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The technology leading to very large aperture telescopes and their optics has progressed well in the period since 1984 and plans for many new large aperture telescopes have been made. Focal plane instrumentation continues to become more sophisticated or more efficient: multi-object capabilities, automatic instrument control and operation, and increasing use of CCDs are examples of areas to which this applies. The proportion of time devoted to observations using two-dimensional photoelectronic detectors has grown substantially at many observatories, particularly with telescopes of moderate aperture; and the use of high quantum efficiency array detectors is now being extended into the infrared spectral region. Important advances have also been made in instrumentation and techniques for ground-based high angular resolution interferometry.
The Sun’s activity has been evolving in the ascending phase of Solar Cycle 23 since 1996. Similarly, the research on solar activity is also in the ascending phase of a new active period. Numerous new results have been obtained from a large amount of space and ground observations covering a wide spectral range. In particular, observations with YOHKOH, SOHO, and TRACE have revealed a multitude of phenomena and processes in the solar atmosphere which provide us a new picture of the Sun.
On May 7, 1991, several ground-based instruments have been coordinated to observe AR 6615 (S10-W26), before and during the flight of the SERTS rocket experiment (Schmieder et al.,1992):
– Imaging spectroscopy (MSDP) at the VTT telescope of Tenerife (collaboration Paris-Meudon and KIS Freiburg). Hα and NaD1 are observed simultaneously in 2D fields, with 9 and 11 wavelengths respectively (Mein, 1991).
– High resolution “white light” pictures (around 4686Å) at the Swedish Vacuum Solar Telescope (SVST) of La Palma (Scharmer et al., 1985).
We present below some data from both instruments. Magnetic field maps are also available from the Huairou magnetograph (China), and from the GCT telescope (KIS/Tenerife).
We present preliminary results on solar filaments observed from the ground and from SOHO in September 1996. Motions in the network and close to the filament “barbs” are shown at different levels of the chromosphere and the transition region.
The dynamic nature of the outer corona has been revealed in recent years by improved techniques of studying the corona with ground based instruments and from space. Rapid changes in the coronal brightness pattern takes the form of mass ejections in which the outward moving material generally appears to escape the Sun. These events are called coronal transients. Observations have shown that the excess mass and energy in coronal transients are supplied by material expelled from the chromosphere and lower corona in conjunction with Hα surface activity. The transients are the coronal response to release of mass and energy which are manifested by flares and eruptive prominences.
Ground- and space-based observations have confirmed the presence of oscillatory motions in prominences and they have been interpreted in terms of magnetohydrodynamic (MHD) waves. This interpretation opens the door to perform prominence seismology, whose main aim is to determine physical parameters in magnetic and plasma structures (prominences) that are difficult to measure by direct means. Here, two prominence seismology applications are presented.
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