Search Publications
Total solar and spectral irradiance variations from solar cycles 21 to 23
Fröhlich, C.; Pap, J. M.; Floyd, L. +2 more
Total solar and UV irradiances have been measured from various space platforms for more than two decades. More recently, observations of the "Variability of solar IRradiance and Gravity Oscillations" (VIRGO) experiment on SOHO provided information about spectral irradiance variations in the near-UV at 402 nm, visible at 500 nm, and near-IR at 862 …
Variability and dynamic state of active region loops
Gurman, J. B.; Wilhelm, K.; Fredvik, T. +3 more
A set of 218 consecutive CDS rasters taken at the solar limb on October 26-28 1999 has been used to investigate the variability and plasma dynamics of active region loops. Each raster contains simultaneous images in 6 different lines, covering the full temperature range of CDS, 10 000 K (He I) to 2.7 MK (Fe XVI). Activity is seen to go on without …
Slow and fast solar wind acceleration near solar maximum
Breen, A. R.; Moran, P. J.; Tappin, S. J. +4 more
2-site measurements of interplanetary scintillation (IPS) provide measurements of solar wind speed in regions of the heliosphere which are otherwise inaccessible. We present results from co-ordinated observations made with the EISCAT and MERLIN facilities during 1999 and 2000, covering heliocentric distances from 7 to 80 solar radii (R) predominan…
Active longitudes and coronal structures during the rising phase of the solar cycle
Kosovichev, A. G.; Benevolenskaya, E. E.; Scherrer, P. H.
The longitudinal structure of the solar corona has been investigated during the transition period between solar cycles 22 and 23 and at the beginning of the current cycle 23 using the SOHO/EIT data obtained in 171 Å, 195 Å, 284 Å and 304 Å EUV lines. The EIT images were transformed into synoptic maps for each of the spectral lines, and for the 195…
Variability in the solar constant from irradiances shortward of Lyman-Alpha
Tobiska, W. Kent
The variation in the solar constant, S(t), is reproduced by the SOLAR2000 Research Grade v1.05 empirical solar irradiance model and is described for 5 solar cycles between cycles 18 and 23 (February 14, 1947 through May 31, 2000). This solar constant variation is dependent upon the derivation data sets and the formulation of SOLAR2000 which are de…
The solar corona in cycle 23
Del Zanna, G.; Fludra, A.; Thompson, W. T. +1 more
The Coronal Diagnostic Spectrometer (CDS) on SOHO has been recording EUV spectra and monitoring time variability of EUV line intensities, electron temperature and density in the low solar corona during the rising part of Cycle 23. The four-year data set includes daily synoptic observations in four EUV lines along the central meridian since April 1…
An investigation into instrumental nonlinear effects
Walker, S. N.; Balikhin, M. A.; Huff, R. +1 more
High order spectral techniques are one of the most powerful tools for the identification of non-linear processes in space plasma turbulence. Without such tools it is impossible to determine, for example, the occurrence of non-linear interactions between spectral components. However, since the observations made by an instrument involve some interna…
Observations of ultraviolet emission lines in solar coronal holes on the disk with SUMER on SOHO
Dammasch, Ingolf E.; Wilhelm, Klaus; Xia, Lidong
The Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrograph and other instruments on the Solar and Heliospheric Observatory (SOHO) have observed many solar polar coronal holes (PCHs) during the minimum of the sunspot cycle in 1996 and 1997. Based on the results obtained for PCHs, investigations of near-equatorial coronal holes (EC…
Constraints on ion outflow speeds and electron distribution function in the corona derived from sumer electron temperatures and SWICS ion fractions
Esser, R.; Edgar, R. J.
It has been a puzzle for quite some time that spectroscopic measurements in the inner corona indicate electron temperatures far too low to produce the ion fractions observed in the in situ solar wind. In the present paper we show that in order to reconcile the two sets of measurements, a number of conditions have to exist in the inner corona: 1) t…
Sumer observations of solar transition region structures and dynamics
Dammasch, Ingolf E.; Wilhelm, Klaus
Several raster scans of the UV/EUV spectrometer SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on SOHO (the Solar and Heliospheric Observatory of ESA and NASA) in quiet-Sun regions were used to study the region between the chromosphere and the corona, i.e., the transition region with a temperature range between ≈ 30 000 K and 400 000 …