Investigation of global lightning using Schumann resonances measured by high frequency induction coil magnetometers in the UK

In June 2012, the British Geological Survey (BGS) Geomagnetism team installed two high frequency (100 Hz) induction coil magnetometers at the Eskdalemuir Observatory, in the Scottish Borders of the United Kingdom. The induction coils permit us to measure the very rapid changes of the magnetic field in the Extremely Low Frequency (ELF) range in a passband from around 0.1 Hz to 100 Hz. The Eskdalemuir Observatory is one of the longest running geophysical monitoring sites in the UK (in operation since 1904) and is located in a rural valley with a quiet magnetic environment. BGS intend the coils to become part of our long term scientific monitoring of the magnetic field, in this case for ionospheric and agnetospheric research. The data are freely available on request and we are interested in collaboration with other institutes and researchers

Separation of oceanic and continental crustal field signatures using Slepian functions

Models of the crustal magnetic field are typically represented using spherical harmonic coefficients. Rather than spherical harmonics, spherical Slepian functions can be employed to produce a locally and also globally orthogonal basis in which to optimally represent the available data in a region at a given degree. The region can have any arbitrary shape and size. The Slepian functions can be tailored to be either band- or space-limited, allowing a trade-off between spectral and spatial concentration in the region and leakage beyond. Another advantage is that only N Slepian coefficients are required to be solved for to optimally concentrate the energy of the Slepian functions into the region of interest (N = (L+1)2R/4π ; where N is the Shannon Number and R is the size of the region as a fraction of the full sphere) . We use N Slepian functions to optimally separate a crustal field model into its oceanic and continental regions in order to investigate the spectral content of each. Spherical harmonic coefficients are transformed into Slepian coefficients, separated into the appropriate regions and transformed back to spherical harmonic coefficients representing the space-limited extent of the oceans and continents. The spectral power of each region is examined over degrees L = 16-72. We show that both regions display different power levels at discrete bandwidths. For example, the oceanic signal dominates at degrees 16-30, while the continental signal is stronger at degrees 45-65. We compare different crustal models to illustrate that the derived signals are robust

Automatic detection of ionospheric Alfvén resonances using signal and image processing techniques

Induction coils permit the measurement of small and very rapid changes of the magnetic field. A new set of induction coils in the UK (at L = 3.2) record magnetic field changes over an effective frequency range of 0.1–40 Hz, encompassing phenomena such as the Schumann resonances, magnetospheric pulsations and ionospheric Alfvén resonances (IARs). The IARs typically manifest themselves as a series of spectral resonance structures (SRSs) within the 1–10 Hz frequency range, usually appearing as fine bands or fringes in spectrogram plots and occurring almost daily during local night-time, disappearing during the daylight hours. The behaviour of the occurrence in frequency (f) and the difference in frequency between fringes (delta f) varies throughout the year. In order to quantify the daily, seasonal and annual changes of the SRSs, we developed a new method based on signal and image processing techniques to identify the fringes and to quantify the values of f , delta f and other relevant parameters in the data set. The technique is relatively robust to noise though requires tuning of threshold parameters. We analyse 18 months of induction coil data to demonstrate the utility of the method

Efficient analysis and representation of geophysical processes using localized spherical basis functions

While many geological and geophysical processes such as the melting of icecaps, the magnetic expression of bodies emplaced in the Earth's crust, or the surface displacement remaining after large earthquakes are spatially localized, many of these naturally admit spectral representations, or they may need to be extracted from data collected globally, e.g. by satellites that circumnavigate the Earth. Wavelets are often used to study such nonstationary processes. On the sphere, however, many of the known constructions are somewhat limited. And in particular, the notion of `dilation' is hard to reconcile with the concept of a geological region with fixed boundaries being responsible for generating the signals to be analyzed. Here, we build on our previous work on localized spherical analysis using an approach that is firmly rooted in spherical harmonics. We construct, by quadratic optimization, a set of bandlimited functions that have the majority of their energy concentrated in an arbitrary subdomain of the unit sphere. The `spherical Slepian basis' that results provides a convenient way for the analysis and representation of geophysical signals, as we show by example. We highlight the connections to sparsity by showing that many geophysical processes are sparse in the Slepian basis.Comment: To appear in the Proceedings of the SPIE, as part of the Wavelets XIII conference in San Diego, August 200

Sensitivity of geomagnetically induced currents to varying auroral electrojet and conductivity models

Geomagnetically induced currents (GIC) are created by the interaction of rapid changes in the magnitude of the magnetic field with the conductive subsurface of the Earth. The changing magnetic field induces electric currents, which are particularly strong along boundaries between regions of contrasting conductivity structure such as the land and sea. A technique known as the ‘thin-sheet approximation’ can be used to determine the electric field at the Earth’s surface, which in turn allows the calculation of GIC in the earthing connections of high-voltage nodes within a power grid. The thin-sheet approximation uses a spatially varying conductance over the region of interest on a 2D surface, combined with a 1D layered model of upper lithosphere conductance. We produce synthetic models of the auroral electrojet in different locations over the United Kingdom (UK) and investigate the effects of varying the 2D thin-sheet model. We assess different two-dimensional surface conductance models and vary the underlying 1D conductivity models to simulate the effects of resistant through to conductive lithosphere. With an advanced network model of high-voltage electrical distribution grid, we compute the expected GIC at each node in the system given the input surface electric fields from the various synthetic electrojets and conductivity models. We find that the electrojet location is the primary control on the size of GIC, with conductivity being a second-order effect in general, though it can be locally important

On the Downside of Heroism: Grey Zone Limitations on the Value of Social and Physical Risk Heroism

Implicit lay views of heroes are overwhelmingly positive and do not focus on the potential problems that may result from heroic behavior. Similarly, a rarely challenged assumption of heroism research is that heroic behavior represents a social good that should be rewarded, encouraged, and even taught. Yet it is not difficult to demonstrate empirically that heroic behavior, regardless of how well intended, can backfire and hurt, rather than help, the would-be helper, the target of helping, and third parties in the background. By extension, training programs that promote heroism can be of questionable value to the extent that they encourage individuals to engage in heroic behaviors that subsequently produce a negative effect. A two-dimensional action-impact matrix is presented that crosses whether or not a hero acts heroically and whether or not he or she has a positive impact to identify four possible actors: the classic hero, meddling hero, meta-hero, and failed hero. Using famous characters from fiction such as Superman and the officers on Star Trek, as well as real life incidents and case studies, the dynamics of the action-impact matrix are identified in order to explore the reasons why a person should not intervene in some instances

Use of Swarm gradient field data to improve lithospheric field models

The Swarm mission, launched in November 2013, consists of three identical satellites designed to measure the magnetic field to the highest resolution ever. One of the Swarm mission's unique aspects is the ability to measure the magnetic field at approximately the same location using two satellites (Swarm A and Swarm C) which travel close to one another at the same altitude. Using measurements of the gradient of the field between the satellites (i.e. across-track) removes much of the external magnetic field's influence in the data, leaving the contribution from the steady internal field, each time the satellites pass over the same location [Ref. 1]. In combination with measurements of the satellites’ along-track differences this adds a new capability that can be exploited to produce models of the crustal magnetic field with higher accuracy than ever before. As the mission accumulates more data at lower altitudes, our understanding of the Earth’s magnetic field will continue to improve. We apply a Slepian decomposition technique to the new BGS lithospheric field model to analyse the relative contributions to the magnetic field from the ocean and continents, which may be useful for geological applications

Spectral analysis of regional main field and secular variation in CHAOS-4 using spherical Slepian functions

Magnetic models such as CHAOS-4 represent the global field using Spherical Harmonic (SH) functions weighted by a set of numbers known as Gauss coefficients. This representation allows values of the field to be calculated at any location and altitude above the core-mantle boundary, but has limitations when attempting to isolate the contribution to the field from specific areas or regions. Spherical Slepian functions provide an alternative mathematical basis to represent the field [Ref. 1]. They have the advantage of allowing an area of interest to be optimally described in a spatio-spectral sense. In addition, spherical Slepian functions can also be used to separate and decompose the Gauss coefficients from a SH magnetic field model into the components that represent the contribution to the model from individual regions of the globe [Ref. 2]. We investigate the spectral and spatial changes of the main magnetic field of CHAOS-4q [Ref. 3] at the Earth's surface between spherical harmonic degrees 12-35 in eight different regions across the globe: the Americas; Africa; Australia; Eurasia; Antarctica; the Pacific Ocean; the Atlantic Ocean and the Indian Ocean between 1997 and 2011

Monomyth, Transformation and Inspiration: The Hero’s Journey in the Extreme Fitness Exercise Infomercial

The monomyth or hero’s journey is often described as containing the stages of journey, transformation and return. Less attention has focused on a fourth stage, called inspiration, which discusses how the hero can then motivate and mentor a new generation of heroes. The present paper describes how the success stories of people profiled in extreme fitness infomercials can be understood as conforming to the structure of the monomyth. The way in which the infomercials document how the success stories can also be used to motivate and mentor future heroes illustrates the role of inspiration as the final component of the fitness hero’s journey. Ways in which modern technology and social media provide platforms for publicizing stories of fitness transformation are also considered