1. introduction in recent years, regarding climate changes, the analysis of natural variability of climate at different time scales has attracted a lot of attention. while, the data series with short statistical period just shows a likelihood estimation of a few decades of climate variability, the data series with long period shows the fluctuations of several decades with statistical importance...

We present a comparative seismic study of conditions around and beneath isolated sunspots. Using the European Grid of Solar Observations’ Solar Feature Catalogue of sunspots derived from SOHO/MDI continuum and magnetogram data, 1996-2005, we identify a set of isolated sunspots by checking that within a Carrington Rotation there were no other spots detected in the vicinity. We then use level-2 t...

It is well known that the observed amplitude of solar oscillations is lower in sunspots than in quiet regions of the Sun. We show that this local reduction in oscillation amplitudes combined with the phase-speed filtering procedure in time-distance helioseismic analyses could be a source of systematic errors in the range of 5 40% in the measured travel-time anomalies of acoustic waves around su...

In this review we give an overview about the current state-of-knowledge of the magnetic field in sunspots from an observational point of view. We start by offering a brief description of tools that are most commonly employed to infer the magnetic field in the solar atmosphere with emphasis in the photosphere of sunspots. We then address separately the global and local magnetic structure of suns...

Over decades, sunspots and their fine structures have been studied in detail at the photospheric level with different ground-based telescopes, as the surface of the Sun primarily emits light in the visible wavelengths. For a very long period, the upper atmosphere above the sunspot regions, especially the transition region (TR) above sunspots where the plasma emits light in the far ultraviolet (...

We use limb synoptic plots to study long-lived features of the lower solar corona. The most persistent features are the polar sinusoids, which are generated by streamers associated with active regions. We Ðnd that the lifetimes of these structures (up to about 10 solar rotations) are much longer than the lifetimes of individual sunspots (typically less than one solar rotation). The long lifetim...

Infrared spectral observations of sunspots from 1998-2011 have shown that on average sunspots changed; the magnetic fields weakened and the temperatures rose. The data also show that sunspots or dark pores can only form at the solar surface only if the magnetic field strength exceeds about 1500 Gauss. Sunspots appear at the solar surface with a variety of field strengths, and during the period ...

Sunspots are the subject of interest to many astronomers and solar physicists. Sunspot observation, analysis and classification form an important part of furthering the knowledge about the Sun. Sunspot classification is a manual and very labor intensive process that could be automated if successfully learned by a machine. This paper presents machine learning approaches to the problem of sunspot...

The structure of the surface layers of the Sun is changed by magnetic activity which, in turn, changes the eigen-frequencies of the acoustic modes. These frequency shifts have been observed both in low-and high-degree data, and are found to be correlated with the solar cycle. Time-distance helioseismology has shown that waves travelling through sunspots suffer time delays. Also it is known that...

This paper shows that belief?driven economic fluctuations are a general feature of many determinate macroeconomic models. In environments with hidden state variables, forecast?model misspecification can break the link between indeterminacy and sunspots by establishing existence “statistical sunspots” in models have unique rational expectations equilibrium. To form expectations, agents regress o...