Fast (>700 km s(-1)) and slow (~400 km s(-1)) winds stream from the Sun, permeate the heliosphere and influence the near-Earth environment. While the fast wind is known to emanate primarily from polar coronal holes, the source of the slow wind remains unknown. Here we identify possible sites of origin using a slow solar wind source map of the entire Sun, which we construct from specially design...

Time-distance helioseismic measurements in surfaceand deep-focus geometries for wave-paths that distinguish surface magnetic contributions from those due to deeper perturbations beneath a large sunspot are presented and analysed. Travel times showing an increased wave speed region extending down to about 18 Mm beneath the spot are detected in deep-focus geometry that largely avoids use of wave ...

The properties and dynamics of magnetic fields on the Sun’s photosphere and outer layers – notably those within solar active regions – govern the eruptive activity of the Sun. These photospheric magnetic fields also act as the evolving lower boundary of the Sun-Earth coupled system. Quantifying the physical attributes of these magnetic fields and exploring the mechanisms underlying their influe...

Keywords magnetohydrodynamics (MHD) –turbulence –Sun: activity –Sun: magnetic fields We introduce on/offintermittencyinto amean field dynamo model by imposing stochastic fluctuations in either the alpha effect or through theinclusion of afluctuatingelectromotivef orce. Sufficiently strong smallscalefluctuations with time scales of theorder of 0.3–3 years can produce long term variations in thes...

The numbers of faculae at the poles of the Sun have been estimated from white-light images obtained at the Mount Wilson Observatory during 1985–2006 and combined with prior estimates extending back to 1906 when the observations began. The combined data show an 11-yr cyclic variation with faculae maxima occurring during sunspot minima in each of the past 10 sunspot cycles. Also, these numbers of...

Sun-like stars are known to display a wide variety of magnetic activity which is likely to be the signature of a hydromagnetic dynamo mechanism working in stellar interiors. This dynamo mechanism has been studied extensively in the context of the Sun. Here we take ideas and experiences gained from solar dynamo modeling and build upon it to study the inferred scaling laws, involving stellar para...

This Letter discusses the role of a weak toroidal magnetic field in modifying the turbulent transport properties of stably stratified rotating turbulence in the tachocline. A local two-dimensional b-plane model is investigated numerically. In the absence of magnetic fields, nonlinear interactions of Rossby waves lead to the formation of strong mean zonal flows. However, the addition of even a v...

A scheme is presented for mapping the connectivity of a potential magnetic field arising from an arbitrary distribution of discrete sources. The field lines interconnecting the sources are classified into Nd domains, defining the field’s connectivity. The number of domains is shown to depend on the number of sources and on the numbers of nulls and separators according to a simple relation. A cl...

It has been proposed that flares in the solar corona may well be a result of an internal self-organized critical (SOC) process in active regions. We have developed a cellular automaton SOC model that simulates flaring activity extending over an active subflaring background. In the resulting frequency distributions we obtain two distinct power laws. That of the weaker events is shorter and much ...

We analyse the evolution of a sigmoidal (S shaped) active region toward eruption, which includes a coronal mass ejection (CME) but leaves part of the filament in place. The X-ray sigmoid is found to trace out three different magnetic topologies in succession: a highly sheared arcade of coronal loops in its long-lived phase, a bald-patch separatrix surface (BPSS) in the hours before the CME, and...