Frontiers in Astronomy and Space Sciences最新文献

{"title":"The saturation mechanism of thermal instability","authors":"Tim Waters, Daniel Proga","doi":"10.3389/fspas.2023.1198135","DOIUrl":"https://doi.org/10.3389/fspas.2023.1198135","url":null,"abstract":"The literature on thermal instability (TI) reveals that even for a simple homogeneous plasma, the nonlinear outcome ranges from a gentle reconfiguration of the initial state to an explosive one, depending on whether the condensations that form evolve in an isobaric or nonisobaric manner. After summarizing the recent developments on the linear and nonlinear theory of TI, here we derive several general identities from the evolution equation for entropy that reveal the mechanism by which TI saturates; whenever the boundary of the instability region (the Balbus contour) is crossed, a dynamical change is triggered that causes the comoving time derivative of the pressure to change the sign. This event implies that the gas pressure force reverses direction, slowing the continued growth of condensation. For isobaric evolution, this “pressure reversal” occurs nearly simultaneously for every fluid element in condensation and a steady state is quickly reached. For nonisobaric evolution, the condensation is no longer in mechanical equilibrium and the contracting gas rebounds with greater force during the expansion phase that accompanies the gas reaching the equilibrium curve. The cloud then pulsates because the return to mechanical equilibrium becomes wave mediated. We show that both the contraction rebound event and subsequent pulsation behavior follow analytically from an analysis of the new identities. Our analysis also leads to the identification of an isochoric TI zone and makes it clear that unless this zone intersects the equilibrium curve, isochoric modes can only become unstable if the plasma is in a state of thermal non-equilibrium.","PeriodicalId":46793,"journal":{"name":"Frontiers in Astronomy and Space Sciences","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136113755","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A possible mechanism for the formation of an eastward moving auroral spiral","authors":"Katharina N. Maetschke, Elena A. Kronberg, Noora Partamies, Elena E. Grigorenko","doi":"10.3389/fspas.2023.1240081","DOIUrl":"https://doi.org/10.3389/fspas.2023.1240081","url":null,"abstract":"The generation process of auroral spirals is described by different theories varying for their morphology and surrounding conditions. Here, a possible mechanism is proposed for an eastward moving auroral spiral, which was observed in Tromsø, Norway, during the expansion phase of a substorm on 18 September 2013. Measurements from the THEMIS-A and Cluster spacecraft were analyzed, which were located up to ∼10 R E duskward from the spiral generator region in the magnetosphere. Precursory to the spiral observation, concurrent magnetic field dipolarizations, flow bursts and electron injections were measured by the Cluster satellites between 13.6 and 14.2 R E radial distance from Earth. A local Kelvin-Helmholtz-like vortex street in the magnetic field was detected at the same time, which was likely caused by bursty bulk flows. The vortex street was oriented approximately in the X-Y (GSE) plane and presumably propagated towards the source region of the spiral due to a high dawnward velocity component in the flow bursts. The observations suggest that the spiral can have been generated by an associated vortex in the magnetotail and then mapped along the magnetic field lines to the ionosphere. To better understand the role of the ionosphere in auroral spiral generation, in future more mesoscale observations are required.","PeriodicalId":46793,"journal":{"name":"Frontiers in Astronomy and Space Sciences","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135854182","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Turbulent dipolarization regions in the Earth’s magnetotail: ion fluxes and magnetic field changes","authors":"Liudmyla Kozak, Elena A. Kronberg, Bohdan Petrenko, Aljona Blöcker, Roman Akhmetshyn, Istvan Ballai, Viktor Fedun","doi":"10.3389/fspas.2023.1226200","DOIUrl":"https://doi.org/10.3389/fspas.2023.1226200","url":null,"abstract":"In this work, we consider the dynamics of ion fluxes and magnetic field changes in turbulent regions of magnetotail dipolarizations. The data from the Cluster-II mission (magnetic field measurements from fluxgate magnetometers and energetic charged particle observations from RAPID spectrometers) were used for the analysis. We study individual events and investigate statistically the changes of charged particle fluxes during magnetic field dipolarizations observed during 2001–2015. Received changes in the spectral index indicate that CNO+ ions undergo stronger acceleration during dipolarization than protons and helium ions. Before dipolarization front monotonic growth the ions flux is observed (the maximum of flux is observed at 1–1,5 min after the start of dipolarization) in the range of ∼ 92–374 keV for proton; in the energy range ∼ 138–235 keV for He+ and in the energy range of 414–638 keV for CNO+ ions. Flux increase before arriving dipolarization front may result from the reflection of plasma sheet ions at the dipolarization front and the result of the resonant interactions of ions with low-frequency electromagnetic waves.","PeriodicalId":46793,"journal":{"name":"Frontiers in Astronomy and Space Sciences","volume":"61 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135853799","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Using the Perseverance MEDA-RDS to identify and track dust devils and dust-lifting gust fronts","authors":"D. Toledo, V. Apéstigue, J. Martinez-Oter, F. Franchi, F. Serrano, M. Yela, M. de la Torre Juarez, J. A. Rodriguez-Manfredi, I. Arruego","doi":"10.3389/fspas.2023.1221726","DOIUrl":"https://doi.org/10.3389/fspas.2023.1221726","url":null,"abstract":"In the framework of the Europlanet 2024 Research Infrastructure Transnational Access programme, a terrestrial field campaign was conducted from 29 September to 6 October 2021 in Makgadikgadi Salt Pans (Botswana). The main goal of the campaign was to study in situ the impact of the dust devils (DDs) on the observations made by the radiometer Radiation and Dust Sensor (RDS), which is part of the Mars Environmental Dynamics Analyzer instrument, on board NASA’s Mars 2020 Perseverance rover. Several DDs and dust lifting events caused by non-vortex wind gusts were detected using the RDS, and the different impacts of these events were analyzed in the observations. DD diameter, advection velocity, and trajectory were derived from the RDS observations, and then, panoramic videos of such events were used to validate these results. The instrument signal variations produced by dust lifting (by vortices or wind gusts) in Makgadikgadi Pans are similar to those observed on Mars with the RDS, showing the potential of this location as a Martian DD analog.","PeriodicalId":46793,"journal":{"name":"Frontiers in Astronomy and Space Sciences","volume":"109 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136064020","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Full-wave modeling of EMIC wave packets: ducted propagation and reflected waves","authors":"Miroslav Hanzelka, Wen Li, Qianli Ma, Murong Qin, Xiao-Chen Shen, Luisa Capannolo, Longzhi Gan","doi":"10.3389/fspas.2023.1251563","DOIUrl":"https://doi.org/10.3389/fspas.2023.1251563","url":null,"abstract":"Electromagnetic ion cyclotron (EMIC) waves can scatter radiation belt electrons with energies of a few hundred keV and higher. To accurately predict this scattering and the resulting precipitation of these relativistic electrons on short time scales, we need detailed knowledge of the wave field’s spatio-temporal evolution, which cannot be obtained from single spacecraft measurements. Our study presents EMIC wave models obtained from two-dimensional (2D) finite-difference time-domain (FDTD) simulations in the Earth’s dipole magnetic field. We study cases of hydrogen band and helium band wave propagation, rising-tone emissions, packets with amplitude modulations, and ducted waves. We analyze the wave propagation properties in the time domain, enabling comparison with in situ observations. We show that cold plasma density gradients can keep the wave vector quasiparallel, guide the wave energy efficiently, and have a profound effect on mode conversion and reflections. The wave normal angle of unducted waves increases rapidly with latitude, resulting in reflection on the ion hybrid frequency, which prohibits propagation to low altitudes. The modeled wave fields can serve as an input for test-particle analysis of scattering and precipitation of relativistic electrons and energetic ions.","PeriodicalId":46793,"journal":{"name":"Frontiers in Astronomy and Space Sciences","volume":"62 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136294181","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hydrogen atoms near the exobase are cold: independent observations do not support the hot exosphere concept","authors":"Dmytro Kotov, Oleksandr Bogomaz","doi":"10.3389/fspas.2023.1200959","DOIUrl":"https://doi.org/10.3389/fspas.2023.1200959","url":null,"abstract":"OPINION article Front. Astron. Space Sci., 10 October 2023Sec. Space Physics Volume 10 - 2023 | https://doi.org/10.3389/fspas.2023.1200959","PeriodicalId":46793,"journal":{"name":"Frontiers in Astronomy and Space Sciences","volume":"98 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136357222","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Point spread function modelling for astronomical telescopes: a review focused on weak gravitational lensing studies","authors":"Liaudat, Tobias, Starck, Jean-Luc, Kilbinger, Martin, Frugier, Pierre-Antoine","doi":"10.3389/fspas.2023.1158213","DOIUrl":"https://doi.org/10.3389/fspas.2023.1158213","url":null,"abstract":"The accurate modelling of the point spread function (PSF) is of paramount importance in astronomical observations, as it allows for the correction of distortions and blurring caused by the telescope and atmosphere. PSF modelling is crucial for accurately measuring celestial objects’ properties. The last decades have brought us a steady increase in the power and complexity of astronomical telescopes and instruments. Upcoming galaxy surveys like Euclid and Legacy Survey of Space and Time (LSST) will observe an unprecedented amount and quality of data. Modelling the PSF for these new facilities and surveys requires novel modelling techniques that can cope with the ever-tightening error requirements. The purpose of this review is threefold. Firstly, we introduce the optical background required for a more physically motivated PSF modelling and propose an observational model that can be reused for future developments. Secondly, we provide an overview of the different physical contributors of the PSF, which includes the optic- and detector-level contributors and atmosphere. We expect that the overview will help better understand the modelled effects. Thirdly, we discuss the different methods for PSF modelling from the parametric and non-parametric families for ground- and space-based telescopes, with their advantages and limitations. Validation methods for PSF models are then addressed, with several metrics related to weak-lensing studies discussed in detail. Finally, we explore current challenges and future directions in PSF modelling for astronomical telescopes.","PeriodicalId":46793,"journal":{"name":"Frontiers in Astronomy and Space Sciences","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135043745","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Analysis and mapping of lunar wrinkle ridges (LWRs) using automated LWRs detection process with LROC-WAC and LOLA data","authors":"Aqil Tariq, Jianguo Yan, Qingyun Deng, Jean-Pierre Barriot","doi":"10.3389/fspas.2023.1037395","DOIUrl":"https://doi.org/10.3389/fspas.2023.1037395","url":null,"abstract":"Maps of lunar wrinkle ridges (LWRs) were created from 70°N to 70°S and 140°E to 140°W (extracted and highlighted the major LWRs area) using automated LWRs detection process with Lunar Reconnaissance Orbiter Camera wide range angle camera and Lunar Orbiter Laser Altimeter data. Automatic detection of LWRs is challenging because the ridges are of irregular shapes and many ridges have been eroded and/or degraded over time. It’s a preliminary study of automated ridge detection from DEM data. Statistics and measurements of the extracted LWRs, including orientation, extent, length, height, and elevation offset, were performed based on the mapping of lunar ridges. The identified ridges were classified based on their orientation, distribution, direction, and each class were further divided over basalts, and nearby highlands. According to the findings, 3,375 segments with a total length of 26,455.01 km were identified, and the average elevation offset, width, and height of all the wrinkle ridges were 40.39 m, 3.47 km, and 0.29 km respectively after weighting by length. The LWRs were divided into three morphologies and distributions: parallel ridges, isolated ridges, and concentric ridges. The vast majority of LWRs were found in basalts area, with an extension into neighboring highland. The relations between the morphological parameters were further quantitatively analyzed, and a similar linear correlation between the width and height was found in each class of lunar ridges, implying that small and large ridges were formed as a continuum and that the three classes of ridges were probably formed by some common processes. Finally, the relations between the lunar wrinkle ridges and other geomorphic phenomena were analyzed, indicating that purely volcanic origin or buried premare structures are difficult to reconcile with the investigation. In addition, the consistency between the occurrence of the lunar wrinkle ridges and the thickness of lunar maria indicates that the formation of lunar wrinkle ridges is closely related to the lunar maria; nevertheless, the statistical NW direction of individual classes of LWRs also proposes the presence of an appropriate stress field during the process of their formation.","PeriodicalId":46793,"journal":{"name":"Frontiers in Astronomy and Space Sciences","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135350972","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A statistical analysis and comparison of the fine structures of the ion upflow associated with the double-peak subauroral ion drift","authors":"Qiang Zhang, De-Sheng Han, Shang-Chun Teng, Zhi-Wei Wang, Q.-H. Zhang, Zan-Yang Xing, Yong Wang, Yu-Zhang Ma","doi":"10.3389/fspas.2023.1254243","DOIUrl":"https://doi.org/10.3389/fspas.2023.1254243","url":null,"abstract":"The ion upflow associated with the subauroral ion drift (SAID) is a crucial component in the exchange of particles between the ionosphere and the ring currents. The ion upflow associated with the double-peak subauroral ion drift (DSAID), which is a subclass of the SAID, is more complex compared to SAID. In this study, we conducted a statistical analysis of the ion upflow associated with DSAID using Defense Meteorological Satellite Program (DMSP) F16–F18 data spanning 11 years (2010–2020) in the Northern Hemisphere. Our findings revealed that ion upflow associated with DSAID can exhibit either a double-peak or a one-peak upflow. The statistical characteristics of these two types of events displayed significant differences. In DSAID with a double-peak upflow event, the velocity of DSAID around the high-latitude peak was greater than that around the low-latitude peak. However, in DSAID with a one-peak upflow event, the DSAID velocities around the two peaks were very similar. Based on the formation mechanism of DSAID and the process of frictional heating in the ionosphere, we proposed that the formation of DSAID with a double-peak upflow and DSAID with a one-peak upflow are likely related to the formation process of DSAID.","PeriodicalId":46793,"journal":{"name":"Frontiers in Astronomy and Space Sciences","volume":"64 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135590697","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A review of N+ observations in the ionosphere-magnetosphere system","authors":"Raluca Ilie, Mei-Yun Lin, Muhammad Fraz Bashir, Abhiraj Majumder","doi":"10.3389/fspas.2023.1224659","DOIUrl":"https://doi.org/10.3389/fspas.2023.1224659","url":null,"abstract":"Most studies have yet to consider and assess the transport and energization of N + ions throughout the ionosphere-magnetosphere system, in addition to that of O + and other heavy ion species. The limited observational record of N + presence in near-Earth plasma, partly due to instrument limitations to distinguish ion species of similar masses, has obscured its significant contribution to the near-Earth plasma. This letter reviews the most notable observations of N + ions, starting from the early low altitude measurements from Sputnik III in the ionosphere to the measurements reported by the Enhanced Polar Outflow Probe (e-POP) mission. The available observational data set suggests that nitrogen ions are constant companions of outflowing oxygen ions, and their abundances vary with season, solar cycle, time of day, and geomagnetic activity. This strong record of nitrogen presence in the ionosphere-magnetosphere system raises the question of ionic composition and the need for caution when interpreting O + measurements from current missions.","PeriodicalId":46793,"journal":{"name":"Frontiers in Astronomy and Space Sciences","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135592209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}