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Spectroscopic studies of coronal structures using ground and space based data (Record no. 18992)

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000 -LEADER
fixed length control field 06048nam a2200217Ia 4500
003 - CONTROL NUMBER IDENTIFIER
control field IN-BaIIA
005 - DATE AND TIME OF LATEST TRANSACTION
control field 20211112145258.0
008 - FIXED-LENGTH DATA ELEMENTS--GENERAL INFORMATION
fixed length control field 211028s9999 xx 000 0 eng d
040 ## - CATALOGING SOURCE
Transcribing agency IIA Library
100 ## - MAIN ENTRY--PERSONAL NAME
Personal name Krishna Prasad, S
9 (RLIN) 36251
Relator term Author
245 #0 - TITLE STATEMENT
Title Spectroscopic studies of coronal structures using ground and space based data
Remainder of title a thesis submitted for the award of the degree of doctor of philosophy in physics, Mangalore university
Statement of responsibility, etc. S. Krishna Prasad
Medium [Ph.D Thesis]
260 ## - PUBLICATION, DISTRIBUTION, ETC.
Place of publication, distribution, etc. Bangalore
Name of publisher, distributor, etc. Indian Institute of Astrophysics
Date of publication, distribution, etc. 2013
300 ## - PHYSICAL DESCRIPTION
Extent [various pagings.]
502 ## - DISSERTATION NOTE
Degree type Doctor of Philosophy
Name of granting institution Mangalore University, Karnataka
Year degree granted 2014
520 ## - SUMMARY, ETC.
Summary, etc. Solar corona, the tenuous outer atmosphere of the Sun, is very hot with temperatures of the order of a few million kelvin. The main energy source for heating the corona and the physical mechanism behind the acceleration of fast solar wind are not clearly<br/>understood yet. These are major long-standing problems in solar physics and serve as a common motivation for most of the coronal studies. Our knowledge on these issues is advancing with the recent advent of instruments with high spatial, temporal, and<br/>spectral resolutions, which at the same time brought many new problems into light. A few such problems motivated the studies presented in this thesis. Broadly, two di_erent issues are addressed, one connected with the variation of spectral line parameters and the other related to the ambiguity on the nature of propagating intensity disturbances. Data from a ground-based coronagraph, a space-based Extreme Ultraviolet (EUV) imager and a space-based EUV spectrometer were used for this purpose. The thermal structure of a coronal loop is crucial for determining the plasma heating mechanism. Temperature variation along 18 di_erent loop structures was studied us-ing high resolution spectroscopic data from Norikura coronagraph. Observations were made simultaneously in multiple iron emission lines. Using the temperature sensitive emission line ratios [Fe xiv] 5303 _A/[Fe xiii] 10747 _A, and [Fe xi] 7892 _A/[Fe x]6374 _A the temperature and its gradients were computed for all the structures. It was found that the temperature gradients are negative for most of the structures observed in hotter lines and positive for those observed in colder lines. This indicates that the loop tops in general appear cooler or hotter depending on the line pair chosen. To explain this complex behaviour, a gradual interaction between di_erent temperature plasma was proposed. Interestingly, extensive analysis in the past, on line width vari-ation with altitude, also indicated a similar behaviour, in agreement with this mixing scenario. This behaviour is now veri_ed for polar regions. It was found that the FWHM of red emission line ([Fe x] 6374 _A) increase with height whereas that of green emission line ([Fe xiv] 5303 _A) decrease with height consistent with the results from equatorial regions. An interesting behaviour of green line was observed when latitudinal comparison was made. Line widths are higher in polar regions for all the<br/>emission lines studied except for the green line. The higher line widths in polar regions are often associated with the existence of a non-thermal source powering the fast solar wind. But, the observed behaviour of green line seem to disagree with this. Some of the recent observations question the uniqueness of the interpretation of prop- agating disturbances (PDs) as slow magneto-acoustic waves. It is argued that the<br/>high-speed quasi-periodic upows produce similar signatures and it is di_cult to dis-tinguish them. In an attempt to resolve this ambiguity, these PDs were studied indi_erent open structures. In polar regions, space-time maps were constructed for sev-eral plume and interplume structures using arti_cial slits that are wider than usual.<br/>This is to suppress the e_ect of fainter jets, if any present, causing the upows. Stronger jets were identi_ed from movies. Despite these measures, PDs were seen in all the structures studied. Moreover, they were found to be insensitive to changes in slit width. This implies the coherent nature of these disturbances. The average propagation speeds were found to be dependent on the temperature. These properties<br/>favour the interpretation of PDs as due to slow waves rather than high speed upows. Same technique cannot be applied for AR fan loops since they are relatively thin. To compensate for this, simultaneous spectroscopic and imaging data were used to study PDs in active region fan loops. Two di_erent periodicities short (<3 min) and long (_9 min) were observed with di_erent nature. The shorter periodicities showed oscil- lations in intensity, Doppler shift and line width whereas the longer ones did not show any line width oscillations. The line pro_les are symmetric with no visible blue-shifted<br/>component. The apparent propagation speeds were computed for the longer periods from the co-temporal imaging data which show the temperature dependence. Theobserved properties suggest the longer periods are due to slow MHD waves and the shorter ones could be due to the simultaneous presence of more than one MHD modes. To further supplement the previous study, spatial damping was studied in di_erent openstructures both on-disk and o_-limb. Powermaps constructed at three di_erent period ranges indicate that the PDs with long periods travel farther distances before getting<br/>damped. Similar behaviour is observed in all the structures. Spatial damping was also studied in di_erent temperature channels. Results indicate lower amplitudes and<br/>faster damping in hotter channels. All these observed properties were explained using a simple slow wave model considering thermal conduction as the damping mechanism.<br/>
650 ## - SUBJECT ADDED ENTRY--TOPICAL TERM
Topical term or geographic name entry element Spectroscopy
9 (RLIN) 1535
700 ## - ADDED ENTRY--PERSONAL NAME
Personal name Jagdev singh, Dipankar Banerjee
9 (RLIN) 36252
Relator term Supervisor
700 ## - ADDED ENTRY--PERSONAL NAME
Personal name Singh, Jagdev
9 (RLIN) 36253
856 ## - ELECTRONIC LOCATION AND ACCESS
Uniform Resource Identifier <a href="http://prints.iiap.res.in/handle/2248/6590">http://prints.iiap.res.in/handle/2248/6590</a>
Link text Click Here to Access eThesis
942 ## - ADDED ENTRY ELEMENTS (KOHA)
Koha item type Thesis & Dissertations
Source of classification or shelving scheme Universal Decimal Classification
Holdings
Withdrawn status Lost status Source of classification or shelving scheme Damaged status Not for loan Home library Current library Shelving location Date acquired Cost, normal purchase price Barcode Date last seen Cost, replacement price Price effective from Koha item type Purchase Price
    Universal Decimal Classification     IIA Library-Bangalore IIA Library-Bangalore General Stacks 16/03/2015 1965.00 19914 05/11/2021 1965.00 16/03/2015 Thesis & Dissertations Rs. 1965.00

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