Annales Geophysicae最新文献

{"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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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}

{"title":"Impulse-driven oscillations of the near-Earth's magnetosphere","authors":"H. Sato, H. Pécseli, J. Trulsen, P. Sandholt, C. Farrugia","doi":"10.5194/angeo-40-641-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-641-2022","url":null,"abstract":"Abstract. It is argued that a simple model based on magnetic image arguments suffices to give a convincing insight into both the basic static as well as some transient dynamic properties of the near-Earth's magnetosphere, particularly accounting for damped oscillations being excited in response to impulsive perturbations. The parameter variations of the frequency are given. Qualitative results can also be obtained for heating due to the compression of the radiation belts. The properties of this simple dynamic model for the solar wind–magnetosphere interaction\u0000are discussed and compared to observations. In spite of its simplicity,\u0000the model gives convincing results concerning the magnitudes of the near-Earth's magnetic and electric fields. The database contains\u0000ground-based results for magnetic field variation in response to shocks in the solar wind. Here, the observations also include data from the two Van Allen satellites.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79758772","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":"Multi-instrument observations of polar cap patches and traveling ionospheric disturbances generated by solar wind Alfvén waves coupling to the dayside magnetosphere","authors":"P. Prikryl, Robert G. Gillies, D. Themens, J. Weygand, E. Thomas, S. Chakraborty","doi":"10.5194/angeo-40-619-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-619-2022","url":null,"abstract":"Abstract. During minor to moderate geomagnetic storms, caused by corotating\u0000interaction regions (CIRs) at the leading edge of high-speed streams (HSSs), solar wind\u0000Alfvén waves modulated the magnetic reconnection at the dayside\u0000magnetopause. The Resolute Bay Incoherent Scatter Radars (RISR-C and\u0000RISR-N), measuring plasma parameters in the cusp and polar cap, observed\u0000ionospheric signatures of flux transfer events (FTEs) that resulted in the\u0000formation of polar cap patches. The patches were observed as they moved over the RISR, and the Canadian High-Arctic Ionospheric Network (CHAIN)\u0000ionosondes and GPS receivers. The coupling process modulated the ionospheric convection and the intensity of ionospheric currents, including the auroral electrojets. The horizontal equivalent ionospheric currents (EICs) are estimated from ground-based magnetometer data using an inversion technique. Pulses of ionospheric currents that are a source of Joule heating in the lower thermosphere launched atmospheric gravity waves, causing traveling\u0000ionospheric disturbances (TIDs) that propagated equatorward. The TIDs were\u0000observed in the SuperDual Auroral Radar Network (SuperDARN) high-frequency (HF) radar ground\u0000scatter and the detrended total electron content (TEC) measured by globally\u0000distributed Global Navigation Satellite System (GNSS) receivers.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74322581","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":"Magnetic local time (MLT) dependence of auroral peak emission height and morphology","authors":"N. Partamies, D. Whiter, K. Kauristie, S. Massetti","doi":"10.5194/angeo-40-605-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-605-2022","url":null,"abstract":"Abstract. We investigate the bulk behaviour of auroral structures and peak emission height as a function of magnetic local time (MLT). These data are collected from the Fennoscandian Lapland and Svalbard latitudes from seven identical auroral all-sky cameras (ASC) over about one solar cycle. The analysis focusses on green auroral emission, which is where the morphology is most clearly visible and the number of images is the highest. The typical peak emission height of the green and blue aurora varies from 110 km on the nightside to about 118 km in the morning MLT over the Lapland region. It stays systematically higher (at 118–120 km) at high latitudes (Svalbard) during the nighttime and reaches 140 km at around magnetic noon. During high solar wind speed (above 500 km s−1), nightside emission heights appear about 5 km lower than during slow solar wind speed (below 400 km s−1). The sign of the interplanetary magnetic field (IMF) has nearly no effect on the emission heights in the night sector, but the northward IMF causes lower emission heights at dawn over Lapland and during the noon hours over Svalbard. While the former is interpreted as a change in the particle population within the field-of-view (FoV), the latter is rather due to the movement of the cusp location due to the IMF orientation. The morning sector heights also show a pronounced difference when previously detected pulsating aurora (PsA) events have been excluded/included in the dataset, suggesting that this type of aurora is a dominant phenomenon in the morning and an important dissipation mechanism. An increase of complex auroral structures in the midnight hours agrees with the average substorm occurrence. This increase is amplified during stronger solar wind driving and during higher geomagnetic activity (as measured by auroral electrojet index, AL). During high solar wind speed, the high latitude auroral evolution shows particularly complex morphology, which is not limited to the nightside but rather only excludes the magnetic noon hours. An increase in the geomagnetic activity further enhances the structural complexity of the aurora in the morning sector.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73453670","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}