88 research outputs found
Past and future sunspot indices: New goals for SoTerIA
No full texthttp://esoads.eso.org/abs/2011JASTP..73..182
A global small sunspot deficit at the base of the index anomalies of solar cycle 23
No full texthttp://esoads.eso.org/abs/2011A%26A...536L..11
A global small sunspot deficit at the base of the index anomalies of solar cycle 23
No full textContext. The variability of the 11-year cycle of solar activity on secular timescales is well established through the sunspot record, but it remains unpredictable. Indeed, the duration of the last solar cycle 23 was exceptionally long and took the solar physics community by surprise. The long minimum was marked by particularly low and often unprecedented levels of the international sunspot index Ri and most other solar indices. Earlier in the course of cycle 23, discrepancies appeared between several of those indices, raising a new issue: is there something wrong in the recent index values or is a real physical change occurring inside the Sun?
Aims. By exploiting detailed sunspot information, we look for independent evidence of a concrete and significant global change in sunspot properties appearing in the course of cycle 23.
Methods. To achieve this goal, we compared existing sunspot indices, such as the international sunspot number (Ri), and exploited the most complete information currently available on individual sunspots, obtained by merging two recent and complementary catalogs. Detailed statistics were obtained according to group type and spot size.
Results. We find that the Sun has shown an important deficit in small spots since the last activity maximum around 2000. While the number of large-scale spots remained largely unaffected, the occurrence rate of the smallest sunspots, and among them the ones with the shortest lifetimes, was more than halved during cycle 23. This explains the divergence between indices, weighted in favor of the largest active regions/magnetic structures, and sunspot counts that do not include such a weighting. It also confirms an actual intrinsic transition in the magnetic field generation inside the Sun, arising years before the exceptional activity minimum.
Conclusions. Our results thus reveal the potential of such detailed sunspot analyses for understanding and predicting future trends in the solar cycle. The change found here in the small individual sunspots suggests that solar and solar-terrestrial proxies should be redefined for the current state of the Sun, replacing the present ones. This scale-dependent change also provides support to dynamo models involving the coexistence of a deep and a superficial dynamo
Are the sunspots really vanishing?. Anomalies in solar cycle 23 and implications for long-term models and proxies
No full texthttp://esoads.eso.org/abs/2012JSWSC...2A..06
Slow magnetoacoustic waves in coronal loops : EIT and TRACE
Get PDFOn May 13, 1998 the EIT (Extreme ultraviolet Imaging Telescope) on board of SoHO (Solar and Heliospheric Observatory) and TRACE (Transition Region And Coronal Explorer) instruments produced simultaneous high cadence image sequences of the same active region (AR 8218). TRACE achieved a 25 s cadence in the FeIX (171 Å) bandpass while EIT achieved a 15 s cadence (operating in "shutterless mode", SoHO JOP 80) in the FeXII (195 Å) bandpass. These high cadence observations in two complementary wavelengths have revealed the existence of weak transient disturbances in an extended coronal loop system. These propagating disturbances (PDs) seem to be a common phenomenon in this part of the active region. The disturbances originate from small scale brightenings at the footpoints of the loops and propagate along the loops. The projected propagation speeds roughly vary between 65 and 150 km s-1 for both instruments which is close to and below the expected sound speed in the coronal loops. The measured slow magnetoacoustic propagation speeds seem to suggest that the transients are sound (or slow) wave disturbances. This work differs from previous studies in the sense that it is based on a multi-wavelength observation of an entire loop bundle at high cadence by two EUV imagers. The observation of sound waves along the same path shows that they propagate along the same loop, suggesting that loops contain sharp temperature gradients and consist of either concentric shells or thin loop threads, at different temperatures
Nonlinear solar cycle forecasting: theory and perspectives
No full textAbstract. In this paper we develop a modern approach to solar cycle forecasting, based on the mathematical theory of nonlinear dynamics. We start from the design of a static curve fitting model for the experimental yearly sunspot number series, over a time scale of 306 years, starting from year 1700 and we establish a least-squares optimal pulse shape of a solar cycle. The cycle-to-cycle evolution of the parameters of the cycle shape displays different patterns, such as a Gleissberg cycle and a strong anomaly in the cycle evolution during the Dalton minimum. In a second step, we extract a chaotic mapping for the successive values of one of the key model parameters – the rate of the exponential growth-decrease of the solar activity during the n-th cycle. We examine piece-wise linear techniques for the approximation of the derived mapping and we provide its probabilistic analysis: calculation of the invariant distribution and autocorrelation function. We find analytical relationships for the sunspot maxima and minima, as well as their occurrence times, as functions of chaotic values of the above parameter. Based on a Lyapunov spectrum analysis of the embedded mapping, we finally establish a horizon of predictability for the method, which allows us to give the most probable forecasting of the upcoming solar cycle 24, with an expected peak height of 93±21 occurring in 2011/2012.
</jats:p
Nonlinear solar cycle forecasting: theory and perspectives
No full textIn this paper we develop a modern approach to solar cycle forecasting, based
on the mathematical theory of nonlinear dynamics. We start from the design
of a static curve fitting model for the experimental yearly sunspot number
series, over a time scale of 306 years, starting from year 1700 and we
establish a least-squares optimal pulse shape of a solar cycle. The
cycle-to-cycle evolution of the parameters of the cycle shape displays
different patterns, such as a Gleissberg cycle and a strong anomaly in the
cycle evolution during the Dalton minimum. In a second step, we extract a
chaotic mapping for the successive values of one of the key model parameters
– the rate of the exponential growth-decrease of the solar activity during
the n-th cycle. We examine piece-wise linear techniques for the approximation
of the derived mapping and we provide its probabilistic analysis:
calculation of the invariant distribution and autocorrelation function. We
find analytical relationships for the sunspot maxima and minima, as well as
their occurrence times, as functions of chaotic values of the above
parameter. Based on a Lyapunov spectrum analysis of the embedded
mapping, we finally establish a horizon of predictability for the method,
which allows us to give the most probable forecasting of the upcoming solar
cycle 24, with an expected peak height of 93±21 occurring in 2011/2012
- …
