Dods, Joe (2016) A network analysis of space weather. PhD thesis, University of Warwick.

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Abstract

Geomagnetic perturbations (space weather) can have a significant impact for an ever increasingly technological society. Substorms can cause disturbances that affect radio communication and technologies such as magnetic guidance drilling. Understanding the processes underlying space weather has been a central topic of magnetospheric research for several decades. While current advances in research have been driven by in-situ satellite based observations, historically magnetic field perturbations that were measured from ground and inspected by the human eye were used. With the inception of SuperMAG, an initiative that collates and processes the data from almost all ground magnetometer stations observations into a single repository, new ways of analysing this historical data are now possible.

In this thesis we use a dynamical network framework to analyse the magnetospheric/ionospheric system for the time. We utilise all available ground based magnetometer measurements in the northern hemisphere to construct dynamical networks. The stations are connected in the network when the correlation between the vector magnetometer time series from pairs of stations within a running time window exceeds a threshold. We develop methods to optimise the choice of correlation threshold to account for the differing local characteristics of the different magnetometer station groups.

We use this framework to approach two different aspects of magnetospheric research. We apply network methodology to analyse four isolated substorm test cases as well as a steady magnetic convection (SMC) event and a day in which no substorms occur. The events were chosen so as to have similar magnetometer station coverage at the onset of the events. Dimensionless parameters can then be obtained that characterise the network and by extension, the spatio-temporal dynamics of the substorms under observation. These test case substorms are found to give a consistent characteristic network response at onset in terms of their spatial correlation. Such responses are differentiable from responses to the SMC event and non-substorm times.

We also characterise the response of the quiet-time large scale ionospheric convection system to north-south and south-north interplanetary magnetic field (IMF) turnings by using dynamical networks. We map network information on to a regular grid in magnetic local time and magnetic latitude (MLT and Mlat) and aggregate over several hundred events. We find that regions that experience large increases in correlation post-turning coincide with typical locations of a two cell convection system and are influenced by the IMF By. Our method determines the time between the turnings reaching the magnetopause and a network response to be 8-10 minutes.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Space environment, Magnetospheric physics, Magnetospheric substorms, Solar wind, System analysis
Official Date:	2016
Dates:	Date Event 2016 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Chapman, Sandra C.
Format of File:	pdf
Extent:	viii, 164 pages : illustrations, charts
Language:	eng

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