Annales Geophysicae最新文献

{"title":"Diagnostic study of geomagnetic storm-induced ionospheric changes over very low-frequency signal propagation paths in the mid-latitude D region","authors":"V. Nwankwo, W. Denig, S. Chakrabarti, O. Ogunmodimu, M. P. Ajakaiye, J. Fatokun, Paul I. Anekwe, Omodara E. Obisesan, O. E. Oyanameh, O. V. Fatoye","doi":"10.5194/angeo-40-433-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-433-2022","url":null,"abstract":"Abstract. We performed a diagnostic study of geomagnetic storm-induced disturbances that are coupled to the mid-latitude D region by quantifying the propagation characteristics of very low-frequency (VLF) radio signals from transmitters located in Cumbria, UK (call sign GQD), and Rhauderfehn, Germany (DHO), and received in southern France (A118). We characterised the diurnal VLF amplitudes from two propagation paths into five metrics, namely the mean amplitude before sunrise (MBSR), the midday amplitude peak (MDP), the mean amplitude after sunset (MASS), the sunrise terminator (SRT) and the sunset terminator (SST). We analysed and monitored trends in the variation of signal metrics for up to 20 storms to relate the deviations in the signal amplitudes that were attributable to the storms. Five storms and their effects on the signals were examined in further detail. Our results indicate that relative to pre-storm levels the storm day MDP exhibited characteristic decreases in about 80 % (67 %) of the events for the DHO-A118 (GQD-A118) propagation path. The MBSR showed decreases of about 60 % (77 %), whereas the MASS decreased by 67 % (58 %). Conversely, the SRT and SST showed amplitude decreases of 33 % (25 %) and 47 % (42 %), respectively. Of the two propagation paths, the amplitude decreases for the DHO-A118 propagation path signal were greater, as previously noted by Nwankwo et al. (2016). To better understand the state of the ionosphere over the signal propagation paths and how it might have affected the VLF amplitudes, we further analysed the virtual heights (h'E, h'F1 and h'F2) and critical frequencies (foE, foF1 and foF2) from ionosondes located near the transmitters. The results of this analysis showed significant increases and fluctuations in both the F-region critical frequencies and virtual heights during the geomagnetic storms. The largest increases in the virtual heights occurred near the DHO transmitter in Rhauderfehn (Germany), suggesting a strong storm response over the region which might account for the larger MDP decrease along the DHO-A118 propagation path.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"72 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2022-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88003918","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":"On the colour of noctilucent clouds","authors":"Anna Lange, G. Baumgarten, Alexei Rozanov, C. von Savigny","doi":"10.5194/angeo-40-407-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-407-2022","url":null,"abstract":"Abstract. The high-latitude phenomenon of noctilucent clouds (NLCs) is characterised by a silvery-blue or pale blue colour. In this study, we employ the radiative transfer model SCIATRAN to simulate spectra of solar radiation scattered by NLCs for a ground-based observer and assuming spherical NLC particles. To determine the resulting colours of NLCs in an objective way, the CIE (International Commission on Illumination) colour-matching functions and chromaticity values are used. Different processes and parameters potentially affecting the colour of NLCs are investigated, i.e. the size of the NLC particles, the abundance of middle atmospheric O3 and the importance of multiply scattered solar radiation. We affirm previous research indicating that solar radiation absorption in the O3 Chappuis bands can have a significant effect on the colour of the NLCs. A new result of this study is that for sufficiently large NLC optical depths and for specific viewing geometries, O3 plays only a minor role for the blueish colour of NLCs. The simulations also show that the size of the NLC particles affects the colour of the clouds. Cloud particles of unrealistically large sizes can lead to a reddish colour. Furthermore, the simulations show that the contribution of multiple scattering to the total scattering is only of minor importance, providing additional justification for the earlier studies on this topic, which were all based on the single-scattering approximation.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"9 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2022-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72500276","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":"Finite-difference time-domain analysis of ELF radio wave propagation in the spherical Earth–ionosphere waveguide and its validation based on analytical solutions","authors":"V. Marchenko, A. Kulak, J. Mlynarczyk","doi":"10.5194/angeo-40-395-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-395-2022","url":null,"abstract":"Abstract. The finite-difference time-domain (FDTD) model of electromagnetic wave propagation in the\u0000Earth–ionosphere cavity was developed under assumption of an axisymmetric system, solving the reduced Maxwell equations in a 2D\u0000spherical coordinate system. The model was validated on different\u0000conductivity profiles for the electric and magnetic field components for\u0000various locations on Earth along the meridian. The characteristic electric\u0000and magnetic altitudes, phase velocity, and attenuation rate were\u0000calculated. We compared the results of numerical and analytical calculations\u0000and found good agreement between them. The undertaken FDTD modeling enables\u0000us to analyze the Schumann resonances and the propagation of individual\u0000lightning discharges occurring at various distances from the receiver. The\u0000developed model is particularly useful when analyzing ELF measurements.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"1 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2022-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85219910","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 “SafeSpace” database of ULF power spectral density and radial diffusion coefficients: dependencies and application to simulations","authors":"C. Katsavrias, A. Nasi, I. Daglis, S. Aminalragia-Giamini, N. Dahmen, C. Papadimitriou, M. Georgiou, A. Brunet, S. Bourdarie","doi":"10.5194/angeo-40-379-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-379-2022","url":null,"abstract":"Abstract. Radial diffusion has been established as one of the most important\u0000mechanisms contributing to both the acceleration and loss of\u0000relativistic electrons in the outer radiation belt, as well as to the\u0000supply of particles to the inner radiation belt. In the framework of\u0000the “SafeSpace” project, we have used 9 years (2011–2019) of multi-point\u0000magnetic and electric field measurements from THEMIS A, D and E\u0000satellites to create a database of radial diffusion coefficients\u0000(DLL) and ultra-low-frequency (ULF) wave power spectral densities\u0000(PSDs) spanning an L∗ range from 3 to 8. In this work we\u0000investigate the dependence of the DLL on the various solar wind\u0000parameters, geomagnetic indices and coupling functions, as well as the\u0000L-shell, during the solar cycle 24. Moreover, we discuss the\u0000uncertainties introduced on the estimation of DLL time series by\u0000the partial azimuthal coverage provided by in situ\u0000measurements. Furthermore, we investigate, via a superposed analysis,\u0000the dependence of the DLL on solar wind drivers. We show, for the\u0000first time to the best of our knowledge, that the interplanetary coronal mass\u0000ejection (ICME)-driven disturbances accompanied by high solar wind\u0000pressure values combined with intense magnetospheric compression can\u0000produce DLLB values comparable to or even greater than the\u0000ones of DLLE. This feature cannot be captured by\u0000semi-empirical models and introduces a significant energy dependence\u0000on the DLL. Finally, we show the advantages of using DLL\u0000time series by means of numerical simulations of relativistic electron\u0000fluxes performed with the Salammbô code and significant deviations in the predictions of several semi-empirical models depending on the level of geomagnetic activity and L-shell.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"5 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2022-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90416323","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":"Fine structure and motion of the bow shock and particle energisation mechanisms inferred from Magnetospheric Multiscale (MMS) observations","authors":"K. Stasiewicz, Z. Kłos","doi":"10.5194/angeo-40-315-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-315-2022","url":null,"abstract":"Abstract. This study presents new observations of fine structure and motion of the bow shock formed in the solar wind, upstream of the Earth's\u0000magnetosphere. NASA's Magnetospheric Multiscale (MMS) mission has recorded data during 11 encounters with a shock oscillating with frequency of\u00001 mHz. Shocks move with a speed of 4–17 km s−1; have thickness of 100 km, i.e. an ion gyroradius; and represent\u0000cascades of compressional magnetic field and plasma density structures of increasing frequencies or smaller spatial scales. Induced density\u0000gradients initiate chains of cross-field current-driven instabilities that heat solar wind ions by the stochastic Ẽ×B wave\u0000energisation mechanism. The theoretical ion energisation limits are confirmed by observations. We have identified the ion acceleration mechanism\u0000operating at shocks and explained double-beam structures in the velocity space. The nature of this mechanism has been revealed as a stochastic\u0000resonant acceleration (SRA). The results provide for the first time a consistent picture of a chain of plasma processes that generate collisionless\u0000shocks and are responsible for particle energisation.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"72 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2022-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81728676","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":"Terrestrial exospheric dayside H-density profile at 3–15 <i>R</i>_E from UVIS/HDAC and TWINS Lyman-<i>α</i> data combined","authors":"J. Zoennchen, H. Connor, Jaewoong Jung, U. Nass, H. Fahr","doi":"10.5194/angeo-40-271-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-271-2022","url":null,"abstract":"Abstract. Terrestrial ecliptic dayside observations of the exospheric Lyman-α column intensity between 3–15 Earth radii (RE) by UVIS/HDAC (UVIS – ultraviolet imaging spectrograph; HDAC – hydrogen-deuterium absorption\u0000cell) Lyman-α photometer at CASSINI have been analyzed to derive the neutral exospheric H-density profile at the Earth's ecliptic dayside in this radial range. The data were measured during CASSINI's swing-by maneuver at the Earth on 18 August 1999 and are published by Werner et al. (2004). In this study the dayside HDAC Lyman-α observations published by Werner et al. (2004) are compared to calculated Lyman-α intensities based on the 3D H-density model derived from TWINS (Two Wide-angle Imaging Neutral-atom Spectrometers) Lyman-α observations between 2008–2010 (Zoennchen et al., 2015). It was found that both Lyman-α profiles show a very similar radial dependence in particular between 3–8 RE. Between 3.0–5.5 RE impact distance Lyman-α observations of both TWINS and UVIS/HDAC exist at the ecliptic dayside. In this overlapping region the cross-calibration of the HDAC profile against the calculated TWINS profile was done, assuming that the exosphere there was similar for both due to comparable space weather conditions. As a result of the cross-calibration the conversion factor between counts per second and rayleigh, fc=3.285 counts s−1 R−1, is determined for these HDAC observations. Using this factor the radial H-density profile for the Earth's ecliptic dayside was derived from the UVIS/HDAC observations, which constrained the neutral H density there at 10 RE to a value of 35 cm−3. Furthermore, a faster radial H-density decrease was found at distances above 8 RE (≈r-3) compared to the lower distances of 3–7 RE (≈r-2.37). This increased loss of neutral H above 8 RE might indicate a higher rate of H ionization in the vicinity of the magnetopause at 9–11 RE (near subsolar point) and beyond, because of increasing charge exchange interactions of exospheric H atoms with solar wind ions outside the magnetosphere.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"78 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2022-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76180324","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":"Responses of intermediate layers to geomagnetic activity during the 2009 deep solar minimum over the Brazilian low-latitude sector","authors":"Ângela M. Santos, C. Brum, I. Batista, J. Sobral, M. Abdu, J. R. Souza","doi":"10.5194/angeo-40-259-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-259-2022","url":null,"abstract":"Abstract. This work presents the daytime behavior of the intermediate\u0000layer (ILs) parameters (the virtual height – h'IL, and the top frequency – ftIL) over\u0000the low-latitude region of Cachoeria Paulista (CP, 22.42∘ S;\u000045∘ W, I: −34.59∘) during the 2009 deep solar minimum.\u0000Under such a unique condition, this research reveals the ILs' quiet state seasonal\u0000behavior as well as its responses to moderate changes in the geomagnetic\u0000activity. The main results show that even small variations of geomagnetic\u0000activity (quantified by the planetary Kp index) are able to modify the\u0000dynamics of the ILs parameters. For the first time, it was observed that during\u0000the summer, the h'IL decreases rapidly with the increase of geomagnetic\u0000activity, mainly in the early morning hours, while in the following hours, a\u0000smoothed rise of the IL was found in all seasons analyzed. Regarding the\u0000IL frequency, it was observed that after 12:00 LT, there is a tendency to\u0000decrease with the increase of magnetic disturbances, this\u0000characteristic being more intense after 16:00 LT for summer and winter. For the\u0000equinox, such variation was detected, however with half of the amplitude of\u0000the other seasons. In addition, the domain of the annual\u0000periodicity of the ftIL stands out, while the h'IL presents a semiannual component under the\u0000condition of geomagnetic quiet.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"30 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2022-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88834869","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":"Propagating characteristics of mesospheric gravity waves observed by an OI 557.7 nm airglow all-sky camera at Mt. Bohyun (36.2° N, 128.9° E)","authors":"Junhyuk Hwang, Young‐Sook Lee, Y. Kim, H. Kam, Seueng-Min Song, Y. Kwak, Tae-Yong Yang","doi":"10.5194/angeo-40-247-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-247-2022","url":null,"abstract":"Abstract. We analysed all-sky camera images observed at Mt. Bohyun observatory (36.2∘ N, 128.9∘ E) for the period 2017–2019. The image\u0000data were acquired with a narrowband filter centred at 557.7 nm for the OI airglow emission at ∼ 96 km altitude. A total of\u0000150 wave events were identified in the images of 144 clear nights. The interquartile ranges of wavelength, phase speed and periods of the\u0000identified waves are 20.5–35.5 km, 27.4–45.0 m s−1 and 10.8–13.7 min with the median values of 27.8 km,\u000036.3 m s−1 and 11.7 min, respectively. The summer and spring bias of propagation directions of north-eastward and northward,\u0000respectively, can be interpreted as the effect of filtering by the prevailing winds in the lower atmosphere. In winter the subdominant\u0000north-westward waves may be observed due to a nullified filtering effect by slow northward background wind or secondary waves generated in the upper\u0000atmosphere. Intrinsic phase speeds and periods of the waves were also derived by using the wind data simultaneously observed by a nearly co-located\u0000meteor radar. The nature of vertical propagation was evaluated in each season. The majority of observed waves are found to be freely propagating\u0000and thus can be attributed to wave sources in the lower or upper atmosphere.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"7 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2022-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78572593","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":"Dayside magnetopause reconnection and flux transfer events under radial interplanetary magnetic field (IMF): BepiColombo Earth-flyby observations","authors":"Weijie Sun, J. Slavin, R. Nakamura, D. Heyner, K. Trattner, J. Mieth, Jiutong Zhao, Q. Zong, S. Aizawa, N. André, Y. Saito","doi":"10.5194/angeo-40-217-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-217-2022","url":null,"abstract":"Abstract. This study analyzes the flux transfer event (FTE)-type flux ropes and magnetic reconnection around the dayside magnetopause during BepiColombo's\u0000Earth flyby. The magnetosheath has a high plasma β (∼ 8), and the interplanetary magnetic field (IMF) has a significant radial component. Six flux ropes are identified around the magnetopause. The motion of flux ropes together with the maximum magnetic shear model suggests that the reconnection X-line possibly swipes BepiColombo near the magnetic equator due to an increase in the radial component of the IMF. The flux rope\u0000with the highest flux content contains a clear coalescence signature, i.e., two smaller flux ropes merge, supporting theoretical predictions that the flux contents of flux ropes can grow through coalescence. The coalescence of the two FTE-type flux ropes takes place through secondary reconnection\u0000at the point of contact between the two flux ropes. The BepiColombo measurements indicate a large normalized guide field and a reconnection rate\u0000comparable to that measured at the magnetopause (∼ 0.1).\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"66 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2022-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80236589","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 Lehtinen–Pirjola method modified for efficient modelling of geomagnetically induced currents in multiple voltage levels of a power network","authors":"R. Pirjola, D. Boteler, L. Tuck, S. Marsal","doi":"10.5194/angeo-40-205-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-205-2022","url":null,"abstract":"Abstract. The need for accurate assessment of the geomagnetic hazard to power systems is driving a requirement to model geomagnetically induced currents (GIC) in multiple voltage levels of a power network. The Lehtinen–Pirjola method for modelling GIC is widely used but was developed when the main aim was\u0000to model GIC in only the highest voltage level of a power network. Here we present a modification to the Lehtinen–Pirjola (LP) method designed to\u0000provide an efficient method for modelling GIC in multiple voltage levels. The LP method calculates the GIC flow to ground from each node. However,\u0000with a network involving multiple voltage levels, many of the nodes are ungrounded, i.e. have infinite resistance to ground, which is numerically inconvenient. The new modified Lehtinen–Pirjola (LPm) method replaces the earthing impedance matrix [Ze] with the corresponding earthing admittance matrix\u0000[Ye] in which the ungrounded nodes have zero admittance to ground. This is combined with the network admittance matrix [Yn] to give a combined matrix ([Yn] + [Ye]), which is a sparse symmetric\u0000positive definite matrix allowing efficient techniques, such as Cholesky decomposition, to be used to provide the nodal voltages. The nodal voltages\u0000are then used to calculate the GIC in the transformer windings and the transmission lines of the power network. The LPm method with Cholesky\u0000decomposition also provides an efficient method for calculating GIC at multiple time steps. Finally, the paper shows how software for the LP method\u0000can be easily converted to the LPm method and provides examples of calculations using the LPm method.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":"150 1","pages":""},"PeriodicalIF":1.9,"publicationDate":"2022-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75774842","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}