Localized Heating of the Martian Topside Ionosphere Through the Combined Effects of Magnetic Pumping by Large‐Scale Magnetosonic Waves and Pitch Angle Diffusion by Whistler Waves

We present Mars Atmosphere and Volatile EvolutioN (MAVEN) observations of periodic (~ 25 s) large scale (100s km) magnetosonic waves propagating into the Martian dayside upper ionosphere. These waves adiabatically modulate the superthermal electron distribution function, and the induced electron temperature anisotropies drive the generation of observed electromagnetic whistler waves. The localized (in altitude) minimum in the ratio fpe / fce provides conditions favorable for the local enhancement of efficient wave-particle interactions, so that the induced whistlers act back on the superthermal electron population to isotropize the plasma through pitch angle scattering. These wave-particle interactions break the adiabaticity of the large scale magnetosonic wave compressions, leading to local heating of the superthermal electrons during compressive wave `troughs'. Further evidence of this heating is observed as the subsequent phase shift between the observed perpendicular-to-parallel superthermal electron temperatures and compressive wave fronts. Such a heating mechanism may be important at other unmagnetized bodies such as Venus and comets.

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Large- and small-scale vortical motions in a shear layer perturbed by tabs

Journal of Fluid Mechanics ◽

10.1017/s0022112098003887 ◽

1999 ◽

Vol 382 ◽

pp. 307-329 ◽

Cited By ~ 60

Author(s):

JUDITH K. FOSS ◽

K. B. M. Q. ZAMAN

Keyword(s):

Shear Layer ◽

Pitch Angle ◽

Large Scale ◽

Dimensional Space ◽

Three Dimensional ◽

Small Scale ◽

Streamwise Vortices ◽

Streamwise Vorticity ◽

Cross Sectional ◽

Scale Population

The large- and small-scale vortical motions produced by ‘delta tabs’ in a two-stream shear layer have been studied experimentally. An increase in mixing was observed when the base of the triangular shaped tab was affixed to the trailing edge of the splitter plate and the apex was pitched at some angle with respect to the flow axis. Such an arrangement produced a pair of counter-rotating streamwise vortices. Hot-wire measurements detailed the velocity, time-averaged vorticity (Ωx) and small-scale turbulence features in the three-dimensional space downstream of the tabs. The small-scale structures, whose scale corresponds to that of the peak in the dissipation spectrum, were identified and counted using the peak-valley-counting technique. The optimal pitch angle, θ, for a single tab and the optimal spanwise spacing, S, for a multiple tab array were identified. Since the goal was to increase mixing, the optimal tab configuration was determined from two properties of the flow field: (i) the large-scale motions with the maximum Ωx, and (ii) the largest number of small-scale motions in a given time period. The peak streamwise vorticity magnitude [mid ]Ωx−max[mid ] was found to have a unique relationship with the tab pitch angle. Furthermore, for all cases examined, the overall small-scale population was found to correlate directly with [mid ]Ωx−max[mid ]. Both quantities peaked at θ≈±45°. It is interesting to note that the peak magnitude of the corresponding circulation in the cross-sectional plane occurred for θ≈±90°. For an array of tabs, the two quantities also depended on the tab spacing. An array of contiguous tabs acted as a solid deflector producing the weakest streamwise vortices and the least small-scale population. For the measurement range covered, the optimal spacing was found to be S≈1.5 tab widths.

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Resonant scattering of energetic electrons in the plasmasphere by monotonic whistler-mode waves artificially generated by ionospheric modification

Annales Geophysicae ◽

10.5194/angeo-32-507-2014 ◽

2014 ◽

Vol 32 (5) ◽

pp. 507-518 ◽

Cited By ~ 3

Author(s):

S. S. Chang ◽

B. B. Ni ◽

J. Bortnik ◽

C. Zhou ◽

Z. Y. Zhao ◽

...

Keyword(s):

Test Particle ◽

Pitch Angle ◽

Low Frequency ◽

Resonant Scattering ◽

High Energy ◽

Whistler Waves ◽

Energetic Electrons ◽

High Energy Electrons ◽

Angle Scattering ◽

Vlf Waves

Abstract. Modulated high-frequency (HF) heating of the ionosphere provides a feasible means of artificially generating extremely low-frequency (ELF)/very low-frequency (VLF) whistler waves, which can leak into the inner magnetosphere and contribute to resonant interactions with high-energy electrons in the plasmasphere. By ray tracing the magnetospheric propagation of ELF/VLF emissions artificially generated at low-invariant latitudes, we evaluate the relativistic electron resonant energies along the ray paths and show that propagating artificial ELF/VLF waves can resonate with electrons from ~ 100 keV to ~ 10 MeV. We further implement test particle simulations to investigate the effects of resonant scattering of energetic electrons due to triggered monotonic/single-frequency ELF/VLF waves. The results indicate that within the period of a resonance timescale, changes in electron pitch angle and kinetic energy are stochastic, and the overall effect is cumulative, that is, the changes averaged over all test electrons increase monotonically with time. The localized rates of wave-induced pitch-angle scattering and momentum diffusion in the plasmasphere are analyzed in detail for artificially generated ELF/VLF whistlers with an observable in situ amplitude of ~ 10 pT. While the local momentum diffusion of relativistic electrons is small, with a rate of < 10−7 s−1, the local pitch-angle scattering can be intense near the loss cone with a rate of ~ 10−4 s−1. Our investigation further supports the feasibility of artificial triggering of ELF/VLF whistler waves for removal of high-energy electrons at lower L shells within the plasmasphere. Moreover, our test particle simulation results show quantitatively good agreement with quasi-linear diffusion coefficients, confirming the applicability of both methods to evaluate the resonant diffusion effect of artificial generated ELF/VLF whistlers.

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Electron Pitch Angle Distributions in the Compressional Pc5 Waves

10.5194/egusphere-egu21-14090 ◽

2021 ◽

Author(s):

Xiao Ma ◽

Anmin Tian ◽

Quanqi Shi ◽

Shichen Bai ◽

Ji Liu ◽

...

Keyword(s):

Pitch Angle ◽

Interaction Effects ◽

Plasma Pressure ◽

Whistler Waves ◽

Whistler Mode ◽

Compressional Waves ◽

The Earth ◽

Pressure Anisotropy ◽

Electron Distributions ◽

Whistler Mode Waves

In the two flanks of the Earth&#8217;s magnetosphere, the compressional Pc5 waves are often observed. Previous study suggests that these waves are usually excited by plasma pressure anisotropy such as drift mirror instability. Interestingly, whistler mode waves are often observed in the magnetic trough regions of the compressional Pc5 waves. In this study, we use 10 years (2007-2016) THEMIS A data to study the electron distributions in the compressional Pc5 waves associated with the whistler mode waves. We find three typical electron pitch angle distributions (PADs) in these compressional waves: cigar-shape, donut-shape and pancake-shape. They predominantly occur at tens to hundreds eV, several keV and >10 keV, respectively. The interaction effects between the electrons and whistler waves inside the magnetic troughs are stressed in understanding the formation of these PADs.

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Particle-In-Cell simulations of resonant interactions between whistler waves and electrons in the near-Sun solar wind: scattering of the strahl into the halo and heat flux regulation.

10.5194/egusphere-egu21-10198 ◽

2021 ◽

Author(s):

Alfredo Micera ◽

Andrei Zhukov ◽

Rodrigo A. López ◽

Maria Elena Innocenti ◽

Marian Lazar ◽

...

Keyword(s):

Magnetic Field ◽

Heat Flux ◽

Solar Wind ◽

Velocity Distribution ◽

Pitch Angle ◽

Electron Velocity ◽

Magnetic Field Direction ◽

Whistler Waves ◽

Electron Velocity Distribution ◽

Particle In Cell

Electron velocity distribution functions, initially composed of core and strahl populations as typically encountered in the near-Sun solar wind and as recently observed by Parker Solar Probe, have been modeled via fully kinetic Particle-In-Cell simulations. It has been demonstrated that, as a consequence of the evolution of the electron velocity distribution function, two branches of the whistler heat flux instability can be excited, which can drive whistler waves propagating in the direction parallel or oblique to the background magnetic field. First, the strahl undergoes pitch-angle scattering with oblique whistler waves, which provokes the reduction of the strahl drift velocity and the simultaneous broadening of its pitch angle distribution. Moreover, the interaction with the oblique whistler waves results in the scattering towards higher perpendicular velocities of resonant strahl electrons and in the appearance of a suprathermal halo population which, at higher energies, deviates from the Maxwellian distribution. Later on, the excited whistler waves shift towards smaller angles of propagation and secondary scattering processes with quasi-parallel whistler waves lead to a redistribution of the scattered particles into a more symmetric halo. All processes are accompanied by a significant decrease of the heat flux carried by the strahl population along the magnetic field direction, although the strongest heat flux rate decrease is simultaneous with the propagation of the oblique whistler waves.

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Synchronous combined effects of fishing and climate within a demersal community

ICES Journal of Marine Science ◽

10.1093/icesjms/fss181 ◽

2012 ◽

Vol 70 (2) ◽

pp. 319-328 ◽

Cited By ~ 25

Author(s):

Antoni Quetglas ◽

Francesc Ordines ◽

Manuel Hidalgo ◽

Sebastià Monserrat ◽

Susana Ruiz ◽

...

Keyword(s):

Climate Variability ◽

Age Structure ◽

Large Scale ◽

Southern Oscillation ◽

Climatic Variability ◽

Early Period ◽

Combined Effects ◽

Population Fluctuations ◽

Fishing Activity ◽

The Mediterranean

Abstract Quetglas, A., Ordines, F., Hidalgo, M., Monserrat, S., Ruiz, S., Amores, Á., Moranta, J., and Massutí, E. 2013. Synchronous combined effects of fishing and climate within a demersal community. – ICES Journal of Marine Science, 70: 319–328. Accumulating evidence shows that fishing exploitation and environmental variables can synergistically affect the population dynamics of exploited populations. Here, we document an interaction between fishing impact and climate variability that triggered a synchronic response in the population fluctuations of six exploited species in the Mediterranean from 1965–2008. Throughout this period, the fishing activity experienced a sharp increase in fishing effort, which caused all stocks to shift from an early period of underexploitation to a later period of overexploitation. This change altered the population resilience of the stocks and brought about an increase in the sensitivity of its dynamics to climate variability. Landings increased exponentially when underexploited but displayed an oscillatory behaviour once overexploited. Climatic indices, related to the Mediterranean mesoscale hydrography and large-scale north Atlantic climatic variability, seemed to affect the species with broader age structure and longer lifespan, while the global-scale El Niño Southern Oscillation index (ENSO) positively influenced the population abundances of species with a narrow age structure and short lifespan. The species affected by ENSO preferentially inhabit the continental shelf, suggesting that Mediterranean shelf ecosystems are sensitive to the hydroclimatic variability linked to global climate.

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Passive Disconnection of an SPM-Moored LNG Carrier in Waves

24th International Conference on Offshore Mechanics and Arctic Engineering: Volume 2 ◽

10.1115/omae2005-67105 ◽

2005 ◽

Cited By ~ 1

Author(s):

Mamoun Naciri ◽

Walter Maurel ◽

Jean-Pierre Que´au

Keyword(s):

Small Proportion ◽

Equilibrium Position ◽

Pitch Angle ◽

Large Scale ◽

Harsh Environments ◽

Passive System ◽

Low Friction ◽

Centre Of Gravity ◽

Equilibrium Angle ◽

Large Matrix

The Soft Yoke Mooring and Offloading system (SYMO®) has been developed in SBM to allow the tandem mooring of an LNG carrier to the stern of an LNG FPSO or a Floating, Storage & Regasification Unit in harsh environments. The SYMO® system consists of two mooring legs supported by a crane. A yoke structure is suspended at the bottom of the two mooring legs by uni-joints. The tip of the yoke is connected to the bow of the LNG carrier via roll, pitch and yaw articulations. When connected the yoke structure is horizontal. Upon disconnection, the yoke settles at an equilibrium position characterized by a pitch angle of 35° to 40° with respect to the horizontal. Owing to the low friction articulations, the yoke oscillations decay very slowly and the yoke may come too close to the LNG carrier bow. A passive system has been developed to improve the SYMO® dynamics at disconnection whereby a small proportion of the overall yoke weight is replaced by water. This water is allowed to move in a suitably designed tank network thus shifting around the overall centre of gravity and yoke equilibrium angle as pitch oscillations take place. The above principle has first been investigated using a kinematics program before being model tested at a large scale of 1:16. A large matrix of tests has been performed to investigate the effect of the water ballast volume and the layout of the tank network. Once the principle was confirmed experimentally, CFD computations were performed in a blind fashion and compared to the experiments.

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Length Parameter for Scaling Abutment Scour Depth

Water ◽

10.3390/w12123508 ◽

2020 ◽

Vol 12 (12) ◽

pp. 3508

Author(s):

Puer Xu ◽

Niansheng Cheng ◽

Maoxing Wei

Keyword(s):

Large Scale ◽

Scour Depth ◽

Length Scale ◽

Bed Shear Stress ◽

Combined Effects ◽

Flow Depth ◽

Vortex System ◽

Bridge Abutment ◽

Abutment Scour ◽

Scale Turbulence

Flow constriction caused by bridge abutment increases bed shear stress and thus enhances local scour. For scaling the maximum scour depth at the abutment, either abutment length or flow depth has been empirically used in previous studies. By performing a step-by-step analysis, this study proposes a new length scale, which is able to represent combined effects of abutment length, approach flow depth and channel width. Physically, the new length scale describes the maximum possible dimension of the associated vortex system (or large-scale turbulence). Six series of data compiled from the published literature were used in the analysis. The results indicate that the new length scale helps improve the agreement of predictions with the experimental data.

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