Annales Geophysicae最新文献

{"title":"Influence of meteoric smoke particles on the incoherent scatter measured with EISCAT VHF","authors":"Tinna L. Gunnarsdottir, Ingrid Mann, Wuhu Feng, Devin R. Huyghebaert, Ingemar Haeggstroem, Yasunobu Ogawa, Norihito Saito, Satonori Nozawa, Takuya D. Kawahara","doi":"10.5194/angeo-42-213-2024","DOIUrl":"https://doi.org/10.5194/angeo-42-213-2024","url":null,"abstract":"Abstract. Meteoric ablation in the Earth's atmosphere produces particles of nanometer size and larger. These particles can become charged and influence the charge balance in the D region (60–90 km) and the incoherent scatter observed with radar from there. Radar studies have shown that, if enough dust particles are charged, they can influence the received radar spectrum below 100 km, provided the electron density is sufficiently high (>109 m3). Here, we study an observation made with the EISCAT VHF radar on 9 January 2014 during strong particle precipitation so that incoherent scatter was observed down to almost 60 km altitude. We found that the measured spectra were too narrow in comparison to the calculated spectra. Adjusting the collision frequency provided a better fit in the frequency range of ± 10–30 Hz. However, this did not lead to the best fit in all cases, especially not for the central part of the spectra in the narrow frequency range of ±10 Hz. By including a negatively charged dust component, we obtained a better fit for spectra observed at altitudes of 75–85 km, indicating that dust influences the incoherent-scatter spectrum at D-region altitudes. The observations at lower altitudes were limited by the small number of free electrons, and observations at higher altitudes were limited by the height resolution of the observations. Inferred dust number densities range from a few particles up to 104 cm−3, and average sizes range from approximately 0.6 to 1 nm. We find an acceptable agreement with the dust profiles calculated with the WACCM-CARMA (Whole Atmosphere Community Climate Model-Community Aerosol Radiation Model for Atmospheres) model. However, these do not include charging, which is also based on models.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141257065","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":"Does high-latitude ionospheric electrodynamics exhibit hemispheric mirror symmetry?","authors":"Spencer Mark Hatch, Heikki Vanhamäki, Karl Magnus Laundal, Jone Peter Reistad, Johnathan K. Burchill, Levan Lomidze, David J. Knudsen, Michael Madelaire, Habtamu Tesfaw","doi":"10.5194/angeo-42-229-2024","DOIUrl":"https://doi.org/10.5194/angeo-42-229-2024","url":null,"abstract":"Abstract. 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 y 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 J⋅E (in general not equal to Joule heating ηJ2) 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 magnetic coordinates (denoted Apex), 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 indicates 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":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141257027","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":"Application of generalized aurora computed tomography to the EISCAT_3D project","authors":"Yoshimasa Tanaka, Yasunobu Ogawa, Akira Kadokura, Takehiko Aso, Björn Gustavsson, Urban Brändström, Tima Sergienko, Genta Ueno, Satoko Saita","doi":"10.5194/angeo-42-179-2024","DOIUrl":"https://doi.org/10.5194/angeo-42-179-2024","url":null,"abstract":"Abstract. EISCAT_3D is a project to build a multi-site phased-array incoherent scatter radar system in northern Fenno-Scandinavia. We demonstrate via numerical simulation how useful monochromatic images taken by a multi-point imager network are for auroral research in the EISCAT_3D project. We apply the generalized aurora computed tomography (G-ACT) method to modelled observational data from real instruments, such as the Auroral Large Imaging System (ALIS) and the EISCAT_3D radar. G-ACT is a method for reconstructing the three-dimensional (3D) distribution of auroral emissions and ionospheric electron density (corresponding to the horizontal two-dimensional (2D) distribution of energy spectra of precipitating electrons) from multi-instrument data. It is assumed that the EISCAT_3D radar scans an area of 0.8° in geographic latitude and 3° in longitude at an altitude of 130 km with 10 × 10 beams from the radar core site at Skibotn (69.35° N, 20.37° E). Two neighboring discrete arcs are assumed to appear in the observation region of the EISCAT_3D radar. The reconstruction results from G-ACT are compared with those from the normal ACT as well as the ionospheric electron density from the radar. It is found that G-ACT can interpolate the ionospheric electron density at a much higher spatial resolution than that observed by the EISCAT_3D radar. Furthermore, the multiple arcs reconstructed by G-ACT are more precise than those by ACT. In particular, underestimation of the ionospheric electron density and precipitating electrons' energy fluxes inside the arcs is significantly improved by G-ACT including the EISCAT_3D data. Even when the ACT reconstruction is difficult due to the unsuitable locations of the imager sites relative to the discrete arcs and/or a small number of available images, G-ACT allows us to obtain better reconstruction results.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141189724","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":"Impact ionization double peaks analyzed in high temporal resolution on Solar Orbiter","authors":"Samuel Kočiščák, Andreas Kvammen, Ingrid Mann, Nicole Meyer-Vernet, David Píša, Jan Souček, Audun Theodorsen, Jakub Vaverka, Arnaud Zaslavsky","doi":"10.5194/angeo-42-191-2024","DOIUrl":"https://doi.org/10.5194/angeo-42-191-2024","url":null,"abstract":"Abstract. Solar Orbiter is equipped with electrical antennas performing fast measurements of the surrounding electric field. The antennas register high-velocity dust impacts through the electrical signatures of impact ionization. Although the basic principle of the detection has been known for decades, the understanding of the underlying process is not complete, due to the unique mechanical and electrical design of each spacecraft and the variability of the process. We present a study of electrical signatures of dust impacts on Solar Orbiter's body, as measured with the Radio and Plasma Waves electrical suite. A large proportion of the signatures present double-peak electrical waveforms in addition to the fast pre-spike due to electron motion, which are systematically observed for the first time. We believe this is due to Solar Orbiter's unique antenna design and a high temporal resolution of the measurements. The double peaks are explained as being due to two distinct processes. Qualitative and quantitative features of both peaks are described. The process for producing the primary peak has been studied extensively before, and the process for producing the secondary peak has been proposed before (Pantellini et al., 2012a) for Solar Terrestrial Relations Observatory (STEREO), although the corresponding delay of 100–300 µs between the primary and the secondary peak has not been observed until now. Based on this study, we conclude that the primary peak's amplitude is the better measure of the impact-produced charge, for which we find a typical value of around 8 pC. Therefore, the primary peak should be used to derive the impact-generated charge rather than the maximum. The observed asymmetry between the primary peaks measured with individual antennas is quantitatively explained as electrostatic induction. A relationship between the amplitude of the primary and the secondary peak is found to be non-linear, and the relation is partially explained with a model for electrical interaction through the antennas' photoelectron sheath.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141189727","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":"Permutation entropy and complexity analysis of large-scale solar wind structures and streams","authors":"Emilia K. J. Kilpua, Simon Good, Matti Ala-Lahti, Adnane Osmane, Venla Koikkalainen","doi":"10.5194/angeo-42-163-2024","DOIUrl":"https://doi.org/10.5194/angeo-42-163-2024","url":null,"abstract":"Abstract. In this work, we perform a statistical study of magnetic field fluctuations in the solar wind at 1 au using permutation entropy and complexity analysis and the investigation of the temporal variations of the Hurst exponents. Slow and fast wind, magnetic clouds, interplanetary coronal mass ejection (ICME)-driven sheath regions, and slow–fast stream interaction regions (SIRs) have been investigated separately. Our key finding is that there are significant differences in permutation entropy and complexity values between the solar wind types at larger timescales and little difference at small timescales. Differences become more distinct with increasing timescales, suggesting that smaller-scale turbulent features are more universal. At larger timescales, the analysis method can be used to identify localised spatial structures. We found that, except in magnetic clouds, fluctuations are largely anti-persistent and that the Hurst exponents, in particular in compressive structures (sheaths and SIRs), exhibit a clear locality. Our results shows that, in all cases apart from magnetic clouds at the largest scales, solar wind fluctuations are stochastic, with the fast wind having the highest entropies and low complexities. Magnetic clouds, in turn, exhibit the lowest entropy and highest complexity, consistent with them being coherent structures in which the magnetic field components vary in an ordered manner. SIRs, slow wind and ICME sheaths are intermediate in relation to magnetic clouds and fast wind, reflecting the increasingly ordered structure. Our results also indicate that permutation entropy–complexity analysis is a useful tool for characterising the solar wind and investigating the nature of its fluctuations.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141165555","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":"Quadratic Magnetic Gradients from 7-SC and 9-SC Constellations","authors":"Chao Shen, Gang Zeng, Rungployphan Kieokaew","doi":"10.5194/egusphere-2024-1330","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1330","url":null,"abstract":"<strong>Abstract.</strong> To reveal the dynamics of magnetised plasma, it is essential to know the geometrical structure of the magnetic field, which is closely related to its linear and quadratic gradients. Estimation of the linear magnetic gradient requires at least four magnetic measurements, whereas calculation of the quadratic gradients of the magnetic field generally requires at least ten. This study is therefore aimed at yielding linear and quadratic gradients of the magnetic field based on magnetic measurements from nine-spacecraft HelioSwarm or seven-spacecraft Plasma Observatory constellations. Time-series magnetic measurements and transfer relationships between different reference frames were used to yield the apparent velocity of the magnetic structure as well as the components of the quadratic magnetic gradient along the direction of motion, while simultaneously elucidating the linear gradient and remaining components of the quadratic magnetic gradient using the least-squares method. Calculation via several iterations was applied to achieve satisfactory accuracy. The tests for the situations of magnetic flux ropes and dipole magnetic field have verifies the validity and accuracy of this approach. The results suggest that using time-series magnetic measurements from constellations comprising at least seven spacecraft and nonplanar configurations can yield linear and quadratic gradients of the magnetic field.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141059656","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":"Finding reconnection lines and flux rope axes via local coordinates in global ion-kinetic magnetospheric simulations","authors":"M. Alho, G. Cozzani, I. Zaitsev, F. Kebede, U. Ganse, M. Battarbee, M. Bussov, M. Dubart, S. Hoilijoki, Leo Kotipalo, K. Papadakis, Y. Pfau‐Kempf, J. Suni, V. Tarvus, A. Workayehu, Hongyang Zhou, M. Palmroth","doi":"10.5194/angeo-42-145-2024","DOIUrl":"https://doi.org/10.5194/angeo-42-145-2024","url":null,"abstract":"Abstract. Magnetic reconnection is a crucially important process for energy conversion in plasma physics, with the substorm cycle of Earth's magnetosphere and solar flares being prime examples. While 2D models have been widely applied to study reconnection, investigating reconnection in 3D is still, in many aspects, an open problem. Finding sites of magnetic reconnection in a 3D setting is not a trivial task, with several approaches, from topological skeletons to Lorentz transformations, having been proposed to tackle the issue. This work presents a complementary method for quasi-2D structures in 3D settings by noting that the magnetic field structures near reconnection lines exhibit 2D features that can be identified in a suitably chosen local coordinate system. We present applications of this method to a hybrid-Vlasov Vlasiator simulation of Earth's magnetosphere, showing the complex magnetic topologies created by reconnection for simulations dominated by quasi-2D reconnection. We also quantify the dimensionalities of magnetic field structures in the simulation to justify the use of such coordinate systems.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140967702","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":"Simultaneous OI 630 nm imaging observations of thermospheric gravity waves and associated revival of fossil depletions around midnight near the equatorial ionization anomaly (EIA) crest","authors":"Navin Parihar, Saranya Padincharapad, Anand Kumar Singh, Prasanna Mahavarkar, Ashok Priyadarshan Dimri","doi":"10.5194/angeo-42-131-2024","DOIUrl":"https://doi.org/10.5194/angeo-42-131-2024","url":null,"abstract":"Abstract. We report F-region airglow imaging of fossil plasma depletions around midnight that revived afresh under persisting thermospheric gravity wave (GW) activity. An all-sky imager recorded these events in OI 630 nm imaging over Ranchi (23.3° N, 85.3° E; mlat. ∼19° N), India, on 16 April 2012. Northward-propagating and east–west-aligned GWs (λ∼210 km, v∼64 m s−1, and τ∼0.91 h) were seen around midnight. Persisting for ∼2 h, this GW activity revived two co-existing and eastward-drifting fossil depletions, DP1 and DP2. GW-driven revival was prominently seen in depletion DP1, wherein its apex height grew from ∼600 to >800 km, and the level of intensity depletion increased from ∼17 % to 50 %. The present study is novel in the sense that simultaneous observations of thermospheric GW activity and the associated evolution of depletion in OI 630 nm airglow imaging, as well as that around local midnight, have not been reported earlier. The current understanding is that GW phase fronts aligned parallel to the geomagnetic field lines and eastward-propagating are more effective in seeding Rayleigh–Taylor (RT) instability. Here, GW fronts were east–west-aligned (i.e., perpendicular to the geomagnetic field lines) and propagated northward, yet they revived fossil depletions.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140882507","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":"Acoustic–gravity waves and their role in ionosphere–lower thermosphere coupling","authors":"Gordana Jovanovic","doi":"10.5194/angeo-2024-4","DOIUrl":"https://doi.org/10.5194/angeo-2024-4","url":null,"abstract":"<strong>Abstract.</strong> The properties of acoustic–gravity waves (AGWs) in the ionospheric D layer and their role in the D layer–lower thermosphere coupling are studied using the dispersion equation and the reflection coefficient. These analytical equations are an elegant tool for evaluating the contribution of upward–propagating acoustic and gravity waves to the dynamics of the lower thermosphere. It was found that infrasound waves with frequencies ω &gt; 0.035 <em>s</em>⁻¹, which propagate almost vertically, can reach the lower thermosphere. Also, gravity waves with frequencies lower than ω &lt; 0.0087 <em>s</em>⁻¹, with horizontal phase velocities in the range 159 <em>m</em>/<em>s</em> &lt; <em>v_h</em> &lt; 222 <em>m</em>/<em>s</em>, and horizontal wavelength 115 km &lt; λ_<em>p</em> &lt; 161 km, are important for the lower thermosphere dynamics. These waves can cause temperature rise in the lower thermosphere and have the potential to generate middle–scale traveling ionospheric disturbances (TIDs). The reflection coefficient for AGWs is highly temperature dependent. During maximum solar activity, the temperature of the lower thermosphere can rise several times. This is the situation where infrasound waves become a prime candidate for the ionospheric D layer–lower thermosphere coupling, since strongly reflected gravity waves remain trapped in the D layer. Knowing the temperatures of the particular atmospheric layers, we can also know the characteristics of AGWs and vice versa.","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140832248","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":"Short large-amplitude magnetic structures (SLAMS) at Mercury observed by MESSENGER","authors":"T. Karlsson, F. Plaschke, A. Glass, J. Raines","doi":"10.5194/angeo-42-117-2024","DOIUrl":"https://doi.org/10.5194/angeo-42-117-2024","url":null,"abstract":"Abstract. We present the first observations of short large-amplitude magnetic structures (denoted SLAMS) at Mercury. We have investigated approximately 4 years of MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) data to identify SLAMS in the Mercury foreshock. Defining SLAMS as magnetic field compressional structures, with an increase in magnetic field strength of at least twice the background magnetic field strength, when MESSENGER is located in the solar wind, we find 435 SLAMS. The SLAMS are found either in regions of a general ultra-low frequency (ULF) wave field, at the boundary of such a ULF wave field, or in a few cases isolated from the wave field. We present statistics on several properties of the SLAMS, such as temporal scale size, amplitude, and the presence of whistler-like wave emissions. We find that SLAMS are mostly found during periods of low interplanetary magnetic field strength, indicating that they are more common for higher solar wind Alfvénic Mach number (MA). We use the Tao solar wind model to estimate solar wind parameters to verify that MA is indeed larger during SLAMS observations than otherwise. Finally, we also investigate how SLAMS observations are related to foreshock geometry.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140658404","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}