Title: Solar Irradiance Variations: Measurements and Results
Author: Claus Fröhlich
Affil: PMOD/WRC, Davos, Switzerland
Email: cfrohlich@pmodwrc.ch
Abstract: Since November 1978 with the start of the NIMBUS7 total solar irradiance monitoring started a complete set of TSI measurements from space are available, yielding a time series of more than 20 years. From measurements made by five of these radiometers a composite record of solar total irradiance can be compiled. The radiometric, instrumental and operational influences and constraints are discussed in order to assess the precision and accuracy of this composite. This assessment is based on an extensive study of the behaviour of the radiometers on VIRGO/SOHO. Moreover, it is the basis for an evaluation of the influence of solar activity on total solar irradiance. An empirical model that parameterizes the combined influences of dark sunspots and bright faculae features on solar irradiance is able to explain more than 90% of the variance. After removing the magnetic influence with the model, the remaining `quiet sun' shows no trend over the whole period, indicating that the sun's output has not changed over the past two solar cycles besides the modulation with activity. There are, however, deviations, the physical origin of which are still to be explored.
The spectral measurements at 402, 500 and 862 nm by the sunphotometer within VIRGO/SOHO provide a continuous time series of the spectral distribution from minimum to maximum of solar cycle 23. These results allow to study the spectral redistribution within the energetically important part of TSI.
Title: Solar Ultraviolet Irradiance Research: Status and Prospects
Author: Linton Floyd
Affil: NRL/Interferometrics, Inc.
Email: floyd@susim.nrl.navy.mil
Abstract: The solar ultraviolet (UV) irradiance (in the 120-400 nm wavelength range) profoundly affects our planet, especially its atmosphere. The first observations at mid-century established its approximate magnitude, its wavelength-dependent penetration of Earth's atmosphere, and its resolution into emission and absorption lines and continua. For the past 25 years, numerous measurements of the solar UV have been made from balloons, rockets, the space shuttle, and satellites. The focus of this ongoing measurement program is the establishment of its wavelength- dependent intensity with improved measurement accuracy and its variation over solar rotation (27 day) and solar activity cycle (11 year) timescales and beyond. These measurement results have provided the basis for theoretical and modeling research. For the most part, the goals of these studies have been the characterization of the measured irradiance and its variation in terms of either more easily measured proxies or observed solar structures from solar images, the modeling and projection of likely irradiance scenarios into the past and future, and, perhaps most importantly, increased understanding of solar and geophysical processes in terms of the underlying physics. This presentation will attempt to provide an overview of past, present and future measurements, our current understanding, and theoretical and modeling of the solar UV irradiance.
Title: Solar EUV Irradiance Variations: Measurements and Results
Author: Darrell L. Judge
Affil: University of Southern California
Email: judge@physics.usc.edu
Authors: D. McMullin, H. Ogawa
Abstract: The SOHO EUV absolute irradiance measurements of the full disk solar flux obtained by the SOHO CELIAS/SEM spectrometer since December 1995 will be presented. The spectral and temporal characteristics of the solar EUV variability and its correlation with established CME’s, and other dynamic events will be presented.