18 research outputs found
Wavelet Analysis of Solar Activity
Using wavelet analysis approach, the temporal variations of solar activity on
time scales ranging from days to decades, are examined from the daily time
series of sunspot numbers. A hierarchy of changing complex periods are careful
detected and related cycles compared with results from recent similar analyses.
A general determination of the main Schwabe cycle length variations is also
suggested on the basis of the wavelet amplitude distribution extracted from the
local wavelet power map.Comment: Postscript v1.1, 11 pages with 3 color figure
Solar cycle activity: an early prediction for cycle #25
Solar activity forecasting is an important topic for numerous scientific and
technological areas, such as space mission operations, electric power
transmission lines, power transformation stations and earth geophysical and
climatic impact. Nevertheless, the well-known difficulty is how to accurately
predict, on the basis of various recorded solar activity indices, the complete
evolution of future solar cycles, due to highly complex dynamical and
stochastic processes involved, mainly related to interaction of different
components of internal magnetic fields. There are two main distinct classes of
solar cycle prediction methods: the precursor-like ones and the
mathematical-numerical ones. The main characteristic of precursor techniques,
both purely solar and geomagnetic, is their physical basis. Conversely, the
non-precursor methods use different mathematical and/or numerical properties of
the known temporal evolution of solar activity indices to extract useful
information for predicting future activity. For current solar cycle #24 we
obtained fairly good statistical performances from both precursor and purely
numerical methods, such as the so-called solar precursor and nonlinear ones. To
further check the performances of these prediction techniques, we compared the
early predictions for the next solar cycle #25. Preliminary results support
some coherence of the prediction methods considered and confirm the current
trend of a relatively low solar activity.Comment: 6 pages, 1 figur
Solar cycle full-shape predictions: a global error evaluation for cycle 24
There are many proposed prediction methods for solar cycles behavior. In a
previous paper we updated the full-shape curve prediction of the current solar
cycle 24 using a non-linear dynamics method and we compared the results with
the predictions collected by the NOAA/SEC prediction panel, using observed data
up to October 2010. The aim of the present paper is to give a quantitative
evaluation, a posteriori, of the performances of these prediction methods using
a specific global error, updated on a monthly basis, which is a measure of the
global performance on the predicted shape (both amplitude and phase) of the
solar cycle. We suggest also the use of a percent cycle similarity degree, to
better evaluate the predicted shape of the solar cycle curve.Comment: 12 pages, 4 figure
On the better constraints from the South Pole Telescope Sunyaev-Zel'dovich galaxy clusters survey: a FoM evaluation for the equation of state of Dark Energy
In a recent article by Benson et al., 2011, the authors show the latest
measurements from the South Pole Telescope (SPT) Sunyaev Zel'dovich (SZ)
cluster survey to better constrain some cosmological parameters. In particular,
the authors found that adding the SPT cluster data significantly improves the
constraints on equation of state of dark energy, w, beyond those found when
using measurements of the CMB, supernovae, BAO and the Hubble constant. The
main aim of the present research note is to give a further quantitative
estimation of the above better constraints, through the computation of the
Figure of Merit (FoM) applied to \Omega_m and w plots for the 68% and 95%
confidence regions. This allows a better evaluation and a better comparison of
the continuous improvements on the cosmological constraints, obtained using new
different cosmological probes and different surveys.Comment: 9 pages, 3 figure
On the Distinct Periodicities of Sunspot Counts in Flaring and Non-flaring Active Regions
In a recent work, Kilcik et al. (2017), have detected the temporal and
periodic behavior of sunspot counts (SSC) in flaring (i.e. C, M, or X class
flares), and non-flaring active regions for the last two solar cycles, covering
the period: 1996 - 2016. The main results obtained are: 1) The temporal
behavior of monthly means of daily total SSC in flaring and non-flaring active
regions are different and these differences are also varying from cycle to
cycle; 2) The periodicities detected in SSC of flaring and non-flaring active
regions are quite different and these variations are also different from one
cycle to another; the highest detected period in the flaring active regions is
113 days, while there are much higher periodicities (327, 312, and 256 days) in
non-flaring regions. The detection of typical different periodicities in
flaring and non-flaring regions can suggests both important differences and
physical interpretation in the magneto-hydrodynamic behavior of the Sun. For
this reason in the present paper we show a further periodicity analysis of the
sunspot counts in flaring and in non-flaring active regions using the same data
source of that used by the above cited authors and applying a powerful wavelet
analysis tool which is particularly useful to detect multiscale features of
complex unsteady and unevenly sampled time series. In order to futher support
the differences and similarities found in the time behavior of SSC in flaring
and non-flaring regions, we also computed the behavior of the wavelet entropy,
a proper time function which allow us to measure the degree of complexity in
the dynamics of the related time series.Comment: 11 pages, 3 figure
Wavelet entropy as a measure of solar cycle complexity
Using wavelet analysis approach, we can derive a measure of the disorder
content of solar activity, following the temporal evolution of the so-called
wavelet entropy. The interesting feature of this parameter is its ability to
extract a dynamical complexity information, in terms of frequency distribution
of the energy content, avoiding restrictions, common in the nonlinear dynamics
theory, such as stationarity. The analysis is performed on the monthly time
series of sunspot numbers. From the time behaviour of the wavelet entropy we
found a clear increase in the disorder content of solar activity for the
current 23th solar cycle. This result suggests general low accuracies for
current solar cycleprediction methods. Moreover, we pointed out a possible
connection between wavelet entropy behaviour and solar excursion phases of
solar dipole.Comment: 4 pages with 3 figures. Accepted for publication in Astronomy and
Astrophysics Journa
Wavelet analysis of solar magnetic strength indices
Wavelet analysis of different solar activity indices, sunspot numbers,
sunspot areas, flare index, magnetic fields, etc., allows us to investigate the
time evolution of some specific features of the solar activity and the
underlying dynamo mechanism. The main aim of this work is the analysis of the
time-frequency behavior of some magnetic strengtht indices currently taken at
the Mt. Wilson Observatory 150-Foot Solar Tower. In particular, we analyzed
both the long time series (Jan 19, 1970 - Jan 22, 2013) of the Magnetic Plage
Strength Index (MPSI) values and of the Mt. Wilson Sunspot Index (MWSI) values,
covering the descending phase of cycle 20, the full solar cycles 21-23 and the
current part of the 24 solar cycle. This study is a further contribution to
detect the changes in the multiscale quasiperiodic variations in the integrated
magnetic solar activity with a comparison between past solar cycles and the
current one, which is one of the weaker recorded in the past 100 years. Indeed,
it is well known that an unusual and deep solar minimum occurred between solar
cycles 23 and 24 and the time-frequency behavior of some magnetic strengtht
indices can help to better interpret the responsible mechanisms.Comment: 8 pages, 2 figure
On the Solar Component in the Observed Global Temperature Anomalies
In this paper, starting from the updated time series of global temperature
anomalies, Ta, we show how the solar component affects the observed behavior
using, as an indicator of solar activity, the Solar Sunspot Number SSN. The
results that are found clearly show that the solar component has an important
role and affects significantly the current observed stationary behavior of
global temperature anomalies. The solar activity behavior and its future role
will therefore be decisive in determining whether or not the restart of the
increase of temperature anomalies observed since 1975 will occur.Comment: 9 pages, 7 figure
Time Series Forecasting: A Multivariate Stochastic Approach
This note deals with a multivariate stochastic approach to forecast the
behaviour of a cyclic time series. Particular attention is devoted to the
problem of the prediction of time behaviour of sunspot numbers for the current
23th cycle. The idea is to consider the previous known n cycles as n particular
realizations of a given stochastic process. The aim is to predict the future
behaviour of the current n+1th realization given a portion of the curve and the
structure of the previous n realizations. The model derived is based on the
cross-correlations between the current n+1th realization and the previous n
ones and the solution of the related least squares problem. As example we
applied the method to smoothed monthly sunspots numbers from SIDC archives, in
order to predict the behaviour of the current 23th solar cycle.Comment: Postscript v1.1, 6 pages with 3 figure
Time Series Forecasting: A Nonlinear Dynamics Approach
The problem of prediction of a given time series is examined on the basis of
recent nonlinear dynamics theories. Particular attention is devoted to forecast
the amplitude and phase of one of the most common solar indicator activity, the
international monthly smoothed sunspot number. It is well known that the solar
cycle is very difficult to predict due to the intrinsic complexity of the
related time behaviour and to the lack of a succesful quantitative theoretical
model of the Sun magnetic cycle. Starting from a previous recent work, we
checked the reliability and accuracy of a forecasting model based on concepts
of nonlinear dynamical systems applied to experimental time series, such as
embedding phase space, Lyapunov spectrum, chaotic behaviour. The model is based
on a local hypothesis of the behaviour on the embedding space, utilizing an
optimal number k of neighbour vectors to predict the future evolution of the
current point with the set of characteristic parameters determined by several
previous parametric computations. The performances of this method suggest its
valuable insertion in the set of the so-called statistical-numerical prediction
techniques, like Fourier analyses, curve fitting, neural networks,
climatological, etc. The main task is to set up and to compare a promising
numerical nonlinear prediction technique, essentially based on an inverse
problem, with the most accurate predictive methods like the so-called
"precursor methods" which appear now reasonably accurate in predicting "long
term" Sun activity, with particular reference to the "solar" precursor methods
based on a solar dynamo theory.Comment: Postscript v1.2, 22 pages with 12 color figure