371 research outputs found
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
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
Regional cosmic ray induced ionization and geomagnetic field changes
Cosmic ray induced ionization (CRII) is an important factor of outer space influences on atmospheric properties. Variations of CRII are caused by two different processes – solar activity variations, which modulate the cosmic ray flux in interplanetary space, and changes of the geomagnetic field, which affects the cosmic ray access to Earth. Migration of the geomagnetic dipole axis may greatly alter CRII in some regions on a time scale of centuries and longer. Here we present a study of CRII regional effects of the geomagnetic field changes during the last millennium for two regions: Europe and the Far East. We show that regional effects of the migration of the geomagnetic dipole axis may overcome global changes due to solar activity variations
Reconstruction of solar activity for the last millennium using Be data
In a recent paper (Usoskin et al., 2002a), we have reconstructed the
concentration of the cosmogenic Be isotope in ice cores from the
measured sunspot numbers by using physical models for Be production in
the Earth's atmosphere, cosmic ray transport in the heliosphere, and evolution
of the Sun's open magnetic flux. Here we take the opposite route: starting from
the Be concentration measured in ice cores from Antarctica and
Greenland, we invert the models in order to reconstruct the 11-year averaged
sunspot numbers since 850 AD. The inversion method is validated by comparing
the reconstructed sunspot numbers with the directly observed sunspot record
since 1610. The reconstructed sunspot record exhibits a prominent period of
about 600 years, in agreement with earlier observations based on cosmogenic
isotopes. Also, there is evidence for the century scale Gleissberg cycle and a
number of shorter quasi-periodicities whose periods seem to fluctuate in the
millennium time scale. This invalidates the earlier extrapolation of
multi-harmonic representation of sunspot activity over extended time intervals.Comment: Submitted to A&
Solar total and spectral irradiance reconstruction over the last 9000 years
Changes in solar irradiance and in its spectral distribution are among the
main natural drivers of the climate on Earth. However, irradiance measurements
are only available for less than four decades, while assessment of solar
influence on Earth requires much longer records. The aim of this work is to
provide the most up-to-date physics-based reconstruction of the solar total and
spectral irradiance (TSI/SSI) over the last nine millennia. The concentrations
of the cosmogenic isotopes 14C and 10Be in natural archives have been converted
to decadally averaged sunspot numbers through a chain of physics-based models.
TSI and SSI are reconstructed with an updated SATIRE model. Reconstructions are
carried out for each isotope record separately, as well as for their composite.
We present the first ever SSI reconstruction over the last 9000 years from the
individual 14C and 10Be records as well as from their newest composite. The
reconstruction employs physics-based models to describe the involved processes
at each step of the procedure. Irradiance reconstructions based on two
different cosmogenic isotope records, those of 14C and 10Be, agree well with
each other in their long-term trends despite their different geochemical paths
in the atmosphere of Earth. Over the last 9000 years, the reconstructed secular
variability in TSI is of the order of 0.11%, or 1.5 W/m2. After the Maunder
minimum, the reconstruction from the cosmogenic isotopes is consistent with
that from the direct sunspot number observation. Furthermore, over the
nineteenth century, the agreement of irradiance reconstructions using isotope
records with the reconstruction from the sunspot number by Chatzistergos et al.
(2017) is better than that with the reconstruction from the WDC-SILSO series
(Clette et al. 2014), with a lower chi-square-value
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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