White-light measurements made by the SOHO LASCO C2 and C3 coronagraphs and the Mk III Mauna Loa K-coronameter, ranging from 1.15 to 30 have been combined with Kitt Peak daily He I R _ , 1083 nm coronal hole maps, and full Sun Y ohkoh soft X-ray images, to show that the boundaries of polar coronal holes, as determined by measurements of path-integrated density, extend approximately radially into...

We present a 3D simulation of the dynamic emergence of a twisted magnetic flux tube from the top layer of the solar convection zone into the solar atmosphere and corona. It is found that after a brief initial stage of flux emergence during which the two polarities of the bipolar region become separated and the tubes intersecting the photosphere become vertical, significant rotational motion set...

Magnetism dominates the structure and dynamics of the solar corona. Current theories suggest that it may also be responsible for coronal heating. Despite the importance of the magnetic field in the physics of the corona and despite the tremendous progress made recently in the remote sensing of solar magnetic fields, reliable measurements of the coronal magnetic field strength and orientation do...

The SunÏs corona, which is composed of plasma at a temperature of a few millions of degrees, can be best viewed in two electromagnetic domains, one from wavelengths of a few angstroms to hundreds of angstroms (in the soft X-ray and EUV domain), the other from wavelengths of a few centimeters to several tens of centimeters (in the radio domain). In this paper, we present a quantitative compariso...

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...

We investigate the heating of the quiet corona by measuring the increase of coronal luminosity with the amount of magnetic flux in the underlying network at solar minimum when there were no active regions on the face of the Sun. The coronal luminosity is measured from Fe ix/x–Fe xii pairs of coronal images from SOHO/EIT, under the assumption that practically all of the coronal luminosity in our...

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 ...

The ‘‘coronal heating problem’’ has been with us over 60 years, and hundreds of theoretical models have been proposed without an obvious solution in sight. In this paper we point out that observations show no evidence for local heating in the solar corona, but rather for heating below the corona in the transition region and upper chromosphere, with subsequent chromospheric evaporation as known ...

We develop a practical forward fitting method based on the SIMPLEX algorithm with shaking, which allows the derivation of the magnetic field and other parameters along a solar flaring loop using microwave imaging spectroscopy of gyrosynchrotron emission. We illustrate the method using a model loop with spatially varying magnetic field, filled with uniform ambient density and an evenly distribut...

A simple, yet powerful, algorithm for computed tomography of the solar corona is demonstrated using synthetic EUV data. A minimum of three perspectives are required. These may be obtained from STEREO/EUVI plus an instrument near Earth, e.g. TRACE or SOHO/EIT. Subject headings: methods: data analysis — Sun: corona — techniques: image processing