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15 pages, 13702 KiB

Open AccessArticle

Preliminary Results of the Three-Dimensional Plasma Drift Velocity at East Asian Low-Latitudes Observed by the Sanya Incoherent Scattering Radar (SYISR)

by Yuyan Jin, Biqiang Zhao, Honglian Hao, Xinan Yue, Feng Ding, Baiqi Ning, Lingqi Zeng and Zishen Li

Remote Sens. 2023, 15(11), 2842; https://doi.org/10.3390/rs15112842 - 30 May 2023

Cited by 3 | Viewed by 1317

Abstract

As the first advanced modular phase array incoherent scatter radar (ISR) established in the Eastern Hemisphere at low latitudes, Sanya ISR (SYISR) can measure the line-of-sight (LOS) velocity of ion drift in multiple directions, potentially yielding the spatial distribution of ionospheric plasma drift. [...] Read more.

As the first advanced modular phase array incoherent scatter radar (ISR) established in the Eastern Hemisphere at low latitudes, Sanya ISR (SYISR) can measure the line-of-sight (LOS) velocity of ion drift in multiple directions, potentially yielding the spatial distribution of ionospheric plasma drift. Three beam-scanning modes are designed for plasma drift detection: meridian, zonal and cross-shaped (both meridian and zonal) plane, which will provide the distribution of plasma drift in latitude/longitude as well as altitude. The altitude profile of plasma drift and the first presented distribution of low latitude plasma drift in the meridian plane for March to May 2021 are inversed through LOS velocity using cross-shaped and meridian beam-scanning modes, respectively. A statistical correlation coefficient between the

v_{p n}

and crest-to-trough ratio (CTR) of equatorial ionization anomaly (EIA) TEC and a case study of magnetic storm response in plasma drift show that the inversed plasma drift can be a good indicator in response to the changes in atmospheric tide and solar wind at different time scales and explain the corresponding ionospheric electron density variations at low and equatorial latitudes. This study proves that the SYISR-measured plasma drift is reliable and will play an important role in the atmosphere-ionosphere-magnetospheric coupling study in the East Asian region. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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13 pages, 3810 KiB

Open AccessArticle

Study on the Method of Extracting Plasma Lines Based on Sanya Incoherent Scatter Radar

by Honglian Hao, Biqiang Zhao, Xinan Yue, Feng Ding, Baiqi Ning and Lingqi Zeng

Remote Sens. 2023, 15(10), 2634; https://doi.org/10.3390/rs15102634 - 18 May 2023

Cited by 1 | Viewed by 1279

Abstract

The plasma lines observed by Sanya incoherent scatter radar (SYISR) are dependent on the enhancement of Langmuir waves due to superthermal photoelectrons generated by solar EUV radiation. The plasma line power spectrum can be obtained using long-pulse and alternating-code transmission signals during the [...] Read more.

The plasma lines observed by Sanya incoherent scatter radar (SYISR) are dependent on the enhancement of Langmuir waves due to superthermal photoelectrons generated by solar EUV radiation. The plasma line power spectrum can be obtained using long-pulse and alternating-code transmission signals during the period from sunrise to noon almost every day. For the power spectrum of the long pulse, the CLEAN algorithm that has been applied in this field is used to verify the feasibility of this method for SYISR in only a few cases. However, it is difficult to deal with alternating code with such a low SNR using the general deconvolution method. The irreversible-migration filtering (IMF) method has been developed to separate signal noise from the measurements of the alternating code. Some experimental results from the SYISR measurements validate the excellent performance of the IMF method for alternating code. Additionally, an example observation of the electron density with a high time and range resolution is derived. The results show that plasma line detection can be a powerful new observational capability for SYISR as an ionospheric experimental mode for ionospheric calibration, when possible, which can be simultaneously measured with the ion line for constant radar calibration in the standard fitting of the ion line. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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16 pages, 6029 KiB

Open AccessArticle

Wavenumber-4 Structure in COSMIC-2 Observations: Vertical Plane Perspective

by Lalit Mohan Joshi, Lung-Chih Tsai and Shin-Yi Su

Remote Sens. 2023, 15(8), 2105; https://doi.org/10.3390/rs15082105 - 17 Apr 2023

Cited by 1 | Viewed by 1387

Abstract

High-rate radio occultation (RO) in COSMIC-2 (FORMOSAT7) enables us to investigate the finer details of the ionosphere owing to the measurements being made at a significantly high spatiotemporal resolution, which was unthinkable a decade ago. In the vertical plane, local-time ionospheric wavenumber-4 (WN4) [...] Read more.

High-rate radio occultation (RO) in COSMIC-2 (FORMOSAT7) enables us to investigate the finer details of the ionosphere owing to the measurements being made at a significantly high spatiotemporal resolution, which was unthinkable a decade ago. In the vertical plane, local-time ionospheric wavenumber-4 (WN4) structures display tilted phase-fronts over the equatorial ionization anomaly (EIA) belt. The longitudinal extent of a tilted WN4 phase-front approximates the zonal wavelength of nonmigrating DE3 tide in the local-time frame of reference, i.e., ~90⁰. The WN4-filtered (residual) component indicates a greater tilt (when visible), with a larger longitudinal extent of a wavenumber structure in the vertical plane. The WN4 structure over the EIA crest region is found to be out of phase (in phase) with respect to that over the EIA trough region during daytime (nighttime), which also depended on the altitude under consideration. Intriguingly, above 400 km, the WN4 structures in the EIA crest and trough regions are seen to be in phase with each other at all local times. The phenomenon of the “longitudinal co-location” of WN4 over the EIA crest and trough regions at altitudes above ~400 km at all local times remains unexplained. Results also highlight that the formation of WN4 is governed by a complex interplay of direct forcing of nonmigrating tides and the zonal electric field whose characteristics within the EIA belt vary drastically with latitude and altitude under consideration. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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19 pages, 8596 KiB

Open AccessArticle

The Movement of GPS Positioning Discrepancy Clouds at a Mid-Latitude Region in March 2015

by Janis Balodis, Madara Normand and Ansis Zarins

Remote Sens. 2023, 15(8), 2032; https://doi.org/10.3390/rs15082032 - 12 Apr 2023

Cited by 3 | Viewed by 1814

Abstract

The geomagnetic storm on 17 March 2015 had a strong impact on the global navigation satellite systems (GNSS) positioning results in many GNSS Continuously Operating Reference Stations (CORS) in Europe. The analysis of global positioning system (GPS) observations in Latvian CORS stations discovered [...] Read more.

The geomagnetic storm on 17 March 2015 had a strong impact on the global navigation satellite systems (GNSS) positioning results in many GNSS Continuously Operating Reference Stations (CORS) in Europe. The analysis of global positioning system (GPS) observations in Latvian CORS stations discovered a strong impact of this space weather event over the whole country. The impact appeared as a moving cloud of positioning discrepancies across the country. However, the analysis of the days before 17 March revealed other smaller duration ionospheric scintillation events. The objective was to analyze the GPS positioning discrepancy cloud movement, total electron content (TEC), and rate of change of the TEC index (ROTI) relationships, as well as discrepancy statistics. The area of analysis on 16–18 March was increased by including the EGNOS ground-based Ranging and Integrity Monitoring Stations (RIMS): GVLA and GVLB, LAPA and LAPB, and WRSA and WRSB. The conclusion of the study is that each “shot” after 90 s gives a completely new cloud with a new impacted station subset, its configuration, and completely irregular discrepancy values. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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23 pages, 11159 KiB

Open AccessArticle

Comparative Analysis of Global and Regional Ionospheric Responses during Two Geomagnetic Storms on 3 and 4 February 2022

by Rumiana Bojilova and Plamen Mukhtarov

Remote Sens. 2023, 15(7), 1739; https://doi.org/10.3390/rs15071739 - 23 Mar 2023

Cited by 11 | Viewed by 1894

Abstract

The present work examines the spatial and temporal distribution of positive and negative TEC anomalies on the global and regional scale. To study the local response of the ionosphere, foF2 data from ground ionosonde stations and TEC data from Madrigal and CODE databases [...] Read more.

The present work examines the spatial and temporal distribution of positive and negative TEC anomalies on the global and regional scale. To study the local response of the ionosphere, foF2 data from ground ionosonde stations and TEC data from Madrigal and CODE databases have been used. The relative deviation, which also determines the type of TEC response during geomagnetic storms on 3 and 4 February 2022, is considered. In the present study, the regions of positive and negative TEC anomalies and their evolution during storms are examined in detail. As a result of the study, estimates of the following were obtained: (i) the location of the sectors of the polar regions, in where the particle precipitation from the solar wind is observed, (ii) the mid-latitude regions, in which the mechanism of influence of the O/N₂ ratio dominates, and (iii) the region around the equator, in which the influence of the electric field dominates. An attempt was made to determine which mechanism of influence of geomagnetic storms on the ionospheric electron density is dominant in different regions. The following main mechanisms are considered: (a) the additional ionization from the particles’ precipitation, (b) the change of the ratio of atomic oxygen (O) to molecular nitrogen (N₂) due to the heating of the neutral air, and (c) the influence on the equatorial ionospheric anomaly. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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18 pages, 4121 KiB

Open AccessArticle

A Statistical Study of Ion Upflow during Periods of Dawnside Auroral Polarization Streams and Subauroral Polarization Streams

by Chengyu Qian and Hui Wang

Remote Sens. 2023, 15(5), 1320; https://doi.org/10.3390/rs15051320 - 27 Feb 2023

Cited by 3 | Viewed by 1642

Abstract

We have investigated the effect of the dawnside subauroral polarization stream (SAPS) and dawnside auroral polarization stream (DAPS) on the ionospheric ion upflow in the Northern Hemisphere by using four years of Defense Meteorological Satellite Program (DMSP) observations. The occurrence rate of DAPS [...] Read more.

We have investigated the effect of the dawnside subauroral polarization stream (SAPS) and dawnside auroral polarization stream (DAPS) on the ionospheric ion upflow in the Northern Hemisphere by using four years of Defense Meteorological Satellite Program (DMSP) observations. The occurrence rate of DAPS is higher than that of dawnside SAPS. Obvious ion upflow occurs in the topside ionosphere around the DAPS region. The effect of the dawnside SAPS on the vertical flow is weakened when geomagnetic activity increases. There are prominent upflow fluxes around the DAPS, while there are insignificant upflow fluxes around the SAPS region. The plasma density trough during SAPS periods becomes shallower with increasing magnetic activity. These variations with magnetic activity might be due to the weakened ion-neutral collision heating efficiency during highly disturbed periods. There is no obvious plasma density trough or ion temperature drop around the DAPS region at the altitude of ~800 km. The ion temperature around the SAPS area decreases, while the electron temperature increases around the DAPS and SAPS regions. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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19 pages, 4881 KiB

Open AccessArticle

Multi-Instrumental Observations of Midlatitude Plasma Irregularities over Eastern Asia during a Moderate Magnetic Storm on 16 July 2003

by Hailun Ye, Wen Yi, Baozhu Zhou, Jianfei Wu, Bingkun Yu, Penghao Tian, Jianyuan Wang, Chi Long, Maolin Lu, Xianghui Xue, Tingdi Chen and Xiangkang Dou

Remote Sens. 2023, 15(4), 1160; https://doi.org/10.3390/rs15041160 - 20 Feb 2023

Cited by 5 | Viewed by 2103

Abstract

This study presents the observations of midlatitude plasma irregularities over Eastern Asia during a moderate magnetic storm on 16 July 2003. Multi-instrumental observations, including the ground-based ionosondes, the GNSS networks, and the CHAMP and ROCSAT-1 satellites, were utilized to investigate the occurrence and [...] Read more.

This study presents the observations of midlatitude plasma irregularities over Eastern Asia during a moderate magnetic storm on 16 July 2003. Multi-instrumental observations, including the ground-based ionosondes, the GNSS networks, and the CHAMP and ROCSAT-1 satellites, were utilized to investigate the occurrence and characteristics of midlatitude plasma irregularities. The midlatitude strong spread F (SSF) mainly occurred in the midnight–morning sector as observed by ionosondes over Japan during this storm. SSF was related to plasma depletions, which is also recorded by GNSS network in the form of the enhancement of the rate of total electron content (TEC) change index (ROTI). The possible mechanism for the generation of SSF is that the enhanced eastward electric fields, associated with the prompt penetration electric fields and disturbance dynamo electric fields, cause the uplift and latitudinal extension of equatorial plasma bubbles (EPBs) to generate the observed midlatitude SSF further. Meanwhile, plasma density increased significantly under the influence of this storm. In addition, other common type of spread F, frequency spread F (FSF), was observed over Japan on the non-storm day and/or at high latitude station WK545, which seems to be closely related to the coupling of medium-scale traveling ionospheric disturbances (MSTIDs) and sporadic E (Es) layer. The above results indicate that various types of midlatitude spread F can be produced by different physical mechanisms. It is found that SSF can significantly affect the performance of radio wave propagation compared with FSF. Our results show that space weather events have a significant influence on the day-to-day variability of the occurrence and characteristics of ionospheric F-region irregularities at midlatitudes. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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18 pages, 4974 KiB

Open AccessArticle

Ionospheric Oscillation with Periods of 6–30 Days at Middle Latitudes: A Response to Solar Radiative, Geomagnetic, and Lower Atmospheric Forcing

by Zhenlin Yang, Sheng-Yang Gu, Yusong Qin, Chen-Ke-Min Teng, Yafei Wei and Xiankang Dou

Remote Sens. 2022, 14(22), 5895; https://doi.org/10.3390/rs14225895 - 21 Nov 2022

Cited by 3 | Viewed by 1834

Abstract

This research studies the medium timescale (6–30 days) ionospheric response over the Wuhan area to solar radiative, recurrent geomagnetic, and lower atmospheric forcing. The ionospheric response is examined by wavelet analysis of the total electron content (TEC) over the Wuhan area from 2001 [...] Read more.

This research studies the medium timescale (6–30 days) ionospheric response over the Wuhan area to solar radiative, recurrent geomagnetic, and lower atmospheric forcing. The ionospheric response is examined by wavelet analysis of the total electron content (TEC) over the Wuhan area from 2001 to 2020. Ionospheric oscillations with periods centering at the harmonic oscillations of the 27-day solar rotation (e.g., 27 days, 13.5 days, 9 days, and 6.75 days) are focused upon. The results show that the quasi-27-day TEC oscillations at the middle latitude have a better overall correlation with solar radiation than recurrent geomagnetic activity, but the correlation between TEC and recurrent geomagnetic activity has a significant increase at the solar minimum stage. As for ionospheric oscillations with periods shorter than 15 days, these oscillations correlate better with recurrent geomagnetic activity. Moreover, a quasi-27-day TEC oscillation event at the middle latitude caused by convective activity from the lower atmosphere was studied. This suggests that lower atmospheric forcing is also an important factor causing ionospheric oscillations. In addition, the ionospheric oscillations over the Wuhan area also show unique regional characteristics, as the regional ionosphere does not respond well to the Kp oscillation with periods shorter than 20 days, particularly, 13.5 days. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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11 pages, 1340 KiB

Open AccessCommunication

Fast Ionogram Observations of Ascending Thin Layers Locally Transported from the E to F Region at Equatorial and Low Latitudes

by Lianhuan Hu, Guozhu Li, Zonghua Ding, Wenjie Sun, Xiukuan Zhao, Haiyong Xie, Zhengping Zhu, Tatsuhiro Yokoyama, Jiaping Lan, Zhaoguo Huang and Baiqi Ning

Remote Sens. 2022, 14(22), 5811; https://doi.org/10.3390/rs14225811 - 17 Nov 2022

Viewed by 1605

Abstract

By using fast ionogram observations, we report the first simultaneous observations of ascending ion layers at equatorial and low latitudes. The ionosonde measurements at Sanya (18.3°N, 109.6°E; dip lat. 12.2°N) and Chumphon (10.7°N, 99.4°E; dip lat. 3.8°N) show that a high Es layer, [...] Read more.

By using fast ionogram observations, we report the first simultaneous observations of ascending ion layers at equatorial and low latitudes. The ionosonde measurements at Sanya (18.3°N, 109.6°E; dip lat. 12.2°N) and Chumphon (10.7°N, 99.4°E; dip lat. 3.8°N) show that a high Es layer, which might contain metallic ions, was directly lifted upward from the local E region to F region bottomside at morning hours, in a pattern similar to the vertical drift of the F region background ionosphere driven by the daytime eastward electric field. A statistical analysis with Sanya ionosonde measurements shows that the low latitude ascending ion layer is not a rare phenomenon, with a maximum occurrence of 22% during equinox. The results indicate that at the latitudes far away from the magnetic equator, the local E region metallic ions could be directly brought into the F region with the ascending layer. It can be expected that fast ionogram measurements, which can easily capture the rapid evolution of the background ionosphere, will play an important role in studying the formation of some unexpected high altitude metallic layers. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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22 pages, 11055 KiB

Open AccessArticle

A Machine Learning-Based Method for Modeling TEC Regional Temporal-Spatial Map

by Yiran Liu, Jian Wang, Cheng Yang, Yu Zheng and Haipeng Fu

Remote Sens. 2022, 14(21), 5579; https://doi.org/10.3390/rs14215579 - 4 Nov 2022

Cited by 10 | Viewed by 2797

Abstract

In order to achieve the high-accuracy prediction of the total electron content (TEC) of the regional ionosphere for supporting the application of satellite navigation, positioning, measurement, and controlling, we proposed a modeling method based on machine learning (ML) and use this method to [...] Read more.

In order to achieve the high-accuracy prediction of the total electron content (TEC) of the regional ionosphere for supporting the application of satellite navigation, positioning, measurement, and controlling, we proposed a modeling method based on machine learning (ML) and use this method to establish an empirical prediction model of TEC for parts of Europe. The model has three main characteristics: (1) The principal component analysis (PCA) is used to separate TEC’s temporal and spatial variation characteristics and to establish its corresponding map, (2) the solar activity parameters of the 12-month mean flux of the solar radio waves at 10.7 cm (F10.7₁₂) and the 12-month mean sunspot number (R₁₂) are introduced into the temporal map as independent variables to reflect the temporal variation characteristics of TEC, and (3) The modified Kriging spatial interpolation method is used to achieve the spatial reconstruction of TEC. Finally, the regression learning method is used to determine the coefficients and harmonic numbers of the model by using the root mean square error (RMSE) and its relative value (RRMSE) as the evaluation standard. Specially, the modeling process is easy to understand, and the determined model parameters are interpretable. The statistical results show that the monthly mean values of TEC predicted by the proposed model in this paper are highly consistent with the observed values curve of TEC, and the RRMSE of the predicted results is 12.76%. Furthermore, comparing the proposed model with the IRI model, it can be found that the prediction accuracy of TEC by the proposed model is much higher than that of the IRI model either with CCIR or URSI coefficients, and the improvement is 38.63% and 35.79%, respectively. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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20 pages, 11416 KiB

Open AccessArticle

Analysis of the Ionospheric Irregularities and Phase Scintillation at Low and Middle Latitudes Based on Swarm Observations

by Jiawei Kuai, Kang Wang, Jiahao Zhong, Xin Wan, Fuqing Huang, Hao Sun, Jiawen Chen, Xingyan Song and Hao Han

Remote Sens. 2022, 14(19), 4780; https://doi.org/10.3390/rs14194780 - 24 Sep 2022

Cited by 4 | Viewed by 2072

Abstract

This study presents a statistical analysis of the ionospheric irregularities and topside ionospheric scintillation at low and middle latitudes by using in situ electron density and upward-looking total electron content data measured by the Swarm constellation during 2014–2021. The main purpose of this [...] Read more.

This study presents a statistical analysis of the ionospheric irregularities and topside ionospheric scintillation at low and middle latitudes by using in situ electron density and upward-looking total electron content data measured by the Swarm constellation during 2014–2021. The main purpose of this study is to determine whether the phase scintillation could present similar seasonal, longitudinal, latitudinal, local time, and solar activity features as the in situ ionospheric irregularities do at low and middle latitudes, and how the irregularities affect the phase scintillation. The results are summarized as follows: (1) At low latitudes, the occurrence rate of equatorial plasma irregularities (EPIs) at the equinoxes and December solstice peaks before midnight, but during the June solstice, the EPIs mainly occur after midnight. The occurrence rate of EPIs has a positive correlation with solar activity. The distribution of topside scintillation occurrence is relatively consistent with EPIs, but during the June solstice, the scintillation occurrence rate remains at a very low level. (2) The midlatitude irregularities mainly occur after midnight, and their occurrence rate is negatively correlated with solar activity. Midlatitude irregularities mainly occur during the solstices, concentrated over the Pacific region during the June solstice and over the Pacific American sector during the December solstice. Especially, the distribution of midlatitude irregularities has hemispheric asymmetry, with a higher occurrence rate in the winter hemisphere. However, the occurrence of midlatitude scintillation is comparable in both hemispheres during the June solstice, and it concentrates in the southern hemisphere during the December solstice. (3) The EPIs concentrate more at the altitudes of Swarm A, while the midlatitude irregularities mainly occur at the altitudes of Swarm B. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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14 pages, 5390 KiB

Open AccessArticle

The Comparison of Electron Density between CSES In Situ and Ground-Based Observations in China

by Jing Liu, Tong Xu, Zonghua Ding and Xuemin Zhang

Remote Sens. 2022, 14(18), 4498; https://doi.org/10.3390/rs14184498 - 9 Sep 2022

Cited by 2 | Viewed by 1691

Abstract

As the observation accuracy of parameters in the ionosphere cannot be directly checked, the comparison with other observations is the main way to evaluate the data quality of satellite measurements. Through the comparative analysis between the in situ electron density (Ne) observed by [...] Read more.

As the observation accuracy of parameters in the ionosphere cannot be directly checked, the comparison with other observations is the main way to evaluate the data quality of satellite measurements. Through the comparative analysis between the in situ electron density (Ne) observed by the China Seismo-Electromagnetic Satellite (CSES) and Ne at about 500 km altitude detected by Qujing Incoherent Scatter Radar (ISR), it was found that the pattern of CSES Ne is consistent with that of ISR Ne, and the correlation coefficient between the two sets of data is above 0.88 for different groups according to the magnitude. The value of CSES Ne is lower than that of ISR Ne, and the median value of the ratio for the difference between the conjugate data is 84.04%. Based on the comparison in the daytime between CSES Ne and ionosonde observations in China, it was found that the trend of the two datasets is mostly similar, and the correlation coefficient in some locations can reach up to 0.7. The distribution of CSES Ne and correlation coefficients at different latitudes show that the relationship is relatively better around the peak of the equatorial ionization anomaly (EIA). The differences in the value between CSES Ne and ionosonde data also exist, the relative change of which is about 80–95% in the daytime. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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17 pages, 20234 KiB

Open AccessArticle

A Novel Method for Improving Quality of Oblique Incidence Sounding Ionograms Based on Eigenspace-Based Beamforming Technology and Capon High-Resolution Range Profile

by Wuyong Zhang, Tongxin Liu, Guobin Yang, Chunhua Jiang, Yaogai Hu, Ting Lan and Zhengyu Zhao

Remote Sens. 2022, 14(17), 4305; https://doi.org/10.3390/rs14174305 - 1 Sep 2022

Cited by 3 | Viewed by 1437

Abstract

Ground-based oblique incidence sounding (OIS) is an important means to investigate the ionosphere. As the OIS ionogram is a visual representation of the OIS parameters, such as group distance and maximum usable frequency (MUF), it is of great significance for improving the quality [...] Read more.

Ground-based oblique incidence sounding (OIS) is an important means to investigate the ionosphere. As the OIS ionogram is a visual representation of the OIS parameters, such as group distance and maximum usable frequency (MUF), it is of great significance for improving the quality and the range resolution. This will facilitate the automatic interpretation and inversion of OIS ionograms to obtain the fine structure and spatial–temporal evolutions of the ionosphere. In this paper, a novel OIS signal processing scheme is proposed based on the Eigenspace-based (ESB) beamforming technology and Capon high-resolution range profile (HRRP). First, by applying the ESB beamformer to a compact L-shaped antenna array, the energy of the OIS signals received by multiple antennas can be added, while the interference and noise will be suppressed. Subsequently, the Capon HRRP algorithm is used to improve the range resolution. This is achieved due to the slow variation in the characteristics of the ionosphere resulting in good short-term coherence of the narrowband signals. The experimental results show that the two-stage signal-processing method significantly improves the imaging quality of OIS ionograms. In particular, the structure inside the ionosphere and its temporal and spatial evolution can be observed more precisely after the range resolution of the OIS ionogram is improved; therefore, it has great application potential. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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13 pages, 3834 KiB

Open AccessTechnical Note

Driver of the Positive Ionospheric Storm over the South American Sector during 4 November 2021 Geomagnetic Storm

by Changzhi Zhai, Shenquan Tang, Wenjie Peng, Xiaoyun Cheng and Dunyong Zheng

Remote Sens. 2023, 15(1), 111; https://doi.org/10.3390/rs15010111 - 25 Dec 2022

Cited by 15 | Viewed by 1879

Abstract

During geomagnetic storms, ionospheric storms can be driven by several mechanisms. Observations performed using ground- and space-based instruments were used to reveal the driver of the positive ionospheric storm over the South American sector during the 4 November 2021 geomagnetic storm. The positive [...] Read more.

During geomagnetic storms, ionospheric storms can be driven by several mechanisms. Observations performed using ground- and space-based instruments were used to reveal the driver of the positive ionospheric storm over the South American sector during the 4 November 2021 geomagnetic storm. The positive storm appeared from 10:30 UT to 18:00 UT and covered the region from 40°S to 20°N. The maximum magnitudes of TEC (Total Electron Content) enhancement and relative TEC enhancement were about 20 TECU and 100%, respectively. Defense Meteorological Satellite Program (DMSP) also observed a significant electron density increase over South America and the eastern Pacific Ocean. In the meantime, about 50% ∑O/N₂ enhancement was observed by the Global-scale Observations of the Limb and Disk (GOLD) satellite at low latitudes. Ionosonde observations (AS00Q and CAJ2M) registered an ~80 km uplift in F2 peak height (HmF2) and a prominent F2 peak electron density (NmF2) increase ~3 h after the uplift. A prominent enhancement in the cross-polar cap potential (CPCP) in the southern hemisphere was also observed by Super Dual Auroral Radar Network (SuperDARN) one hour earlier than the HmF2 uplift. Measurements of the Ionospheric Connection Explorer satellite (ICON) showed that the outward E×B drift was enhanced significantly and that the horizontal ion drift was poleward. According to the ICON ion drift observations, the HmF2 uplift was caused by an electric field rather than equatorward neutral wind. We propose that the enhanced eastward electric field dominated the positive ionospheric storm and that the thermospheric composition variation may have also contributed. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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12 pages, 5405 KiB

Open AccessTechnical Note

Longitudinal Evolution of Storm-Enhanced Densities: A Case Study

by Bo Li, Huijun Le, Wenbo Li, Yiding Chen and Libo Liu

Remote Sens. 2022, 14(24), 6340; https://doi.org/10.3390/rs14246340 - 14 Dec 2022

Cited by 2 | Viewed by 1958

Abstract

Due to the limitations on observational data, most storm-enhanced density (SED) studies have focused on the North American sector. The complete picture of the longitudinal evolution of SEDs is still not clear. In this study, we investigated the dynamic evolution of SEDs from [...] Read more.

Due to the limitations on observational data, most storm-enhanced density (SED) studies have focused on the North American sector. The complete picture of the longitudinal evolution of SEDs is still not clear. In this study, we investigated the dynamic evolution of SEDs from the European sector to the North American sector during a geomagnetic storm that occurred on the 15 July 2012, the main phase of which lasted nearly 30 h, maintaining the stable interplanetary magnetic field (IMF) and solar wind input conditions. Multiple data sets were analyzed, including convection data from the Super Dual Auroral Radar Network (SuperDARN), total electron contents (TECs) from the Madrigal database, plasma data from the Millstone Hill incoherent scatter radar (MHISR), solar wind and geomagnetic indices from OMNIWeb, and regional auroral electrojet indices from SuperMAG. The observations showed that the positions of SEDs shifted from local noon over the European sector towards dusk over the American sector and simultaneously moved to lower latitudes. The peak values of SED TECs were found to be greater in the European sector and to decrease with universal time. A double SED phenomenon appeared in the North American sector, which is the first of its kind to be reported. Further analysis showed that the temporal and spatial changes in the SEDs were associated with the eastward auroral electrojet. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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11 pages, 1048 KiB

Open AccessTechnical Note

Variations in the Equatorial Ionospheric F Region Current during the 2022 Tonga Volcanic Eruption

by Hui Wang, Hao Xia and Kedeng Zhang

Remote Sens. 2022, 14(24), 6241; https://doi.org/10.3390/rs14246241 - 9 Dec 2022

Cited by 8 | Viewed by 1669

Abstract

In this work, the temporal variations in the ionospheric F region current (FRC) during the 2022 volcanic eruption in Tonga are reported for the first time. The FRC increased and underwent several polarity reversals following the eruption, as observed by the dual Swarm [...] Read more.

In this work, the temporal variations in the ionospheric F region current (FRC) during the 2022 volcanic eruption in Tonga are reported for the first time. The FRC increased and underwent several polarity reversals following the eruption, as observed by the dual Swarm satellites. By combining neutral wind observations derived from the Ionospheric Connection Explorer (ICON) satellite, we attempt to reveal the potential physical mechanisms responsible for these variations. The ICON and Swarm satellites were located at almost the same distance from the epicenter of the volcanic wave, thus providing a good opportunity for analyzing coordinated observations. The F-layer neutral wind data reflect eastward and westward fluctuations that are basically consistent with the polarity reversals identified in the FRC. The E-layer neutral wind also exhibits polarity reversals that affect the equatorial ionosphere electron density anomaly. These results show that the atmospheric fluctuations caused by the analyzed volcanic eruption affected the wind pattern distribution in the E-F region, thus further affecting the spatial distribution of the FRC and electron density in the F layer. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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10 pages, 1711 KiB

Open AccessTechnical Note

The Temporal Evolution of F-Region Equatorial Ionization Anomaly Owing to the 2022 Tonga Volcanic Eruption

by Kedeng Zhang, Hui Wang, Yunfang Zhong, Hao Xia and Chengyu Qian

Remote Sens. 2022, 14(22), 5714; https://doi.org/10.3390/rs14225714 - 11 Nov 2022

Cited by 8 | Viewed by 1726

Abstract

The dynamic evolutions of the noon ionospheric Equatorial Ionization Anomaly (EIA) owing to the 2022 Tonga volcanic eruption were investigated using the ionospheric plasma measurements from the Swarm satellite, the science experiment of the Constellation Observing Systems for Meteorology, Ionosphere, and Climate (COSMIC) [...] Read more.

The dynamic evolutions of the noon ionospheric Equatorial Ionization Anomaly (EIA) owing to the 2022 Tonga volcanic eruption were investigated using the ionospheric plasma measurements from the Swarm satellite, the science experiment of the Constellation Observing Systems for Meteorology, Ionosphere, and Climate (COSMIC) mission, and the thermospheric wind observations from the Ionospheric Connection Explorer (ICON). At 14.1 universal time (UT), the noon EIA was enhanced for the upward plasma drifts, when the F₂-layer was significantly uplifted from 360 km to 410 km. At 15.6 UT, because of the downward drifts, the intensity of the EIA reduced, and hmF₂ decreased to 270 km. At 17–18 UT, the EIA recovered and reformed, and hmF₂ increased to 350 km. A two-peak structure in the plasma was observed at Swarm altitudes. The temporal evolution might be related to the vertical plasma drifts (both downward and upward) from the E-region electric field. Full article

(This article belongs to the Special Issue Applications of Remote Sensing in Monitoring Ionospheric Physics and Ionospheric Weather Forecasting)

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