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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 air’s 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
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
Occurrence of extreme solar particle events: Assessment from historical proxy data
The probability of occurrence of extreme solar particle events (SPEs) with
the fluence of (>30 MeV) protons F30>10^{10} cm^{-2} is evaluated based on data
of cosmogenic isotopes 14C and 10Be in terrestrial archives
centennial-millennial time scales. Four potential candidates with
F30=(1-1.5)x10^{10} cm^{-2} and no events with F30>2x10^{10} cm^{-2} are
identified since 1400 AD in the annually resolved 10Be data. A strong SPE
related to the Carrington flare of 1859 AD is not supported by the data. For
the last 11400 years, 19 SPE candidates with F30=(1-3)x10^{10} cm^{-2} are
found and clearly no event with F30>5x10^{10} cm^{-2} (50-fold the SPE of
23-Feb-1956) occurring. This values serve as an observational upper limit for
the strength of SPE on the time scale of tens of millennia. Two events, ca. 780
and 1460 AD, appear in different data series making them strong candidates to
extreme SPEs. We built a distribution of the occurrence probability of extreme
SPEs, providing a new strict observational constraint. Practical limits can be
set as F30~1x, 2-3x, and 5x10^{10} cm^{-2} for the occurrence probability
~10^{-2}, 10^{-3} and 10^{-4} year^{-1}, respectively. Because of
uncertainties, our results should be interpreted as a conservative upper limit
of the SPE occurrence near Earth. The mean SEP flux is evaluated as ~40 (cm2
sec)^{-1} in agreement with estimates from the lunar rocks. On average, extreme
SPEs contribute about 10% to the total SEP fluence.Comment: accepted to Astrophys.
A solar cycle lost in 1793--1800: Early sunspot observations resolve the old mystery
Because of the lack of reliable sunspot observation, the quality of sunspot
number series is poor in the late 18th century, leading to the abnormally long
solar cycle (1784--1799) before the Dalton minimum. Using the newly recovered
solar drawings by the 18--19th century observers Staudacher and Hamilton, we
construct the solar butterfly diagram, i.e. the latitudinal distribution of
sunspots in the 1790's. The sudden, systematic occurrence of sunspots at high
solar latitudes in 1793--1796 unambiguously shows that a new cycle started in
1793, which was lost in traditional Wolf's sunspot series. This finally
confirms the existence of the lost cycle that has been proposed earlier, thus
resolving an old mystery. This letter brings the attention of the scientific
community to the need of revising the sunspot series in the 18th century. The
presence of a new short, asymmetric cycle implies changes and constraints to
sunspot cycle statistics, solar activity predictions, solar dynamo theories as
well as for solar-terrestrial relations.Comment: Published by Astrophys. J. Let
A new model of cosmogenic production of radiocarbon 14C in the atmosphere
We present the results of full new calculation of radiocarbon 14C production
in the Earth atmosphere, using a numerical Monte-Carlo model. We provide, for
the first time, a tabulated 14C yield function for the energy of primary cosmic
ray particles ranging from 0.1 to 1000 GeV/nucleon. We have calculated the
global production rate of 14C, which is 1.64 and 1.88 atoms/cm2/s for the
modern time and for the pre-industrial epoch, respectively. This is close to
the values obtained from the carbon cycle reservoir inventory. We argue that
earlier models overestimated the global 14C production rate because of outdated
spectra of cosmic ray heavier nuclei. The mean contribution of solar energetic
particles to the global 14C is calculated as about 0.25% for the modern epoch.
Our model provides a new tool to calculate the 14C production in the Earth's
atmosphere, which can be applied, e.g., to reconstructions of solar activity in
the past.Comment: Published in EPSL, 337, 114, 201
New reconstruction of event-integrated spectra (spectral fluences) for major solar energetic particle events
Fluences of solar energetic particles (SEPs) are not easy to evaluate,
especially for high-energy events (i.e. ground-level enhancements, GLEs).
Earlier estimates of event-integrated SEP fluences for GLEs were based on
partly outdated assumptions and data, and they required revisions. Here, we
present the results of a full revision of the spectral fluences for most major
SEP events (GLEs) for the period from 1956 -- 2017 using updated low-energy
flux estimates along with greatly revisited high-energy flux data and applying
the newly invented reconstruction method including an improved neutron-monitor
yield function. Low- and high-energy parts of the SEP fluence were estimated
using a revised space-borne/ionospheric data and ground-based neutron monitors,
respectively. The measured data were fitted by the modified Band function
spectral shape. The best-fit parameters and their uncertainties were assessed
using a direct Monte Carlo method. As a result, a full reconstruction of the
event-integrated spectral fluences was performed in the energy range above 30
MeV, parametrised, and tabulated for easy use along with estimates of the 68%
confidence intervals. This forms a solid basis for more precise studies of the
physics of solar eruptive events and the transport of energetic particles in
the interplanetary medium, as well as the related applications.Comment: 19 pages, 3 figures, to be published in Astronomy and Astrophysic
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