Annales Geophysicae最新文献

{"title":"Ionospheric effects of the 5–6 January 2019 eclipse over the People's Republic of China: results from oblique sounding","authors":"L. Chernogor, K. Garmash, Q. Guo, V. Rozumenko, Yu. Zheng","doi":"10.5194/angeo-40-585-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-585-2022","url":null,"abstract":"Abstract. This paper deals with the variations in the Doppler spectra and in the relative amplitudes of the signals observed at oblique\u0000incidence over the People's Republic of China (PRC) during the partial solar eclipse of 5–6 January 2019 and on reference days. The observations were made using the multifrequency multipath radio system for sounding the\u0000ionosphere at oblique incidence. The receiver system is located at the\u0000Harbin Engineering University, PRC, and 14 HF broadcasting station\u0000transmitters are used for taking measurements along the following radio-wave propagation paths: Lintong/Pucheng to Harbin, Hwaseong to Harbin, Chiba/Nagara to Harbin, Hailar/Nanmen to Harbin, Beijing to Harbin (three paths), Goyang to Harbin, Ulaanbaatar/Khonkhor to Harbin, Yakutsk to Harbin (two paths), Shijiazhuang to Harbin, Hohhot to Harbin, and Yamata to Harbin. The specific feature of this partial solar eclipse was that it occurred during the local morning with a geomagnetic disturbance (Kp ≈ 3−) in the background. The response of the ionosphere to the solar eclipse has been inferred from temporal variations in the Doppler spectra, the Doppler shift, and the signal relative amplitude. The partial solar eclipse was found to be associated with broadening of the Doppler spectrum, up\u0000to ± 1.5 Hz, alternating sign Doppler-shift variations, up to ± 0.5 Hz, in the main ray, and quasi-periodic Doppler-shift changes. The relative amplitude of electron density disturbances in the 15 min period of atmospheric gravity wave field and in the 4–5 min period of infrasound wave field is estimated to be 1.6 %–2.4 % and 0.2 %–0.3 %, respectively. The estimates of a maximum decrease in the electron density are in agreement with the observations.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76462549","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":"Mid-latitude neutral wind responses to sub-auroral polarization streams","authors":"D. Billett, K. McWilliams, R. Kerr, J. Makela, Alex T. Chariter, J. Ruohoniemi, S. Kapali, M. Migliozzi, J. Riccobono","doi":"10.5194/angeo-40-571-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-571-2022","url":null,"abstract":"Abstract. We investigate the response of the mid-latitude thermospheric neutral winds to a sub-auroral polarization stream (SAPS) event. Using red line (F region) airglow data from two Fabry–Pérot interferometers (FPIs), and F-region ionospheric flow velocities from four Super Dual Auroral Radar Network (SuperDARN) radars, the drivers behind changes seen in the neutral winds are explored within the context of the larger SAPS structure. Different, although strong, neutral wind responses to the SAPS are seen at the two FPI sites, even though they are relatively close geographically. We attribute the wind differences to the varying balance of pressure gradient, ion drag, and Coriolis forces, which ultimately depend on proximity to the SAPS. At the FPI site equatorward of the SAPS, pressure gradient and Coriolis forces drive the winds equatorward and then westward. At the FPI site co-located with the SAPS, the ion drag is strong and results in the winds surging westward before turning eastward when becoming influenced by dawnside sunward plasma convection drifts.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90068706","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":"Temporal and altitudinal variability of the spread F observed by the VHF radar over Christmas Island","authors":"Ricardo Yvan de La Cruz Cueva, Eurico Rodrigues de Paula, Acácio Cunha Neto","doi":"10.5194/angeo-40-563-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-563-2022","url":null,"abstract":"Abstract. The goal of this work is to study the time and altitude\u0000echo characteristics under different solar and seasonality conditions using the VHF radar range–time–intensity (RTI) images. The occurrence of equatorial spread F depends on the existence of conditions that can seed the Rayleigh–Taylor instability, and these conditions can change with solar flux, seasonality,\u0000longitude distributions, and day-to-day variability. So, the equatorial\u0000spread F is observed as its time and altitude occurrence. The VHF radar of\u0000Christmas Island (2.0∘ N, 157.4∘ W, 2.9∘ N dip\u0000latitude) has been operational in the equatorial region for some time,\u0000allowing long-term observations. The occurrence of echoes during solar\u0000minimum conditions is observed throughout the night since the post-reversal westward electric field is weaker than the solar maximum and the\u0000possibilities of the vertical plasma drift becoming positive are larger. On the other hand, echoes during solar maximum will be controlled by dynamics near the time of the pre-reversal peak (PRE). Our results indicate that the\u0000peak time occurrence of echoes along this period shows a well-defined\u0000pattern, with echoes distributed as closer to local sunset during solar\u0000maximum and around/closer to midnight during solar minimum conditions; meanwhile, the peak altitude occurrence of echoes shows a slightly regular\u0000pattern with higher-altitude occurrences during solar maxima and lower altitudes during solar minimum conditions.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79975683","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":"Multiple conjugate observations of magnetospheric fast flow bursts using THEMIS observations","authors":"Homayon Aryan, J. Bortnik, Jinxing Li, J. Weygand, X. Chu, V. Angelopoulos","doi":"10.5194/angeo-40-531-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-531-2022","url":null,"abstract":"Abstract. Magnetotail earthward fast flow bursts can transport most magnetic flux and energy into the inner magnetosphere. These fast flow bursts\u0000are generally an order of magnitude higher than the typical convection speeds that are azimuthally localised (1–3 RE) and are flanked by\u0000plasma vortices, which map to ionospheric plasma vortices of the same sense of rotation. This study uses a multipoint analysis of conjugate\u0000magnetospheric and ionospheric observations to investigate the magnetospheric and ionospheric responses to fast flow bursts that are associated\u0000with both substorms and pseudobreakups. We study in detail what properties control the differences in the magnetosphere–ionosphere responses between\u0000substorm fast flow bursts and pseudobreakup events, and how these differences lead to different ionospheric responses. The fast flow bursts and\u0000pseudobreakup events were observed by the Time History of Events and Macroscale Interaction during Substorms (THEMIS), while the primary ionospheric\u0000observations were made by all-sky cameras and magnetometer-based equivalent ionospheric currents. These events were selected when the satellites\u0000were at least 6 RE from the Earth in radial distance and a magnetic local time (MLT) region of ± 5 h from local midnight. The\u0000results show that the magnetosphere and ionosphere responses to substorm fast flow bursts are much stronger and more structured compared to\u0000pseudobreakups, which are more likely to be localised, transient and weak in the magnetosphere. The magnetic flux in the tail is much stronger for\u0000strong substorms and much weaker for pseudobreakup events. The Blobe decreases significantly for substorm fast flow bursts compared to\u0000pseudobreakup events. The curvature force density for pseudobreakups are much smaller than substorm fast flow events, indicating that the\u0000pseudobreakups may not be able to penetrate deep into the inner magnetosphere. This association can help us study the properties and activity of the\u0000magnetospheric earthward flow vortices from ground data.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79507785","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":"Arecibo measurements of D-region electron densities during sunset and sunrise: implications for atmospheric composition","authors":"C. Baumann, A. Kero, S. Raizada, M. Rapp, M. Sulzer, P. Verronen, J. Vierinen","doi":"10.5194/angeo-40-519-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-519-2022","url":null,"abstract":"Abstract. Earth's lower ionosphere is the region where terrestrial weather and space weather come together. Here, between 60 and 100 km altitude,\u0000solar radiation governs the diurnal cycle of the ionized species. This altitude range is also the place where nanometre-sized dust particles,\u0000recondensed from ablated meteoric material, exist and interact with free electrons and ions of the ionosphere. This study reports electron density\u0000measurements from the Arecibo incoherent-scatter radar being performed during sunset and sunrise conditions. An asymmetry of the electron density is\u0000observed, with higher electron density during sunset than during sunrise. This asymmetry extends from solar zenith angles (SZAs) of 80 to\u0000100∘. This D-region asymmetry can be observed between 95 and 75 km altitude. The electron density observations are compared to the\u0000one-dimensional Sodankylä Ion and Neutral Chemistry (SIC) model and a variant of the Whole Atmosphere Community Climate Model incorporating a\u0000subset SIC's ion chemistry (WACCM-D). Both models also show a D-region sunrise–sunset asymmetry. However, WACCM-D compares slightly better to the\u0000observations than SIC, especially during sunset, when the electron density gradually fades away. An investigation of the electron density continuity\u0000equation reveals a higher electron–ion recombination rate than the fading ionization rate during sunset. The recombination reactions are not fast\u0000enough to closely match the fading ionization rate during sunset, resulting in excess electron density. At lower altitudes electron attachment to\u0000neutrals and their detachment from negative ions play a significant role in the asymmetry as well. A comparison of a specific SIC version\u0000incorporating meteoric smoke particles (MSPs) to the observations revealed no sudden changes in electron density as predicted by the model. However,\u0000the expected electron density jump (drop) during sunrise (sunset) occurs at 100∘ SZA when the radar signal is close to the noise floor,\u0000making a clear falsification of MSPs' influence on the D region impossible.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73120026","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":"Study of the equatorial and low-latitude total electron content response to plasma bubbles during solar cycle 24–25 over the Brazilian region using a Disturbance Ionosphere indeX","authors":"G. Picanço, C. Denardini, P. Nogueira, L. Resende, C. S. Carmo, S. S. Chen, P. F. Barbosa-Neto, E. Romero‐Hernández","doi":"10.5194/angeo-40-503-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-503-2022","url":null,"abstract":"Abstract. This work uses the Disturbance Ionosphere indeX (DIX) to evaluate\u0000the ionospheric responses to equatorial plasma bubble (EPB) events from\u00002013 to 2020 over the Brazilian equatorial and low latitudes. We have\u0000compared the DIX variations during EPBs to ionosonde and All-Sky Imager\u0000data, aiming to evaluate the physical characteristics of these events. Our\u0000results show that the DIX was able to detect EPB-related TEC disturbances in terms of their intensity and occurrence times. Thus, the EPB-related DIX\u0000responses agreed with the ionosphere behavior before, during, and after the\u0000studied cases. Finally, we found that the magnitude of those disturbances\u0000followed most of the trends of solar activity, meaning that the EPB-related\u0000total electron content variations tend to be higher (lower) in high (low) solar activity.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78120234","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":"Sounding of sporadic E layers from China Seismo-Electromagnetic Satellite (CSES) radio occultation and comparing with ionosonde measurements","authors":"Chengkun Gan, Jiayu Hu, Xiaomin Luo, Chao Xiong, S. Gu","doi":"10.5194/angeo-40-463-2022","DOIUrl":"https://doi.org/10.5194/angeo-40-463-2022","url":null,"abstract":"Abstract. GNSS radio occultation (RO) plays an important role in\u0000ionospheric electron density inversion and sounding of sporadic E layers. As\u0000China's first electromagnetic satellite, China Seismo-Electromagnetic\u0000Satellite (CSES) has collected the RO data from both GPS and BDS-2\u0000satellites since March 2018. In this study, we extracted the signal-to-noise\u0000ratio (SNR) data of CSES and calculated the standard deviation of normalized\u0000SNR. A new criterion is developed to determine the Es events, that is, when\u0000the mean value of the absolute value of the difference between the\u0000normalized SNR is greater than 3 times the standard deviation. The\u0000statistics show that sporadic E layers have strong seasonal variations with\u0000highest occurrence rates in summer season at middle latitudes. It is also\u0000found that the occurrence height of Es is mainly located at 90–110 km, and\u0000the period 14:00–20:00 LT is the high incidence period of Es. In\u0000addition, the geometric altitudes of a sporadic E layer detected in CSES\u0000radio occultation profiles and the virtual heights of a sporadic E layer\u0000obtained by the Wuhan Zuoling station (ZLT) ionosonde show three different\u0000space-time matching criteria. Our results reveal that there is a good\u0000agreement between both parameters which is reflected in the significant\u0000correlation.\u0000","PeriodicalId":50777,"journal":{"name":"Annales Geophysicae","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84619114","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":"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":null,"pages":null},"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":"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":null,"pages":null},"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":"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":null,"pages":null},"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}