Recent discoveries of MHD wave motions in the solar corona done with EUV imaging telescopes onboard SOHO and TRACE provide an observational basis for the MHD seismology of the corona. Measuring the properties of MHD waves and oscillations (periods, wavelengths, amplitudes, temporal and spatial signatures), combined with theoretical modeling of the wave phenomena, allow us to determine values of the mean parameters of the corona (the magnetic field strength, transport coefficients, etc.). As an example, we consider post-flare decaying oscillations of loops, observed with TRACE (14th July 1998 at 12:55 UT). An analysis of the oscillations shows that they are quasi-harmonic, with a period of about 265 s, and quickly decaying with the decay time of about 14.5 min. The period of oscillations allows us to determine the Alfvén speed in the oscillating loop about 770 km/s. This value can be used for deduction of the value of the magnetic field in the loop (giving 10-30 G). The decay time, in the assumption that the decay is caused by viscous (or resistive) dissipation, gives us the Reynolds number of 105.3-6.1 (or the Lundquist number of 105.0-5.8).

We present results from a study of extreme-ultraviolet (EUV) off-limb spectra obtained with the SUMER instrument on the spacecraft SOHO. Using EUV line intensities, we deduce plasma temperatures and densities in the off-limb solar plasma. We make use of this information to study the FIP effect in the solar corona. We have looked for FIP effect in EUV spectra obtained by SUMER in a considerable detail. In particular, we report K/Ar, Si/Ar and S/Ar relative element abundances and investigate the height dependence of the FIP bias in the solar corona. Also, we study the relative Mg/Ne abundance in an active region at the solar limb to investigate the correlation of the FIP bias with magnetic loop structures in the field of view.

To allow an objective study of transition region blinkers an automated identification program has been developed to analyse the CDS/SoHO data. The general properties of blinkers identified by this method confirmed the properties of those identified by eye in previous studies. Blinkers have typical lifetimes of about 20 minutes, areas of about 2.8 × 107 km2 and intensity enhancement factors of about 2. For the first time, blinkers have been identified in active regions. These blinkers have the same general properties as quiet-region blinkers. The automated approach found many more blinkers than previously had been found giving a global birth rates of about 9 s−1 for quiet-region blinkers and 16 s−1 for active-region blinkers. Most blinkers, active or quiet region, are red shifted with typical velocities of about 13 km s−1. Finally, we can confirm that blinkers are not enhancements in temperature, but either enhancements in density or increases in the filling factor.

Observations of the solar corona with the LASCO and EIT instruments on SOHO provide an unprecedented opportunity to study coronal mass ejections (CMEs) from their initiation through their evolution out to 30 R⊙. The objective of this study is to gain an understanding of the source regions from which the CMEs emanate. To this end, we have developed a list of 32 CMEs whose source regions are located on the solar disk and are well observed in EIT 195 Å data during the solar minimum phase of January 1996-May 1998. We compare the EIT source regions with photospheric magnetograms from the Michelson Doppler Imager (MDI) instrument on SOHO and the NSO/Kitt Peak Observatory and also with Hα data from various sources. The overall results of our study show that 59% of the CME related transients observed in EIT 195 Å images are associated with active regions without prominences, 22% are associated with eruptions of prominences embedded in active regions and 19% are associated with eruptions of quiescent prominences. We describe 3 especially well observed events, one from each of these 3 categories. These case studies suggest that active region CMEs are associated with active regions with lifetimes between 11-80 days. They are also often associated with small scale emerging or cancelling flux over timescales of 6-7 hours. CMEs associated with active region prominence eruptions, on the other hand, are typically associated with old active regions with lifetimes ~ 6-7 months.

We present observations taken in the corona above a flare that occurred on the west limb of the Sun. SUMER spectra show large red (350 km s−1) and blue (650 km s−1) Dopplershifts in Fe XX (107 K), Cr XVI (5 × 106 K), Si IX (106 K) and O III (105 K) emission lines. These shifts are associated with a fast moving (400 km s−1) optical emission front detected in high cadence images, taken with the coronagraph MICA. SXT images show fast soft X-ray ejecta that can be extrapolated back to the position of pre-flare coronal arcade structure seen in EIT 195 images. The observations are interpreted as evidence of a blast wave propagating through the active region coronal loop structure very early in the flare evolution.

The solar rotation is determined tracing coronal EUV and soft X-ray bright points, active regions, parts of coronal holes and foot points of coronal loops. Full-disc solar images in the EUV part of the spectrum from the SOHO spacecraft (EIT, Fe XV, 28.4 nm) and from the Yohkoh satellite (SXT, 2 nm) are used.

We investigate brightness variations of the quiet Sun using movies obtained with CDS and SUMER time series on SOHO. We compare the variability and relative variability detected with the two instruments and find that SUMER reveals a factor 2-3 higher variability than CDS.

By solving simultaneously the radiative transfer and statistical equilibrium equations we compute lines profiles for the Ca II H and K lines, Mg II h and k lines and He I at 584,3 Å for several prominence models given by the hydrogen atom. The computed profiles are compared with the observations in order to constrain the physical plasma parameters of solar prominences.

CaII K line has been measured regularly nearly every month since 1974 at Kitt Peak. Our study on the data of CaII K profiles over two solar cycles indicates that in center disc spectra, the distance of the K1 component of the CaII K line from the line center and its intensity show periodical variations, but has a time delay of 1.2 years with respect to the sunspot number. Non-LTE computation implies a cyclic temperature variation of about 17 K of the temperature minimum region (TMR) in the quiet-Sun atmosphere and a cyclic variation of about 15-20 km of the position of the TMR.

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.

The three-dimensional structure of the magnetic field in the source region of CMEs is the key to understand how the stored magnetic energy eventually causes an eruption. A CME accompanied by a filament eruption on 2000 February 26-27 is particularly a good event to study the three-dimensional magnetic field structure. This event was very well observed with the EIT and LASCO of SOHO and the SXT of Yohkoh, and shows the following clues of the magnetic field structure which caused the CME. (1) The filament had a helical structure before the eruption and it was kept throughout the eruption. (2) The coronal loop structure shows that this event was an eruption of a part of the quadrapolar magnetic field structure consisting of two active regions. In this proceeding, we present a brief overview of the event.

Observations with the SORO/CDS NIS detector prior to the recovery of SOHO showed strong correlations between line shifts and local intensity gradients along the slit, probably caused by an elliptical, tilted point spread function. This must be taken into account when interpreting NIS observations with strong intensity gradients. An initial analysis of post-recovery data does not display the same pattern, indicating that this particular problem was eliminated by changes in the optics during SOHO's “vacation”.

We report statistical features of 49 eruptive prominences observed near solar maximum (1999-2000) with Nobeyama Radiohelograph. Here we focus on the location and related phenomena of the prominence activity. By using white light synoptic maps from LASCO C2 coronagraph, we found that most of the events are associated with some heating process taking place around the prominence site, and occur along pre-existing streamers associated with CMEs as well as small mass ejections. These features suggest that streamers connect the activity on the solar surface toward the outer corona.

We discuss the nature of polar rays, based on limb synoptic images constructed from Yohkoh/SXT and SORafElT data. In the literature, polar rays and polar plumes are often mentioned interchangably. We find that polar rays are projection effects caused by hot plasma from equatorial active areas and are not physically associated with the coronal polar holes. Instead, the rise in number and strength of polar rays toward solar activity maximum may be responsible for hiding the polar holes and polar plumes.

High resolution temporal observations performed with the SUMER spectrometer on SoHO provide us the opportunity to investigate the electron density variations in the solar mid-transition region due to explosive event-like phenomena. The O IV 1401.16/1404.81 density sensitive line intensity ratio shows a clear increase during a strong explosive event, corresponding to an electron density enhancement of a factor of ~ 3 with respect to pre-event values. This is consistent with recent MHD simulations (2.5 D).

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 this paper a summary of results from coordinated observations of streamers acquired by the SOHO Coronal Diagnostic Spectrometer (CDS) and Ultra Violet Coronograph Spectrometer (UVCS) experiments is presented (Parenti et al. 2000). Data from different altitudes within the solar corona were taken, with the purpose of determining their physical parameters – densities, electron temperatures and element abundances – and their changes over the altitude range between 1.02 and 1.6 R⊙. Further UVCS streamer data, taken about two months later are used to compare with the behaviour seen in two different streamers. The streamers resulted to have a different behaviour in temperature and density. The low corona, covered by CDS data, shows little evidence of abundance variation with respect to photospheric values, while, at UVCS altitudes, a depletion of all element abundances is clearly evident.

Frequency distributions of the intensities of EUV emission lines in the quiet Sun have in the past usually been modelled using two Gaussians. Here we test this and other distribution functions against observed distributions with exceptional statistics. The data were obtained in a number of spectral lines observed with CDS and SUMER. We show that the frequency distribution of the radiance is best modelled by a lognormal distribution. The fact that the radiance distribution of the quiet Sun including the network and the intranetwork is better reproduced by a single lognormal distribution function than by two Gaussians suggests that the same heating processes are acting in both types of features.

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.

In this paper, the theory and method of fuzzy classification are applied to analyse CME properties, with the use of the data in preliminary report during 1979-1981, the theoretical computation for CME category is performed. According to the original data of average properties for 9 structural classes of CME, the standardized value is obtained by average value and standard deviation. The fuzzy similitude matrix and equivalent matrix are built by use of the correlation coefficient transformation and the method of similitude coefficient, then we can divide 9 different structures into different categories according to different threshold value. Halo was the most energetic, and Single Spike, Diffuse Fan CMEs were the least energetic.