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Solar modulation in surface atmospheric electricity
The solar wind modulates the flux of galactic cosmic rays impinging on Earth inversely with solar activity. Cosmic ray ionisation is the major source of airâs electrical conductivity over the oceans and well above the continents. Differential solar modulation of the cosmic ray energy spectrum modifies the cosmic ray ionisation at different latitudes,varying the total atmospheric columnar conductance. This redistributes current flow in the global atmospheric electrical circuit, including the local vertical current density and the related surface potential gradient. Surface vertical current density and potential
gradient measurements made independently at Lerwick Observatory,Shetland,from 1978 to 1985 are
compared with modelled changes in cosmic ray ionisation arising from solar activity changes. Both the
lower troposphere atmospheric electricity quantities are significantly increased at cosmic ray maximum(solar minimum),with a proportional change greater than that of the cosmic ray change
Inconsistency of the Wolf sunspot number series around 1848
Aims. Sunspot number is a benchmark series in many studies, but may still
contain inhomogeneities and inconsistencies. In particular, an essential
discrepancy exists between the two main sunspot number series, Wolf (WSN) and
group (GSN) sunspot numbers, before 1848. The source of this discrepancy has so
far remained unresolved. However, the recently digitized series of solar
observations in 1825-1867 by Samuel Heinrich Schwabe, who was the primary
observer of the WSN before 1848, makes such an assessment possible. Methods. We
construct sunspot series, similar to WSN and GSN, but using only Schwabe's
data. These series, called WSN-S and GSN-S, respectively, were compared with
the original WSN and GSN series for the period 1835-1867 to look for possible
inhomogeneities. Results. We show that: (1) The GSN series is homogeneous and
consistent with the Schwabe data throughout the entire studied period; (2) The
WSN series decreases by roughly ~20% around 1848 caused by the change of the
primary observer from Schwabe to Wolf and an inappropriate individual
correction factor used for Schwabe in the WSN; (3) This implies a major
inhomogeneity in the WSN, which needs to be corrected by reducing its values by
20% before 1848; (4) The corrected WSN series is in good agreement with the GSN
series. This study supports the earlier conclusions that the GSN series is more
consistent and homogeneous in the earlier part than the WSN series.Comment: Published as: Leussu, R., I.G. Usoskin, R. Arlt and K. Mursula,
Inconsistency of the Wolf sunspot number series around 1848, Astron.
Astrophys., 559, A28, 201
A History of Solar Activity over Millennia
Presented here is a review of present knowledge of the long-term behavior of
solar activity on a multi-millennial timescale, as reconstructed using the
indirect proxy method. The concept of solar activity is discussed along with an
overview of the special indices used to quantify different aspects of variable
solar activity, with special emphasis upon sunspot number. Over long
timescales, quantitative information about past solar activity can only be
obtained using a method based upon indirect proxies, such as the cosmogenic
isotopes \super{14}C and \super{10}Be in natural stratified archives (e.g.,
tree rings or ice cores). We give an historical overview of the development of
the proxy-based method for past solar-activity reconstruction over millennia,
as well as a description of the modern state. Special attention is paid to the
verification and cross-calibration of reconstructions. It is argued that this
method of cosmogenic isotopes makes a solid basis for studies of solar
variability in the past on a long timescale (centuries to millennia) during the
Holocene. A separate section is devoted to reconstructions of strong solar
energetic-particle (SEP) events in the past, that suggest that the present-day
average SEP flux is broadly consistent with estimates on longer timescales, and
that the occurrence of extra-strong events is unlikely. Finally, the main
features of the long-term evolution of solar magnetic activity, including the
statistics of grand minima and maxima occurrence, are summarized and their
possible implications, especially for solar/stellar dynamo theory, are
discussed.Comment: A review, 91 pages, 28 figures. available online at
http://solarphysics.livingreviews.org/Articles/lrsp-2013-1
Solar activity during the Holocene: the Hallstatt cycle and its consequence for grand minima and maxim
Cosmogenic isotopes provide the only quantitative proxy for analyzing the
long-term solar variability over a centennial timescale. While essential
progress has been achieved in both measurements and modeling of the cosmogenic
proxy, uncertainties still remain in the determination of the geomagnetic
dipole moment evolution. Here we improve the reconstruction of solar activity
over the past nine millennia using a multi-proxy approach. We used records of
the 14C and 10Be cosmogenic isotopes, current numerical models of the isotope
production and transport in Earth's atmosphere, and available geomagnetic field
reconstructions, including a new reconstruction relying on an updated
archeo-/paleointensity database. The obtained series were analyzed using the
singular spectrum analysis (SSA) method to study the millennial-scale trends. A
new reconstruction of the geomagnetic dipole field moment, GMAG.9k, is built
for the last nine millennia. New reconstructions of solar activity covering the
last nine millennia, quantified in sunspot numbers, are presented and analyzed.
A conservative list of grand minima and maxima is provided. The primary
components of the reconstructed solar activity, as determined using the SSA
method, are different for the series based on 14C and 10Be. These primary
components can only be ascribed to long-term changes in the terrestrial system
and not to the Sun. They have been removed from the reconstructed series. In
contrast, the secondary SSA components of the reconstructed solar activity are
found to be dominated by a common ~2400-yr quasi-periodicity, the so-called
Hallstatt cycle, in both the 14C and 10Be based series. This Hallstatt cycle
thus appears to be related to solar activity. Finally, we show that the grand
minima and maxima occurred intermittently over the studied period, with
clustering near highs and lows of the Hallstatt cycle, respectively.Comment: In press in Astronomy & Astrophysics, doi:
10.1051/0004-6361/20152729
Latitudinal dependence of low cloud amount on cosmic ray induced ionization
A significant correlation between the annual cosmic ray flux and the amount
of low clouds has recently been found for the past 20 years. However, of the
physical explanations suggested, none has been quantitatively verified in the
atmosphere by a combination of modelling and experiment. Here we study the
relation between the global distributions of the observed low cloud amount and
the calculated tropospheric ionization induced by cosmic rays. We find that the
time evolution of the low cloud amount can be decomposed into a long-term trend
and inter-annual variations, the latter depicting a clear 11-year cycle. We
also find that the relative inter-annual variability in low cloud amount
increases polewards and exhibits a highly significant one-to-one relation with
inter-annual variations in the ionization over the latitude range
20--55S and 10--70N. This latitudinal dependence gives strong
support for the hypothesis that the cosmic ray induced ionization modulates
cloud properties.Comment: GRL, in pres
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