HR: 1330h
AN: SH12A-1152 [PDF]
TI: Spectral Solar Irradiance Variability from {VIRGO} on {SOHO}: 1996 to present
AU: * Fr\"ohlich, C
EM: cfrohlich@pmodwrc.ch
AF: Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, Dorfstrasse 33, Davos Dorf,
7260
Switzerland
AU: Wachter, R
EM:
AF: Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, Dorfstrasse 33, Davos Dorf,
7260
Switzerland
AU: Wehrli, C
EM:
AF: Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, Dorfstrasse 33, Davos Dorf,
7260
Switzerland
AB:
Since February 1996 VIRGO filterradiometers on SOHO monitor spectral solar irradiance at 402, 500 and 862nm with a bandwidth
of 5nm. SOHO's vantage point at L1 allows uninterrupted observations of the Sun, 24 h a day and 365 days an year. Besides the
3-month gap during the SOHO vacation in summer 1998 and a few other minor gaps the record covers more than 99% of the
period up to now of almost 8 years of observations. The long-term behaviour of the operational channels is dominated by
instrumental degradation masking the solar variability signature. However, comparisons with the back-up channels allows to
take off some of the instrumental long-term variation, and the resulting time series can now provide reliable information
about variability with periods up to about 4--500 days. Time series with the long-term variation removed and the
corresponding periodogram show many similarities between the three channels and total solar irradiance. Details about the
spectral redistribution during changes of TSI are investigated by multivariate spectral analysis. Furthermore, comparison of
the spectral analysis of the cleaned 1-minute sampled time series during solar minimum (1996/7) and maximum (2001/2) allows
to asses the variation of power with the activity cycle in a range from about 30 nHz (about 1 year period) up to 8 mHz
(5-minute oscillations). The variability with activity of the three colours is compared with the one of TSI.
DE: 7536 Solar activity cycle (2162)
DE: 7537 Solar and stellar variability
DE: 7538 Solar irradiance
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting