The theoretical foundation of 3-D Alfvén resonances : time-dependent solutions

Both authors were funded in part by STFC (through Consolidated Grant ST/N000609/1) and The Leverhulme Trust (through Research Grant RPG-2016-071).We present results from a 3-D numerical simulation which investigates the coupling of fast and Alfvén magnetohydrodynamic (MHD) waves in a nonuniform dipole equilibrium. This represents the time-dependent extension of the normal mode (∝ exp(−iωt)) analysis of Wright and Elsden (2016), and provides a theoretical basis for understanding 3-D Alfvén resonances. Wright and Elsden (2016) show that these are fundamentally different to resonances in 1D and 2D. We demonstrate the temporal behavior of the Alfvén resonance, which is formed within the "Resonant Zone"; a channel of the domain where a family of solutions exists such that the natural Alfvén frequency matches the fast-mode frequency. At early times, phase mixing leads to the production of prominent ridges in the energy density, whose shape is determined by the Alfvén speed profile and the chosen background magnetic field geometry. These off resonant ridges decay in time, leaving only a main 3-D resonant sheet in the steady state. We show that the width of the 3-D resonance in time and in space can be accurately estimated by adapting previous analytical estimates from 1-D theory. We further provide an analytical estimate for the resonance amplitude in 3-D, based upon extending 2-D theory.Publisher PDFPeer reviewe

The effect of fast normal mode structure and magnetopause forcing on FLRs in a 3‐D waveguide

T. Elsden and A. N. Wright were funded by the Leverhulme Trust through Research grant RPG-2016-071. A. N. Wright was also funded by STFC through Consolidated grant ST/N000609/1.This paper investigates the excitation of waveguide modes in a nonuniform dipole equilibrium and, further, their coupling to field line resonances (FLRs). Waveguide modes are fast compressional ultralow frequency (ULF) waves, whose structure depends upon the magnetospheric equilibrium and the solar wind driving conditions. Using magnetohydrodynamic simulations, we consider how the structure of the excited waveguide mode is affected by various forms of magnetopause driving. We find that the waveguide supports a set of normal modes that are determined by the equilibrium. However, the particular normal modes that are excited are determined by the structure of the magnetopause driver. A full understanding of the spatial structure of the normal modes is required in order to predict where coupling to FLRs will occur. We show that symmetric pressure driving about the noon meridian can excite normal modes which remain around to drive resonances for longer than antisymmetric driving. Further, the critical quantity in terms of efficient coupling is the magnetic pressure gradient aligned with the resonance.Publisher PDFPeer reviewe

Properties of magnetohydrodynamic normal modes in the Earth’s magnetosphere

Funding: MDH was supported by NASA 80NSSC19K0127, 80NSSC19K0907, 80NSSC21K1683, 80NSSC21K1677, 80NSSC23K0903, and NSF AGS-2307204. KT was supported by NASA 80NSSC19K0259 and 80NSSC21K0453. MOA was supported by a UKRI (STFC / EPSRC) Stephen Hawking Fellowship EP/T01735X/1. The research of A.W. was funded in part by Science and Technology Facilities Council (STFC) grant ST/W001195/1 (UK). T.E. was funded in part by a Leverhulme Early Career Fellowship ECF-2019-155 (UK). AA and XZ were supported by NASA 80NSSC21K0729 and 80NSSC23K0108. We acknowledge support from ISSI Bern through ISSI International Team projects 483 “The Identification And Classification Of 3D Alfven Resonances” and 546 “Magnetohydrodynamic Surface Waves at Earth’s Magnetosphere (and Beyond).” We acknowledge NASA contract NAS5-02099.The Earth's magnetosphere supports a variety of Magnetohydrodynamic (MHD) normal modes with Ultra Low Frequencies (ULF) including standing Alfvén waves and cavity/waveguide modes. Their amplitudes and frequencies depend in part on the properties of the magnetosphere (size of cavity, wave speed distribution). In this work, we use ∼13 years of Time History of Events and Macroscale Interactions during Substorms satellite magnetic field observations, combined with linearized MHD numerical simulations, to examine the properties of MHD normal modes in the region L > 5 and for frequencies 5 depend on both the magnetopause location and the location of peaks in the radial Alfvén speed profile. Finally, we discuss how these results might be used to better model radiation belt electron dynamics related to ULF waves.PostprintPeer reviewe

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

Electron paramagnetic resonance and other properties of hydrogenases isolated from Desulfovibrio vulgaris (strain Hildenborough) and Megasphaera elsdenii

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65872/1/j.1432-1033.1983.tb07727.x.pd

Redox properties of the iron-sulfur clusters in activated Fe-hydrogenase from Desulfovibrio vulgaris (Hildenborough)

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65750/1/j.1432-1033.1992.tb17261.x.pd

Microbial−mammalian cometabolites dominate the age-associated urinary metabolic phenotype in Taiwanese and American populations

Understanding the metabolic processes associated with aging is key to developing effective management and treatment strategies for age-related diseases. We investigated the metabolic profiles associated with age in a Taiwanese and an American population. 1H NMR spectral profiles were generated for urine specimens collected from the Taiwanese Social Environment and Biomarkers of Aging Study (SEBAS; n = 857; age 54–91 years) and the Mid-Life in the USA study (MIDUS II; n = 1148; age 35–86 years). Multivariate and univariate linear projection methods revealed some common age-related characteristics in urinary metabolite profiles in the American and Taiwanese populations, as well as some distinctive features. In both cases, two metabolites—4-cresyl sulfate (4CS) and phenylacetylglutamine (PAG)—were positively associated with age. In addition, creatine and β-hydroxy-β-methylbutyrate (HMB) were negatively correlated with age in both populations (p < 4 × 10–6). These age-associated gradients in creatine and HMB reflect decreasing muscle mass with age. The systematic increase in PAG and 4CS was confirmed using ultraperformance liquid chromatography–mass spectrometry (UPLC–MS). Both are products of concerted microbial–mammalian host cometabolism and indicate an age-related association with the balance of host–microbiome metabolism