Reconstruction of TSI and Ly- Back to 1913
Claus Fröhlich [cfrohlich@pmodwrc.ch], Physikalisch Meteorologisches Observatorium
Davos (PMOD), World Radiation Center (WRC), Davos, Switzerland
The PMOD composite has been updated with a new version of VIRGO TSI which
improves the internal consistency. With this composite a 4-component proxy model is
calibrated over the full range of the last three solar cycles and explains more than 85 % of the
variance. The model is based on a new version of the photometric sunspot index (PSI) using
SOON data since 1976, on a composite MgII index from space observations, separated into
long- and short-term components and a trend deduced from the open magnetic flux from the
Sun at activity minima. This model can be expanded with PSI from Royal Greenwich
Observatory sunspot data back to 1876, with CaII K observations from Mt. Wilson since
1913 and with the open field from e.g. the aa index back to late 19th century. The daily CaII
K observations are transformed into a MgII proxy which then can be separated into long- and
short-term components and thus the proxy model can be expanded back to 1913. With these
data and the calibration during the last 3 cycles TSI is reconstructed. Moreover, as the model
explains also the Ly- record, a correspondingly reliable reconstruction back to 1913 is
presented.