Research

13 pages, 2652 KiB

Open AccessArticle

Nonlinear Three-Dimensional Simulations of the Gradient Drift and Secondary Kelvin–Helmholtz Instabilities in Ionospheric Plasma Clouds

by Lujain Almarhabi, Chirag Skolar, Wayne Scales and Bhuvana Srinivasan

Atmosphere 2023, 14(4), 676; https://doi.org/10.3390/atmos14040676 - 03 Apr 2023

Viewed by 995

Abstract

A newly developed three-dimensional electrostatic fluid model solving continuity and current closure equations aims to study phenomena that generate ionospheric turbulence. The model is spatially discretized using a pseudo-spectral method with full Fourier basis functions and evolved in time using a four-stage, fourth-order [...] Read more.

A newly developed three-dimensional electrostatic fluid model solving continuity and current closure equations aims to study phenomena that generate ionospheric turbulence. The model is spatially discretized using a pseudo-spectral method with full Fourier basis functions and evolved in time using a four-stage, fourth-order Runge Kutta method. The 3D numerical model is used here to investigate the behavior and evolution of ionospheric plasma clouds. This problem has historically been used to study the processes governing the evolution of the irregularities in the F region of the ionosphere. It has been shown that these artificial clouds can become unstable and structure rapidly (i.e., cascade to smaller scales transverse to the ambient magnetic field). The primary mechanism which causes this structuring of ionospheric clouds is the

E \times B

, or the gradient drift instability (GDI). The persistence and scale sizes of the resulting structures cannot be fully explained by a two-dimensional model. Therefore, we suggest here that the inclusion of three-dimensional effects is key to a successful interpretation of mid-latitude irregularities, as well as a prerequisite for a credible simulation of these processes. We investigate the results of 2D and 3D nonlinear simulations of the GDI and secondary Kelvin–Helmholtz instability (KHI) in plasma clouds for three different regimes: highly collisional (≈200

km

), collisional (≈300

km

), and inertial (≈450

km

). The inclusion of inertial effects permits the growth of the secondary KHI. For the three different regimes, the overall evolution of structuring of plasma cloud occurs on longer timescales in 3D simulations. The inclusion of three-dimensional effects, in particular, the ambipolar potential in the current closure equation, introduces an azimuthal “twist“ about the axis of the cloud (i.e., the magnetic field

B

). This azimuthal “twist” is observed in the purely collisional regime, and it causes the perturbations to have a non-flute-like character (

k_{‖} \neq 0

). However, for the 3D inertial simulations, the cloud rapidly diffuses to a state in which the sheared azimuthal flow is substantially reduced; subsequently, the cloud becomes unstable and structures, by retaining the flute-like character of the perturbations (

k_{‖} = 0

). Full article

(This article belongs to the Special Issue Ionospheric Science and Ionosonde Applications)

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15 pages, 8754 KiB

Open AccessArticle

Separation of Ambient Radio Noise and Radio Signals Received via Ionospheric Propagation

by Ben A. Witvliet, Rosa M. Alsina-Pagès, David Altadill, Erik van Maanen and Geert Jan Laanstra

Atmosphere 2023, 14(3), 529; https://doi.org/10.3390/atmos14030529 - 09 Mar 2023

Cited by 2 | Viewed by 1738

Abstract

Systems for atmospheric research and wireless communication use the High Frequency (HF) radio spectrum. At these frequencies, typically up to 20 MHz, the ambient electromagnetic noise is stronger than the noise generated by the receiver itself, thereby limiting the sensitivity of the instruments. [...] Read more.

Systems for atmospheric research and wireless communication use the High Frequency (HF) radio spectrum. At these frequencies, typically up to 20 MHz, the ambient electromagnetic noise is stronger than the noise generated by the receiver itself, thereby limiting the sensitivity of the instruments. Especially in urban areas, the noise level is high. In remote rural environments, where artificial noise sources are absent, a much lower noise level is observed. It has been shown that this noise arrives via ionospheric propagation and consists of impulsive noise from lightning and a background component that resembles additive white Gaussian noise. To establish the absolute field strength of this background noise component, a direction- and polarization-agnostic antenna is realized by adding the power of two orthogonal antenna elements in the digital domain. To suppress radio signals arriving via ionospheric propagation—of which the spectral and temporal aspects are not known a priori—a novel adaptive filter is demonstrated that separates the background noise from the radio signals in the joint frequency-time domain. This method is demonstrated using measurements from a polarimetric experiment on 7 MHz in a remote rural area in Catalonia. The results are submitted to the International Telecommunication Union for the validation of ambient noise models. Full article

(This article belongs to the Special Issue Ionospheric Science and Ionosonde Applications)

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13 pages, 3256 KiB

Open AccessEditor’s ChoiceArticle

Airglow Observation and Statistical Analysis of Plasma Bubbles over China

by Xin Ma, Mengjie Wu, Peng Guo and Jing Xu

Atmosphere 2023, 14(2), 341; https://doi.org/10.3390/atmos14020341 - 08 Feb 2023

Viewed by 1278

Abstract

Airglow observation is a very effective method to investigate plasma bubbles, and can obtain their horizontal structure. In this study, the image processing method was used to process airglow data, including image enhancement, azimuth correction, and image projection, and the clear image products [...] Read more.

Airglow observation is a very effective method to investigate plasma bubbles, and can obtain their horizontal structure. In this study, the image processing method was used to process airglow data, including image enhancement, azimuth correction, and image projection, and the clear image products of equatorial plasma bubbles (EPBs) were obtained. Based on the optical data of the airglow imager in Hainan, we investigated the main optical features of EPBs, and statistically analyzed the occurrence of EPBs from September 2014 to August 2015. The observation results show that EPB exhibits plume-shaped structures, usually tilting westward, and EPB extends to a long distance along the geomagnetic field lines. It is found that the west wall of EPB is relatively stable, while there are some bifurcations on the east wall of EPB, and the bifurcation of EPB becomes more pronounced with time. Moreover, the spatial scale of EPB gradually increases with time, which is about several hundred kilometers, and the drift velocity of EPB is in the range of 40–130 m/s (+/−20 m/s). The statistical results show that EPBs mainly occur in the months of September to November and February to April, with a higher occurrence rate. In terms of seasonal occurrence, EPBs tend to appear more frequently in spring and autumn, and the occurrence rate of EPBs is relatively low in winter and summer. Full article

(This article belongs to the Special Issue Ionospheric Science and Ionosonde Applications)

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28 pages, 11346 KiB

Open AccessEditor’s ChoiceArticle

Identification of Large-Scale Travelling Ionospheric Disturbances (LSTIDs) Based on Digisonde Observations

by Ioanna Tsagouri, Anna Belehaki, Konstantinos Koutroumbas, Konstantinos Tziotziou and Themistocles Herekakis

Atmosphere 2023, 14(2), 331; https://doi.org/10.3390/atmos14020331 - 07 Feb 2023

Cited by 3 | Viewed by 2187

Abstract

In this paper we analyze Digisonde observations obtained in the European region to specify the effects of large-scale travelling ionospheric disturbances (LSTIDs) on the ionospheric characteristics that define the conditions in the bottomside ionosphere. While this type of disturbances affects all frequency ranges [...] Read more.

In this paper we analyze Digisonde observations obtained in the European region to specify the effects of large-scale travelling ionospheric disturbances (LSTIDs) on the ionospheric characteristics that define the conditions in the bottomside ionosphere. While this type of disturbances affects all frequency ranges in the F region, the most pronounced effect is detected in the foF2 critical frequency, where the density is the highest. During LSTID activity, a significant uplifting of the F2 layer is observed to accompany an oscillation pattern in the foF2. Concurrent variations in the height of the peak electron density hmF2 and the corresponding scale height, Hm are also observed. These findings are used to propose a new methodology for the identification of LSTIDs, comprising a combination of different criteria. The efficiency of the proposed methodology is tested at middle latitudes during geomagnetically quiet and disturbed intervals as well as during time periods of lower atmosphere forcing affecting the ionosphere. Full article

(This article belongs to the Special Issue Ionospheric Science and Ionosonde Applications)

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16 pages, 49855 KiB

Open AccessArticle

Study of Ionosphere Irregularities over the Iberian Peninsula during Two Moderate Geomagnetic Storms Using GNSS and Ionosonde Observations

by Saioa A. Campuzano, Fernando Delgado-Gómez, Yenca Migoya-Orué, Gracia Rodríguez-Caderot, Miguel Herraiz-Sarachaga and Sandro M. Radicella

Atmosphere 2023, 14(2), 233; https://doi.org/10.3390/atmos14020233 - 24 Jan 2023

Viewed by 1660

Abstract

Studies on the irregularities of the ionosphere during disturbed geomagnetic conditions are fundamental to understanding the complex dynamics taking place in the upper atmosphere. In this work, different data sources are used to study the ionosphere effects of two moderate geomagnetic storms, 26–27 [...] Read more.

Studies on the irregularities of the ionosphere during disturbed geomagnetic conditions are fundamental to understanding the complex dynamics taking place in the upper atmosphere. In this work, different data sources are used to study the ionosphere effects of two moderate geomagnetic storms, 26–27 February 2014 and 17–18 September 2021, over the Iberian Peninsula. Data are obtained from digital ionosondes in Spain, Italy and Greece; the Global Navigation Satellite System (GNSS) derived Total Electron Content (TEC) and Rate Of TEC Index (ROTI) from several receiver stations in Spain, Portugal and Morocco; and the UPC Quarter-of-an-hour time resolution Rapid GIM (UQRG), vertical TEC global ionosphere maps (GIMs), produced at 15 min intervals by the Universitat Politecnica de Catalunya (UPC, Spain). This analysis showed that, during the two moderate storms, spread-F and high values of ROTI, indicating the presence of irregularities, are found in a very localized area (Southern Iberian Peninsula and northwest Africa) and local times (night-time). However, no irregularities are found eastwards and northwards of the location indicated. We propose some possible explanations for these observations for both the storms, one of them related to the position of the Equatorial Ionosphere Anomaly (EIA) and the other one attributed to the Perkins’ instabilities. Full article

(This article belongs to the Special Issue Ionospheric Science and Ionosonde Applications)

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21 pages, 4883 KiB

Open AccessArticle

Performance Analysis of a Portable Low-Cost SDR-Based Ionosonde

by Oleksandr Koloskov, Anton Kashcheyev, Oleksandr Bogomaz, Andriy Sopin, Bogdan Gavrylyuk and Andriy Zalizovski

Atmosphere 2023, 14(1), 159; https://doi.org/10.3390/atmos14010159 - 11 Jan 2023

Cited by 4 | Viewed by 1961

Abstract

This work presents a software-defined radio ionosonde (ISDR) developed at the Abdus Salam International Centre for Theoretical Physics (Italy) and the Institute of Radio Astronomy (Ukraine) and installed at the Ukrainian Antarctic Station in 2017. For the first time, the results of the [...] Read more.

This work presents a software-defined radio ionosonde (ISDR) developed at the Abdus Salam International Centre for Theoretical Physics (Italy) and the Institute of Radio Astronomy (Ukraine) and installed at the Ukrainian Antarctic Station in 2017. For the first time, the results of the long-term data comparison of the ISDR with the conventional ionosonde IPS-42 produced by KEL Aerospace are presented and discussed. The matching of the ionograms obtained during the whole year of 2021, as well as a comparison of the critical frequencies and virtual heights of F, E, and Es layers manually scaled from the ionograms showed that the ISDR has a similar level of performance to IPS-42. At the same time, the ISDR is a more versatile instrument that supports a bistatic operation, provides Doppler measurements and polarization information, and has a significantly lower cost and transmission power. Different configurations of the ISDR are considered. The basic configuration allows for using the ISDR as a conventional vertical ionospheric sounder. An enhanced configuration of the ISDR allows for oblique sounding, as well as polarization information that enables the O- and X-propagation modes of the ionospheric signal to be distinguished. The enhanced passive version of the ISDR was successfully tested onboard the research vessel “Noosfera” on distances up to 1,400 km from the transmitting ISDR. Full article

(This article belongs to the Special Issue Ionospheric Science and Ionosonde Applications)

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21 pages, 6185 KiB

Open AccessArticle

Evidence for the Magnetoionic Nature of Oblique VHF Reflections from Midlatitude Sporadic-E Layers

by Chris Deacon, Cathryn Mitchell, Robert Watson and Ben A. Witvliet

Atmosphere 2022, 13(12), 2027; https://doi.org/10.3390/atmos13122027 - 02 Dec 2022

Cited by 1 | Viewed by 1554

Abstract

Mid-latitude sporadic-E (Es) is an intermittent phenomenon of the lower E region of the ionosphere. Es clouds are thin, transient, and patchy layers of intense ionization, with ionization densities which can be much higher than in the background ionosphere. Oblique reflection of radio [...] Read more.

Mid-latitude sporadic-E (Es) is an intermittent phenomenon of the lower E region of the ionosphere. Es clouds are thin, transient, and patchy layers of intense ionization, with ionization densities which can be much higher than in the background ionosphere. Oblique reflection of radio signals in the very high frequency (VHF) range is regularly supported, but the mechanism for it has never been clearly established—specular reflection, scattering, and magnetoionic double refraction have all been suggested. This article proposes using the polarization behaviour of signals reflected from intense midlatitude sporadic-E clouds as an indicator of the true reflection mechanism. Results are presented from a measurement campaign in the summer of 2018, which gathered a large amount of data at a receiving station in the UK using 50 MHz amateur radio beacons as signal sources. In all cases the signals received were elliptically polarized, despite being transmitted with linear polarization; there were also indications that polarization behaviour varied systematically with the orientation of the path to the geomagnetic field. This represents, for all the examples recorded, clear evidence that signals were reflected from midlatitude Es by magnetoionic double refraction. Full article

(This article belongs to the Special Issue Ionospheric Science and Ionosonde Applications)

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13 pages, 8020 KiB

Open AccessArticle

Directivity of Coseismic Ionospheric Disturbances Propagation Following the 2016 West Sumatra Earthquake Using Three-Dimensional Tomography GNSS-TEC

by Mokhamad Nur Cahyadi, Deasy Arisa, Ihsan Naufal Muafiry, Buldan Muslim, Ririn Wuri Rahayu, Meilfan Eka Putra, Mega Wulansari, Bambang Setiadi, Andria Arisal, Pakhrur Razi and Syachrul Arief

Atmosphere 2022, 13(9), 1532; https://doi.org/10.3390/atmos13091532 - 19 Sep 2022

Cited by 1 | Viewed by 1866

Abstract

Ionospheric disturbances caused by the 2016 West Sumatra earthquake have been studied using total electron content (TEC) measurements by Global Navigation Satellite System (GNSS) observation stations evenly distributed in Sumatra and Java, Indonesia. Previous observation focused on the coseismic ionospheric disturbances (CID) detected [...] Read more.

Ionospheric disturbances caused by the 2016 West Sumatra earthquake have been studied using total electron content (TEC) measurements by Global Navigation Satellite System (GNSS) observation stations evenly distributed in Sumatra and Java, Indonesia. Previous observation focused on the coseismic ionospheric disturbances (CID) detected 11–16 min after the earthquake. The maximum TEC amplitude measured was 2.9 TECU (TEC Unit) with speed between 1 and 1.72 km/s. A comprehensive analysis needs to be done to see how the growth and direction of the movement of the CID due to the earthquake is using the 3D tomography method. The dimensions of 3D tomographic model are setup to 1° × 1.2° × 75 km. The continuity constraints were used to stabilize the solution, and multiple resolution tests with synthetic data were conducted to evaluate the precision of the results. This research focuses on the anomalous movement of the ionosphere observed in three dimensions. From the model, the positive anomaly initially appeared 11 min after the earthquake at the altitude of 300 km, which is the highest ionization layer and correspond to the electron density profile using IRI model. The anomalous movement appeared 12 min after the mainshock and moved 1° toward the geomagnetic field every minute. The density anomaly of the ionosphere began to weaken 8 min after the appearance of CID. To check the accuracy of the 3D tomography model, we carried out two types of tests, namely checkerboard resolution test and the second resolution test. Full article

(This article belongs to the Special Issue Ionospheric Science and Ionosonde Applications)

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14 pages, 2783 KiB

Open AccessArticle

Investigation of Two Prediction Models of Maximum Usable Frequency for HF Communication Based on Oblique- and Vertical-Incidence Sounding Data

by Jian Wang, Yafei Shi and Cheng Yang

Atmosphere 2022, 13(7), 1122; https://doi.org/10.3390/atmos13071122 - 15 Jul 2022

Cited by 9 | Viewed by 1667

Abstract

As one of the key technologies of HF communication, the maximum usable frequency (MUF) prediction method has been widely discussed. To experimentally confirm the reliability of commonly used MUFs prediction models for high-frequency communication, we have compared maximum observed frequencies (MOFs) and predicted [...] Read more.

As one of the key technologies of HF communication, the maximum usable frequency (MUF) prediction method has been widely discussed. To experimentally confirm the reliability of commonly used MUFs prediction models for high-frequency communication, we have compared maximum observed frequencies (MOFs) and predicted MUFs to assess the accuracy of two typical prediction models. The root-mean-square error (RMSE) and relative RMSE (RRMSE) between oblique sounding MOFs and the predicted MUFs were used to assess the model’s accuracy. The oblique sounding path was from Changchun to Jinyang, and the vertical-sounding ionosonde was located in Beijing, which was approximately the midpoint of the oblique sounding circuit. The statistical analysis results show that: (a) the trend of prediction results from the Lockwood and the Istituto Nazionale di Geofisica e Vulcanologia (INGV) model are in good agreement with the observations: the mean RMSE and RRMSE of the INGV model are less than those of the Lockwood model; (b) in the four different periods (sunrise, daytime, sunset, and nighttime) of the whole day, the maximum difference of RMSE between the Lockwood and INGV model is 0.14 MHz (the INGV performs better than the LWM), with the corresponding differences of RRMSE being 0.31% at sunrise and 0.68% at daytime; (c) in the four seasons of spring, summer, autumn, and winter, the minimum RMSE values of the Lockwood and INGV models are 1.51 MHz and 1.37 MHz, respectively, which are obtained in winter, and the corresponding RRMSEs are 11.47% and 11.79%, respectively; (d) in the high and low solar activity epochs, the mean RMSEs of the Lockwood and INGV models are 1.63 MHz, and 1.54 MHz, with corresponding mean RRMSE values of 11.47% and 11.55%. In conclusion, the INGV model is more suitable for MUF prediction over Beijing and its adjacent mid-latitude regions from the RMSE comparison of the two models. Full article

(This article belongs to the Special Issue Ionospheric Science and Ionosonde Applications)

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14 pages, 1283 KiB

Open AccessArticle

Multiple Cusp Signatures in Ionograms Associated with Rocket-Induced Infrasonic Waves

by Justin Mabie and Terence Bullett

Atmosphere 2022, 13(6), 958; https://doi.org/10.3390/atmos13060958 - 12 Jun 2022

Viewed by 1306

Abstract

We are interested in understanding how and when infrasonic waves propagate in the thermosphere, specifying the physical properties of those waves, and understanding how they affect radio wave propagation. We use a combination of traditional ionosonde observations and fixed frequency Doppler soundings to [...] Read more.

We are interested in understanding how and when infrasonic waves propagate in the thermosphere, specifying the physical properties of those waves, and understanding how they affect radio wave propagation. We use a combination of traditional ionosonde observations and fixed frequency Doppler soundings to make high quality observations of vertically propagating infrasonic waves in the lower thermosphere/bottom side ionosphere. The presented results are the first simultaneous observations of infrasonic wave-induced deformations in ionograms and high-time-resolution observations of corresponding plasma displacements. Deformations in ionospheric echoes, which manifest as additional cusps and range variations, are shown to be caused by infrasonic wave-induced plasma displacements. Full article

(This article belongs to the Special Issue Ionospheric Science and Ionosonde Applications)

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15 pages, 5438 KiB

Open AccessArticle

Analysis of Pre-Earthquake Space Electric Field Disturbance Observed by CSES

by Zhong Li, Baiyi Yang, Jianping Huang, Huichao Yin, Xuming Yang, Haijun Liu, Fuzhi Zhang and Hengxin Lu

Atmosphere 2022, 13(6), 934; https://doi.org/10.3390/atmos13060934 - 09 Jun 2022

Cited by 9 | Viewed by 2021

Abstract

In order to explore the abnormal disturbance of the space electric field caused by earthquakes using the electric field data of the ULF and VLF frequency bands of the electric field observed by the ZH-1 satellite, and taking the Mw7.7 earthquake in the [...] Read more.

In order to explore the abnormal disturbance of the space electric field caused by earthquakes using the electric field data of the ULF and VLF frequency bands of the electric field observed by the ZH-1 satellite, and taking the Mw7.7 earthquake in the Caribbean Sea in the southern sea area of Cuba on 29 January 2020 as an example, the signal-to-noise ratio of the NAA and NLK artificial source VLF transmitting stations in the Northern Hemisphere and the height of the lower ionosphere was calculated. The disturbance of the electric field in the ULF band was extracted using the S-G filtering method. The results indicate that: (1) The ionospheric anomaly caused by this earthquake appeared 20 days before the earthquake, and before the earthquake, there were significant anomalous changes in all parameters within the pregnant seismic zone. The signal-to-noise ratios of the NAA and NLK artificial source transmitter stations decreased by 30%, and the height of the low ionosphere decreased by 5–10 km, while there were anomalous perturbations in several orbits of the ULF electric field, and the magnitude of the perturbations exceeded three times the standard deviation. (2) The SNR of the artificial source transmitting stations before and after the earthquake was significantly reduced in the third period before the earthquake and recovered after the earthquake. (3) The low ionospheric height appears to be reduced before the earthquake and recovers after the earthquake. (4) The decrease in the S/N ratio occurred simultaneously with the decrease in ionospheric height 15 days–10 days before the earthquake. This provides a reference for extracting pre-earthquake ionospheric precursor anomalies. Full article

(This article belongs to the Special Issue Ionospheric Science and Ionosonde Applications)

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