363 research outputs found

    MHD‐driven kinetic dissipation in the solar wind and corona

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    Mechanisms for the deposition of heat in the lower coronal plasma are discussed, emphasizing recent attempts to reconcile the fluid and kinetic perspectives. Structures at magnetohydrodynamic (MHD) scales may drive a nonlinear cascade, preferentially exciting high perpendicular wavenumber fluctuations. Relevant dissipative kinetic processes must be identified that can absorb the associated energy flux. The relationship between the MHD cascade and direct cyclotron absorption, including cyclotron sweep, is discussed. We conclude that for coronal and solar wind parameters the perpendicular cascade cannot be neglected and may be more rapid than cyclotron sweep. Solar wind observational evidence suggests the relevance of the ion inertial scale, which is associated with current sheet thickness during reconnection. We conclude that a significant fraction of dissipation in the corona and solar wind likely proceeds through a perpendicular cascade and small-scale reconnection, coupled to kinetic processes that act at oblique wavevectors

    Collisionless Damping of Fast MHD Waves in Magneto-rotational Winds

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    We propose collisionless damping of fast MHD waves as an important mechanism for the heating and acceleration of winds from rotating stars. Stellar rotation causes magnetic field lines anchored at the surface to form a spiral pattern and magneto-rotational winds can be driven. If the structure is a magnetically dominated, fast MHD waves generated at the surface can propagate almost radially outward and cross the field lines. The propagating waves undergo collisionless damping owing to interactions with particles surfing on magnetic mirrors that are formed by the waves themselves. The damping is especially effective where the angle between the wave propagation and the field lines becomes moderately large (20\sim 20 to 8080^{\circ}). The angle tends naturally to increase into this range because the field in magneto-rotational winds develops an increasingly large azimuthal component. The dissipation of the wave energy produces heating and acceleration of the outflow. We show using specified wind structures that this damping process can be important in both solar-type stars and massive stars that have moderately large rotation rates. This mechanism can play a role in coronae of young solar-type stars which are rapidly rotating and show X-ray luminosities much larger than the sun. The mechanism could also be important for producing the extended X-ray emitting regions inferred to exist in massive stars of spectral type middle B and later.Comment: 12 pages, including 7 figures, accepted for publication in Ap

    Heating of the solar wind with electron and proton effects

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    We examine the effects of including effects of both protons and electrons on the heating of the fast solar wind through two different approaches. In the first approach, we incorporate the electron temperature in an MHD turbulence transport model for the solar wind. In the second approach, we adopt more empirically based methods by analyzing the measured proton and electron temperatures to calculate the heat deposition rates. Overall, we conclude that incorporating separate proton and electron temperatures and heat conduction effects provides an improved and more complete model of the heating of the solar wind

    Phenomenology for the decay of energy-containing eddies in homogeneous MHD turbulence

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    We evaluate a number of simple, one‐point phenomenological models for the decay of energy‐containing eddies in magnetohydrodynamic(MHD) and hydrodynamicturbulence. The MHDmodels include effects of cross helicity and Alfvénic couplings associated with a constant mean magnetic field, based on physical effects well‐described in the literature. The analytic structure of three separate MHDmodels is discussed. The single hydrodynamic model and several MHDmodels are compared against results from spectral‐method simulations. The hydrodynamic model phenomenology has been previously verified against experiments in wind tunnels, and certain experimentally determined parameters in the model are satisfactorily reproduced by the present simulation. This agreement supports the suitability of our numerical calculations for examining MHDturbulence, where practical difficulties make it more difficult to study physical examples. When the triple‐decorrelation time and effects of spectral anisotropy are properly taken into account, particular MHDmodels give decay rates that remain correct to within a factor of 2 for several energy‐halving times. A simple model of this type is likely to be useful in a number of applications in space physics, astrophysics, and laboratory plasma physics where the approximate effects of turbulence need to be included

    No Fukushima Dai-ichi derived plutonium signal in marine sediments collected 1.5-57km from the reactors

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    Based on AMS analysis, it is shown that no Pu signals from the Fukushima accident could be discerned in marine sediments collected 1.5-57km away from the Fukushima Da-ichi power plant (FDNPP), which were clearly influenced by accident-derived radiocesium. The 240Pu/239Pu atom ratios (0.21-0.28) were significantly higher than terrestrial global fallout (0.182 ± 0.005), but still in agreement with pre-FDNPP accident baseline data for Pu in near coastal seawaters influenced by global fallout and long-range transport of Pu from the Pacific Proving Grounds.This study has been funded by the Norwegian Research Council through its Centre of Excellence (CoE) funding scheme (Project No. 223268/F50)

    Electron and proton heating by solar wind turbulence

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    Previous formulations of heating and transport associated with strong magnetohydrodynamic (MHD) turbulence are generalized to incorporate separate internal energy equations for electrons and protons. Electron heat conduction is included. Energy is supplied by turbulent heating that affects both electrons and protons, and is exchanged between them via collisions. Comparison to available Ulysses data shows that a reasonable accounting for the data is provided when (i) the energy exchange timescale is very long and (ii) the deposition of heat due to turbulence is divided, with 60% going to proton heating and 40% into electron heating. Heat conduction, determined here by an empirical fit, plays a major role in describing the electron data

    Resolving the patents paradox in the era of COVID-19 and climate change: Towards a patents taxonomy

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    This paper revisits the patents debate and considers the role of intellectual property rights and their impact on society in the context of inventions designed to protect global common pool resources (CPRs) such as public health and the environment. A review of the theoretical and empirical literature suggests that there has never been a clear consensus among researchers on the benefits of the patent system and intellectual property rights. As Robinson notes, “The patent system introduces some of the greatest of the complexities in the capitalist rules of the game and leads to many anomalies.” We explore these anomalies by specifying a taxonomy of patents for different classes of inventions, including inventions to protect CPRs. This includes vaccines and inventions that reduce externalities, such as, CFC gases and greenhouse gas emissions. In these instances, the effectiveness of innovations depends critically on rapid global diffusion. Our theoretical analysis utilises Ostrom's CPR dilemma to analyse the complexities surrounding innovation and CPRs. We find that the effectiveness of innovations to protect CPRs depends on industrial characteristics and the wider regulatory environment. Empirical evidence is brought to bear on these conclusions via 2 case studies that each embodies a natural experiment; one on vaccines pre- and post-TRIPS and one on environmental technologies to reduce CFC gases and CO2 emissions with and without an agreed UN Protocol. The insights gained are explored in our policy section. Our analysis suggests the need for a more nuanced approach to patent policy that is embedded in the wider context of innovation systems and takes account of the anomalies raised by CPRs. For CPR protecting innovations subject to positive network externalities, we advocate that policy should prioritise diffusion over private incentives for R&D and use alternative policies to patents to stimulate investment in R&D
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