Seminar

Title : Three-dimensional magnetic field structure of a flux emerging region in the solar atmosphere

Date : 15-11-2019
Time : 16:00:00
Speaker : Dr. Rahul Yadav
Area : Udaipur Solar Observatory (USO)
Venue : USO Seminar Hall

Abstract

We analyze high-resolution spectropolarimetric observations of a flux emerging region (FER) in order to understand its magnetic and kinematic structure. Our spectropolarimetric observations in the He I 1083.0 nm spectral region of a FER are recorded with GRIS at the 1.5 m aperture GREGOR telescope. A Milne-Eddington based inversion code was employed to extract the photospheric information of the Si I spectral line, whereas the He I triplet line was analyzed with the Hazel inversion code, which takes into account the joint action of the Hanle and the Zeeman effect. The spectropolarimetric analysis of Si I line displays a complex magnetic structure near the vicinity of FER. Moreover, we find supersonic downflows of 40 km/sec appears near the footpoints of loops connecting two pores of opposite polarity, whereas a strong upflows of 22 km/sec appears near the apex of the loops. Furthermore, non-force-free field extrapolations were performed separately at two layers in order to understand the magnetic field topology of the FER. We determine, using extrapolations from the photosphere and the observed chromospheric magnetic field, that the average formation height of the He triplet line is 2 Mm from the solar surface. The reconstructed loops using photospheric extrapolations along an arch filament system have a maximum height of 10.5 Mm from the solar surface with a foot-points separation of 19 Mm, whereas the loops reconstructed using chromospheric extrapolations are around 8.4 Mm high from the solar surface with a foot-point separation of 16 Mm at the chromospheric height. The magnetic topology in the FER suggests the presence of small-scale loops beneath the large loops. Under suitable conditions, due to magnetic reconnection, these loops can trigger various heating events in the vicinity of the FER.

Date : 15-11-2019
Time : 16:00:00
Speaker : Mr. Subir Mandal
Area : Space and Atmospheric Sciences Division
Venue : Ground Floor Lecture Hall

Abstract

Gravity waves (GWs) are omnipresent in the upper atmosphere and they redistribute the energy in the medium as they propagate away from their source region. They are known to play important roles in modifying various upper atmospheric phenomena. Conventionally, optical methods are used to study GWs. Recently, we have devised a methodology to derive daytime GW characteristics using radio technique (Digisonde). Earlier works have shown that the daytime upper atmosphere prepares the conditions conducive or otherwise for nighttime irregularities to occur. Several days of data have been analysed to understand the upper atmospheric behaviour over equatorial latitudes. We have attempted to address the issue of occurrence of nighttime plasma irregularities (i.e., ESF, Equatorial Spread F) with regard to daytime GW characteristics over equatorial location. A broad overview of the various factors in the daytime that affect ESF occurrence will be given and some new results with respect to GW characteristics on days with and without the occurrence of post sunset ESF will be presented in this seminar.