Timothy Wemimo David, Chizurumoke Michael Michael, Darren M. Wright, Adetoro Temitope Talabi, Abayomi E. Ajetunmobi
{"title":"Ionospheric Upwelling and the Level of Associated Noise at Solar Minimum","authors":"Timothy Wemimo David, Chizurumoke Michael Michael, Darren M. Wright, Adetoro Temitope Talabi, Abayomi E. Ajetunmobi","doi":"10.5194/angeo-2023-37","DOIUrl":"https://doi.org/10.5194/angeo-2023-37","url":null,"abstract":"<strong>Abstract.</strong> We have studied the ionospheric upwelling with magnitude above 10<sup>13</sup> <em>m</em><sup>−2</sup> <em>s</em><sup>−1</sup> using the data during the IPY-ESR 2007 campaign, which coincides with solar minimum. The noise level in low, medium and high-flux upflows is investigated. We found that the noise level in high-flux upflow is about 93 % while the low and medium categories are 62 % and 80 %, respectively. This shows that robust and stringent filtering techniques must be ensured when analysing incoherent data in order not to bias the result. Analysis reveals that the frequency of the low-flux upflow events is about 8 and 73 times the medium and high-flux upflow events, respectively. Seasonal observation shows that the noise level in the upflow classes is predominantly during winter. The noise is minimal in summer, with a notable result indicating occurrence of actual data above noise in the low-flux class. Moreover, the percentage occurrence of the noise level in the data increases with increasing flux strength, irrespective of the season. Further analysis reveals that the noise level in the local time variation peaked around 17 – 18 LT and minimum around local noon.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"19 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2024-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139092217","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fabrizio Sassi, Angeline Burrell, Sarah McDonald, Jennifer Tate, John McCormack
{"title":"On the importance of middle atmosphere observations on ionospheric dynamics using WACCM-X and SAMI3","authors":"Fabrizio Sassi, Angeline Burrell, Sarah McDonald, Jennifer Tate, John McCormack","doi":"10.5194/egusphere-2023-3065","DOIUrl":"https://doi.org/10.5194/egusphere-2023-3065","url":null,"abstract":"<strong>Abstract.</strong> Recent advances in atmospheric observations and modelling have enabled the investigation of thermosphere-ionosphere interactions as a whole atmosphere problem. This study examines how dynamical variability in the middle atmosphere (MA) affects day-to-day changes in the thermosphere and ionosphere. Specifically, this study investigates ionosphere-thermosphere interactions during different time periods of January 2013 using the Specified Dynamics Whole Atmosphere Community Climate Model, eXtended version (WACCM-X) coupled to the Naval Research Laboratory (NRL) ionosphere of the Sami3 is Another Model of the Ionosphere (SAMI3) model. To represent the weather of the day, the coupled thermosphere-ionosphere system is nudged below 90 km toward the atmospheric specifications provided by the Navy Global Environmental Model for High-Altitude (NAVGEM-HA). Hindcast simulations during January 2013 are carried out with the full data set of observations normally assimilated by NAVGEM-HA, and with a degraded dataset where observations above 40 km are not assimilated. Ionospheric regions with statistically significant changes are identified using key ionospheric properties, including the electron density, peak electron density, and height of the peak electron density. Ionospheric changes show a spatial structure that illustrates the impact of two different types of coupling between the thermosphere and the ionosphere: wind-dynamo coupling through electric conductivity and ion-neutral interactions in the upper thermosphere. The two simulations presented in this study show that changing the state of the MA affects ionosphere-thermosphere coupling through changes in the behavior and amplitude of non-migrating tides, resulting in improved key ionospheric specifications.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"31 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2024-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139092309","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Thomas B. Leyser, Tima Sergienko, Urban Brändström, Björn Gustavsson, Michael T. Rietveld
{"title":"On mechanisms for high-frequency pump-enhanced optical emissions at 557.7 and 630.0 nm from atomic oxygen in the high-latitude F-region ionosphere","authors":"Thomas B. Leyser, Tima Sergienko, Urban Brändström, Björn Gustavsson, Michael T. Rietveld","doi":"10.5194/angeo-41-589-2023","DOIUrl":"https://doi.org/10.5194/angeo-41-589-2023","url":null,"abstract":"Abstract. The EISCAT (European Incoherent Scatter Scientific Association) Heating facility was used to transmit powerful high-frequency (HF) electromagnetic waves into the F-region ionosphere to enhance optical emissions at 557.7 and 630.0 nm from atomic oxygen. The emissions were imaged by several stations of ALIS (Auroral Large Imaging System) in northern Sweden, and the EISCAT UHF incoherent scatter radar was used to obtain plasma parameter values. The ratio of the 557.7 to 630.0 nm column emission rates changed from I5577/I6300≈0.2 for the HF pump frequency f0=6.200 MHz ≈4.6fe to I5577/I6300≈0.5 when f0=5.423 MHz ≲4fe, where fe is the ionospheric electron gyro frequency. The observations are interpreted in terms of decreased electron heating efficiency and thereby weaker enhancement at 630.0 nm for f0=5.423 MHz ≲ 4 fe. The emissions at 557.7 nm are attributed to electron acceleration by upper hybrid waves of metre-scale wavelengths that can be excited with f0=5.423 MHz ≲ 4 fe.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"24 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138580262","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ariel Tello Fallau, Charlotte Goetz, Cyril Simon Wedlund, Martin Volwerk, Anja Moeslinger
{"title":"Revisiting mirror modes in the plasma environment of comet 67P/Churyumov–Gerasimenko","authors":"Ariel Tello Fallau, Charlotte Goetz, Cyril Simon Wedlund, Martin Volwerk, Anja Moeslinger","doi":"10.5194/angeo-41-569-2023","DOIUrl":"https://doi.org/10.5194/angeo-41-569-2023","url":null,"abstract":"Abstract. The plasma environment of comet 67P provides a unique laboratory to study plasma phenomena in the interplanetary medium. There, waves are generated which help the plasma relax back to stability through wave–particle interactions, transferring energy from the wave to the particles and vice versa. In this study, we focus on mirror-mode-like structures (low-frequency, transverse, compressional and quasi-linearly polarised waves). They are present virtually everywhere in the solar system as long as there is a large temperature anisotropy and a high plasma beta. Previous studies have reported the existence of mirror modes at 67P, but no further systematic investigation has so far been done. This study aims to characterise the occurrence of mirror modes in this environment and identify possible generation mechanisms through well-studied previous methods. Specifically, we make use of the magnetic-field-only method, implementing a B–n anti-correlation and a new peak/dip identification method. We investigate the magnetic field measured by Rosetta from November 2014 to February 2016 and find 565 mirror mode signatures. Mirror modes were mostly found as single events, with only one mirror-mode-like train in our dataset. Also, the occurrence rate was compared with respect to the gas production rates, cometocentric distance and magnetic field strength, leading to a non-conclusive relation between these quantities. The lack of mirror mode wave trains may mean that mirror modes somehow diffuse and/or are overshadowed by the large-scale turbulence in the inner coma. The detected mirror modes are likely highly evolved as they were probably generated upstream of the observation point and have traversed a highly complex and turbulent plasma to reach their detection point. The plasma environment of comets behaves differently compared to planets and other objects in the solar system. Thus, knowing how mirror modes behave at comets could lead us to a more unified model for mirror modes in space plasmas.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"257 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138628066","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jonas Suni, Minna Palmroth, Lucile Turc, Markus Battarbee, Giulia Cozzani, Maxime Dubart, Urs Ganse, Harriet George, Evgeny Gordeev, Konstantinos Papadakis, Yann Pfau-Kempf, Vertti Tarvus, Fasil Tesema, Hongyang Zhou
{"title":"Local bow shock environment during magnetosheath jet formation: results from a hybrid-Vlasov simulation","authors":"Jonas Suni, Minna Palmroth, Lucile Turc, Markus Battarbee, Giulia Cozzani, Maxime Dubart, Urs Ganse, Harriet George, Evgeny Gordeev, Konstantinos Papadakis, Yann Pfau-Kempf, Vertti Tarvus, Fasil Tesema, Hongyang Zhou","doi":"10.5194/angeo-41-551-2023","DOIUrl":"https://doi.org/10.5194/angeo-41-551-2023","url":null,"abstract":"Abstract. Magnetosheath jets are plasma structures that are characterised by enhanced dynamic pressure and/or plasma velocity. In this study, we investigate the formation of magnetosheath jets in four two-dimensional simulation runs of the global magnetospheric hybrid-Vlasov model Vlasiator. We focus on jets whose origins were not clearly determined in a previous study using the same simulations (Suni et al., 2021) to have been associated with foreshock structures of enhanced dynamic pressure and magnetic field. We find that these jets can be divided into two categories based on their direction of propagation, either predominantly antisunward or predominantly toward the flanks of the magnetosphere. As antisunward-propagating jets can potentially impact the magnetopause and have effects on the magnetosphere, understanding which foreshock and bow shock phenomena are associated with them is important. The antisunward-propagating jets have properties indistinguishable from those of the jets found in the previous study. This indicates that the antisunward jets investigated in this paper belong to the same continuum as the jets previously found to be caused by foreshock structures; however, due to the criteria used in the previous study, they did not appear in this category before. These jets together make up 86 % of all jets in this study. The flankward-propagating jets make up 14 % of all jets and are different, showing no clear association with foreshock structures and exhibiting temperature anisotropy unlike the other jets. We suggest that they could consist of quasi-perpendicular magnetosheath plasma, indicating that these jets could be associated with local turning of the shock geometry from quasi-parallel to quasi-perpendicular. This turning could be due to bow shock reformation at the oblique shock caused by foreshock ultralow-frequency (ULF) wave activity.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"83 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138547908","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Proton Plasma Asymmetries between the Convective-Electric-Field Hemispheres of Venus' Dayside Magnetosheath","authors":"Sebastián Rojas Mata, Gabriella Stenberg Wieser, Tielong Zhang, Yoshifumi Futaana","doi":"10.5194/egusphere-2023-2570","DOIUrl":"https://doi.org/10.5194/egusphere-2023-2570","url":null,"abstract":"<strong>Abstract.</strong> Proton plasma asymmetries with respect to the convective electric field (<strong>E</strong>) are characterized in Venus’ dayside magnetosheath using measurements taken by an ion mass-energy spectrometer and a magnetometer. Investigating the spatial structure of the magnetosheath plasma in this manner provides insight into the coupling between solar-wind protons and planetary ions. A previously developed methodology for statistically quantifying asymmetries is further developed and applied to an existing database of proton bulk-parameter measurements in the dayside magnetosheath. The density and speed exhibit weak asymmetries favoring the hemisphere in which <strong>E</strong> points towards the planet, while the magnetic-field strength has a weak asymmetry favoring the opposite hemisphere. The temperatures perpendicular and parallel to the background magnetic field as well as their ratio present no significant asymmetries. Deflection of the solar wind due to momentum exchange with planetary ions is revealed by (1) the O<sup>+</sup> Larmor-radius trends of the asymmetries of the bulk-velocity components perpendicular to the upstream solar-wind flow and (2) the <strong>E</strong>×<strong>B</strong><em><sub>IMF</sub></em> -drift trends of the bulk-velocity component along the cross-flow component of the interplanetary magnetic field (<strong>B</strong><em><sub>IMF</sub></em>). These interpretations are enabled by comparisons to studies of solar-wind deflection at Mars and comet 67P/Churyumov-Gerasimenko, highlighting the benefits of comparative planetology studies.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"14 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138541755","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Spencer Mark Hatch, Heikki Vanhamäki, Karl Magnus Laundal, Jone Peter Reistad, Johnathan Burchill, Levan Lomidze, David Knudsen, Michael Madelaire, Habtamu Tesfaw
{"title":"Does high-latitude ionospheric electrodynamics exhibit hemispheric mirror symmetry?","authors":"Spencer Mark Hatch, Heikki Vanhamäki, Karl Magnus Laundal, Jone Peter Reistad, Johnathan Burchill, Levan Lomidze, David Knudsen, Michael Madelaire, Habtamu Tesfaw","doi":"10.5194/egusphere-2023-2920","DOIUrl":"https://doi.org/10.5194/egusphere-2023-2920","url":null,"abstract":"<strong>Abstract.</strong> Ionospheric electrodynamics is a problem of mechanical stress balance mediated by electromagnetic forces. Joule heating (the total rate of frictional heating of thermospheric gases and ionospheric plasma) and ionospheric Hall and Pedersen conductances comprise three of the most basic descriptors of this problem. More than half a century after identification of their central role in ionospheric electrodynamics several important questions about these quantities, including the degree to which they exhibit hemispheric symmetry under reversal of the sign of dipole tilt and the sign of the <em>y</em> component of the interplanetary magnetic field (so-called \"mirror symmetry\"), remain unanswered. While global estimates of these key parameters can be obtained by combining existing empirical models, one often encounters some frustrating sources of uncertainty: the measurements from which such models are derived, usually magnetic field and electric field or ion drift measurements, are typically measured separately and do not necessarily align. The models to be combined moreover often use different input parameters, different assumptions about hemispheric symmetry, and/or different coordinate systems. We eliminate these sources of uncertainty in model predictions of electromagnetic work <strong>J</strong>⋅<strong>E</strong> (in general not equal to Joule heating <em>η</em><em>J</em><sup>2</sup>) and ionospheric conductances by combining two new empirical models of the high-latitude ionospheric electric potential and ionospheric currents that are derived in a mutually consistent fashion: these models do not assume any form of symmetry between the two hemispheres; are based on Apex coordinates, spherical harmonics, and the same model input parameters; and are derived exclusively from convection and magnetic field measurements made by the Swarm and CHAMP satellites. The model source code is open source and publicly available. Comparison of high-latitude distributions of electromagnetic work in each hemisphere as functions of dipole tilt and interplanetary magnetic field clock angle indicate that the typical assumption of mirror symmetry is largely justified. Model predictions of ionospheric Hall and Pedersen conductances exhibit a degree of symmetry, but clearly asymmetric responses to dipole tilt and solar wind driving conditions are also identified. The distinction between electromagnetic work and Joule heating allows us to identify where and under what conditions the assumption that the neutral wind corotates with the earth is not likely to be physically consistent with predicted Hall and Pedersen conductances.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"195 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138541798","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"F-region drift current and magnetic perturbation distribution by the X-wave heating ionosphere","authors":"Yong Li, Hui Li, Jian Wu, Xingbao Lv, Chengxun Yuan, Ce Li, Zhongxiang Zhou","doi":"10.5194/angeo-41-541-2023","DOIUrl":"https://doi.org/10.5194/angeo-41-541-2023","url":null,"abstract":"Abstract. We present a theoretical and numerical study of the drift current and magnetic perturbation model in the ionosphere by incorporating the ohmic heating model and the magnetohydrodynamic (MHD) momentum equation. Based on these equations, the ionospheric electron temperature and drift current are investigated. The results indicate that the maximum change in electron temperature ΔTe is about 570 K, and the ratio is ΔTe/Te ∼ 48 %. The maximum drift current density is 8×10-10 A m−2, and its surface integral is 5.76 A. Diamagnetic drift current is the main form of current. The low collision frequency between charged particles and neutral particles has little effect on the current, and the collision frequency of electrons and ions is independent of the drift current. The current density profile is a flow ring. We present the effective conductivity as a function of the angle between the geomagnetic field and the radio wave; the model explains why the radiation efficiency was strongest when the X wave is heating along the magnetic dip angle, as reported in recent observations by Kotik et al. (2013). We calculate the magnetic field variation in the heating region based on the MHD theory: the results show that the maximum magnetic field perturbation in the heating area is 48 pT.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"15 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138541797","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"The Role of Gravity Waves in the Mesosphere Inversion Layers (MILs) over low-latitude (3–15° N) Using SABER Satellite Observations","authors":"Chalachew Lingerew, Jaya Prakash Raju","doi":"10.5194/angeo-2023-34","DOIUrl":"https://doi.org/10.5194/angeo-2023-34","url":null,"abstract":"<strong>Abstract.</strong> The Mesosphere transitional region over low latitude is a distinct and highly turbulent zone of the atmosphere. A transition MLT region is connected with dynamic processes, particularly gravity waves, as a causative of an inversion phenomenon. MLT inversions have been the subject of numerous investigations, but their formation mechanisms are still poorly understood. In this article, an attempt has been made to investigate the upper and lower inversion phenomena and their causative mechanisms using long-term SABER observations in the height range of 60–100 km during the period of 2005–2020 over a low-latitude region (3–15° N). The results indicate that the frequency of occurrence rate for the upper inversion is below 40 %, whereas for the lower inversion, it is below 20 %, indicating that the upper inversion is dominant over the lower inversion. The upper inversion exists in the height range of 78–91 km with an inversion amplitude of ~20–80 k and a thickness of ~3–12 km, whereas the lower inversion is confined in the height range of 70–80 km with an inversion amplitude of ~10–60 k and a thickness of ~4–10 km. The gravity wave indicator potential energy depicts high energy (below 100 J/kg) in the upper MLT region (90 and 85 km) compared to the lower MLT region (75 and 70 km) with less than 50 J/kg. The stability criteria from Brunt-Vaisala frequency (N<sup>2</sup>) indicate instability in the upper MLT region (90 and 85 km) with very low values relative to the lower MLT region (75 and 70 km), which supports the higher frequency of upper inversion compared to lower inversion. This result leads us to the conclusion that a high amount of gravity wave potential energy is a consequence of the high instability in the upper inversion relative to the lower inversion.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"13 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138541742","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Noora Partamies, Bas Dol, Vincent Teissier, Liisa Juusola, Mikko Syrjäsuo, Hjalmar Mulders
{"title":"Auroral breakup detection in all-sky images by unsupervised learning","authors":"Noora Partamies, Bas Dol, Vincent Teissier, Liisa Juusola, Mikko Syrjäsuo, Hjalmar Mulders","doi":"10.5194/egusphere-2023-2857","DOIUrl":"https://doi.org/10.5194/egusphere-2023-2857","url":null,"abstract":"<strong>Abstract.</strong> Due to a large number of automatic auroral camera systems on the ground, the image data analysis requires more efficiency than what a human expert visual inspection can provide. Furthermore, there is no solid consensus on how many different types or shapes exist in auroral displays. We report the first attempt to classify auroral morphological forms by unsupervised learning method on an image set that contains both nightside and dayside aurora. We used six months of full-colour auroral all-sky images captured at a high-arctic observatory on Svalbard, Norway, in 2019–2020. The selection of images containing aurora was performed manually. These images were then input to a convolutional neural network called SimCLR for feature extraction. The clustered and fused features resulted in 37 auroral morphological classes. In the classification of auroral image data with two different time resolutions we found that the occurrence of eight morphological classes strongly increased when the image cadence was high (24 seconds), while the occurrence of 13 morphological classes experienced little or no change with changes in input image cadence. We therefore investigated the temporal evolution of the group of eight \"active auroral classes\". Time periods for which \"active auroral classes\" persisted for longer than two consecutive images with maximum cadence of six minutes coincided with ground-magnetic deflections and their occurrence was found clustered around the magnetic midnight. The active auroral onsets typically included vortical auroral structures and equivalent current patterns typical for substorms. Our findings therefore suggest that our unsupervised image classification method can be used to detect auroral breakups in ground-based image datasets with a temporal accuracy determined by the image cadence.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"33 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138541756","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}