Simultaneous multifrequency observations of Jovian S bursts

The shifted-Wald model is a popular analysis tool for one-choice reaction-time tasks. In its simplest version, the shifted-Wald model assumes a constant trial-independent drift rate parameter. However, the presence of endogenous processes—fluctuation in attention and motivation, fatigue and boredom—suggest that drift rate might vary across experimental trials. Here we show how across-trial variability in drift rate can be accounted for by assuming a trial-specific drift rate parameter that is governed by a positive-valued distribution. We consider two candidate distributions: the truncated normal distribution and the gamma distribution. For the resulting distributions of first-arrival times, we derive analytical and sampling-based solutions, and implement the models in a Bayesian framework. Recovery studies and an application to a data set comprised of 1469 participants suggest that (1) both mixture distributions yield similar results; (2) all model parameters can be recovered accurately except for the drift variance parameter; (3) despite poor recovery, the presence of the drift variance parameter facilitates accurate recovery of the remaining parameters; (4) shift, threshold, and drift mean parameters are correlated.

A single trial analysis of EEG in recognition memory: Tracking the neural correlates of memory strength

A circular analogue of the diffusion model adapted for continuous response tasks is applied to a continuous-outcome source memory task. In contrast to existing models of source retrieval that attribute all of the variability in responding to memory, the circular diffusion model decomposes noise into variability arising from memory and from decision processes. We compared three models: (1) a single diffusion process with trial-to-trial variability in drift rate, (2) a mixture of two diffusion processes, one with positive drift that does not vary from trial-to-trial, and a second zero-drift process that represents discrete guessing, and (3) a hybrid model that mixed positive and zero-drift processes with trial-to-trial variability in the positive drift process. Comparison of model fits to joint response error and response-time (RT) data suggest that a memory strength threshold under which no information is retrieved appears to underlie responding in a continuous-report source memory task. Additionally, we also conditioned participants' source responding on their confidence in an old/new recognition task, ruling out the possibility that participant guessing was only due to unrecognized items. Overall, our findings support an all-or-none or some-or none view of source memory retrieval and pose a challenge to continuous models of source memory.

Introduction: The properties of the S-bursts observed during the storm on 20–21 June 2022 in frequency band 10–32 MHz by the radio telescope URAN-2 are discussed in this paper. The storm was highly populated with other solar bursts, such as Type III bursts and drift pairs. The occurrence rate of S-bursts was very high reaching 60 bursts per minute. All observed S-bursts were characterized by low fluxes with respect to the background radio emission. Thus special processing methods are used to retrieve spectral properties of the bursts. Some individual “long” S-bursts covered the whole frequency band of the URAN-2 radio telescope from 10 to 32 MHz. Such extended in frequency S-bursts were recorded for the first time. 50 extended S-bursts were selected for the further analysis.Methods: The S-bursts dynamic spectra with time-frequency resolutions of 100 ms and 4 kHz as well as single-frequency profiles were used in the analysis. Due to low S-bursts intensities the drift rates were estimated from the time-differentiated dynamic spectra, highlighting the tracks of the bursts maxima. Polarization dynamic spectra were used for measuring the degree and sense of the S-bursts circular polarization. Individual S-bursts tracks were used for instant coronal inhomogeneities diagnostics. Mean S-bursts parameters retrieved from the statistical processing of the set of 50 bursts were compared with previously obtained ones.Results: We concluded that by the mean durations, drift rates, frequency extent and the polarization all observed S-bursts could be divided into two separate groups, the “short” and the “long” S-bursts. The power-law index of the drift rate-frequency dependence averaged over all 50 selected bursts was found to be 1.7. It was shown that sources of S-bursts most likely move through the Newkirk corona with the velocities of 0.06–0.08c. The power-law dependence of the “long” S-bursts durations on frequency in frequency band of 12–30 MHz was obtained. Its index equal to −0.61 appeared to be very close to that for Type III bursts. From this dependence the electron velocity dispersion in the beam, responsible for S-bursts generation was calculated. Its value of 0.02 indicates that the beams, responsible for S-bursts generation are almost monoenergetic.Discussion: It is assumed that non-monotonic appearance of individual S-bursts tracks on the dynamic spectrum reflects density inhomogeneities encountered by the sources on their paths. From the dynamic spectra of such S-bursts the characteristic size and amplitude of these coronal inhomogeneities were detected. From the S-bursts durations and the velocities of their sources the longitudinal sizes of the latter were estimated. It was then shown that the sizes of small-scale coronal inhomogeneities were comparable to those of “long” S-bursts sources. Thus we concluded that individual tracks of the “long” S-bursts can be used for fie diagnostics the coronal plasma at heliocentric heights range from 1.7 to 3.2 Rs, where Rs is the solar radius. On the other hand, these tracks being ensemble-averaged give the information about the long-term large scale properties of the corona.

The study of the direct current (dc) glow discharge plasma parameters and active species kinetics in HBr ( p =30-250 Pa, i d =10-30 mA) was carried out using the 0-dimensional self-consistent steady-state model. The model included the Boltzmann kinetic equation, the balance equations for both neutral and charge particles, plasma conductivity equation and the quasi-neutrality conditions for volume densities of charged particles as well as for their fluxes to the reactor walls. The final set of cross-sections of electron impact processes for HBr molecules was optimized based on the recent literature data. The data on the steady-state electron energy distribution function, electron gas characteristics (mean energy, drift rate and transport coefficients) and volume-averaged densities of plasma active species were obtained as functions of gas pressure and discharge current.

Jupiter's radio emissions are dominated in intensity by decametric radio emissions due to the Io‐Jupiter interaction. Previous analyses suggest that these emissions are cyclotron‐maser emissions in the flux tubes connecting Io or Io's wake to Jupiter. The electrons that trigger the emission are thought to be accelerated toward Jupiter. We present simulations of this hot electron population under the assumption of impulsive acceleration, consistent with the accelerated electron populations seen in the Io's wake by Galileo during its flyby in 1995. After the impulsive acceleration phase, the electrons are supposed to have an adiabatic motion along the magnetic field lines. Near Jupiter, a loss cone and a shell appear in the magnetically mirrored electron population. Such features are able to amplify extraordinary (X) mode radio waves. We compute the X‐mode growth rate, which allows us to build theoretical dynamic spectra of the resulting Jovian radio emissions. The study of the growth rates obtained by simulation and their comparison with ground‐based radio observations provide strong constraints on the acceleration process and energy sources at the origin of the Io‐controlled decameter emissions.

Jupiter's radio emissions are dominated in intensity by decametric radio emissions due to the Io‐Jupiter interaction. A significant part of these emissions consists of short radio bursts (so‐called S‐bursts) drifting in time and frequency. Previous analyses suggest that these emissions are cyclotron‐maser emissions in the flux tube connecting Io or Io's wake to Jupiter. We present simulations of these electrons under the assumption of acceleration by Alfvén waves in the Io flux tube. Near Jupiter, a loss cone and a ring distribution appear in the magnetically mirrored electron population, which can then amplify extraordinary (X) mode radio waves. The X‐mode growth rate is computed, which allows us to build theoretical dynamic spectra of the resulting Jovian radio emissions. Additional potential structures are assumed in the Jovian auroral region. We reconstruct their impact on the morphology of the emission. They match some of the time‐frequency patterns observed with Jovian S‐bursts. This provides the first evidence of bipolar electrostatic structures in the Jovian auroral region.

On the option value of old-growth forest

Linking the diffusion model and general recognition theory: Circular diffusion with bivariate-normally distributed drift rates

Solar flares are one of the most extreme drivers of space weather in our solar system. The impulsive solar radio emission associated with a solar flare is known as a solar radio burst (SRB). They are generally studied in dynamic spectra and are classified into five major spectral classes, ranging from Type I to Type V, based on their form and frequency, and time duration. Due to their intricate characterisation, generating a training set for object-detection and classification models of such phenomena is a difficulty in machine learning. Current algorithms implement parametric modelling where the quantity, grouping, intensity, drift rate, heterogeneity, start–end frequency and start–end time of Type-III and Type-II radio bursts are all random. However, this model does not factor in the true shape or general features seen in real dynamic spectra observations of the Sun, which can be crucial when training classification or object-detection algorithms. In this research, we introduce a methodology named a Generative Adversarial Network (GAN) for generating realistic SRB simulations. By using real examples of Type-III and Type-II SRB data, we can train GANs to generate images almost comparable to real observed data. Furthermore, we evaluate the results of the generated model using human perception, then we compare and contrast the results using a metric known as the Fréchet Inception Distance.

Extreme ultraviolet (EUV) waves are global waves in the solar corona that accelerate particles. The efficiency of this acceleration depends on local plasma characteristics such as the Alfvén speed and the geometry of the magnetic field. This shock-driven particle acceleration produces radio signatures such as Type II radio bursts and herringbone emission. Here we investigate signatures of particle acceleration by a weak coronal shock on 10 March 2024. In particular, we combined EUV images with radio imaging and spectral observations to determine how and where this weak shock could accelerate energetic particles. A potential field source surface extrapolation was used to examine the pre-eruption ambient magnetic field, while the evolution of the global wave was probed using running-difference and base-difference EUV images. The EUV images enabled the speed and Alfvèn Mach number of the EUV wave to be characterised. The combination of radio images and dynamic spectra provides evidence of beams of shock-accelerated electrons localised to a dimming region at the time the EUV wave passes through it. The speeds and energies of these electrons were estimated from the drift rates of their herringbones. The EUV wave initially propagated due west, channelled by two large loop systems, before changing direction northwards. From the EUV intensity jump at the wavefront, the Alfvén Mach number was estimated to be approximately 1.005 at the time the herringbones were produced. The herringbone drift rates reveal accelerated electron energies of 75.32 to 122.10 keV, using Newkirk density models with scaling factors of 1.3 to 2.6. These observations suggest that the weak lateral shock impacted a quasi-perpendicular open field in a dimming region, enabling localised particle acceleration. This indicates that the geometry of the ambient magnetic field relative to the shock strongly governs where particles are accelerated.

<p>Observations by the JUNO spacecraft revealed energetic, bidirectional particle populations with broadband energy distributions in the high-latitude region of Jupiter. These measurements indicate that an acceleration mechanism of stochastic nature plays a dominant role for the generation of the intense main auroral oval. In our current work, we investigate the acceleration of energetic electrons and protons recently observed by JUNO in the Io flux tube wake near Jupiter. We try to infer on the relevant physical acceleration process by considering a resonant as well as a non-resonant wave-particle interaction mechanism, both based on Alfven waves. We focus on necessary temporal scales to drive these mechanisms efficiently and also on the released wave energy by means of the transported Poynting flux along the flux tube.</p>

The role of drift on the diurnal anisotropy and on temporal changes in the energy spectra of the 11-year variation for galactic cosmic rays

In the framework of a macroinvertebrate drift study, the oligochaete community was analysed over one year (1989) at six sites located in a partly impounded reach of the Upper Rhone River (France). Drift composition between sites was somewhat affected by the environmental conditions. These differences were caused by significant deviations in drift rates (P 0.05) among the swimming Naididae. As the latter strongly dominated, global spatial differences in the drift were weak. Temporal changes constituted the main source of variability in drifting oligochaetes. Life cycles and reproductive ecology of four major swimming Naidid species, Nais elinguis, Stylaria lacustris, Nais christinae, and Nais barbata, explained most of the drift structure over the year. Hydrological fluctuations also affected drift structure, both for swimming and non-swimming species. Taxon richness and relative abundance in the drift were very similar to those obtained in the river benthos from a reference reach previously studied. There was a lack of stygobiont and stygophilous species that are frequent in area of groundwater seepage. Biological and environmental implications of oligochaete drift are stressed. The drift phenomenon is appropriated to provide ecological informations on oligochaete communities in fast flowing and deep, large rivers.

In Jupiter's magnetosphere, plasma originating from Io's escaping atmosphere is radially transported outward via two modes of centrifugally driven dynamics. In flux tube interchange events from the Rayleigh–Taylor instability, the cold and dense flux tube moves outward, while hot and depleted flux tubes are injected inwards. In the ballooning mode of the firehose instability, the flux tube breaks off with bursts of plasma blobs. Both modes suggest outward transport of cold, dense plasma blobs. In this study, we survey the cold blobs, analyzing 147 events based on thermal plasma measurements from the Juno/JADE‐I instrument. The cold blobs are identified by searching time‐of‐flight spectra for very narrow signatures in the energy distributions. Plasma parameters determined by forward modeling reveal two types of cold blob events. The first type of event, occurring outside 25 R J , exhibits high density and fast radial velocity accompanied by magnetic nulls and mainly occurs on the dawnside, suggesting an origin from the ballooning mode. The second type of event, occurring within 35 R J , shows simultaneous outward moving cold, dense plasma with inward moving hot, tenuous plasma with no dependence on local time, indicating flux tube interchange. Based on statistics between 15 R J and 30 R J , the mass transport rate of the cold blobs is estimated to be about 100 kg/s, which is insufficient to account for the plasma production rate at Io.