Date: Sun, 6 May 2001 02:23:08 -0600 (MDT) From: Cedar project To: carol.hanchett@noaa.gov, emery@ucar.edu, richmond@ucar.edu Subject: 2001 Abstract from Claus Fröhlich ------------------------------------------------------------- 2001 CEDAR-SCOSTEP Abstract sent to emery, richmond, hanchett ------------------------------------------------------------- Year Yrday Month Month Day UTHour Min = 2001 126 5 6 8 23 Corresponder Name: Corresponder E-mail: cfrohlich@pmodwrc.ch Special requests or comments: ---------------------------------------- Type of abstract: Invited Presenter Name: Claus Frohlich Status of first author: ---------------------------------------- Title: Solar Irradiance Variations: Measurements and Results ---------------------------------------- Authors: Claus Frohlich Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, CH-7260 Davos Dorf, Switzerland e-mail: 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, this composite 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'. ---------------------------------------- International Solar Cycle Studies (ISCS/SCOSTEP) Solar Atmosphere Long-Term Relations in Sun-Earth Climate (part of S-RAMP/SCOSTEP)