On the Close Correspondence between Storm-time ULF Wave Power and the POES VLF Chorus Wave Amplitude Proxy

Ground-based Pc5 ULF wave power in multiple ground-based meridians is compared to the VLF wave amplitude proxy, derived from POES precipitation, for the 33 storms studied by Li et al. [2015]. The results reveal common L-shell and time profiles for the ULF waves and VLF proxy for every single storm, especially at $L\leq 6$, and identical discrimination between efficient and inefficient radiation belt electron acceleration. The observations imply either ULF waves play a role in driving precipitation which is falsely interpreted as VLF wave power in the proxy, ULF waves drive VLF waves (the reverse being energetically unfeasible), or both have a common driver with nearly identical L-shell and time-dependence. Global ground-based ULF wave power coherence implies a small number of meridians can be used to estimate storm-time radial diffusion coefficients. However, the strong correspondence between ULF wave power and VLF wave proxy complicates causative assessments of electron acceleration.Comment: 16 pages, 4 figures, 1 table, published in Geophysical Research Letters. Supporting Information is included as a PDF in the source file

Aerobic respiratory costs of swimming in the negatively buoyant brief squid Lolliguncula brevis

Because of the inherent inefficiency of jet propulsion, squid are considered to be at a competitive disadvantage compared with fishes, which generally depend on forms of undulatory/oscillatory locomotion. Some squid, such as the brief squid Lolliguncula brevis, swim at low speeds in shallow-water complex environments, relying heavily on fin activity. Consequently, their swimming costs may be lower than those of the faster, more pelagic squid studied previously and competitive with those of ecologically relevant fishes. To examine aerobic respiratory swimming costs, O2 consumption rates were measured for L. brevis of various sizes (2–9 cm dorsal mantle length, DML) swimming over a range of speeds (3–30 cm s–1) in swim tunnel respirometers, while their behavior was videotaped. Using kinematic data from swimming squid and force data from models, power curves were also generated. Many squid demonstrated partial (J-shaped) or full (U-shaped) parabolic patterns of O2 consumption rate as a function of swimming speed, with O2 consumption minima at 0.5–1.5 DML s–1. Power curves derived from hydrodynamic data plotted as a function of swimming speed were also parabolic, with power minima at 1.2–1.7 DML s–1. The parabolic relationship between O2 consumption rate/power and speed, which is also found in aerial flyers such as birds, bats and insects but rarely in aquatic swimmers because of the difficulties associated with low-speed respirometry, is the result of the high cost of generating lift and maintaining stability at low speeds and overcoming drag at high speeds. L. brevis has a lower rate of O2 consumption than the squid Illex illecebrosus and Loligo opalescens studied in swim tunnel respirometers and is energetically competitive (especially at O2 consumption minima) with fishes, such as striped bass, mullet and flounder. Therefore, the results of this study indicate that, like aerial flyers, some negatively buoyant nekton have parabolic patterns of O2 consumption rate/power as a function of speed and that certain shallow-water squid using considerable fin activity have swimming costs that are competitive with those of ecologically relevant fishes

Swimming mechanics and behavior of the shallow-water brief squid Lolliguncula brevis

Although squid are among the most versatile swimmers and rely on a unique locomotor system, little is known about the swimming mechanics and behavior of most squid, especially those that swim at low speeds in inshore waters. Shallow-water brief squid Lolliguncula brevis, ranging in size from 1.8 to 8.9 cm in dorsal mantle length (DML), were placed in flumes and videotaped, and the data were analyzed using motion-analysis equipment. Flow visualization and force measurement experiments were also performed in water tunnels. Mean critical swimming speeds (Ucrit) ranged from 15.3 to 22.8 cm s–1, and mean transition speeds (Ut; the speed above which squid swim exclusively in a tail-first orientation) varied from 9.0 to 15.3 cm s–1. At low speeds, negatively buoyant brief squid generated lift and/or improved stability by positioning the mantle and arms at high angles of attack, directing high-speed jets downwards (angles \u3e50°) and using fin activity. To reduce drag at high speeds, the squid decreased angles of attack and swam tail-first. Fin motion, which could not be characterized exclusively as drag- or lift-based propulsion, was used over 50–95 % of the sustained speed range and provided as much as 83.8 % of the vertical and 55.1 % of the horizontal thrust. Small squid (DML) used different swimming strategies from those of larger squid, possibly to maximize thrust benefits from vortex ring formation. Furthermore, brief squid employed various unsteady behaviors, such as manipulating funnel diameter during jetting, altering arm position and swimming in different orientations, to boost swimming performance. These results demonstrate that locomotion in slow-swimming squid is complex, involving intricate spatial and temporal interactions between the mantle, fins, arms and funnel

Accurately characterising the importance of wave-particle interactions in radiation belt dynamics: the pitfalls of statistical wave representations

Wave-particle interactions play a crucial role in energetic particle dynamics in the Earth's radiation belts. However the relative importance of different wave-modes in these dynamics is poorly understood. Typically this is assessed during geomagnetic storms using statistically averaged empirical wave models as a function of geomagnetic activity in advanced radiation belt simulations. However statistical averages poorly characterise extreme events such as geomagnetic storms in that storm-time ULF wave power is typically larger than that derived over a solar cycle and Kp is a poor proxy for storm-time wave power

Quantum chaos in open systems: a quantum state diffusion analysis

Except for the universe, all quantum systems are open, and according to quantum state diffusion theory, many systems localize to wave packets in the neighborhood of phase space points. This is due to decoherence from the interaction with the environment, and makes the quasiclassical limit of such systems both more realistic and simpler in many respects than the more familiar quasiclassical limit for closed systems. A linearized version of this theory leads to the correct classical dynamics in the macroscopic limit, even for nonlinear and chaotic systems. We apply the theory to the forced, damped Duffing oscillator, comparing the numerical results of the full and linearized equations, and argue that this can be used to make explicit calculations in the decoherent histories formalism of quantum mechanics.Comment: 18 pages standard LaTeX + 9 figures; extensively trimmed; to appear in J. Phys.

Automated determination of auroral breakup during the substorm expansion phase using all sky imager data

This technique paper describes a novel method for quantitatively and routinely identifying auroral breakup following substorm onset using the Time History of Events and Macroscale Interactions During Substorms (THEMIS) all-sky imagers (ASIs). Substorm onset is characterised by a brightening of the aurora that is followed by auroral poleward expansion and auroral breakup. This breakup can be identified by a sharp increase in the auroral intensity i(t) and the time derivative of auroral intensity i'(t). Utilising both i(t) and i'(t) we have developed an algorithm for identifying the time interval and spatial location of auroral breakup during the substorm expansion phase within the field of view of ASI data based solely on quantifiable characteristics of the optical auroral emissions. We compare the time interval determined by the algorithm to independently identified auroral onset times from three previously published studies. In each case the time interval determined by the algorithm is within error of the onset independently identified by the prior studies. We further show the utility of the algorithm by comparing the breakup intervals determined using the automated algorithm to an independent list of substorm onset times. We demonstrate that up to 50% of the breakup intervals characterised by the algorithm are within the uncertainty of the times identified in the independent list. The quantitative description and routine identification of an interval of auroral brightening during the substorm expansion phase provides a foundation for unbiased statistical analysis of the aurora to probe the physics of the auroral substorm as a new scientific tool for aiding the identification of the processes leading to auroral substorm onset

Energetic Electron and Proton Interactions with Pc5 Ultra Low Frequency (ULF) Waves during the Great Geomagnetic Storm of 15–16 July 2000

The dynamics of the outer zone radiation belt has received a lot of attention mainly due to the correlation between the occurrence of enhancing relativistic electron flux and spacecraft operation anomalies or even failures (e.g., Baker et al. 1994). Relativistic electron events are often observed during great storms associated with ultra low frequency (ULF) waves. For example, a large buildup of relativistic electrons was observed during the great storm of March 24, 1991 (e.g., Li et al. 1993; Hudson et al. 1995; Mann et al. 2013). However, the dominant processes which accelerate magnetospheric radiation belt electrons to MeV energies are not well understood. In this paper, we present observations of Pc5 ULF waves in the recovery phase of the Bastille day storm of July 16, 2000 and electron and proton flux simultaneously oscillating with the same frequencies as the waves. The mechanism for the observed electron and proton flux modulations is examined using groundbased and satellite observations. During this storm time, multiple packets of discrete frequency Pc5 ULF waves appeared associated with energetic particle flux oscillations. We model the drift paths of electrons and protons to determine if the particles drift through the ULF wave to understand why some particle fluxes are modulated by the ULF waves and others are not. We also analyze the flux oscillations of electrons and protons as a function of energy to determine if the particle modulations are caused by a ULF wave drift resonance or advection of a particle density gradient. We suggest that the energetic electron and proton modulations by Pc5 ULF waves provide further evidence in support of the important role that ULF waves play in outer radiation belt dyanamics during storm times

Transition to light-like trajectories in thin shell dynamics

It was recently shown that a massive thin shell that is sandwiched between a flat interior and an exterior geometry given by the outgoing Vaidya metric becomes null in a finite proper time. We investigate this transition for a general spherically-symmetric metric outside the shell and find that it occurs generically. Once the shell is null its persistence on a null trajectory can be ensured by several mechanisms that we describe. Using the outgoing Vaidya metric as an example we show that if a dust shell acquires surface pressure on its transition to a null trajectory it can evade the Schwarzschild radius through its collapse. Alternatively, the pressureless collapse may continue if the exterior geometry acquires a more general form.SCOAP