Overview

Project Highlights:

  • This project will use an exciting new dataset and will offer close collaboration with the research team at British Geological Survey.
  • Magnetic field variations in the 1-40 Hz band allow us to probe the geophysics of troposphere, upper atmosphere and magnetosphere, learning and applying novel time series analysis techniques.
  • The project will explore a novel and rich dataset in order to understand space weather effects on the upper atmosphere.

In June 2012, the BGS Geomagnetism team installed two 100 Hz sampling rate induction coil magnetometers in the Scottish Borders, which measure very rapid changes of the geomagnetic field. Figure 1 shows a spectrogram (power at each frequency versus time) from one of the coils in the frequency band of 0.1-40 Hz. The vertical bands of peak power at 8 Hz and harmonics are the Schumann resonances, while the weaker signals at 1-25 Hz between 18:00 and 06:00 UT are due to the so-called Ionospheric Alfvén Resonances (IAR).

The Schumann Resonances (SR) are generated by the emission of broadband lightning strikes typically in the equatorial regions. Around 100 strikes per second ‘echoing’ around the earth-ionosphere cavity creates a fundamental frequency around 7.8 Hz and higher harmonics, although these frequencies vary over time.

The IAR are generated by the vibration of magnetic field lines passing through the ionosphere up to 1000 km altitude in space. The IAR structures typically arise with a frequency around 1Hz and fan out into discrete lines, increasing in frequency from late evening to midnight and then decreasing during early morning, as the ionospheric electron density (and hence the Alfvén speed) varies.

The SR are sensitive to season, peaking in northern hemisphere summer, at a minimum in winter and are supposedly further modified by other quasi-periodic atmospheric oscillations such as the Madden-Julian Oscillation, though robust correlation with such atmospheric phenomena remains to be definitively proven.


The IAR show a strong solar cycle modulation becoming more prominent at the (present-day) solar minimum. They show unexplained behaviours which are presently not understood. For example, a debate is still on-going as to their excitation source, and the frequency and number of the observed individual fringes extending out to 30 Hz remain unexplained. The changes to the IAR signatures are strongly modulated by space weather. Of particular importance is the total electron content (TEC) of the cavity in which they resonate. Such TEC changes are a major cause of space weather disruption to global navigation satellite systems, and understanding and predicting these changes is a high priority for space weather research.

Spectrogram of the Channel 2 (east-west orientated) induction coil data for 16-Jan-2013

Methodology

The candidate will examine the two main resonances in the induction coil data, looking firstly at the longer term changes of the Schumann Resonances and their relation to solar, seasonal and space weather atmospheric phenomena. This includes examining the polarisation variations and comparison to other induction coil data from the northern hemisphere (Canada, Japan).

For the IAR, we wish to investigate the source excitation (lightning?) and the theoretical generation and propagation mechanisms from the literature and compare to the observations at Eskdalemuir. The candidate will extract the relevant IAR parameters (frequency, number of fringes, bandwidth, Q-factor) and use these to explore the space weather influences and factors governing the development and evolution of IAR on any given day.

From the new understanding of how ionosphere and magnetosphere space weather influence the SR and IAR, we will seek to invert for these parameters using the ground-based magnetic field data.

Training and Skills

The project will build upon 20 years of experience within the Radio and Space Plasma Physics (RSPP) and BGS geomagnetism groups in the analysis of ground-based magnetometer data. Training in magnetometer instrumentation techniques, relevant plasma and atmospheric physics will be provided as well as training in computer programming, simulations and the data analysis required. The student will gain a great deal of expertise in research methods, data management, analytical thinking and computer programming. All students contribute regularly to research group meetings through presentation of their work.

Timeline

Year 1: Explore the characteristics of the observed Schumann resonances to quantify how they vary according to the changing to solar cycle activity, and seasonal and atmospheric oscillations

Year 2: Apply time series analysis techniques to investigate the Ionospheric Alfvén Resonator characteristics (occurrence, frequencies, number of fringes) and compare these observations to current theoretical generation and propagation models, and previous observations from different locations.

Year 3: Based on the investigations above, establish the possibilities and potential for using the observed resonance characteristics as diagnostics of the state of the ionosphere magnetosphere system, with the ultimate aim of performing a parameter inversion for the retrieval of the characteristics of the ionosphere-magnetosphere-atmosphere system.

Partners and collaboration (including CASE)

The external partners for this project are Dr Ciaran Beggan, who has worked on the induction coil programme for the past seven years and Prof Alan Thomson, geomagnetism team leader at BGS. This project includes additional funding from the British Geological Survey as part of their BUFI programme to support visits and collaboration with BGS Edinburgh. The BGS will supply the induction coil data and support for the project in terms of supervisor time and provide the opportunity of a three-month placement in the Edinburgh office with the Geomagnetism team.

 

Further Details

Prof. Tim Yeoman

Radio and Space Plasma Physics Group

School of Physics and Astronomy

University of Leicester

University Road, Leicester

LE1 7RH

Tel: +44 116 2523564

Email: yxo@le.ac.uk