Annales Geophysicae最新文献

{"title":"Effect of intermittent structures on the spectral index of the magnetic field in the slow solar wind","authors":"Xin Wang, Xuanhao Fan, Yuxin Wang, Honghong Wu, Lei Zhang","doi":"10.5194/angeo-41-129-2023","DOIUrl":"https://doi.org/10.5194/angeo-41-129-2023","url":null,"abstract":"Abstract. Intermittent structures are ubiquitous in the solar wind turbulence,\u0000and they can significantly affect the power spectral index (which reflects the cascading process of\u0000the turbulence) of\u0000magnetic field fluctuations. However, to date, an analytical relationship between the intermittency level and the magnetic spectral index has not been shown. Here, we\u0000present the continuous variation in the magnetic spectral index in\u0000the inertial range as a function of the intermittency level. Using the measurements from the Wind spacecraft, we find 42 272\u0000intervals with different levels of intermittency and with a\u0000duration of 5–6 min from 46 slow-wind streams between 2005 and\u00002013. Among them, each of the intermittent intervals is composed of\u0000one dominant intermittent structure and background turbulent\u0000fluctuations. For each interval, a magnetic spectral index αB is\u0000determined for the Fourier spectrum of the magnetic field fluctuations\u0000in the inertial range between 0.01 and 0.3 Hz. A parameter\u0000Imax, which corresponds to the maximum of the trace of the partial\u0000variance increments of the intermittent structure, is introduced as\u0000an indicator of the intermittency level. Our statistical result\u0000shows that, as Imax increases from 0 to 20, the magnetic\u0000spectrum becomes gradually steeper and the magnetic spectral index αB\u0000decreases from −1.63 to −2.01. Accordingly, for the first time, an empirical\u0000relation is established between αB and Imax: αB=0.4exp⁡(-Imax/5)-2.02. The\u0000result will help us to uncover more details about the contributions of\u0000the intermittent structures to the magnetic power spectra and, furthermore, about\u0000the physical nature of the energy cascade taking place in the solar\u0000wind. It will also help to improve turbulence theories that contain intermittent structures.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"34 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74131336","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":"Morphological evolution and spatial profile changes of poleward moving auroral forms","authors":"A. Goertz, N. Partamies, D. Whiter, L. Baddeley","doi":"10.5194/angeo-41-115-2023","DOIUrl":"https://doi.org/10.5194/angeo-41-115-2023","url":null,"abstract":"Abstract. We investigated the morphology of poleward moving auroral forms (PMAFs)\u0000qualitatively by visual inspection of all-sky camera (ASC) images\u0000and quantitatively using the arciness index. The PMAFs in this study\u0000were initially identified with a meridian scanning photometer (MSP) located\u0000at the Kjell Henriksen Observatory (KHO), Svalbard, and analyzed using\u0000ASC images taken by cameras at the KHO and in Ny-Ålesund, Svalbard. We\u0000present a detailed six-step evolution of PMAF morphology in two dimensions.\u0000This evolution includes (1) an equatorward expansion of the auroral\u0000oval and an intensification of auroral brightness at the open–closed\u0000boundary (OCB), (2) the appearance of an arc-like structure in the oval,\u0000(3) poleward and possible west/eastward propagation,\u0000(4) azimuthal expansion events, (5) re-brightening of the PMAF and\u0000eventual (6) fading away. This is the first work dedicated to the\u0000morphological evolution of PMAFs and it includes more detailed discussion\u0000and novel aspects, such as the observation of initial merging of 557.7 nm\u0000auroral patches to form a PMAF. Moreover, the morphology of PMAFs\u0000is quantified using the arciness index, which is a number describing\u0000how arc-like auroral forms appear in ASC images. This allows an unbiased\u0000statistical investigation of auroral morphology. We present the results\u0000of a superposed epoch analysis of arciness in relation to PMAF occurrence.\u0000This analysis uncovered that arciness increases suddenly during the\u0000onset of a PMAF event and decreases over the PMAF lifetime to return\u0000to its baseline value once the event has concluded. This behavior\u0000may be understood based on changes in the morphology of PMAFs and\u0000validates our understanding of PMAF morphology. Furthermore, our findings\u0000relating to arciness may enable automatic identification of PMAFs,\u0000which has been found to be notoriously difficult.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"19 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89479708","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":"Modulation of polar mesospheric summer echoes (PMSEs) with high-frequency heating during low solar illumination","authors":"Tinna L. Gunnarsdottir, A. Poggenpohl, I. Mann, A. Mahmoudian, P. Dalin, Ingemar Haeggstroem, M. Rietveld","doi":"10.5194/angeo-41-93-2023","DOIUrl":"https://doi.org/10.5194/angeo-41-93-2023","url":null,"abstract":"Abstract. Polar mesospheric summer echo (PMSE) formation is linked to charged dust/ice particles in the mesosphere. We investigate the modulation of PMSEs with radio waves based on measurements with EISCAT VHF radar and EISCAT heating facility during low solar illumination. The measurements were made in August 2018 and 2020 around 20:02 UT. Heating was operated in cycles with intervals of 48 s on and 168 s off.\u0000More than half of the observed heating cycles show a PMSE modulation with a decrease in PMSE when the heater is on and an increase when it is switched off again. The PMSE often increases beyond its initial strength.\u0000Less than half of the observed modulations have such an overshoot.\u0000The overshoots are small or nonexistent at strong PMSE, and they are not observed when the ionosphere is influenced by particle precipitation.\u0000We observe instances of very large overshoots at weak PMSE. PMSE modulation varies strongly from one cycle to the next, being highly variable on spatial scales smaller than a kilometer and timescales shorter than the timescales assumed for the variation in dust parameters. Average curves over several heating cycles are similar to the overshoot curves predicted by theory and observed previously. Some of the individual curves show stronger overshoots than reported in previous studies, and they exceed the values predicted by theory. A possible explanation is that the dust-charging conditions are different either because of the reduced solar illumination around midnight or because of long-term changes in ice particles in the mesosphere. We conclude that it is not possible to reliably derive the dust-charging parameters from the observed PMSE modulations.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"69 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77997995","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":"Magnetopause as conformal mapping","authors":"Y. Narita, S. Toepfer, D. Schmid","doi":"10.5194/angeo-41-87-2023","DOIUrl":"https://doi.org/10.5194/angeo-41-87-2023","url":null,"abstract":"Abstract. An axi-symmetric two-dimensional magnetopause\u0000model is constructed by making use of the conformal\u0000mapping in the complex plane.\u0000The model is an analytic continuation of the\u0000power-law damped (or asymptotically elongated) parabolic shape.\u0000The complex-plane expression of the magnetopause\u0000opens the door to properly map the magnetopause and magnetosheath\u0000coordinates from one model to another.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"33 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84630763","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":"Machine learning detection of dust impact signals observed by the Solar Orbiter","authors":"A. Kvammen, Kristoffer Wickstrøm, S. Kočiščák, J. Vaverka, L. Nouzák, A. Zaslavsky, Kristina Rackovic, Amalie Gjelsvik, D. Píša, J. Souček, I. Mann","doi":"10.5194/angeo-41-69-2023","DOIUrl":"https://doi.org/10.5194/angeo-41-69-2023","url":null,"abstract":"Abstract. This article presents the results of automatic detection of dust impact signals observed by the Solar Orbiter – Radio and Plasma Waves instrument. A sharp and characteristic electric field signal is observed by the Radio and Plasma Waves instrument when a dust particle impacts the spacecraft at high velocity. In this way, ∼ 5–20 dust impacts are daily detected as the Solar Orbiter travels through the interplanetary medium. The dust distribution in the inner solar system is largely uncharted and statistical studies of the detected dust impacts will enhance our understanding of the role of dust in the solar system. It is however challenging to automatically detect and separate dust signals from the plural of other signal shapes for two main reasons. Firstly, since the spacecraft charging causes variable shapes of the impact signals, and secondly because electromagnetic waves (such as solitary waves) may induce resembling electric field signals. In this article, we propose a novel machine learning-based framework for detection of dust impacts. We consider two different supervised machine learning approaches: the support vector machine classifier and the convolutional neural network classifier. Furthermore, we compare the performance of the machine learning classifiers to the currently used on-board classification algorithm and analyze 2 years of Radio and Plasma Waves instrument data. Overall, we conclude that detection of dust impact signals is a suitable task for supervised machine learning techniques. The convolutional neural network achieves the highest performance with 96 % ± 1 % overall classification accuracy and 94 % ± 2 % dust detection precision, a significant improvement to the currently used on-board classifier with 85 % overall classification accuracy and 75 % dust detection precision. In addition, both the support vector machine and the convolutional neural network classifiers detect more dust particles (on average) than the on-board classification algorithm, with 16 % ± 1 % and 18 % ± 8 % detection enhancement, respectively. The proposed convolutional neural network classifier (or similar tools) should therefore be considered for post-processing of the electric field signals observed by the Solar Orbiter.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"34 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79978359","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":"A technique for volumetric incoherent scatter radar analysis","authors":"J. Stamm, J. Vierinen, B. Gustavsson, A. Spicher","doi":"10.5194/angeo-41-55-2023","DOIUrl":"https://doi.org/10.5194/angeo-41-55-2023","url":null,"abstract":"Abstract. Volumetric measurements of the ionosphere are important for investigating spatial variations of ionospheric features, like auroral arcs and energy deposition in the ionosphere. In addition, such measurements make it possible to distinguish between variations in space and time. While spatial variations in scalar quantities such as electron density or temperature have been investigated with incoherent scatter radar (ISR) before, spatial variation in the ion velocity, which is a vector quantity, has been hard to measure. The upcoming EISCAT3D radar will be able to do volumetric measurements of ion velocity regularly for the first time. In this paper, we present a technique for relating volumetric measurements of ion velocity to neutral wind and electric field.\u0000To regularize the estimates, we use Maxwell's equations and fluid-dynamic constraints.\u0000The study shows that accurate volumetric estimates of electric field can be achieved. Electric fields can be resolved at altitudes above 120 km, which is the altitude range where auroral current closure occurs. Neutral wind can be resolved at altitudes below 120 km.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"41 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79030772","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":"Storm time polar cap expansion: interplanetary magnetic field clock angle dependence","authors":"B. Tulegenov, J. Raeder, W. Cramer, B. Ferdousi, T. Fuller‐Rowell, N. Maruyama, R. Strangeway","doi":"10.5194/angeo-41-39-2023","DOIUrl":"https://doi.org/10.5194/angeo-41-39-2023","url":null,"abstract":"Abstract. It is well known that the polar cap, delineated by the open–closed field line boundary (OCB),\u0000responds to changes in the interplanetary magnetic field (IMF).\u0000In general, the boundary moves equatorward when the IMF turns southward and contracts\u0000poleward when the IMF turns northward. However,\u0000observations of the OCB are spotty and limited in local time,\u0000making more detailed studies of its IMF dependence difficult.\u0000Here, we simulate five solar storm periods with the coupled model consisting of the Open\u0000Geospace General Circulation Model (OpenGGCM) coupled with the Coupled Thermosphere Ionosphere\u0000Model (CTIM) and the Rice Convection Model (RCM),\u0000i.e., the OpenGGCM-CTIM-RCM, to estimate the location and dynamics of the OCB.\u0000For these events, polar cap boundary location observations are also obtained from Defense Meteorological\u0000Satellite Program (DMSP) precipitation spectrograms and compared with the model output.\u0000There is a large scatter in the DMSP observations and in the model output.\u0000Although the model does not predict the OCB with high fidelity for every observation,\u0000it does reproduce the general trend as a function of IMF clock angle.\u0000On average, the model overestimates the latitude of the open–closed field line boundary\u0000by 1.61∘. Additional analysis of the simulated polar cap boundary dynamics across\u0000all local times shows that the MLT of the largest polar cap expansion closely correlates\u0000with the IMF clock angle, that the strongest correlation occurs when the IMF is southward, that\u0000during strong southward IMF the polar cap shifts sunward, and that the polar cap rapidly\u0000contracts at all local times when the IMF turns northward.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"109 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2023-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80902527","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 altitude of green OI 557.7 nm and blue N₂⁺ 427.8 nm aurora","authors":"Daniel K. Whiter, Noora Partamies, Björn Gustavsson, Kirsti Kauristie","doi":"10.5194/angeo-41-1-2023","DOIUrl":"https://doi.org/10.5194/angeo-41-1-2023","url":null,"abstract":"Abstract. We have performed a large statistical study of the peak emission altitude of green O(1D2–1S0) (557.7 nm) and blue N2+ 1 N (427.8 nm) aurora using observations from a network of all-sky cameras stationed across northern Finland and Sweden recorded during seven winter seasons from 2000 to 2007. Both emissions were found to typically peak at about 114 km. The distribution of blue peak altitudes is more skewed than that for the green, and the mean peak emission altitudes were 114.84 ± 0.06 and 116.55 ± 0.07 km for green and blue emissions, respectively. We compare simultaneous measurements of the two emissions in combination with auroral modelling to investigate the emission production mechanisms. During low-energy electron precipitation (<∼ 4 keV), when the two emissions peak above about 110 km, it is more likely for the green emission to peak below the blue emission than vice versa, with the difference between the two heights increasing with their average. Modelling has shown that under these conditions the dominant source of O(1S), the upper state of the green line, is energy transfer from excited N2 (A3Σu+), with a rate that depends on the product of the N2 and O number densities. Since both number densities decrease with higher altitude, the production of O(1S) by energy transfer from N2 peaks at lower altitude than the N2 ionisation rate, which depends on the N2 number density only. Consequently, the green aurora peaks below the blue aurora. When the two emissions peak below about 110 km, they typically peak at very similar altitude. The dominant source of O(1S) at low altitudes must not be energy transfer from N2, since the rate of that process peaks above the N2 ionisation rate and blue emission due to quenching of the long-lived excited N2 at low altitudes. Dissociative recombination of O2+ seems most likely to be a major source at these low altitudes, but our model is unable to reproduce observations fully, suggesting there may be additional sources of O(1S) unaccounted for.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"55 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134969537","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":"Width of plasmaspheric plumes related to the level of geomagnetic storm intensity","authors":"Zhanrong Yang, Haimeng Li, Z. Yuan, Zhihai Ouyang, X. Deng","doi":"10.5194/angeo-40-673-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-673-2022","url":null,"abstract":"Abstract. The plume is a plasma region in the magnetosphere that is detached from the\u0000main plasmasphere. It significantly contributes to the dynamic processes in\u0000both the inner and outer magnetosphere. In this paper, using Van Allen Probe A (VAP-A), the correlation between plume width and the level of geomagnetic storm intensity is studied. First, through the statistical analysis of all potential plume events, we find that there is almost no correlation between plume width and the level of geomagnetic storm intensity. However, for the plumes in the recovery phase after improved sifting, it seems that there is a negative correlation between the plume width and the absolute value of minimum Dst during a storm. Utilizing test particle simulations, we study the dynamic evolution patterns of plumes during two geomagnetic storms. The simulated structures of the two plasmaspheric plumes are roughly consistent with the structures observed by the Van Allen Probe A. This result suggests that the plasmaspheric particles escape quickly during intense geomagnetic storms, causing the width of the plume to be relatively narrow during the recovery phase of intense geomagnetic storms. These results are helpful for understanding the dynamic evolution of the plasmasphere and plume during geomagnetic storms.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"1 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2022-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83013077","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":"Signature of gravity wave propagations from the troposphere to ionosphere","authors":"H. Takahashi, C. Figueiredo, P. Essien, C. M. Wrasse, D. Barros, P. K. Nyassor, I. Paulino, F. Egito, Geângelo de Matos Rosa, Antonio Hélder Rodrigues Sampaio","doi":"10.5194/angeo-40-665-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-665-2022","url":null,"abstract":"Abstract. We observed a gravity wave (GW) signature in the OH\u0000emission layer in the upper mesosphere, and 4 h later, a medium-scale\u0000travelling ionospheric disturbance (MSTID) in the OI 630 nm emission layer.\u0000Spectral analysis of the two waves showed that both have almost the same\u0000wave characteristics: wavelength, period, phase speed and propagation\u0000direction, respectively, 200 km, 60 min, 50 m s−1, toward the southeast. From\u0000the gravity wave ray-tracing simulation for the mesospheric gravity wave, we\u0000found that the wave came from a tropospheric deep convection spot and\u0000propagated up to the 140 km altitude. Regarding the same wave\u0000characteristics between mesospheric GW and ionospheric MSTID, the two\u0000possible cases are investigated: a direct influence of the GW oscillation in\u0000the OI 630 nm emission height and the generation of a secondary wave during\u0000the GW breaking process. This is the first time to report an observational\u0000event of gravity wave propagation from the troposphere, mesosphere to\u0000thermosphere–ionosphere in the South American region.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"261 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2022-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84492600","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}