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Whistler in watercolor : lovely little games
For renowned artist James McNeill Whistler (1834-1903), watercolor was the medium through which he reinvented himself in the 1880s and painted his way into posterity. No one was more smitten with Whistler and his works than Gilded Age industrialist Charles Lang Freer, who amassed the world's largest collection of watercolors by the artist and included them in his bequest to the Smithsonian in 1906. Freer's collection comprises more than fifty examples of Whistler's watercolors, yet these works have never left the confines of the Freer Gallery of Art in Washington, DC. This landmark book takes a fresh look at the exhibition and reception of Whistler's watercolors in Britain and the United States and provides a new scientific analysis of his materials and techniques, from the papers he used to the pigments he chose.
Book
Whistler Chorus Amplification in the Magnetosphere: The Nonlinear Free‐Electron Laser Model and the Ginzburg‐Landau Equation
We present a novel nonlinear model for whistler‐mode chorus amplification based on the free‐electron laser (FEL) mechanism. First, we derive the nonlinear collective variable equations for the whistler‐electron interaction. Consistent with in situ satellite observations, these equations predict that a small seed wave can undergo exponential growth, reaching a peak of a few hundred picoteslas after a few milliseconds, followed by millisecond timescale amplitude modulations. Next, we show that when one accounts for multiple wave frequencies and wave spatial variations, the amplitude and phase of the whistler wave can be described by the Ginzburg‐Landau equation (GLE), providing a framework for the investigation of solitary wave behavior of chorus modes. These findings enhance our understanding of wave‐particle interactions and space weather in the Van Allen radiation belts, deepen the connection between whistler‐electron dynamics and FELs, and reveal a novel connection between whistler‐mode chorus and the GLE.
Journal Article
Pre-acceleration in the Electron Foreshock. II. Oblique Whistler Waves
Thermal electrons have gyroradii many orders of magnitude smaller than the finite width of a shock, thus need to be pre-accelerated before they can cross it and be accelerated by diffusive shock acceleration. One region where pre-acceleration may occur is the inner foreshock, which upstream electrons must pass through before any potential downstream crossing. In this paper, we perform a large-scale particle-in-cell simulation that generates a single shock with parameters motivated from supernova remnants. Within the foreshock, reflected electrons excite the oblique whistler instability and produce electromagnetic whistler waves, which comove with the upstream flow and as nonlinear structures eventually reach radii of up to 5 ion-gyroradii. We show that the inner electromagnetic configuration of the whistlers evolves into complex nonlinear structures bound by a strong magnetic field around four times the upstream value. Although these nonlinear structures do not in general interact with cospatial upstream electrons, they resonate with electrons that have been reflected at the shock. We show that they can scatter, or even trap, reflected electrons, confining around 0.8% of the total upstream electron population to the region close to the shock where they can undergo substantial pre-acceleration. This acceleration process is similar to, yet approximately three times more efficient than, stochastic shock drift acceleration.
Journal Article
Fodor's Vancouver & Victoria
\"Fodor's correspondents highlight the best of British Colombia's cities and countryside escapes, including lively neighborhoods, First Nations culture, beaches, and wine country. Our local experts vet every recommendation to ensure you make the most of your time, whether it's your first trip or your fifth,\"--page [4] of cover.
Book
Global Non-axisymmetric Hall Instabilities in a Rotating Plasma
Non-axisymmetric, flow-driven instabilities in the incompressible Hall-MHD model are studied in a differentially rotating cylindrical plasma. It is found that, in the Hall-MHD regime, both whistler waves and ion-cyclotron waves can extract energy from the flow shear, resulting in two distinct branches of global instability. The non-axisymmetric whistler modes grow significantly faster than non-axisymmetric, ideal MHD modes. A discussion of the global whistler instability mechanism is presented in the large-ion-skin-depth, “electron-MHD” limit. When the magnetic field is azimuthal, a subset of the whistler modes having zero axial wave number are uncovered to be destabilized by the “corotation amplifier” mechanism. It is observed that the effect of the Hall term on the non-axisymmetric modes can be appreciable when di is on the order of a few percent of the width of the cylindrical annulus. Distinct global modes emerge in the strong Hall-MHD regime at significantly stronger magnetic fields than those required for unstable global MHD modes, as the Hall effect weakens the stabilizing “field-line bending” by decoupling ion motion from the magnetic field. These global non-axisymmetric modes may play an important role in weakly ionized accretion disks.
Journal Article
Non‐Lightning‐Generated Whistler Waves in Near‐Venus Space
The occurrence of Venusian lighting has been debated for decades. Terrestrial lightning generates whistler waves, and many whistlers have been observed in Venus's ionosphere and induced magnetosphere. Venusian lightning occurrence rates derived from these whistler observations are relatively high. However, optical flashes on Venus are exceedingly rare and Venus encounters by multiple spacecrafts have not detected lightning. These non‐detections and rare optical observations are consistent with low Venusian lightning occurrence rates, which is incompatible with the high whistler‐derived rates. We present observations of whistlers during a Parker Solar Probe Venus gravity assist and eliminate lightning as a possible source. These waves are observed at an altitude of 0.39 Venus radii on Venus' nightside with planetward propagation and are simultaneous with Langmuir waves. This provides a mechanism for whistler generation near Venus that does not require lightning, and suggests that whistler‐based lightning occurrence rates may be overestimated. Plain Language Summary Whistler waves are a type of plasma wave. These waves can be generated in several ways, including by lightning. Every lightning strike on Earth generates a whistler wave, but only some of the whistler waves in near‐Earth space are generated by lightning. Many whistler waves have been detected near Venus and have been used to argue that lightning likely occurs on Venus at a relatively high rate. However, other signatures of lightning (including flashes of light in the sky) on Venus are very rare, which indicates that Venusian lightning must occur at a very low rate. The discrepancy between these different signatures of lightning on Venus means that we do not know how often Venus actually experiences lightning. We use data from Parker Solar Probe during a Venus gravity assist to study whistler waves that occurred on the nightside of Venus, very close to the planet. We observe that these waves are traveling toward Venus, which means they could not have been generated by lightning. This shows that whistler waves can occur near Venus without being generated by lightning and indicates that the occurrence rates of Venusian lightning based on whistler wave observations might be overestimated. Key Points Whistler waves were observed at an altitude of 0.39 Venus radii on Venus's nightside with planetward Poynting vector Langmuir waves occurred simultaneously with the whistlers, suggesting electron beam driving with magnetotail origins Lightning is eliminated as a possible generation mechanism for these whistler waves
Journal Article
Whistler‐Mode Waves in the Density Double Ducts
We report the recent observation of a density duct structure in the equatorial plasmasphere, identified using data from the NASA Van Allen Probes (RBSP). The structure consists of a low‐density duct located above a high‐density duct, forming a “double duct” system capable of simultaneously trapping and guiding multiple whistler‐mode waves at distinct frequencies. Simulations based on the electron‐MHD model confirm that such density double ducts enable efficient confinement and propagation of whistler‐mode waves along the background magnetic field.
Journal Article
Plasma Wave and Particle Dynamics During Interchange Events in the Jovian Magnetosphere Using Juno Observations
Interchange instability is known to drive fast radial transport of particles in Jupiter's inner magnetosphere. Magnetic flux tubes associated with the interchange instability often coincide with changes in particle distributions and plasma waves, but further investigations are required to understand their detailed characteristics. We analyze representative interchange events observed by Juno, which exhibit intriguing features of particle distributions and plasma waves, including Z‐mode and whistler‐mode waves. These events occurred at an equatorial radial distance of ∼9 Jovian radii on the nightside, with Z‐mode waves observed at mid‐latitude and whistler‐mode waves near the equator. We calculate the linear growth rate of whistler‐mode and Z‐mode waves based on the observed plasma parameters and electron distributions and find that both waves can be locally generated within the interchanged flux tube. Our findings are important for understanding particle transport and generation of plasma waves in the magnetospheres of Jupiter and other planetary systems. Plain Language Summary The centrifugal interchange instability, which has been observed in rapidly rotating planets, like Saturn and Jupiter, moves cold plasmas inside of the magnetosphere further away, and transports hotter, less dense plasmas toward the inner magnetosphere. These moving flux tubes have been observed at Jupiter together with plasma waves, but their detailed characteristics are not fully understood. In the present study, we use observations from the Juno spacecraft to report multiple representative interchange events and evaluate the properties of energetic particles and plasma waves. Furthermore, we use linear theory to calculate the growth rates of Z‐mode and whistler‐mode waves during these events. Our findings reveal the typical features of plasma waves and particles during interchange events, which provide important insights into particle transport and generation of plasma waves at Jupiter and possibly other magnetized planets in our solar system and beyond. Key Points Several plasma transport events associated with interchange instability are identified alongside plasma waves using Juno observations Linear growth rate analyses indicate that waves can be locally generated during interchange events due to anisotropic electron distributions Our findings provide insights into electron transport and plasma wave dynamics during interchange events in planetary magnetospheres
Journal Article