The Solar Aspect System (SAS) of the rotating (15 rpm) RHESSI spacecraft has three subsystems. Each of these measures the position of the limb by sampling the solar chord profile with a linear CCD and a narrow-bandwidth filter at 670 nm. With a plate scale of 1.7 arcsec/pixel, the precision of each of the six simultaneously observed limb positions is observed to be better than 50 mas, using fou...

We show that if the turbulent magnetic diffusivity used in solar dynamos is assumed to be ’quenched’ by increasing toroidal fields, much larger amplitude and more concentrated toroidal fields can be induced by differential rotation from an assumed poloidal field than if there is no quenching. This amplification and concentration mechanism is weakened and bounded by j × B feedbacks on the differ...

At the surface of the Sun acoustic waves appear to be affected by the presence of strong magnetic fields in active regions. We explore the possibility that the inclined magnetic field in sunspot penumbrae may convert primarily vertically propagating acoustic waves into elliptical motion. We use helioseismic holography to measure the modulus and phase of the correlation between incoming acoustic...

Coronal mass ejections (CMEs) originate from closed magnetic field regions on the Sun, which are active regions and quiescent filament regions. The energetic populations such as halo CMEs, CMEs associated with magnetic clouds, geoeffective CMEs, CMEs associated with solar energetic particles and interplanetary type II radio bursts, and shock-driving CMEs have been found to originate from sunspo...

In developed turbulence, the effective magnetic pressure of a large-scale field (non-turbulent plus turbulent contributions) can become negative. This is known to lead to a large-scale instability in strongly stratified turbulence that produces spontaneous magnetic flux concentrations. Previous studies using a horizontal magnetic field resulted in elongated field concentrations with a strength ...

The low ionization state in parts of a sunspot may play an important role in its evolution and dynamical state. The cool magnetic interior region of the sunspot develops a substantial neutral atomic and molecular hydrogen osmotic pressure which can drive a wind outward from the umbra. Ambipolar diffusion against the magnetically pinned ionized plasma component can also distort the umbral magnet...

Time series of high-resolution images of the complex active region NOAA 10786 are studied. The observations were performed in G-band (430.5 nm) and in the nearby continuum (463.3 nm), on July 9, 2005 at the Swedish 1-meter Solar Telecope (SST) in La Palma. Granular proper motions in the surroundings of the sunspots have been quantified. A large-scale radial outflow in the velocity range 0.3 1 k...

This paper describes automatic sunspot recognition and classification from satellite images. Some experimental results on learning sunspot classification using data mining techniques are presented. The classification scheme attempted was the seven-class Modified Zurich scheme. Daily images of the solar disk were taken from the NASA SOHO satellite’s MDI instrument and sunspots extracted using im...

We analyze a simple sunspot model that represents a standard securities market without sidebets on an exogenous sunspot event. The multiple self–fulfilling equilibria that arise in the model are based on investors’ uncertainty about other investors’ beliefs. Hence, these multiple equilibria are “endogenous sunspots.” We show that endogenous sunspots can arise even with complete markets to which...

Context. Analyses of magnetic properties on umbrae boundaries led to the Jurcak criterion, which states that umbra-penumbra in stable sunspots are equally defined by a constant value vertical field, Bver_crit, and 0.5 continuum intensity quiet Sun, Iqs. Umbrae with fields stronger than Bver_crit stable, whereas weaker unstable prone vanishing. Aims. To investigate existence critical field pore ...