ptype porous silicon films in aqueous electrolytes. It is shown that in galvanostatic conditions, two very different light emission regimes can be obtained depending on the anodic potential. At low potentials, during the progressive oxidation of the pore walls, the emission spectra present a maximum in the red-orange wavelengths : the emitted intensity increases with the oxidation level, while the maximum is shifted towards shorter wavelengths. This emission vanishes when the anodic potential starts to increase more rapidly. Upon increasing polarizations, a second regime of light emission with a spectrum centered in the green wavelength range is observed. In this case, the spectrum and the intensity are both stable under extended anodization.
This last regime which is explained by carrier injection into the anodic oxide is not specific of the porous character of samples. On the contrary, the red-orange emission is shown to be closely related to the photoluminescence properties of the porous layer. A phenomenologic model is proposed, which analyses the electroluminescence characteristic dependence upon the oxidation level in terms of competition between the enhancement of the radiative process and the progressive electrical cut-off of the emitting crystallites.
We analyze the intensity and decay time evolution of the porous silicon luminescence upon anodic oxidation, aging, chemiral thinning and temperature variation. Strong analogies are pointed out for the photoluminescence intensity as well as for the photoluminescence decay shape evolution. They are interpreted by the variation of the extension of the carrier wavefunction induced by the modification of potential barrier efficiencies. No additional assumption such as hopping of carriers was necessary to explain the decay shapes well fitted by stretched exponential. On the contrary our observations and our simple model are in favor of a strong localization of carriers. Some experimental results are revisited within the frame of this model.
We have produced lateral porosity modulation in porous silicon layers on a micron scale. Using the photosensitivity of the etching process and optical interferences, stripes are formed periodically on the top but also in the depth of the layer depending on the illumination wavelength. The periodicity of the structure is easily modified by changing the wavelength or the incident angles of the two laser beams used to create the modulated illumination. By rotating the sample, two dimensional structures have also been obtained. The samples formed by this procedure are characterised by light diffraction and photoluminescence both of which show the alternance of high and low porosity ranges. With this kind of in-depth lithography, easy and very cheap fabrication of porous silicon gratings promises a large potential range of applications of this material to integrated optics and photonics.