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Abstract

The Extreme Ultraviolet Imaging Telescope (EIT) on board the SOHO spacecraft has been operational since 2 January 1996. EIT observes the Sun over a 45 ࣾ 45 arc min field of view in four emission line groups: Fe IX, X, Fe XII, Fe XV, and He II. A post-launch determination of the instrument flatfield, the instrument scattering function, and the instrument aging were necessary for the reduction and analysis of the data. The observed structures and their evolution in each of the four EUV bandpasses are characteristic of the peak emission temperature of the line(s) chosen for that bandpass. Reports on the initial results of a variety of analysis projects demonstrate the range of investigations now underway: EIT provides new observations of the corona in the temperature range of 1 to 2 MK. Temperature studies of the large-scale coronal features extend previous coronagraph work with low-noise temperature maps. Temperatures of radial, extended, plume-like structures in both the polar coronal hole and in a low latitude decaying active region were found to be cooler than the surrounding material. Active region loops were investigated in detail and found to be isothermal for the low loops but hottest at the loop tops for the large loops.Variability of solar EUV structures, as observed in the EIT time sequences, is pervasive and leads to a re-evaluation of the meaning of the term 'quiet Sun'. Intensity fluctuations in a high cadence sequence of coronal and chromospheric images correspond to a Kolmogorov turbulence spectrum. This can be interpreted in terms of a mixed stochastic or periodic driving of the transition region and the base of the corona. No signature of the photospheric and chromospheric waves is found in spatially averaged power spectra, indicating that these waves do not propagate to the upper atmosphere or are channeled through narrow local magnetic structures covering a small fraction of the solar surface. Polar coronal hole observing campaigns have identified an outflow process with the discovery of transient Fe XII jets. Coronal mass ejection observing campaigns have identified the beginning of a CME in an Fe XII sequence with a near simultaneous filament eruption (seen in absorption), formation of a coronal void and the initiation of a bright outward-moving shell as well as the coronal manifestation of a 'Moreton wave'.

Global Properties of Solar Flares

“…The "EIT wave" observed in one of the EUV wave bands (typically 171 Å or 195 Å) was a striking observation that came with SOHO's EIT instrument (Moses et al 1997;, although earlier EUV observations of course showed similar structures if not so well from the point of view of imaging (e.g., Neupert 1989). Figure 13 shows one of the early examples, that of SOL1997-04-07T14:03 .…”

On the Nature and Genesis of EUV Waves: A Synthesis of Observations from SOHO, STEREO, SDO, and Hinode (Invited Review)

“…One of the most important, as well as intriguing, discoveries of EIT (Delaboudinière et al, 1995) on-board the Solar and Heliospheric Observatory (SOHO) were the EIT or EUV waves (Moses et al, 1997;Thompson et al, 1998Thompson et al, , 1999. These are brightness fronts which propagate over significant fractions of the solar disk, mostly over quiet Sun (QS) areas, at speeds which can reach several hundred km s −1 (e.g.…”

Nonlinear force-free field extrapolation of the coronal magnetic field using the data obtained by the Hinode satellite

“…[2] In the solar corona, plasmas are confined by the magnetic field as shown in the soft X-ray solar images [Vaiana et al, 1973;Vaiana and Rosner, 1978;Tsuneta et al, 1992;Reale et al, 2007], the extreme ultraviolet (EUV) solar images [Sheeley et al, 1975;Moses et al, 1997;Schrijver et al, 1999;Wiegelmann et al, 2009], as well as the total solar eclipse coronal images [Pasachoff, 2009a[Pasachoff, , 2009bPasachoff et al, 2009]. Trapped plasmas above solar active regions form the coronal loops which reflect the shapes of the field lines [Krieger et al, 1971].…”