Explore the vast range of titles available.

Previous statistical studies have described the distributions and properties of whistler‐mode waves in Jupiter's magnetosphere, but explaining these wave distributions requires modeling wave propagation from their generation near the magnetic equator. In this letter, we conduct ray tracing of whistler‐mode waves based on realistic Jovian magnetic field and density models. The ray tracing results generally agree with the statistical wave distributions based on Juno measurements. The modeled ray paths show that high‐frequency waves generated near the equator are confined within 20° magnetic latitude due to Landau damping, low‐frequency waves can propagate to higher latitudes and lower M‐shells, with changing wave normal angles, and a portion of low‐frequency waves could propagate to high M shells at high latitudes. Our modeling results provide a theoretical interpretation of whistler‐mode wave distributions and properties, providing essential insights for future radiation belt models at Jupiter. Plain Language Summary Scientists have recently been paying more attention to “whistler‐mode waves” in Jupiter's magnetosphere, as these waves play a key role in the movement of high‐energy electrons within Jupiter's radiation belts. A recent study by Ma, Li, Zhang, Kang, et al. (2024), https://doi.org/10.1029/2024gl111882, using data from NASA's Juno spacecraft, provides detailed insights into these waves, especially at frequencies lower than the “equatorial electron gyrofrequency” in Jupiter's magnetosphere. The study uncovers new information on how these waves propagate through Jupiter's magnetic fields, especially in relation to their origin and angles of inclination relative to the background magnetic field. In the present study, we use computer models to trace how these waves propagate through Jupiter's magnetosphere, based on realistic magnetic field and density conditions. Our models reveal that the waves observed at higher latitudes and farther from Jupiter likely originate near the equator at lower frequencies and evolve as they propagate. This interpretation aligns with the findings from the Juno spacecraft and helps explain how these waves propagate within Jupiter's magnetosphere. Key Points Realistic ray tracing is conducted for Jovian whistler mode waves and results are able to reproduce statistical observations High‐frequency waves originated from equator are confined within 20° latitude and separated from high‐latitude waves originated elsewhere Low‐frequency waves maintain high wave power from the equator to high latitudes and can propagate to low M with varying wave normal angles

Whistler mode waves in the plasmasphere and plumes drive significant losses of energetic electrons from the Earth's radiation belts into the upper atmosphere. In this study, we conducted a survey of amplitude‐dependent whistler wave properties and analyzed their associated background plasma conditions and electron fluxes in the plasmasphere and plumes. Our findings indicate that extremely large amplitude (>400 pT) whistler waves (a) tend to occur at L > 4 over the midnight‐dawn‐noon sectors and have small wave normal angles; (b) are more likely to occur during active geomagnetic conditions associated with higher fluxes of anisotropic electrons at 10 s keV energies; and (c) tend to occur at higher latitudes up to 20° with increasing amplitude. These results suggest that extremely large amplitude whistler waves in the plasmasphere and plumes could be generated locally by injected electrons during substorms and further amplified when propagating to higher latitudes. Plain Language Summary Whistler mode waves are known as one of the primary drivers of precipitating energetic electrons from the Earth's radiation belts into the upper atmosphere. We utilize plasma wave observations from the Van Allen Probes mission and conduct a survey of whistler mode waves inside the plasmasphere and plumes, which are plasma regions surrounding the Earth and filled with high‐density cold electrons. Statistical results indicate that extremely large amplitude whistler waves are more likely to occur at large L shells (L shell is defined as the distance from magnetic field lines to the center of the Earth at the magnetic equator) in the post‐midnight sectors during active geomagnetic conditions associated with high fluxes of tens of keV electrons exhibiting anisotropic pitch angle distributions (with a flux peak in the direction that is perpendicular to the background magnetic field). These waves tend to occur at higher latitudes with increasing amplitude. Results suggest that these waves could be generated locally by injected electrons during substorm activity and may be further amplified when propagating to higher latitudes. Key Points Van Allen Probes wave measurements are used to statistically analyze the whistler waves in the plasmasphere or plume regions Extremely large amplitude (>400 pT) whistler waves tend to occur at L shells >4 over 0–18 hr MLT with small wave normal angles (<10°) Larger amplitude whistler waves are observed during more active substorm activities and higher magnetic latitudes

We statistically evaluate the global distribution and energy spectrum of electron precipitation at low‐Earth‐orbit, using unprecedented pitch‐angle and energy resolved data from the Electron Losses and Fields INvestigation CubeSats. Our statistical results indicate that during active conditions, the ∼63 keV electron precipitation ratio peaks at L > 6 at midnight, whereas the spatial distribution of precipitating energy flux peaks between the dawn and noon sectors. ∼1 MeV electron precipitation ratio peaks near midnight at L > ∼6 but is enhanced near dusk during active times. The energy spectrum of the precipitation ratio shows reversal points indicating energy dispersion as a function of L shell in both the slot region and at L > ∼6, consistent with hiss‐driven precipitation and current sheet scattering, respectively. Our findings provide accurate quantification of electron precipitation at various energies in a broad region of the Earth's magnetosphere, which is critical for magnetosphere‐ionosphere coupling. Plain Language Summary Precipitation into the Earth's upper atmosphere is an important loss process of radiation belt electrons and can change the ionospheric conductance and atmospheric chemistry. Electrons can be moved into the loss cone through either wave‐particle interactions or due to special magnetic field geometries, such as current sheet scattering (CSS). To determine the relative contribution of wave‐particle interactions and CSS, it is crucial to investigate the global distribution and energy spectra of the electron precipitation rate. Previous measurements of energetic electron precipitation at low‐Earth‐orbit either had low resolution in pitch angle and energy or were contaminated by ions and penetrating particles. In this study, we used data from the twin Electron Losses and Fields INvestigation CubeSats, which do not suffer from similar deficiencies, to statistically analyze the dependence of energetic electron precipitation rates on geomagnetic activity, with high resolution in both pitch angle and energy. These findings cast new light on the physical mechanisms that determine the precipitation rate from the magnetosphere into the atmosphere and may have implications for future studies of the ionospheric conductivity and atmospheric chemistry. Key Points A global survey of electron precipitation is performed using the pitch angle and energy resolved data from Electron Losses and Fields INvestigation CubeSats At ∼1 MeV, electron precipitation is strongest at L > ∼6 near midnight and is enhanced near dusk during active times The energy spectrum of the precipitation ratio shows reversal points indicating energy dispersion in L shells in the slot region and L > ∼6

Precipitation into the Earth's atmosphere due to pitch angle scattering by plasma waves has been recognized as one of the major loss mechanisms for energetic electrons. In this study, we quantitatively evaluate their roles in precipitating electrons during a conjunction event with modulated electron precipitation observed at low altitudes by Electron Loss and Fields INvestigation and three types of whistler mode waves (hiss, plume hiss, and chorus) measured near the equator by Time History of Events and Macroscale Interactions during Substorms. Electron precipitation was observed from ∼50 keV to <1 MeV with a spatial modulation, suggested by a good correlation between L shell‐sorted precipitation fluxes and wave intensities. A quasi‐linear analysis supports the observed energy range of precipitation and the ratio of precipitating‐to‐trapped flux. Our findings reveal that the modulated energetic electron precipitation is driven by hiss, plume hiss, and chorus waves. Plain Language Summary Energetic electrons precipitated from the inner magnetosphere into the upper atmosphere can form diffuse and discrete aurora and modulate the ionospheric conductance. One of the major drivers of electron precipitation is wave‐particle interaction with whistler mode waves. In this study, we use the Electron Loss and Fields INvestigation CubeSats to measure electron precipitation at low altitudes and the Time History of Events and Macroscale Interactions during Substorms to provide wave and plasma measurements near the magnetic equator in the conjugate locations. We find that the electron precipitation rate is highly correlated to the whistler mode wave intensity near the equator. Through a quasi‐linear analysis, we demonstrate that the modulation of electron precipitation is driven by whistler mode hiss, plume hiss, and chorus waves that occur in an extensive region of the Earth's magnetosphere. Key Points Modulated electron precipitation from tens to hundreds of keV over L shells of 4–9 is observed by Electron Loss and Fields INvestigation at low altitudes A good correlation is observed between the spatial variations of electron precipitation and wave intensities of hiss, plume hiss, and chorus Quasi‐linear modeling based on the observed wave and plasma parameters reproduced the observed electron precipitation

A new proton radiation belt was identified during the geomagnetic superstorm of 10–11 May 2024. To investigate its origin, we use an MHD‐test particle simulation to model solar energetic proton (SEP) trapping and the evolution of the initial trapped proton population during the storm. The simulation weights the injected SEP population with interplanetary proton measurements and the initial trapped proton radial profile with energy‐resolved Weather System Follow‐on‐Microwave (WSF‐M) proton data, enabling quantitative comparison with observations. Results show that SEP contributions are minimal; the new ∼2–18 MeV belt at L ∼ 2 forms mainly through redistribution and energization of the initial trapped population within hours of the CME shock, driven by subsequent electric field impulses, rather than the initial shock alone. These results provide quantitative evidence based on realistic, plasma‐dependent field dynamics and significantly advance understanding of inner radiation belt formation.

Hiss waves frequently occur in the plasmasphere or plumes, playing a key role in energetic electron loss in the Earth's inner magnetosphere. While previous studies have linked hiss wave enhancements in the outer plasmasphere (just inside the plasmapause) to electron injections during substorms, their evolution across various substorm phases remains unclear. Using Van Allen Probes observations over 2013–2019, we evaluate hiss wave evolution during various phases of substorm activity. At L > 4, both hiss wave intensity and energetic electron flux increase shortly after substorm onset, first on the morning side, then progress to later magnetic local times (MLTs) at a rate of ∼1–3 hr MLT per hr in universal time (UT), eventually stabilizing near 13 MLT. Stronger substorms result in larger and faster intensification in hiss wave intensity and have more significant impact at lower L‐shells. Our results highlight the global variation of hiss waves during substorms.

Electromagnetic ion cyclotron (EMIC) waves have been proposed to be an important mechanism in causing relativistic electron precipitation (REP). However, not all EMIC waves are associated with REP. In our study, we perform analysis on 6 years of data from 2013 to 2018, with REP observed by Polar-orbiting Operational Environmental Satellite (POES) and EMIC wave observations from Van Allen Probes. The coincidence occurrence rate between EMIC waves and REP events is about 34%, approximately 10% higher than the random coincidence occurrence rate. This indicates that EMIC waves and REP can be statistically related, but the link is weaker than expected. We demonstrate that the proportion of H+ band EMIC wave events that are associated with REP is slightly higher than for He+ band EMIC wave activity. An even greater proportion of EMIC waves are accompanied by REP events when H+ band and He+ band EMIC waves occur simultaneously. A parametric study further shows that the coincidence occurrence rate of EMIC wave events and REP events increases with respect to increased background plasma density, with increases in the ratio of plasma frequency to local gyrofrequency, increasing EMIC wave power and when the wave frequency approaches the gyrofrequency. The dependence on background electron density is stronger than the dependence on the ratio of plasma frequency to gyrofrequency. The coincidence occurrence rate decreases as the magnetic field increases between 120-270 nT, consistent with a previous study. Next, a rapid loss event of relativistic radiation belt electrons at low L values (2.4-3.2) outside the plasmasphere during a strong geomagnetic storm on 22 June 2015 is investigated along with a local H+ band EMIC wave-driven loss mechanism. Lower He+ composition and enriched O+ composition is found compared to typical values assumed in other studies of REP driven by EMIC waves. Quantitative analysis demonstrates that H+ band EMIC waves are likely to cause the depletion of relativistic electrons (>5.2 MeV) at low L values for the event studied. Lastly, we explore another area of radiation belt dynamics in a study of the cutoff rigidity of solar energetic proton access into the inner magnetosphere.

Electromagnetic Ion Cyclotron (EMIC) waves can drive radiation belt depletion and Low-Earth Orbit (LEO) satellites can detect the resulting electron and proton precipitation. The ELFIN (Electron Losses and Fields InvestigatioN) CubeSats provide an excellent opportunity to study the properties of EMIC-driven electron precipitation with much higher energy and pitch-angle resolution than previously allowed. We collect EMIC-driven electron precipitation events from ELFIN observations and use POES (Polar Orbiting Environmental Satellites) to search for 10s-100s keV proton precipitation nearby as a proxy of EMIC wave activity. Electron precipitation mainly occurs on localized radial scales (0.3 L), over 15-24 MLT and 5-8 L shells, stronger at MeV energies and weaker down to 100-200 keV. Additionally, the observed loss cone pitch-angle distribution agrees with quasilinear predictions at >250 keV (more filled loss cone with increasing energy), while additional mechanisms are needed to explain the observed low-energy precipitation.

Soy protein isolate (SPI) has attracted considerable attention in the field of packaging technology due to its easy processability, biodegradability, and good film-forming characteristics. However, SPI-based films often suffer from inferior mechanical properties and high moisture sensitivity, thus restricting their practical application. In the present study, herein, a biobased nanocomposite film was developed by cross-linking SPI matrix from the synergistic reinforcement of cellulose nanofibers (CNF) and nano-silica (NS) particles. First, we functionalized the CNF with NS using a silane agent (KH560) as an efficient platform to enhance the interfacial interaction between SPI and CNF/NS, resulting from the epoxy-dominated cross-linking reaction. The chemical structure, thermal stability, and morphology of the resultant nanocomposite films were comprehensively investigated via Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). These results supported successful surface modification and indicated that the surface-tailored CNF/NS nanohybrid possesses excellent adhesion with SPI matrix through covalent and hydrogen-bonding interactions. The integration of CNF/NS into SPI resulted in nanocomposite films with an improved tensile strength (6.65 MPa), representing a 90.54% increase compared with the pristine SPI film. Moreover, the resulting composites had a significantly decreased water vapor permeation and a higher water contact angle (91.75°) than that of the unmodified film. The proposed strategy of synergistic reinforcements in the biobased composites may be a promising and green approach to address the critical limitations of plant protein-based materials in practical applications.

Since deep learning requires a large number of training samples, which is not conducive to its application in reality, small sample learning began to get a lot of attention recently. However, under the condition of small samples for training, high dimensional data still impede the efficiency of the general machine learning model. To solve this problem, we propose a dimension reduction method based on small sample entropy learning and apply it on hand-writing image. An index based on entropy is introduced to measure the importance of different features. Group entropy and labeled entropies are defined according to the distribution of the whole and labeled data on it respectively. And their estimating calculation forms are discussed separately in the case that feature is discrete and continuous. Finally, the index is approximated and prepared for dimension reduction. Numerical results on hand-writing image data sets are presented to verify that much irrelevant dimensions of hand-writing image are found and reduced. Average computational time of image classification computing is shortened. And classification accuracy is retained and even enhanced slightly on some labeled proportions. The case for one shot learning is validated as well. As a result, the proposed method is meaningful and has practical application value.