arXiv subjects

Shibu K. Mathew

Publications and source records attributed to Shibu K. Mathew.

22 records · Page 2Linked to original sources

arXiv2009

Supersonic Downflows in a Sunspot Light Bridge

We report the discovery of supersonic downflows in a sunspot light bridge using measurements taken with the spectropolarimeter on board the Hinode satellite. The downflows occur in small patches close to regions where the vector magnetic field changes orientation rapidly, and are associated with anomalous circular polarization profiles. An inversion of the observed Stokes spectra reveals velocities of up to 10 km/s, making them the strongest photospheric flows ever measured in light bridges. Some (but not all) of the downflowing patches are cospatial and cotemporal with brightness enhancements in chromospheric Ca II H filtergrams. We suggest that these flows are due to magnetic reconnection in the upper photosphere/lower chromosphere, although other mechanisms cannot be ruled out.

astro-ph.SR↗

arXiv2009

A Dual Beam H-alpha Doppler System to Acquire, Analyse and Anticipate Solar Eruptive Events Directed towards Earth

A new instrument with a dual-beam H-alpha Doppler system is being developed at the Udaipur Solar Observatory (USO) in order to improve the quality and quantity of data on quiet, activated and erupting filaments and prominences on the Sun, especially those associated with geo-effective coronal mass ejections. These data can be potentially used to construct three-dimensional topology of erupting filaments as they leave the surface of the Sun and can be compared with multi-wavelength data obtained from space missions such as STEREO, SOHO, and Hinode. The characterization of various optical components for the instrument is being carried out, and some preliminary results are described in the paper.

astro-ph.SR↗

arXiv2009

Automated Detection of Filaments and their Disappearance using Full Disc H-alpha Images

A new algorithm is developed that automatically detects filaments on the solar disc in H-alpha images. Preprocessing of H-alpha images include corrections for limb darkening and foreshortening. Further, by applying suitable intensity and size thresholds, filaments are extracted, while other solar features e.g. sunspots and plages are removed. Filaments attributes such as their position on the solar disc, total area, length, and number of fragments are determined. In addition, every filament is also labelled with a unique number. The algorithm is capable of following a particular filament through successive images which allows us to detect the changes and disappearance of the same, and thus provides a real-time warning of eruptive filaments. This aspect would prove to be of particular importance in studies pertaining to space weather. The algorithm will eventually be integrated with an upcoming telescope at Udaipur Solar Observatory for real time monitoring of activated/eruptive filaments.

astro-ph.SR↗

arXiv2008

Enhanced p-Mode Absorption seen near the Sunspot Umbral-Penumbral Boundary

We investigate p-mode absorption in a sunspot using SOHO/MDI high-resolution Doppler images. The Doppler power computed from a three and a half hour data set is used for studying the absorption in a sunspot. The result shows an enhancement in absorption near the umbral-penumbral boundary of the sunspot. We attempt to relate the observed absorption with the magnetic field structure of the sunspot. The transverse component of the potential field is computed using the observed SOHO/MDI line-of-sight magnetograms. A comparison of the power map and the computed potential field shows enhanced absorption near the umbral-penumbral boundary where the computed transverse field strength is higher.

astro-ph↗