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You searched for subject:(Solar Polar Field). Showing records 1 – 2 of 2 total matches.

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Indian Institute of Science

1. Hazra, Gopal. Understanding the Behavior of the Sun's Large Scale Magnetic Field and Its Relation with the Meridional Flow.

Degree: PhD, Faculty of Science, 2018, Indian Institute of Science

Our Sun is a variable star. The magnetic fields in the Sun play an important role for the existence of a wide variety of phenomena on the Sun. Among those, sunspots are the slowly evolving features of the Sun but solar ares and coronal mass ejections are highly dynamic phenomena. Hence, the solar magnetic fields could affect the Earth directly or indirectly through the Sun's open magnetic flux, solar wind, solar are, coronal mass ejections and total solar irradiance variations. These large scale magnetic fields originate due to Magnetohydrodynamic dynamo process inside the solar convection zone converting the kinetic energy of the plasma motions into the magnetic energy. Currently the most promising model to understand the large scale magnetic fields of the Sun is the Flux Transport Dynamo (FTD) model. FTD models are mostly axisymmetric models, though the non-axisymmetric 3D FTD models are started to develop recently. In these models, we assume the total magnetic fields of the Sun consist of poloidal and toroidal components and solve the magnetic induction equation kinematicaly in the sense that velocity fields are invoked motivated from the observations. Differential rotation stretches the poloidal field to generate the toroidal field. When toroidal eld near the bottom of the convection zone become magnetically buoyant, it rises through the solar convection zone and pierce the surface to create bipolar sunspots. While rising through the solar convection zone, the Coriolis force keeps on acting on the flux tube, which introduces a tilt angle between bipolar sunspots. Since the sunspots are the dense region of magnetic fields, they diffuse away after emergence. The leading polarity sunspots (close to equator) from both the hemisphere cancel each other across the equator and trailing polarity sunspots migrate towards the pole to generate effective poloidal fields. This mechanism for generation of poloidal field from the decay of sunspots is known as Babcock-Leighton process. After the poloidal field is generated, the meridional flow carries this field to the pole and further to the bottom of the convection zone where differential rotation again acts on it to generate toroidal field. Hence the solar dynamo goes on by oscillation between the poloidal field and toroidal field, where they can sustain each other through a cyclic feedback process. Just like other physical models, FTD models have various assumptions and approximations to incorporate these different processes. Some of the assumptions are observationally verified and some of them are not. Considering the availability of observed data, many approximations have been made in these models on the theoretical basis. In this thesis, we present various studies leading to better understanding of the different processes and parameters of FTD models, which include magnetic buoyancy, meridional circulation and Babcock-Leighton process. In the introductory Chapter 1, we first present the observational features of the solar magnetic fields, theoretical background of the FTD… Advisors/Committee Members: Choudhuri, Arnab Rai (advisor), Banerjee, Dipankar (advisor).

Subjects/Keywords: Solar Cycle; Sunspots; Solar Magnetic Field; Dynamo Theory; Flux Transport Dynamo Model; Meridional Circulation; Solar Polar Field; Flux Transport Solar Dynamo; Solar Cycles; Sun’s Polar Magnetic Field; Dynamo Model; 3D Babcock-Leighton Solar Dynamo Model; Astrophysics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Hazra, G. (2018). Understanding the Behavior of the Sun's Large Scale Magnetic Field and Its Relation with the Meridional Flow. (Doctoral Dissertation). Indian Institute of Science. Retrieved from http://etd.iisc.ac.in/handle/2005/3791

Chicago Manual of Style (16th Edition):

Hazra, Gopal. “Understanding the Behavior of the Sun's Large Scale Magnetic Field and Its Relation with the Meridional Flow.” 2018. Doctoral Dissertation, Indian Institute of Science. Accessed November 28, 2020. http://etd.iisc.ac.in/handle/2005/3791.

MLA Handbook (7th Edition):

Hazra, Gopal. “Understanding the Behavior of the Sun's Large Scale Magnetic Field and Its Relation with the Meridional Flow.” 2018. Web. 28 Nov 2020.

Vancouver:

Hazra G. Understanding the Behavior of the Sun's Large Scale Magnetic Field and Its Relation with the Meridional Flow. [Internet] [Doctoral dissertation]. Indian Institute of Science; 2018. [cited 2020 Nov 28]. Available from: http://etd.iisc.ac.in/handle/2005/3791.

Council of Science Editors:

Hazra G. Understanding the Behavior of the Sun's Large Scale Magnetic Field and Its Relation with the Meridional Flow. [Doctoral Dissertation]. Indian Institute of Science; 2018. Available from: http://etd.iisc.ac.in/handle/2005/3791

2. Gao, Ye. On the response of polar cap dynamics to its solar wind and magnetotail drivers at high levels of geomagnetic activity.

Degree: Geophysics & Space Physics, 2012, UCLA

In this thesis, I investigate how polar cap dynamics, quantified by the northern polar cap (PCN) index, respond to solar wind direct driving and magnetotail energy unloading during intervals of strong solar wind driving. Using 53 one to two-day intervals with high cross polar cap potential subintervals, I find that, among 11 candidate coupling functions including the electric field of Kan and Lee (1979) and the universal coupling function of Newell et al. (2007), the PCN index correlates most closely with the electric field (EK-R) of Kivelson and Ridley (2008), a form in which the electric field imposed on the ionosphere by low-latitude magnetopause reconnection saturates at high levels of geomagnetic activity. It is found that magnetotail activity, as represented by an unloading AL index (ALU), makes a significant contribution to the PCN index. A linear model is constructed to relate the PCN index to its solar wind and magnetotail drivers. Based on this model, it is estimated that the portion of the PCN index directly driven by the solar wind electric field outweighs the contribution arising from energy release in the magnetotail by roughly a factor of 2. The solar wind dynamic pressure (pdyn) does not play a key role in controlling the PCN index. However, under intense solar wind driving, the number density (n) can influence the solar wind-magnetosphere coupling by changing the solar wind Alfvén conductance, which is incorporated in EK-R. The validity of the linear model is verified by comparing its results with those obtained from a more general, non-linear model, termed additive model. It is found that, except in anomalous events during which the auroral oval expanded poleward to the latitude of the PCN index station and the index increased because of proximity to auroral zone currents, the linear model is a good approximation, since more than 70% of the variation in the PCN index is explained by the linear model. Thus, this linear model provides a useful tool to study the coupling between the solar wind, magnetosphere and ionosphere. This model is applied day-by-day from 1 February 1998 to 31 December 2009 to investigate the driven and unloading contributions to the PCN index. I find that the relative contributions of driven and unloading components varies with solar cycle with a magnitude ±5%, with the driven-to-unloading ratio highest near solar minimum and lowest slightly after solar maximum, and the driven-to-unloading ratio peaks in summer and decreases in winter with a magnitude as large as ±15%. Although the theory of Kivelson and Ridley (2008) is successful in predicting the polar cap dynamics from the solar wind input, there is a competing theory of Siscoe et al. (2002). The similarity and difference between these two theories are explored. It is found that, except for some trivial differences,…

Subjects/Keywords: Physical therapy; Plasma physics; Statistics; AMIE; DMSP; SuperDARN; Cross polar cap potential saturation; Driven and unloading processes; Kivelson-Ridley electric field; Polar cap index; Solar wind; magnetosphere; ionosphere coupling

…connects the magnetic field of the earth to that of the solar wind is, by definition, the polar… …38 2.2.4 Solar wind dynamic pressure driving of the polar cap dynamics… …linear relation between the polar cap index and its controlling factors in solar wind and… …interaction between the solar wind and earth’s magnetic field at high levels of geomagnetic activity… …magnetic field provides an effective obstacle to the solar wind plasma. As the solar wind impacts… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Gao, Y. (2012). On the response of polar cap dynamics to its solar wind and magnetotail drivers at high levels of geomagnetic activity. (Thesis). UCLA. Retrieved from http://www.escholarship.org/uc/item/23r2781b

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Gao, Ye. “On the response of polar cap dynamics to its solar wind and magnetotail drivers at high levels of geomagnetic activity.” 2012. Thesis, UCLA. Accessed November 28, 2020. http://www.escholarship.org/uc/item/23r2781b.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Gao, Ye. “On the response of polar cap dynamics to its solar wind and magnetotail drivers at high levels of geomagnetic activity.” 2012. Web. 28 Nov 2020.

Vancouver:

Gao Y. On the response of polar cap dynamics to its solar wind and magnetotail drivers at high levels of geomagnetic activity. [Internet] [Thesis]. UCLA; 2012. [cited 2020 Nov 28]. Available from: http://www.escholarship.org/uc/item/23r2781b.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Gao Y. On the response of polar cap dynamics to its solar wind and magnetotail drivers at high levels of geomagnetic activity. [Thesis]. UCLA; 2012. Available from: http://www.escholarship.org/uc/item/23r2781b

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

.