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21 pages, 1891 KiB

Open AccessArticle

On the Validation of the Rotation Procedure from HEE to MEMFA Reference Frame in the Presence of Alfvén Waves in the Interplanetary Medium

by Giuseppina Carnevale and Mauro Regi

Remote Sens. 2023, 15(19), 4679; https://doi.org/10.3390/rs15194679 - 24 Sep 2023

Viewed by 1340

Abstract

Alfvén waves play an important role in the stability, heating, and transport of magnetized plasmas. They are found to be ubiquitous in solar winds (SW), which mainly propagate outward from the Sun, especially in high-speed streams that originate from coronal holes. When high-speed [...] Read more.

Alfvén waves play an important role in the stability, heating, and transport of magnetized plasmas. They are found to be ubiquitous in solar winds (SW), which mainly propagate outward from the Sun, especially in high-speed streams that originate from coronal holes. When high-speed streams impinge on the Earth’s magnetosphere, the impact of Alfvénic fluctuations can cause magnetic reconnections between the intermittent southward Interplanetary Magnetic Field (IMF) and the geomagnetic field, resulting in energy injection from the SW into the Earth’s magnetosphere. In this work, we tested a rotation procedure from the Heliocentric Earth Ecliptic (HEE) to the Mean ElectroMagnetic Fields Aligned (MEMFA) reference frame. This is achieved by means of the Empirical Mode Decomposition (EMD) method for both the SW velocity and IMF at 1 AU. Our aim is to check the reliability of the method and its limitations in identifying Alfvénic fluctuations through the spectral analysis of time series in the MEMFA coordinate system. With this procedure, we studied the fluctuations in the main-field-aligned direction and those in the orthogonal plane to the main field. To highlight the peculiarities of each case of study and be able to better identify Alfvén waves when applying this procedure to real data, we reproduced the magnetic and velocity fields of a typical corotating high-speed stream. We tested the procedure in several cases by varying the amplitude of Alfvén waves and noise. We performed the spectral analysis of the Mean Field Aligned (MFA) component of both the magnetic and velocity fields to define the power related to the two main directions: the one aligned to the ambient magnetic field and the one orthogonal to it. The efficiency of the procedure and the results’ reliability are supported by Monte Carlo (MC) tests. The method is also applied to a real case that is represented by a selected corotating SW stream that occurred during August 2008, which fell in the solar minimum of solar cycle 23. The results are also compared with those obtained by using Elsässer variables to analyze the Alfvénicity of fluctuations via the normalized cross helicity and the normalized residual energy. Full article

(This article belongs to the Special Issue Space Weather: Observations and Modeling of the Near Earth Environment II)

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13 pages, 2031 KiB

Open AccessArticle

Structure of the High-Latitude Noon Ionosphere of the Southern Hemisphere

by Alexander Karpachev

Remote Sens. 2023, 15(14), 3649; https://doi.org/10.3390/rs15143649 - 21 Jul 2023

Cited by 3 | Viewed by 890

Abstract

The structure of the winter noon ionosphere of the southern hemisphere was studied. This structure includes the dayside cusp, associated high-latitude ionospheric trough (HLT), main ionospheric trough (MIT), electron density (Ne) peak at latitudes about 70°, mid-latitude ring ionospheric trough (RIT), and low-latitude [...] Read more.

The structure of the winter noon ionosphere of the southern hemisphere was studied. This structure includes the dayside cusp, associated high-latitude ionospheric trough (HLT), main ionospheric trough (MIT), electron density (Ne) peak at latitudes about 70°, mid-latitude ring ionospheric trough (RIT), and low-latitude quasi-trough. Data from the CHAMP satellite in the southern hemisphere for quiet geomagnetic conditions under high solar activity were selected for analysis. The DMSP satellite data and a model of auroral diffuse precipitation were also used. This model represents two zones of auroral diffuse precipitation on the equatorward and poleward edges of the auroral oval. It is shown that the situation in the winter noon ionosphere of the southern hemisphere depends cardinally on longitude. At sunlit longitudes, only the HLT is observed, and MIT is formed in the shadow region. At intermediate longitudes, both troughs can be observed and, therefore, there is a problem of their separation. The positions of all structures of the ionosphere depend on the longitude; in particular, the positions of the daytime MIT are changed by 6°−7°. At latitudes of the dayside cusp, both the peak and the minimum of Ne can be observed. A high and narrow peak of Ne is regularly recorded in the CHAMP data at latitudes of the equatorward zone of diffuse precipitation (68°−72°). In the shadow region, this peak forms the MIT poleward wall, and at sunlit longitudes a quasi-trough equatorward of this peak is sometimes observed. The RIT is rarely formed during the day, only at the American and Atlantic longitudes. Full article

(This article belongs to the Special Issue Space Weather: Observations and Modeling of the Near Earth Environment II)

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23 pages, 22116 KiB

Open AccessArticle

Magnetopause Detection under Low Solar Wind Density Based on Deep Learning

by Yujie Zhang, Tianran Sun, Wenlong Niu, Yihong Guo, Song Yang, Xiaodong Peng and Zhen Yang

Remote Sens. 2023, 15(11), 2771; https://doi.org/10.3390/rs15112771 - 26 May 2023

Cited by 1 | Viewed by 1390

Abstract

Extracting the peak value of the X-ray signal in the original magnetopause detection method of soft X-ray imaging (SXI) for the SMILE satellite is problematic because of the unclear interface of the magnetosphere system under low solar wind density and the short integration [...] Read more.

Extracting the peak value of the X-ray signal in the original magnetopause detection method of soft X-ray imaging (SXI) for the SMILE satellite is problematic because of the unclear interface of the magnetosphere system under low solar wind density and the short integration time. Herein, we propose a segmentation algorithm for soft X-ray images based on depth learning, we construct an SXI simulation dataset, and we segment the magnetospheric system by learning the spatial structure characteristics of the magnetospheric system image. Then, we extract the maximum position of the X-ray signal and calculate the spatial configuration of the magnetopause using the tangent fitting approach. Under a uniform universe condition, we achieved a pixel accuracy of the maximum position of the photon number detected by the network as high as 90.94% and contained the position error of the sunset point of the 3D magnetopause below 0.2 RE. This result demonstrates that the proposed method can detect the peak photon number of magnetospheric soft X-ray images with low solar wind density. As such, its use improves the segmentation accuracy of magnetospheric soft X-ray images and reduces the imaging time requirements of the input image. Full article

(This article belongs to the Special Issue Space Weather: Observations and Modeling of the Near Earth Environment II)

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21 pages, 11199 KiB

Open AccessArticle

Prediction Models of ≥2 MeV Electron Daily Fluences for 3 Days at GEO Orbit Using a Long Short-Term Memory Network

by Xiaojing Sun, Ruilin Lin, Siqing Liu, Bingxian Luo, Liqin Shi, Qiuzhen Zhong, Xi Luo, Jiancun Gong and Ming Li

Remote Sens. 2023, 15(10), 2538; https://doi.org/10.3390/rs15102538 - 12 May 2023

Cited by 2 | Viewed by 1507

Abstract

Geostationary satellites are exposed to harsh space weather conditions, including ≥2 MeV electrons from the Earth’s radiation belts. To predict ≥2 MeV electron daily fluences at 75°W and 135°W at geostationary orbit for the following three days, long short-term memory (LSTM) network models [...] Read more.

Geostationary satellites are exposed to harsh space weather conditions, including ≥2 MeV electrons from the Earth’s radiation belts. To predict ≥2 MeV electron daily fluences at 75°W and 135°W at geostationary orbit for the following three days, long short-term memory (LSTM) network models have been developed using various parameter combinations. Based on the prediction efficiency (PE) values, the most suitable time step of inputs and best combinations of two or three input parameters of models for predictions are recommended. The highest PE values for the following three days with three input parameters were 0.801, 0.658 and 0.523 for 75°W from 1995 to August 2010, and 0.819, 0.643 and 0.508 for 135°W from 1999 to 2010. Based on yearly PE values, the performances of the above models show the solar cycle dependence. The yearly PE values are significantly inversely correlated with the sunspot number, and they vary from 0.606 to 0.859 in predicting the following day at 75°W from 1995 to 2010. We have proven that the poor yearly PE is related to relativistic electron enhancement events, and the first day of events is the most difficult to predict. Compared with previous models, our models are comparable to the top performances of previous models for the first day, and significantly improve the performance for second and third days. Full article

(This article belongs to the Special Issue Space Weather: Observations and Modeling of the Near Earth Environment II)

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21 pages, 3310 KiB

Open AccessArticle

Impacts of Extreme Space Weather Events on September 6th, 2017 on Ionosphere and Primary Cosmic Rays

by Aleksandra Kolarski, Nikola Veselinović, Vladimir A. Srećković, Zoran Mijić, Mihailo Savić and Aleksandar Dragić

Remote Sens. 2023, 15(5), 1403; https://doi.org/10.3390/rs15051403 - 2 Mar 2023

Cited by 10 | Viewed by 2644

Abstract

The strongest X-class solar flare (SF) event in 24th solar cycle, X9.3, occurred on 6 September 2017, accompanied by earthward-directed coronal mass ejections (CMEs). Such space weather episodes are known to cause various threats to human activities ranging from radio communication and navigation [...] Read more.

The strongest X-class solar flare (SF) event in 24th solar cycle, X9.3, occurred on 6 September 2017, accompanied by earthward-directed coronal mass ejections (CMEs). Such space weather episodes are known to cause various threats to human activities ranging from radio communication and navigation disturbances including wave blackout to producing geomagnetic storms of different intensities. In this study, SFs’ ionospheric impacts and effects of accompanied heliospheric disturbances on primary cosmic rays (CR) are investigated. This work offers the first detailed investigation of characteristics of these extreme events since they were inspected both from the perspective of their electromagnetic nature, through very low frequency (VLF) radio waves, and their corpuscular nature of CR by multi-instrumental approach. Aside data recorded by Belgrade VLF and CR stations, data from GOES and SOHO space probes were used for modeling and analysis. Conducted numerical simulations revealed a significant change of ionospheric parameters (sharpness and effective reflection height) and few orders of magnitude increase of electron density. We compared our findings with those existing in the literature regarding the ionospheric response and corresponding parameters. In addition, Forbush decrease (FD) magnitude, corrected for magnetospheric effect, derived from measurements, and one predicted from power exponents used to parametrize the shape of energetic proton fluence spectra at L1 were compared and found to be in good agreement. Presented findings could be useful for investigation of atmospheric plasma properties, particles’ modeling, and prediction of extreme weather impacts on human activities. Full article

(This article belongs to the Special Issue Space Weather: Observations and Modeling of the Near Earth Environment II)

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10 pages, 3808 KiB

Open AccessCommunication

Investigation of the Topside Ionosphere over Cyprus and Russia Using Swarm Data

by Haris Haralambous, Krishnendu Sekhar Paul, Arun Kumar Singh and Tamara Gulyaeva

Remote Sens. 2023, 15(5), 1344; https://doi.org/10.3390/rs15051344 - 27 Feb 2023

Cited by 3 | Viewed by 1586

Abstract

Using the topside electron density (Ne) measurements recorded over Cyprus and Russia, we investigate the latitudinal variation in the topside electron density during the interval 2014–2020, encompassing a period of high-to-low solar activity. The selected topside electron density dataset employed in this study [...] Read more.

Using the topside electron density (Ne) measurements recorded over Cyprus and Russia, we investigate the latitudinal variation in the topside electron density during the interval 2014–2020, encompassing a period of high-to-low solar activity. The selected topside electron density dataset employed in this study is based on the in situ Langmuir probe data on board the European Space Agency (ESA) Swarm satellites, in the vicinity of the three Digisonde stations in Nicosia (35.14°N, 33.2°E), Moscow (55.5°N, 37.3°E) and Saint Petersburg (60.0°N, 30.7°E). Our investigation demonstrates that the ratio Ne__Swarm/NmF2 between the coincident Ne__Swarm and the Digisonde NmF2 observations is higher than one on various occasions over Nicosia during the nighttime, which is not the case over Moscow and Saint Petersburg, signifying a discrepancy feature of the electron density at Swarm altitudes which depends not only on the solar activity and time of day but also on the latitude. Full article

(This article belongs to the Special Issue Space Weather: Observations and Modeling of the Near Earth Environment II)

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22 pages, 3379 KiB

Open AccessArticle

Space Weather Effects Observed in the Northern Hemisphere during November 2021 Geomagnetic Storm: The Impacts on Plasmasphere, Ionosphere and Thermosphere Systems

by Mauro Regi, Loredana Perrone, Alfredo Del Corpo, Luca Spogli, Dario Sabbagh, Claudio Cesaroni, Laura Alfonsi, Paolo Bagiacchi, Lili Cafarella, Giuseppina Carnevale, Marcello De Lauretis, Domenico Di Mauro, Pierluigi Di Pietro, Patrizia Francia, Balázs Heilig, Stefania Lepidi, Carlo Marcocci, Fabrizio Masci, Adriano Nardi, Alessandro Piscini, Gianluca Redaelli, Vincenzo Romano, Umberto Sciacca and Carlo Scotto Show full author list Hide full author list

Remote Sens. 2022, 14(22), 5765; https://doi.org/10.3390/rs14225765 - 15 Nov 2022

Cited by 15 | Viewed by 3565

Abstract

On 3 November 2021, an interplanetary coronal mass ejection impacted the Earth’s magnetosphere leading to a relevant geomagnetic storm (Kp = 8-), the most intense event that occurred so far during the rising phase of solar cycle 25. This work presents the state [...] Read more.

On 3 November 2021, an interplanetary coronal mass ejection impacted the Earth’s magnetosphere leading to a relevant geomagnetic storm (Kp = 8-), the most intense event that occurred so far during the rising phase of solar cycle 25. This work presents the state of the solar wind before and during the geomagnetic storm, as well as the response of the plasmasphere–ionosphere–thermosphere system in the European sector. To investigate the longitudinal differences, the ionosphere–thermosphere response of the American sector was also analyzed. The plasmasphere dynamics was investigated through field line resonances detected at the European quasi-Meridional Magnetometer Array, while the ionosphere was investigated through the combined use of ionospheric parameters (mainly the critical frequency of the F2 layer, foF2) from ionosondes and Total Electron Content (TEC) obtained from Global Navigation Satellite System receivers at four locations in the European sector, and at three locations in the American one. An original method was used to retrieve aeronomic parameters from observed electron concentration in the ionospheric F region. During the analyzed interval, the plasmasphere, originally in a state of saturation, was eroded up to two Earth’s radii, and only partially recovered after the main phase of the storm. The possible formation of a drainage plume is also observed. We observed variations in the ionospheric parameters with negative and positive phase and reported longitudinal and latitudinal dependence of storm features in the European sector. The relative behavior between foF2 and TEC data is also discussed in order to speculate about the possible role of the topside ionosphere and plasmasphere response at the investigated European site. The American sector analysis revealed negative storm signatures in electron concentration at the F2 region. Neutral composition and temperature changes are shown to be the main reason for the observed decrease of electron concentration in the American sector. Full article

(This article belongs to the Special Issue Space Weather: Observations and Modeling of the Near Earth Environment II)

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14 pages, 1473 KiB

Open AccessTechnical Note

Seasonal Transitions in the Thermosphere Inferred from Ionospheric Observations

by Loredana Perrone and Andrey V. Mikhailov

Remote Sens. 2023, 15(8), 2022; https://doi.org/10.3390/rs15082022 - 11 Apr 2023

Viewed by 1153

Abstract

Ionospheric observations along with CHAMP/STAR neutral gas density measurements were used to retrieve thermospheric parameters and to check whether the equinox transition season exists separately from the December solstice and June solstice seasons. Juliusruh and Boulder ionosonde stations located in “far-from-pole” and “near-pole” [...] Read more.

Ionospheric observations along with CHAMP/STAR neutral gas density measurements were used to retrieve thermospheric parameters and to check whether the equinox transition season exists separately from the December solstice and June solstice seasons. Juliusruh and Boulder ionosonde stations located in “far-from-pole” and “near-pole” longitudinal sectors were analyzed during deep solar minimum in 2008–2009. The results were compared to GOLD column O/N₂ ratio observations. The retrieved thermospheric parameters have shown that equinoctial transition period exists separately from the winter one at Juliusruh, while column O/N₂ ratios, exospheric temperatures Tex, and vertical plasma drifts related to thermospheric winds retrieved at Boulder for the winter season do not significantly differ from vernal values. This means that the December solstice season just does not exist as it merges with the vernal season in the “near-pole” longitudinal sector. The obtained results indicate that two longitudinal sectors manifest different seasonal variations both in thermospheric circulation and neutral composition. Full article

(This article belongs to the Special Issue Space Weather: Observations and Modeling of the Near Earth Environment II)

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