Whistler mode wave growth and propagation in the prenoon magnetosphere

Pitch-angle scattering of electrons can limit the stably trapped particle flux in the magnetosphere and precipitate energetic electrons into the ionosphere. Whistler-mode waves generated by a temperature anisotropy can mediate this pitch-angle scattering over a wide range of radial distances and latitudes, but in order to correctly predict the phase-space diffusion, it is important to characterise the whistler-mode wave distributions that result from the instability. We use previously-published observations of number density, pitch-angle anisotropy and phase space density to model the plasma in the quiet pre-noon magnetosphere (defined as periods when AE<100nT). We investigate the global propagation and growth of whistler-mode waves by studying millions of growing ray paths and demonstrate that the wave distribution at any one location is a superposition of many waves at different points along their trajectories and with different histories. We show that for observed electron plasma properties, very few raypaths undergo magnetospheric reflection, most rays grow and decay within 30 degrees of the magnetic equator. The frequency range of the wave distribution at large L can be adequately described by the solutions of the local dispersion relation, but the range of wavenormal angle is different. The wave distribution is asymmetric with respect to the wavenormal angle. The numerical results suggest that it is important to determine the variation of magnetospheric parameters as a function of latitude, as well as local time and L-shell

The challenge of overdiagnosis begins with its definition

Overdiagnosis means different things to different people. S M Carter and colleagues argue that we should use a broad term such as too much medicine for advocacy and develop precise, case by case definitions of overdiagnosis for research and clinical purposes The implicit social contract underpinning healthcare is that it will reduce illness and preventable death and improve quality of life. But sometimes these promises are not delivered. Sometimes health services take people who don’t need intervention, subject them to tests, label them as sick or at risk, provide unnecessary treatments, tell them to live differently, or insist on monitoring them regularly.1 These interventions don’t improve things for people; they produce complications or illness, reduce quality of life, or even cause premature death. Active health intervention is not always a good thing: it can be “too much medicine,” or produce what is often called overdiagnosis. Although the concept of overdiagnosis has been described in the literature for nearly 50 years in relation to cancer screening,2 3 it was Welch and colleagues’ 2011 book, Overdiagnosed: Making People Sick in the Pursuit of Health, that popularised the term.4 Overdiagnosis is now an acknowledged problem for patients, clinicians, researchers, and policymakers; it is discussed in journals5 6 7 and at specialist conferences8 and addressed through policy and practice initiatives.9 10 11 There is, however, no formal, agreed definition of overdiagnosis. Rather, the word has become a banner under which disparate people with similar general concerns can unite. This vagueness and breadth allows the appearance of unity but does not serve the more exacting demands of research and healthcare. Here we examine the meanings of overdiagnosis more closely and discuss related challenges for healthcare professionals, patients, and researchers. If overdiagnosis is to be understood and mitigated, the broad concept should be subdivided into different problems and its ethical dimensions better acknowledged.NHMR

Van Allen probes observations of a three-dimensional field line resonance at a plasmaspheric plume

Funding: JKS, KRM, and IJR acknowledge support from NERC Grants NE/P017185/2, NE/V002554/2, and STFC Grants ST/V006320/1, ST/X001008/1. DPH acknowledges NASA Grant 80NSSC20K1324. ANW was funded in part by STFC Grant ST/W001195/1. AWS was supported by NERC Independent Research Fellowship NE/W009129/1.Field Line Resonances (FLRs) are a critical component in Earth's magnetospheric dynamics, associated with the transfer of energy between Ultra Low Frequency waves and local plasma populations. In this study we investigate how the polarisation of FLRs are impacted by cold plasma density distributions during geomagnetic storms. We present an analysis of Van Allen Probe A observations, where the spacecraft traversed a storm time plasmaspheric plume. We show that the polarisation of the FLR is significantly altered at the sharp azimuthal density gradient of the plume boundary, where the polarisation is intermediate with significant poloidal and toroidal components. These signatures are consistent with magnetohydrodynamic modeling results, providing the first observational evidence of a 3D FLR associated with a plume in Earth's magnetosphere. These results demonstrate the importance of cold plasma in controlling wave dynamics in the magnetosphere, and have important implications for wave-particle interactions at a range of energies.Publisher PDFPeer reviewe

How Do Ultra‐Low Frequency Waves Access the Inner Magnetosphere During Geomagnetic Storms?

Wave‐particle interactions play a key role in radiation belt dynamics. Traditionally, ultra‐low frequency (ULF) wave‐particle interaction is parameterized statistically by a small number of controlling factors for given solar wind driving conditions or geomagnetic activity levels. Here we investigate solar wind driving of ULF wave power and the role of the magnetosphere in screening that power from penetrating deep into the inner magnetosphere. We demonstrate that during enhanced ring current intensity, the Alfvén continuum plummets, allowing lower frequency waves to penetrate deeper into the magnetosphere than during quiet periods. With this penetration, ULF wave power is able to accumulate closer to the Earth than characterized by statistical models. During periods of enhanced solar wind driving such as coronal mass ejection driven storms, where ring current intensities maximize, the observed penetration provides a simple physics‐based reason for why storm time ULF wave power is different compared to nonstorm time waves

What to think of canine obesity? Emerging challenges to our understanding of human-animal health relationships.

The coincident and increasing occurrence of weight-related health problems in humans and canines in Western societies poses a challenge to our understanding of human–animal health relationships. More specifically, the epistemological and normative impetus provided by current approaches to shared health risks and chronic diseases in cohabiting human and animal populations does not account for causal continuities in the way that people and their pets live together. An examination of differences in medical responses to these conditions in human and pet dogs points to the existence of a distinct conceptual and ethical sphere for companion animal veterinary medicine. The disengagement of veterinary medicine for companion animals from human medicine has implications for our understanding what is required for health and disease prevention at the level of populations. This disengagement of companion animal veterinarians from family and preventive medicine, in particular, constrains professional roles, planning processes and, thereby, the potential for better-integrated responses to shared burdens of chronic conditions that increasingly affect the health and welfare of people and companion animals. Keywords: Human–Animal Relationships, Medical Epistemology, Companion Animal Welfare, Veterinary Ethics, Public Health Ethics, One HealthCanadian Institutes of Health Research, Open Operating Gran

Statistical study of ULF waves in the magnetotail by THEMIS observations

Ultra-low-frequency (ULF) waves are ubiquitous in the magnetosphere. Previous studies mostly focused on ULF waves in the dayside or near-Earth region (with radial distance R<12RE). In this study, using the data of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission during the period from 2008 to 2015, the Pc5-6 ULF waves in the tail region with X∗-GSM<0, 8RE<R<32RE (mostly on the stretched magnetic field lines) are studied statistically. A total of 1089 azimuthal oscillating events and 566 radial oscillating events were found. The statistical results show that both the azimuthal and radial oscillating events in the magnetotail region (12RE<R<32RE) are more frequently observed in the post-midnight region. The frequency decreases with increasing radial distance from Earth for both azimuthal oscillating events (8RE<R<16RE) and radial oscillating events (8RE<R<14RE), which is consistent with the field line resonances theory. About 52% of events (including the azimuthal and radial oscillating events) are standing waves in the region of 8-16RE, while only 2% are standing waves in the region of 16-32RE. There is no obvious dawn-dusk asymmetry of ULF wave frequency for events in 8RE<R<32RE, which contrasts with the obvious dawn-dusk asymmetry found by previous studies in the inner magnetosphere (4RE<R<9RE). An examination for possible statistical relationships between the ULF wave parameters and substorm occurrences is carried out. We find that the wave frequency is higher after the substorm onset than before it, and the frequency differences are more obvious in the midnight region than in the flank region

Statistical study of ULF waves in the magnetotail by THEMIS observations

Ultra-low-frequency (ULF) waves are ubiquitous in the magnetosphere. Previous studies mostly focused on ULF waves in the dayside or near-Earth region (with radial distance R&lt;12&thinsp;RE). In this study, using the data of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission during the period from 2008 to 2015, the Pc5–6 ULF waves in the tail region with X∗GSM&lt;0, 8&thinsp;RE&lt;R&lt;32&thinsp;RE (mostly on the stretched magnetic field lines) are studied statistically. A total of 1089 azimuthal oscillating events and 566 radial oscillating events were found. The statistical results show that both the azimuthal and radial oscillating events in the magnetotail region (12&thinsp;RE&lt;R&lt;32&thinsp;RE) are more frequently observed in the post-midnight region. The frequency decreases with increasing radial distance from Earth for both azimuthal oscillating events (8&thinsp;RE&lt;R&lt;16&thinsp;RE) and radial oscillating events (8&thinsp;RE&lt;R&lt;14&thinsp;RE), which is consistent with the field line resonances theory. About 52&thinsp;% of events (including the azimuthal and radial oscillating events) are standing waves in the region of 8–16&thinsp;RE, while only 2&thinsp;% are standing waves in the region of 16–32&thinsp;RE. There is no obvious dawn–dusk asymmetry of ULF wave frequency for events in 8&thinsp;RE&lt;R&lt;32&thinsp;RE, which contrasts with the obvious dawn–dusk asymmetry found by previous studies in the inner magnetosphere (4&thinsp;RE&lt;R&lt;9&thinsp;RE). An examination for possible statistical relationships between the ULF wave parameters and substorm occurrences is carried out. We find that the wave frequency is higher after the substorm onset than before it, and the frequency differences are more obvious in the midnight region than in the flank region.</p

Ultralow-frequency modulation of whistler-mode wave growth

Measurements from ground-based magnetometers and riometers at auroral latitudes have demonstrated that energetic (~30-300keV) electron precipitation can be modulated in the presence of magnetic field oscillations at ultra-low frequencies. It has previously been proposed that an ultra-low frequency (ULF) wave would modulate field and plasma properties near the equatorial plane, thus modifying the growth rates of whistler-mode waves. In turn, the resulting whistler-mode waves would mediate the pitch-angle scattering of electrons resulting in ionospheric precipitation. In this paper, we investigate this hypothesis by quantifying the changes to the linear growth rate expected due to a slow change in the local magnetic field strength for parameters typical of the equatorial region around 6.6RE radial distance. To constrain our study, we determine the largest possible ULF wave amplitudes from measurements of the magnetic field at geosynchronous orbit. Using nearly ten years of observations from two satellites, we demonstrate that the variation in magnetic field strength due to oscillations at 2mHz does not exceed ±10% of the background field. Modifications to the plasma density and temperature anisotropy are estimated using idealised models. For low temperature anisotropy, there is little change in the whistler-mode growth rates even for the largest ULF wave amplitude. Only for large temperature anisotropies can whistler-mode growth rates be modulated sufficiently to account for the changes in electron precipitation measured by riometers at auroral latitudes

Owning the problem: Media portrayals of overweight dogs and the shared determinants of the health of human and companion animal populations

Weight-related health problems have become a common topic in Western mass media. News-coverage has also extended to overweight pets, particularly since 2003 when the U.S. National Academy of Sciences announced that obesity was also afflicting co-habiting companion animals in record numbers. To characterize and track views in popular circulation on causes, consequences and responsibilities vis-à-vis weight gain and obesity, in pets as well as in people, this study examines portrayals of overweight dogs that appeared from 2000 through 2009 in British, American and Australian mass media. The ethnographic content analysis drew inspiration from the literature in population health, animal-human relationships, communication framing and the active nature of texts in cosmopolitan societies. Three main types of media articles about overweight dogs appeared during this period: 1) reports emphasizing facts and figures; 2) stories emphasizing personal prescriptions for dog owners, and 3) societal critiques. To help ordinary people make sense of canine obesity, media articles often highlight that dogs share the lifestyle of their human companion or owner, yet the implications of shared social and physical environments is rarely considered when it comes to solutions. Instead, media coverage exhorts people who share their lives with overweight dogs to ‘own the problem’ and, with resolve, to normalize their dog’s physical condition by imposing dietary, exercise and relationship changes, thereby individualizing culpability rather than linking it to broader systemic issues. Keywords: Companion animals; Media; Narrative analysis; Obesity; Public understandin