Network Lanes Research Articles

Segmentation Of Photospheric And Chromospheric Solar Features

We describe the application of a multi-scale Laplacian-of-Gaussian (LoG) operator and of an iterative version of Medial Axis Transform (i-MAT) as tools for the segmentation of both photospheric and chromospheric solar features. We introduce the multi-scale LoG operator in order to extract compact structures in photospheric intensity or Doppler images. The second method, based on a i-MAT algorithm applied to gray level images, is introduced to recognize reticulated structures like chromospheric network or intergranular lanes. The developed numerical procedures allow a non-subjective segmentation of solar images in order to investigate morphological and topological properties of identified features. We discuss the output of the segmentation procedures when applied to real images.

Analysis of a UV Event in a Polar Coronal Hole

We present observations of a UV event which occurred in a polar coronal hole. They were obtained by SUMER on SOHO in several chromospheric and transition region spectral lines. Its birth site was about 50 arc sec inside the limb and in a network lane showing a net outflow before its initiation. The event had an extension of about 5 arc sec along the slit, a duration of about 3 min and was characterized by a large increase of intensity together with a significant line broadening with, however, downflows of about 50 km s−1 being dominant. Proper motions with a velocity of about 10 km s−1 were also observed. The event appeared at middle transition (O vi) temperatures and it simultaneously showed up in chromospheric (O i, Ly β) and low transition region (C ii) temperatures. We discuss this event in view of different scenarios to account for it. Our event could be a part of the large family of quiet-Sun explosive events observed by Ryutova and Tarbell (2000) taking place in polar coronal holes that are triggered by magnetic reconnection in the low solar atmosphere.

Network Coronal Bright Points: Coronal Heating Concentrations Found in the Solar Magnetic Network

We examine the magnetic origins of coronal heating in quiet regions by combining SOHO/EIT Fe XII coronal images and Kitt Peak magnetograms. Spatial filtering of the coronal images shows a network of enhanced structures on the scale of the magnetic network in quiet regions. Superposition of the filtered coronal images on maps of the magnetic network extracted from the magnetograms shows that the coronal network does indeed trace and stem from the magnetic network. Network coronal bright points, the brightest features in the network lanes, are found to have a highly significant (8 sigma above random chance) coincidence with polarity dividing lines (neutral lines) in the network, and are often at the feet of enhanced coronal structures that stem from the network and reach out over the cell interiors. These results indicate that, similar to the close linkage of neutral-line core fields with coronal heating in active regions, low-lying core fields encasing neutral lines in the magnetic network often drive noticeable coronal heating both within themselves (the network coronal bright points) and on more extended fields lines rooted around them. This behavior favors the possibility that active core fields in the network are the main drivers of the heating of the bulk of the quiet corona, on scales much larger than the network lanes and cells.

Bursts of explosive events in the solar network

Observations of the quiet-Sun network in the UV emission line Siiv 1393 A over a time period of two hours are presented. Bursts of explosive events, highly Doppler-shifted emission, seem to be sporadically emitted from the brighter regions of the network lanes. Individual events have typical lifetimes of ≈ 1–6 min and come in bursts of up to 30 min. The most spectacular burst in this dataset, shown in the accompanying movie, lasts ≈ 30 min and shows a wide variety of line profiles with both red and blue shifts ≈180 km s1. There appears to be no characteristic form or evolutionary pattern to the line profiles in either the individual events or series of events. There are about twice as many blue shifts as red shifts.

Joule heating as an explanation for the differential emission measure structure and systematic redshifts in the sun's lower transition region

view Abstract Citations (22) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Joule Heating as an Explanation for the Differential Emission Measure Structure and Systematic Redshifts in the Sun's Lower Transition Region Roumeliotis, George Abstract A new model is described for the sun's lower transition region which extends the ideas of Antiochos and Noci (1986) and Rabin and Moore (1984) but avoids their use of ad hoc heating functions and extremely small spatial scales, respectively. Specifically, it is proposed that most of the lower transition region plasma is contained in sheared magnetic boundary layers separating adjacent flux loops above the network lanes, and that this plasma is heated by the Joule dissipation of intense, field-aligned electric currents. A simple model for a sheared magnetic boundary layer is developed, and the field-aligned electric currents flowing inside it are calculated. A 1D hydrodynamic model is used to determine the atmospheric structure along a Joule-heated field line embedded in a sheared magnetic boundary layer. It is found that when the electric current density is less than a certain critical value, the atmosphere along the field line evolves toward a 'cool' equilibrium state, with T(max) less than 80,000 K. Publication: The Astrophysical Journal Pub Date: September 1991 DOI: 10.1086/170514 Bibcode: 1991ApJ...379..392R Keywords: Chromosphere; Plasma Heating; Red Shift; Resistance Heating; Solar Corona; Current Density; Electric Current; Field Aligned Currents; Magnetohydrodynamics; Ohmic Dissipation; Plasma Temperature; Solar Physics; HYDROMAGNETICS; PLASMAS; SUN: TRANSITION REGION full text sources ADS |

The magnetic network location of explosive events observed in the solar transition region

Compact short-lived explosive events have been observed in solar transition region lines with the High-Resolution Telescope and Spectrograph (HRTS) flown by the Naval Research Laboratory on a series of rockets and on Spacelab 2. Data from Spacelab 2 are coaligned with a simultaneous magnetogram and near-simultaneous He I 10,380 -A spectroheliogram obtained at the National Solar Observatory at Kitt Peak. The comparison shows that the explosive events occur in the solar magnetic network lanes at the boundaries of supergranular convective cells. However, the events occur away from the larger concentrations of magnetic flux in the network, in contradiction to the observed tendency of the more energetic solar phenomena to be associated with the stronger magnetic fields.