Sunspots are concentrations of magnetic field on the visible solar surface that strongly affect the convective energy transport in their interior and surroundings. The filamentary outer regions (penumbrae) of sunspots show systematic radial outward flows along channels of nearly horizontal magnetic field. These flows were discovered 100 years ago and are present in all fully developed sunspots....

In time-distance helioseismology, wave travel times are measured from the cross-correlation between Doppler velocities recorded at any two locations on the solar surface. However, one of the main uncertainties associated with such measurements is how to interpret observations made in regions of strong magnetic field. Isolating the effects of the magnetic field from thermal or soundspeed perturb...

Solar activity is the dynamic energy source behind all solar phenomena driving space weather. During an active solar period, violent eruptions occur more often on the Sun. The solar flares (SFs) and coronal mass ejections (CMEs) shoot energetic and highly charged particles towards Earth that ensuing ionospheric and geomagnetic disturbances. The some geomagnetic disturbances illuminate night ski...

Observations indicate that in plage areas (i.e. in active regions outside sunspots) acoustic waves travel faster than in quiet sun, leading to shortened travel times and higher p-mode frequencies. Coupled with the 11-year variation of solar activity, this may also explain the solar cycle variation of oscillation frequencies. While it is clear that the ultimate cause of any difference between qu...

Variations in solar activity, at least as observed in numbers of sunspots, have been apparent since ancient times but to what extent solar variability may affect global climate has been far more controversial. The subject had been in and out of fashion for at least two centuries but the current need to distinguish between natural and anthropogenic causes of climate change has brought it again t...

The solar polar fields reverse because magnetic flux from decaying sunspots moves towards the poles, with a preponderance of flux from the trailing spots. If there is a strong asymmetry in the sense that most activity is in the Northern Hemisphere, then that excess flux will move to the North Pole and reverse that pole first. If later on, there is more activity in the South, then that flux will...

An automated neural network-based system for predicting solar flares from their associated sunspots and simulated solar cycle is introduced. A sunspot is the cooler region of the Sun's photosphere which, thus, appears dark on the Sun's disc, and a solar flare is sudden, short lived, burst of energy on the Sun's surface, lasting from minutes to hours. The system explores the publicly available s...

Coronal structure of active regions appearing in coronal holes is studied by using the data obtained with the Soft X-Ray Telescope (SXT) aboard Yohkoh from 1991 November to 1993 March. The following characteristics are found; Many of active regions appearing in coronal holes show a structure that looks like a “sea-anemone”. Such active regions are called anemone ARs. About oneforth of all activ...

We compare spectra of the zonal harmonics large-scale magnetic field Sun using observation results and solar dynamo models. The main activity cycle as recorded in these tracers is a much more complicated phenomenon than eigen solution equations with growth saturated by back reaction dynamo-driven on hydrodynamics. nominal 11(22)-year each mode has specific phase shift varying from to cycle; act...