Wednesday, April 20, 2011

New paper affirms Sun was particularly active in late 20th century

A paper published today in The Journal of Geophysical Research: Space Physics confirms prior studies showing that solar activity was particularly active in the late 20th century. Another recent and related paper by the same lead author Mike Lockwood states,
45 Analysis of cosmogenic isotope abundances in terrestrial reservoirs, after removal of
46 complicating factors, such as the variability of the shielding afforded by the
47 geomagnetic field, reveal the effect of the Sun in reducing the fluxes of galactic
48 cosmic rays (GCRs) reaching the Earth. Because this solar shielding is known to vary
49 with the strength and structure of the heliospheric magnetic field, both of which are
50 modulated on both decadal and centennial timescales by solar activity, cosmogenic
51 isotopes give us an unique insight into solar variability on millennial timescales. Such
52 analyses all indicate that the Sun has been unusually active over recent decades
53 (Solanki et al. 2004; Vonmoos et al. 2006; Muscheler et al. 2007; Steinhilber et al.
54 2008). Solanki et al. (2004) used the 14C isotope abundance found in tree trunk and
55 concluded that the Sun has been more active recently than at any time in the previous
56 8000 years and that it was as active as in recent decades for only 10% of the past
57 11000 years...
The first part of the Lockwood et al paper excerpt above refers to the cosmic ray theory of Svensmark et al, which explains how small changes in solar activity can cause amplified effects upon climate via cloud formation. The new paper by Lockwood et al finds that solar activity during the Maunder minimum (corresponding to the Little Ice Age) was exceptionally low (vs. prior estimates) and that solar activity markedly increased up to the current grand solar maximum in ~1986. There is an associated lag time of solar activity vs. global temperature of approximately 10 years, noted here, which closely corresponds to the peak in global temperature of 1997-1998 (along with the effects of the record 1997-1998 El Nino).


Centennial changes in the heliospheric magnetic field and open solar flux: The consensus view from geomagnetic data and cosmogenic isotopes and its implications

M. Lockwood, Space Environment Physics Group, Department of Meteorology, University of Reading, Reading, UK, Space Science and Technology Department, Rutherford Appleton Laboratory, Chilton, UK

M. J. Owens, Space Environment Physics Group, Department of Meteorology, University of Reading, Reading, UK

Abstract: Svalgaard and Cliver (2010) recently reported a consensus between the various reconstructions of the heliospheric field over recent centuries. This is a significant development because, individually, each has uncertainties introduced by instrument calibration drifts, limited numbers of observatories, and the strength of the correlations employed. However, taken collectively, a consistent picture is emerging. We here show that this consensus extends to more data sets and methods than reported by Svalgaard and Cliver, including that used by Lockwood et al. (1999), when their algorithm is used to predict the heliospheric field rather than the open solar flux. One area where there is still some debate relates to the existence and meaning of a floor value to the heliospheric field. From cosmogenic isotope abundances, Steinhilber et al. (2010) have recently deduced that the near-Earth IMF at the end of the Maunder minimum was 1.80 ± 0.59 nT which is considerably lower than the revised floor of 4nT proposed by Svalgaard and Cliver. We here combine cosmogenic and geomagnetic reconstructions and modern observations (with allowance for the effect of solar wind speed and structure on the near-Earth data) to derive an estimate for the open solar flux of (0.48 ± 0.29) × 1014 Wb at the end of the Maunder minimum. By way of comparison, the largest and smallest annual means recorded by instruments in space between 1965 and 2010 are 5.75 × 1014 Wb and 1.37 × 1014 Wb, respectively, set in 1982 and 2009, and the maximum of the 11 year running means was 4.38 × 1014 Wb in 1986. Hence the average open solar flux during the Maunder minimum is found to have been 11% of its peak value during the recent grand solar maximum.

Related: The Ever Changing Sun

1 comment:

  1. Leif Svalgaard claims there was no grand solar maximum in the latter 20th century, but his own paper shows there was [fig 10 - solar activity correlated to inverse of GCRs]