Showing papers on "Chorus published in 2022"

Short Chorus Wave Packets: Generation Within Chorus Elements, Statistics, and Consequences on Energetic Electron Precipitation

Abstract: Short and intense lower-band chorus wave packets are ubiquitous in the Earth's outer radiation belt. In this article, we perform various Vlasov hybrid simulations, with one or two triggering waves, to study the generation of short chorus packets/subpackets inside long rising tone elements. We show that the length of the generated short wave packets is consistent with a criterion of resonance non-overlap for two independent superposed waves, and that these chorus packets have similar characteristics as in Van Allen Probes observations. We find that short wave packets are mainly formed near the middle/end of long rising tones for moderate linear growth rates, and everywhere for stronger linear growth rates. Finally, we analyze an event characterized by Time History of Events and Macroscale Interactions during Substorms spacecraft measurements of chorus rising tones near the equator and simultaneous measurements by low altitude ELFIN CubeSats of precipitating and trapped electron fluxes in the same sector. The measured precipitating electron fluxes are well recovered by test particle simulations performed using measured plasma and wave properties. We show that short chorus wave packets of moderate amplitudes (160–250 pT) essentially lead to a more diffusive-like transport of 50–200 keV electrons toward the loss cone than long packets. In contrast, long chorus packets are found to produce important nonlinear effects via anomalous trapping, which significantly reduces electron precipitation below 150 keV, especially for higher wave amplitudes.

A Theoretical Framework of Chorus Wave Excitation

Abstract: We propose a self-consistent theoretical framework of chorus wave excitation, which describes the evolution of the whistler fluctuation spectrum as well as the supra-thermal electron distribution function. The renormalized hot electron response is cast in the form of a Dyson-like equation, which then leads to evolution equations for nonlinear fluctuation growth and frequency shift. This approach allows us to analytically derive for the first time exactly the same expression for the chorus chirping rate originally proposed by Vomvoridis et al.,1982. Chorus chirping is shown to correspond to maximization of wave particle power exchange, where each individual wave belonging to the whistler wave packet is characterized by small nonlinear frequency shift. We also show that different interpretations of chorus chirping proposed in published literature have a consistent reconciliation within the present theoretical framework, which further illuminates the analogy with similar phenomena in fusion plasmas and free electron laser physics.

Ducted Chorus Waves Cause Sub‐Relativistic and Relativistic Electron Microbursts

Abstract: During magnetospheric storms, radiation belt electrons are produced and then removed by collisions with the lower atmosphere on varying timescales. An efficient loss process is microbursts, strong, transient precipitation of electrons over a wide energy range, from tens of keV to sub-relativistic and relativistic energies (100s keV and above). However, the detailed generation mechanism of microbursts, especially over sub-relativistic and relativistic energies, remains unknown. Here, we show that these energetic electron microbursts may be caused by ducted whistler-mode lower-band chorus waves. Using observations of equatorial chorus waves nearby low-altitude precipitation as well as data-driven simulations, we demonstrate that the observed microbursts are the result of resonant interaction of electrons with ducted chorus waves rather than nonducted ones. Revealing the physical mechanism behind the microbursts advances our understanding of radiation belt dynamics and its impact on the lower atmosphere and space weather.

One‐Dimensional gcPIC‐ <b> <i>δf</i> </b> Simulation of Hooked Chorus Waves in the Earth’s Inner Magnetosphere

Abstract: Chorus waves are coherent electromagnetic emissions in the inner magnetosphere, generally composed of a series of discrete and repetitive elements. These elements usually have rising frequency chirpings, which are occasionally mingled with one or several elements with a hooked spectrogram. In this letter, we perform a one-dimensional general curvilinear particle-in-cell (gcPIC)-δf simulation of chorus waves excited by temperature anisotropic electrons in a dipole magnetic field, and identify one chorus element with a hooked spectrogram, which is embedded in several chorus elements with a rising frequency chirping. In the hooked chorus element, the frequency increases first, and then decreases. Interestingly, we find that there are clear electron holes in the electron velocity space, no matter whether the chorus element has a rising-tone or hooked-tone spectrogram. Our study presents an important clue for the theoretical analysis of the frequency chirping in the chorus waves.

To Catch A Chorus, Verse, Intro, or Anything Else: Analyzing a Song with Structural Functions

Abstract: Conventional music structure analysis algorithms aim to divide a song into segments and to group them with abstract labels (e.g., ‘A’, ‘B’, and ‘C’). However, explicitly identifying the function of each segment (e.g., ‘verse’ or ‘chorus’) is rarely attempted, but has many applications. We introduce a multi-task deep learning framework to model these structural semantic labels directly from audio by estimating "verseness," "chorusness," and so forth, as a function of time. We propose a 7-class taxonomy (i.e., intro, verse, chorus, bridge, outro, instrumental, and silence) and provide rules to consolidate annotations from four disparate datasets. We also propose to use a spectral-temporal Transformer-based model, called SpecTNT, which can be trained with an additional connectionist temporal localization (CTL) loss. In cross-dataset evaluations using four public datasets, we demonstrate the effectiveness of the SpecTNT model and CTL loss, and obtain strong results overall: the proposed system outperforms state-of-the-art chorus-detection and boundary-detection methods at detecting choruses and boundaries, respectively.

Observational Evidence for the Origin of Repetitive Chorus Emissions

Abstract: Chorus waves, discovered as a series of repetitive coherent emissions, are well known for producing hazard radiation environments in Earth's magnetosphere. Its repetitive nature directly causes the rapid modulation of pulsating aurora in the upper atmosphere and microburst in the ionosphere, but its origin remains a decades-old puzzle. Recent simulation suggested the energetic electrons, injected from the magnetotail and drifting eastward around the Earth, are critical to form the repetitive pattern. Based on a survey of 1.5 year data from Van Allen Probes, we provide the first observational evidence for the origin of repetitive chorus emissions. We find there exists universally an inverse correlation between the repetitive period and drift velocity of energetic electrons, uncovering how the drifting energetic electrons tune the repetitive period of chorus emissions, which is also supported by kinetic simulations. Our finding may apply to understand the generation of repetitive emissions in planetary magnetospheres and laboratory plasmas.

Nonlinear Wave Growth Analysis of Chorus Emissions Modulated by ULF Waves

Abstract: We present Van Allen Probes observations of periodic chorus wave emissions in the troughs of compressional ultralow frequency (ULF) waves. During this event, the spectral gap of chorus waves gradually widens as the spacecraft moves from the equatorial source region towards higher latitudes. Moreover, chorus wave intensity increases and frequency range widens after a substorm injection. We show that the periodic occurrence of chorus waves is attributed to the modulation of threshold amplitude for nonlinear growth of chorus waves by the second spatial derivative of ULF compressional magnetic field. The widening gap can be interpreted in terms of the nonlinear damping mechanism. A good agreement is also found between the nonlinear wave growth theory and the observations regarding the influence of substorm injection on the chorus. These findings support the applicability of the nonlinear theory in describing the chorus wave generation and damping, together with their modulations by ULF waves.

The Angular Distribution of Lower Band Chorus Waves Near Plasmaspheric Plumes

Abstract: Plumes have been identified as an access region for chorus waves to enter the plasmasphere. Here, for the first time, chorus wave properties are parameterized by distance from the plume boundary. Case studies and statistical analysis indicate that the polar wave vector angle, θk, of chorus becomes more oblique near the plume edge. Occurrence rates of θk > 35° on the plume boundary are approximately double that observed further away from the plume. Whilst the increase in θk is apparent on both plume edges, the distribution of θk exhibits different behavior between the Eastward and Westward boundaries. In general, the distribution of azimuthal wave vector angles, ϕk, is symmetric about the anti-Earthwards direction. However, near the Eastward plume boundary, an Eastwards skew of ϕk is reported. This result provides new insight on chorus propagation in the context of the chorus-to-hiss mechanism, and has implications for quantifying wave-particle interactions in the near-plume region.

Impactful Theory: Pathways to Mattering

Abstract: Organization Theory is an academic journal dedicated to the development and dissemination of novel theory in the domain of organizational scholarship. At the same time, an increasing chorus of organizational scholars have advocated for “impact”—broadly defined as producing societal benefit beyond the realm of academia. In this editorial, we question the implicit dichotomy between theory, on the one hand, and impact, on the other, and critically explore the notion of impactful theory. Rather than seeing theory as inherently opposed to impact, we celebrate and elucidate theory as a meaningful way to achieve impact. Specifically, we unpack the apparent oxymoron of impactful theory, and articulate seven distinct pathways whereby theory can be impactful. We close by outlining several critical questions, both for individual scholars and our collective community, as well as future research directions.

Upper Limit of Outer Radiation Belt Electron Acceleration Driven by Whistler‐Mode Chorus Waves

Abstract: We investigate the outer radiation belt electron energy spectra of the highest fluxes observed during storms based on Van Allen Probes measurements, which demonstrate a similar shape despite various levels of geomagnetic activity. Using quasi-linear diffusion simulations, we reproduce the observed electron acceleration by whistler-mode chorus waves during the storm of 25 October 2016, when the maximum fluxes were close to the highest upper limit observed during the 2013–2018 period. The electrons below ∼1 MeV reached the upper limit of chorus acceleration within ∼1 day and then remained at a stable level, while the multi-MeV electrons with sharper energy gradient were subject to the continuous acceleration process. Our results reveal the natural upper limit of electron acceleration by chorus, which strongly depends on the lower energy boundary, and the stable seed population at hundreds of keV (but not the chorus intensity) which is a prerequisite for the relativistic electron acceleration.

Artificial Light at Night Drives Earlier Singing in a Neotropical Bird

Abstract: Simple Summary Urban birds have to cope with dominant stressors as anthropogenic noise and artificial light at night by adjusting their song traits. However, evidence of such adjustments has been studied thus far in temperate cities, rather than tropical cities. Here, I tested whether noise and light pollution influence earlier singing behavior in a tropical bird, the Saffron Finch. Birds in highly urbanized sites sang earlier at dawn and this timing difference was driven by light pollution instead of anthropogenic noise. Overall, these results suggest that light pollution could have a detrimental impact on the circadian rhythms of urban tropical birds such as daily singing routines. Abstract Anthropogenic noise and artificial light at night (ALAN) can disrupt the morning singing routines of urban birds, however, its influence on tropical species remains poorly explored. Here, I assessed the association between light and noise pollution with the dawn chorus onset of the Saffron Finch (Sicalis flaveola) in a city in Colombia. I studied 32 sites comprised of different conditions of urban development based on built cover. I recorded the time of the first song of the Saffron Finch, the conspecific density and measured anthropogenic noise and ALAN using smartphone apps. The findings of this study show that Saffron Finches living in highly developed sites sang earlier at dawn than those occupying less urbanized sites. Unexpectedly, this timing difference was related to ALAN instead of anthropogenic noise, suggesting that light pollution could drive earlier dawn chorus in a tropical urban bird. Saffron Finches could take advantage of earlier singing for signaling territorial ownership among neighbors. Future studies need to assess the influence of ALAN on the dawn chorus timing of Neotropical urban birds.

Backward-propagating source as a component of rising tone whistler-mode chorus generation

Abstract: Whistler-mode chorus waves in the magnetosphere play a crucial role in space weather via wave–particle interactions. The past two decades have observed tremendous advances in theory and simulations of chorus generation; however, several details of the generation mechanism are still actively contended. To simulate chorus generation, a new envelope particle-in-cell code is introduced. The model produces a rising tone chorus element in a parabolic geomagnetic field. The initial chorus element “embryo” frequency is shown to initialize near the equator at the frequency of maximum linear growth. A backward resonant current is then observed to propagate upstream of the equator. The trajectory of the backward current follows that of a freely falling electron that has been de-trapped at the equator superimposed with forward motion at the group velocity. The backward current iteratively radiates a rising tone element where the highest frequency components are generated furthest upstream. The work provides new advancements in modeling chorus and corroborates other recent work that has also demonstrated a backward-moving source during the generation of coherent whistler-mode waves.

If philosophers went on a leadership course: A (serious) farce in three Acts

Abstract: Leadership development is big business, with business schools and private providers offering leadership development programmes claimed to help turn managers into wise, good and able leaders. Leadership development originated in philosophy and, in the Western tradition, dates back at least as far as Socrates. This article asks: how would philosophers qua wisdom-lovers [philo-sophes] respond to contemporary programmes? We use the dramatic licence offered by theatre to imagine Foucault, Butler, Kant, Hume and others participating in a leadership training course. As our play opens, we find them critiquing a 360-degree psychometric assessment instrument they have been asked to complete. Our highly select group argue it solicits docile, servile supplicants to the interests of neoliberal capitalism. They offer an alternative containing key questions putative leaders should explore. The script includes other dramatis personnae and a Chorus (the authors of this paper). Speeches and programme notes provide the necessary bones of an academic paper, such as literature reviews and philosophical contexts. We ask colleagues to join with us in reconnecting leadership development to its philosophical roots in an effort to foster wiser and more ethical leadership.

The Structure and Microstructure of Rising‐Tone Chorus With Frequencies Crossing at <i>f</i> ∼ 0.5 <i>f</i> _ce

Abstract: Intense, midnight-to-dawn sector, near-equatorial, chorus rising tones which cross frequencies of have been analyzed to determine their structures and possible substructures. Upper band () chorus and “gap” () chorus are examined in detail for the first time. It is found that upper band chorus and gap chorus are composed of the same structure as lower band () chorus: they are composed of short-duration subelements, which are monochromatic with . These findings have strong implications for the chorus element generation mechanism. Following Kennel and Petschek (1966, https://doi.org/10.1029/JZ071i001p00001) the overall chorus riser is most likely generated by anisotropic ( > 1) ∼10–100 keV substorm-injected electrons. Assuming cyclotron resonance, the upper band chorus is generated by the low energy portion of the electron spectrum. The often-present gap at is related to Landau/cyclotron damping. This however is not the end of the story. There is another type of two-frequency chorus (called Type 2) for which the lower band is not well connected to the upper band. A Type 2 chorus reported previously by Fu et al. (2014, https://doi.org/10.1002/2014JA020364) has also been studied in detail. Both the lower band and upper band are composed of subelements which are monochromatic. Such a similar fine structure for the different type of chorus may imply a similar generation mechanism, for which the difference between them is just the energy range of resonant energetic electrons. One mechanism discussed here, generation by phase bunched electrons, will be tested in the near future.

Seasonal and diel patterns in singing activity of humpback whales migrating through Bermuda

Abstract: Humpback whales (Megaptera novaeangliae) produce song and non-song vocalisations, which allows their presence to be detected through passive acoustic monitoring. To determine the seasonal and diel acoustic presence and acoustic behaviour of humpback whales at the migratory stopover site off Bermuda, three hydrophones were deployed between March 2018 and April 2019 on Challenger Bank and the Bermuda platform. Song was the predominant vocalisation type encountered, with 65% of song recordings containing whale chorus and a clear seasonal trend of humpback whale occurrence in the spring and winter months from late December to mid-May. A strong diel pattern in singing activity was detected. Singing activity significantly increased at night relative to the daytime (p<0.01), whilst twilight periods were characterised by intermediate levels of singing. The song structure encountered in spring 2018 consisted of 18 units, 6 themes and 5 transitional phrases. The high occurrence of whale chorus and the strong seasonal and diel patterns of male humpback whale singing activity highlights the importance of Bermuda not just on their northward migration during spring, as described historically, but also on their southward migration during winter. Bermuda therefore constitutes a two-way migratory stopover site for humpback whales. The present study also provides Bermuda’s planning authorities with better constraints on the duration and intensity of anthropogenic activities in these waters.

Individual contributions to group chorus dynamics influence access to mating opportunities in wood frogs.

Abstract: A limitation in bioacoustic studies has been the inability to differentiate individual sonic contributions from group-level dynamics. We present a novel application of acoustic camera technology to investigate how individual wood frogs' calls influence chorus properties, and how variation influences mating opportunities. We recorded mating calls and used playback trials to gauge preference for different chorus types in the laboratory. Males and females preferred chorus playbacks with low variance in dominant frequency. Females preferred choruses with low mean peak frequency. Field studies revealed more egg masses laid in ponds where males chorused with low variance in dominant frequency. We also noted a trend towards more egg masses laid in ponds where males called with low mean frequency. Nearest-neighbour distances influenced call timing (neighbours called in succession) and distances increased with variance in chorus frequency. Results highlight the potential fitness implications of individual-level contributions to a bioacoustic signal produced by groups.

Desire to Die: How Does the Patients' Chorus Sound?

Abstract: Patients receiving palliative care often express a desire to die. Forms and backgrounds of these expressions can be diverse. To contribute to a better understanding of this phenomenon, we analyzed patients' desire to die expressions reported by palliative care providers participating in 11 communication trainings on desire to die. The 102 participants were asked to reproduce related patients' statements from their everyday practice. The 165 reported statements could be assigned to the four topics: "Putting an end to life by …," "Social death," "Death images," as well as "Specific and unspecific references to life, death and dying." Across these topics, phrasing differs particularly regarding sentence type (interrogative, declarative, propositional, exclamatory), explicitness and (the way of) referencing others (e.g. attribution of power). The compilation of statements reflects a chorus of expressions, which the palliative care providers might hear throughout their professional career as well as during a patient's process(ing) of disease.

Some Thoughts on Colonial Historians and American Indians

Abstract: The common ground Fenton proposed was Indian-white relations in eastern North America before 1830, and it was no coincidence that he issued his call for action at the Institute of Early American History and Culture, then as now the leading center for study of America’s formative years. The good news, then, is worth celebrating: more people are seeking to understand the native American experience from Columbian Exchange to Jacksonian Removal, and their efforts are being accorded a more prominent place in the lists of book publishers and the pages of scholarly journals. The prospect is not unrelievedly bleak: some scholars have managed to join Indian voices to the chorus now issuing from early American studies. Even works devoting less space to native peoples may exhibit a slightly raised consciousness about America’s original inhabitants.

Deepchorus: A Hybrid Model of Multi-Scale Convolution And Self-Attention for Chorus Detection

Abstract: Chorus detection is a challenging problem in musical signal processing as the chorus often repeats more than once in popular songs, usually with rich instruments and complex rhythm forms. Most of the existing works focus on the receptiveness of chorus sections based on some explicit features such as loudness and occurrence frequency. These pre-assumptions for chorus limit the generalization capacity of these methods, causing misdetection on other repeated sections such as verse. To solve the problem, in this paper we propose an end-to-end chorus detection model DeepChorus, reducing the engineering effort and the need for prior knowledge. The proposed model includes two main structures: i) a Multi-Scale Network to derive preliminary representations of chorus segments, and ii) a Self-Attention Convolution Network to further process the features into probability curves representing chorus presence. To obtain the final results, we apply an adaptive threshold to binarize the original curve. The experimental results show that DeepChorus outperforms existing state-of-the-art methods in most cases.

Research on Chorus Emotion Recognition and Intelligent Medical Application Based on Health Big Data

Abstract: In chorus activities, the conductor leads chorus members to recreate music works. If you want to interpret music works perfectly with sound, emotion and emotional expression are particularly important. In this paper, a cloud HBD (health big data) integration system based on ensemble learning is designed to realize the high-efficiency and high-precision integration of HBD. An emotional speech database containing three emotions such as pleasure, calmness, and boredom is established, and the corpus problems such as emotional feature analysis and extraction needed for chorus emotion recognition research are solved. It also studies the classification and decision-making in emotional changes, and a DBN (deep belief network) chorus emotion recognition algorithm based on multiple emotional features is proposed. Feature DBN (Deep Belief Network) Chorus Emotion Recognition Algorithm This paper extracts various robust low-level features according to different features' ability to describe emotions and then feeds them into the DBN network to extract high-level feature descriptors. Then, the classification results of ELM (extreme learning machine) are voted and fused with the idea of ensemble learning, and the effectiveness of the algorithm is proved on three public datasets.

The Effects of Substorm Injection of Energetic Electrons and Enhanced Solar Wind Ram Pressure on Whistler‐Mode Chorus Waves: A Statistical Study

Abstract: Whistler-mode chorus waves in the inner magnetosphere are typically excited by an electron temperature anisotropy. The anisotropy can be driven by two sources: particle injections from the tail (such as during substorms) and the solar wind ram pressure on the dayside magnetosphere. Based on 5 years of data from Van Allen Probe A, we have separately studied the effects of substorm injection of energetic ∼10–100 keV electrons and their gradient and curvature drifts () and enhanced solar wind ram pressure () on the generation of whistler-mode chorus waves. We use time-modified and indices to take into account time delays. We find that during the period of large but small , chorus waves are mainly observed in the midnight through dawn to noon sectors ( MLT 13) near the magnetic equator (|MLAT| < 10°) at L = 4.5–6.5. With an increase in both the chorus occurrence rates and the wave amplitudes increase. While under the condition of enhanced but small , chorus waves are preferentially detected on the dayside ( MLT 14) in a wide range of latitudes (|MLAT| < 20°) at outer L-shells (L = 5.5–6.5). With the increase of , chorus occurrence rates also increase, while the amplitude remains relatively constant. Our study supports the two mechanisms for chorus excitation in the Earth’s magnetosphere and provides a better understanding of the global distribution and properties of chorus waves.

The Yellow-breasted Barbet (Trachyphonus margaritatus) introduces vocal duets and choruses with a specific multimodal signal, during territorial advertisement

Abstract: Abstract Cooperative behaviour is a prominent feature among many group-living species and continues to pose challenges to our understanding about the evolution of social relationships and task coordination between members of the same social group. Individuals who are willing to cooperate to achieve a joined action need to communicate their intentions and somehow make a common agreement. We investigated how a coordinated chorus song is initiated in a cooperative-breeding bird species, The Yellow-Breasted Barbet ( Trachyphonus margaritatus ). A chorus can be defined as an interactive vocal display involving several individuals who are synchronizing their behaviour to sing in a time coordinated manner. Synchronizing behaviour to sing in chorus might become quite challenging when several individuals are involved. Thus, group members could use a specific signal to induce such collective action. Yet, few studies have investigated the mechanisms of communal display initiation in chorusing bird species. We conducted playback experiments to induce and record territorial defensive reactions from birds with a video camera. We recorded 26 different groups from distinct wild populations in Djibouti which belonged to 17 sites. We found that barbets use a specific vocalization named chewp note to introduce their duet and chorus. Moreover, we found that the individual that initiates such communal displays may broadcast a multimodal signal by combining chewp note series with a typical body posture with the tail raised and fanned. We suggest that the multimodal signal could serve to attract attention and elicit a response from other group members or could enhance the song coordination.

Nonlinear Electron Phase‐Space Dynamics in Spontaneous Excitation of Falling‐Tone Chorus

Abstract: Whistler mode chorus, characterized by frequency chirping, is an important type of waves in planetary magnetospheres. To investigate the role of nonlinear wave particle interactions in excitation of chorus, analysis of electron phase space dynamics is required. While electron phase hole associated with rising tone chorus has been well studied, the phase space structure corresponding to falling tone chorus is less understood. Here, we investigate in detail the electron phase space dynamics in a spontaneously generated falling tone chorus with a parabolic type magnetic field, where field strength decreases away from the equator. We demonstrate the formation and evolution of electron phase space clump from downstream to upstream regions, and show that the variation of frequency chirping rate is caused by the movement of the source region. The results are consistent with the recently proposed Trap-Release-Amplify model, and should be useful to understand the mechanism of chorus frequency chirping.

Quantifying the Size and Duration of a Microburst‐Producing Chorus Region on 5 December 2017

Abstract: Microbursts are impulsive (<1 s) injections of electrons into the atmosphere, thought to be caused by nonlinear scattering by chorus waves. Although attempts have been made to quantify their contribution to outer belt electron loss, the uncertainty in the overall size and duration of the microburst region is typically large, so that their contribution to outer belt loss is uncertain. We combine datasets that measure chorus waves (Van Allen Probes [RBSP], Arase, ground-based VLF stations) and microburst (>30 keV) precipitation (FIREBIRD II and AC6 CubeSats, POES) to determine the size of the microburst-producing chorus source region beginning on 5 December 2017. We estimate that the long-lasting (∼30 hr) microburst-producing chorus region extends from 4 to 8 MLT and 2–5 L. We conclude that microbursts likely represent a major loss source of outer radiation belt electrons for this event.

Dawn and dusk chorus as a potential zeitgeber

Abstract: ABSTRACT Over millennia, environmental light-dark cycle provided a dependable indicator of time of day. It showed the effects of light on physiology and behaviour in every animal. Furthermore, sunrise and sunset (dawn and dusk) usually refer to the duration of day length when the upper edge of the sun’s disk is on the horizon. Interestingly, before the onset of sunrise and after sunset there is twilight (dawn and dusk), during which there is natural light provided by the upper atmosphere. Evidences suggested that transitions (twilight) are more essential to synchronize organisms circadian (circa = about; dian = day) and circannual (circa = about; annum = year) rhythms (seasonal events). Overall, we say that all the characteristics of light pose major changes in the behavior and physiology of animals and plant system. In this mini-review, we discuss the noteworthy aspects of dawn and dusk chorus and the behavioural changes observed during this switching between day and night times.

Slow Contraction of Flash Aurora Induced by an Isolated Chorus Element Ranging From Lower‐Band to Upper‐Band Frequencies in the Source Region

Abstract: Flash aurora driven by an isolated chorus element can be a useful ionospheric indicator for identifying the source wave properties via wave-particle interactions. Using ground observation and modeling approaches, here we report the temporal characteristics of flash aurora that depend on the chorus frequency width and the sweep rate. We found that the contraction time increases more than the expansion time in patchy auroral variations, due to the difference in the minimum electron energies resonated with the chorus wave packet away from the equatorial source to higher latitudes. Especially, the contraction time strongly depends on the higher-frequency chorus waves due to cyclotron resonance with lower-energy electrons. The model calculations support that the chorus element ranges from lower-band to upper-band frequencies with respect to half the gyrofrequency at the exact generation region. Our study provides the prompt (milliseconds) chorus-driven electron dynamics through the spatiotemporal characteristics of flash aurora in the ionosphere.