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The exact solution of the jump conditions on the RD/SMS discontinuity system in a two-and-half-dimensional (2 1/2-D) symmetrical reconnection model enables one to analyse the outflowing jet characteristics in dependence on the inflow velocity, and to follow changes in transition to the two-dimensional model. Implications arising from the exact solution and its relevance for solar flares are discussed.
Inspired by the fact that the waiting time of solar flares presents a power-law distribution, this paper is aimed to investigate the waiting time distribution of coronal mass ejections (CMEs). SOHO/LASCO data from 1996 to 2001 are collected. It is shown that the observed CMEs reveal a similar power-law behavior as flares, and the power- law indices for both phenomena are almost identical. This finding...
This work presents the first quiet Sun spectropolarimetric observations carried out in the visible and the infrared (IR) simultaneously. The Fe i lines at 6301.5, 6302.5, 15648, and 15652 Å were observed co-spatially, and at the same time (with a time lag of only 1 minute), with high sensitive spectropolarimeters operated in two di erent telescopes (VTT and THEMIS at the Observatorio del Teide). We...
We present a topological model of the active region NOAA 9077, where the large two-ribbon flare (3B/X5.7) occurred on July 14, 2000. The coronal magnetic field was reconstructed on the basis of SOHO magnetograms. The model interprets the two-ribbon structure of the flare, the location and the form of the bright chromospheric ribbons and the appearance of bright kernels on the ribbons’ ends, observed...
We present results from polarimetric data on sunspot penumbrae obtained with the Vacuum Tower Telescope at the Observatorio del Teide, Tenerife, using the ‘Göttingen’ Fabry-Pérot Interferometer. Speckle image reconstruction has been performed giving us a spatial resolution of 0.6″. The observations were taken in the Fe II 6149.2 Å line which, given its particular Zeeman splitting, has no instrumental...
An analysis of the August 20, 2002 flare using RHESSI, Hα, and radio observations is presented. Radio data in the decimetric frequency range showed a type IIId (relativistic) burst at the time of the X-ray maximum. At this time a very flat (γphot = 1.8) X-ray spectrum was measured. Fitted double power-law spectra in the thick-target model revealed an increase of the low energy cuto in the electron...
RISE/PSPT full disk solar images (2k × 2k) with a resolution of 1 arcsec per pixel, observed in 1999 at Mauna Loa Observatory (MLSO), Hawaii, are used to measure the contrast of facular areas as function of the two variables μ and Ek, where μ is the cosine of the heliocentric angle Θ and Ek is the Ca ii K excess. The analysis comprises...
Data from the SOHO LASCO CME catalogue are used to investigate the acceleration-velocity relationship of CMEs. We analyse 5012 individual events reported in the catalogue from 1996 to 2001. The dependence of acceleration on velocity is considered using the mean distance and width of CMEs as parameters. The obtained relationship is interpreted in the frame of a magnetohydrodynamic drag. The results...
We study RHESSI data for 14 impulsive M class flares which show a soft-hard-soft spectral evolution. The photon spectral index and the flux at a reference energy of 35 keV are in all cases anti-correlated. The data can be fitted by a simple empirical model of a power-law relation between the flux and the spectral index.
SOHO/CDS measurements of the quiet Sun chromospheric He i 584.33 Å and transition region O v 629.73 Å spectral lines are used to study the ability of the CDS instrument to detect Doppler shifts of spectral lines in the supergranular network and internetwork using short exposures. A precise analysis revealed that the CDS instrument is not suitable for the detection of mass motion in the internetwork,...
Analysis of a blinker, observed with the SUMER/SOHO spectrometer in the C ii 1036.34 Å, C ii 1037.01 Å, O vi 1037.61 Å lines and in C i continuum, is presented. We find that the blinker is highly pronounced in both the chromosphere and transition region. Intensities of chromospheric and transition region lines behave similarly although the blinker is more pronounced in the upper transition region.
We analyze daily numbers of solar Hα flares with regard to their periodical occurrences related to rotational modulations (∼20d–30d) and the so-called “activity”periods (∼150d–160d). We focus on the separate analysis of the northern and southern solar hemisphere as well as on an energy dependence of the flare...
Spectro-polarimetric measurements of the D3-He i 5876 Å line profile in 35 prominences have been performed in 2003 with the Gregory-Coudé Telescope in Locarno. Two different experimental techniques (ZIMPOL and beam exchange method) have been successfully employed to determine all four Stokes components. Both give compatible results. The preliminary results as well as the measurement techniques are...
As it is well known, sunspots contain both vertical and horizontal strong magnetic fields. We are interested in the line-of-sight velocity structures in sunspots, with emphasis on penumbral motions. There are two types of regular motion of the solar plasma in the sunspot penumbra, namely the Evershed effect and oscillations. We were successful in the identification of a relation between some oscillatory...
46 solar flares showing 228 impulsive SXR brightenings have been investigated using Yohkoh data. For 18 flares we made a quantitative comparison between footpoints seen in soft and hard X-rays. We present evidence that in the flare impulsive phase chromospheric evaporation is driven mainly by low-energy non-thermal electrons.
Line-of-sight velocity fields in an irregular sunspot (NOAA 8990) have been determined from Stokes-I spectra of the line Fe i 630.15 nm, obtained with the La Palma Stokes Polarimeter at the Swedish Vacuum Solar Telescope on May 13, 2000. We show and discuss the resulting velocity maps and asymmetry of the Fe i line.
We analyzed tilt angles and daily tilt angle changes of bipolar magnetic regions (BMRs). We find that generally regular BMRs grouped by age do not show the phenomenon of toroidal relaxation towards the east-west direction. We interpret this by the disconnection of Ω-loops from the bottom of the convection zone.
Here we present the lowest-in-altitude observed signatures of the fast solar wind streams. They originate from coronal holes (CH) network boundaries, as seen in the low transition region (TR) line O iii 703.87 Å (Te ≈ 8 × 104 K). Higher in the solar corona, the plasma outflow is seen in the Mg ix 706.02 Å line (Te ≈ 106 K), as an increased...
High frequency acoustic waves have been proposed as a mechanism to heat the solar chromosphere in internetwork regions. Such waves are di cult to detect using ground based observations because of seeing. Space based solar observatories like SOHO and TRACE are not hampered by such high frequency disturbances caused by the Earth’s atmosphere. We have used detailed NLTE radiation hydrodynamic simulations...
Magnetic helicity (MH) has been recognized as a useful tool to study the link between active regions (ARs) and magnetic clouds (MCs). In this work, we compare the MH and flux of the MC of October 18–19, 1995, and its associated AR. We compute both quantities and we find that the AR flux is one order of magnitude larger than in the MC, while the coronal MH is lower after an ejection linked to a long...
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