Research

26 pages, 32452 KiB

Open AccessArticle

Ionospheric Variations Induced by Thunderstorms in the Central Region of Argentina during the RELAMPAGO–CACTI Campaign

by Constanza Inés Villagrán Asiares, María Gabriela Nicora, Amalia Meza, María Paula Natali, Eldo Edgardo Ávila, Marcos Rubinstein and Farhad Rachidi

Atmosphere 2023, 14(9), 1386; https://doi.org/10.3390/atmos14091386 - 01 Sep 2023

Viewed by 929

Abstract

The ionosphere can be perturbed by solar and geomagnetic activity, earthquakes, thunderstorms, etc. In particular, electromagnetic pulses produced by thunderstorms can generate wave structures in the ionospheric plasma, which are known as atmospheric gravity waves (AGWs), which can be detected by measuring the [...] Read more.

The ionosphere can be perturbed by solar and geomagnetic activity, earthquakes, thunderstorms, etc. In particular, electromagnetic pulses produced by thunderstorms can generate wave structures in the ionospheric plasma, which are known as atmospheric gravity waves (AGWs), which can be detected by measuring the total electron content (TEC). We studied ionospheric variations resulting from thunderstorms on 10 November 2018, between 00:00 and 08:00 UTC, in the central region of Argentina, site of the RELAMPAGO–CACTI Project (Remote sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observations; Clouds, Aerosols, and Complex Terrain Interactions). Atmospheric electrical activity data were provided by the Earth Networks Total Lightning Network (ENTLN) and the TEC was computed from Global Navigation Satellite System (GNSS) measurements provided by the Argentinian Continuous Satellite Monitoring Network (RAMSAC by its Spanish acronym). We found AGWs with periods less than or equal to 100 min and peak-to-peak Differential Vertical Total Electron Content (DVTEC) amplitude values up to 1.35 TECU (1 total electron content unit

= 10^{16}

electrons/m

^{2}

). We observed that AGWs show the highest peak-to-peak amplitudes during intense thunderstorm periods. On a day without thunderstorms, the peak-to-peak amplitudes were approximately 2.91 times lower. Full article

(This article belongs to the Special Issue Recent Advances in Ionosphere Observation and Investigation)

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24 pages, 18199 KiB

Open AccessArticle

Impact of ICME- and SIR/CIR-Driven Geomagnetic Storms on the Ionosphere over Hungary

by Kitti Alexandra Berényi, Andrea Opitz, Zsuzsanna Dálya, Árpád Kis and Veronika Barta

Atmosphere 2023, 14(9), 1377; https://doi.org/10.3390/atmos14091377 - 31 Aug 2023

Viewed by 988

Abstract

We investigate the differences between the effects of geomagnetic storms due to Interplanetary Coronal Mass Ejections (ICME) and due to Stream Interaction Regions or Corotating Interaction Regions (SIR/CIR) on the ionospheric F2-layer during the maximum of solar cycle 24. We have created a [...] Read more.

We investigate the differences between the effects of geomagnetic storms due to Interplanetary Coronal Mass Ejections (ICME) and due to Stream Interaction Regions or Corotating Interaction Regions (SIR/CIR) on the ionospheric F2-layer during the maximum of solar cycle 24. We have created a unique list of the ICME- and SIR/CIR-driven geomagnetic storm events for the time interval between November 2012 and October 2014. Finally, 42 clear ICME and 34 clear SIR/CIR events were selected for this analysis. The individual geomagnetic storm periods were grouped by seasons, time of day, and local time of Dst_min and were analyzed using three different methods: linear correlation analysis using 4-h averages of foF2 parameters and the geomagnetic indices (1st), daily variation of deltafoF2 (2nd), and 3D plotting: geomagnetic indices vs. time vs. deltafoF2 (3rd). The main phase day of the ICME- and SIR/CIR-induced geomagnetic storms was our main focus. We used manually evaluated ionospheric foF2 parameters measured at the Sopron ionosonde station and the geomagnetic indices (Kp, Dst, and AE) for this analysis. We have found that in most cases, the variation of the Dst index is the best indicator of the impact caused in the F2 layer. We conclude as well that the representation of the data by the third method gives a better description of the ICME and SIR/CIR-triggered storm behavior. In addition, our investigation shows that the SIR/CIR-related perturbations can be predicted with greater accuracy with the second method. Full article

(This article belongs to the Special Issue Recent Advances in Ionosphere Observation and Investigation)

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17 pages, 10460 KiB

Open AccessArticle

Insights on Polar Day Antarctica Radio Propagation Using Amateur Radio Beacons on Circumnavigating Balloons

by Todd McKinney, Nick Perlaky, Mike Newchurch and Bill Brown

Atmosphere 2023, 14(7), 1118; https://doi.org/10.3390/atmos14071118 - 05 Jul 2023

Cited by 2 | Viewed by 1405

Abstract

We deployed six pico balloons with 20 m transmitters (14.09 MHz) from Neumayer Station III in the 2022 Antarctic summer. Our objective was to evaluate ionospheric propagation in lower latitudes. Leveraging the Weak Signal Propagation Reporter (WSPR) protocol, we transmitted and received telemetry [...] Read more.

We deployed six pico balloons with 20 m transmitters (14.09 MHz) from Neumayer Station III in the 2022 Antarctic summer. Our objective was to evaluate ionospheric propagation in lower latitudes. Leveraging the Weak Signal Propagation Reporter (WSPR) protocol, we transmitted and received telemetry data on a global scale. Each balloon remained airborne for over a month, with one completing eight circumnavigations of the southern hemisphere, transmitting WSPR beacon data for 98 days. Our analysis focused on signal propagation characteristics in the polar ionosphere and surrounding regions, considering factors such as location relative to the WSPR network and solar elevation angles. Alignment between solar elevation angles at transmitting and receiving stations indicated a relationship with signal reception; lower solar elevation angles proved crucial for long-range propagation. We discovered that, beyond a solar angle of 60 degrees above the horizon, no decodes were recorded beyond 7500 km. Most signal spots were observed within a 1000–5000 km range and solar elevation angles ranging from 1 to 80 degrees. Over Antarctica, spot occurrences peaked around 4 UTC, particularly during the early hours of the day. Our findings demonstrate the usefulness of pico balloons for propagation studies, providing insights into the WSPR network’s coverage over Antarctica and surrounding lower latitudes. Full article

(This article belongs to the Special Issue Recent Advances in Ionosphere Observation and Investigation)

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12 pages, 4864 KiB

Open AccessCommunication

Ionospheric 14.5 Day Periodic Oscillation during the 2019 Antarctic SSW Event

by Jinze Li, Qiong Tang, Yiyun Wu, Chen Zhou and Yi Liu

Atmosphere 2023, 14(5), 796; https://doi.org/10.3390/atmos14050796 - 27 Apr 2023

Viewed by 1104

Abstract

The International Global Navigation Satellite Systems Service (IGS) ionospheric total electron content (TEC) data are used to study the periodic perturbation in the ionosphere during the 2019 Antarctic sudden stratospheric warming (SSW) event, a rare Southern Hemisphere minor SSW event in the last [...] Read more.

The International Global Navigation Satellite Systems Service (IGS) ionospheric total electron content (TEC) data are used to study the periodic perturbation in the ionosphere during the 2019 Antarctic sudden stratospheric warming (SSW) event, a rare Southern Hemisphere minor SSW event in the last 40 years. A 14.5 day periodic signal with a zonal wavenumber of 0 is observed in the mesosphere and the lower thermosphere (MLT) region and the ionosphere during this SSW period, which could be related to the lunar tide. The 14.5 day periodic disturbance in the IGS TEC exhibits local time dependence and latitudinal variation, with the maximum amplitude appearing between 1000 and 1600 LT in the equatorial ionization anomaly (EIA) crest regions. Additionally, the 14.5 day periodic oscillation shows an obvious longitudinal variability, with the weakest amplitude appearing in the longitudinal region of 30° W–60° E. Full article

(This article belongs to the Special Issue Recent Advances in Ionosphere Observation and Investigation)

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32 pages, 15329 KiB

Open AccessArticle

Possible Pre-Seismic Indications Prior to Strong Earthquakes That Occurred in Southeastern Mediterranean as Observed Simultaneously by Three VLF/LF Stations Installed in Athens (Greece)

by Dimitrios Z. Politis, Stelios M. Potirakis, Sudipta Sasmal, Filopimin Malkotsis, Dionisis Dimakos and Masashi Hayakawa

Atmosphere 2023, 14(4), 673; https://doi.org/10.3390/atmos14040673 - 01 Apr 2023

Cited by 2 | Viewed by 1289

Abstract

In this work, we present the analysis of VLF/LF sub-ionospheric propagation data to study anomalies possibly related to very recent strong (M > 5.5) earthquakes (EQs) that occurred in the southeastern Mediterranean in September–October 2021 and January 2022. We used the signal of [...] Read more.

In this work, we present the analysis of VLF/LF sub-ionospheric propagation data to study anomalies possibly related to very recent strong (M > 5.5) earthquakes (EQs) that occurred in the southeastern Mediterranean in September–October 2021 and January 2022. We used the signal of one transmitter located at Negev in Israel (29.7 kHz) as received by three VLF/LF receivers (two of them using identical SW and HW) installed, at a close distance to each other, in Athens (Greece). This study employed multiple methods and techniques to analyze the reception amplitude data to identify any possible EQ-related anomalies. More specifically, first, we used both statistical and criticality analysis methods such as the “nighttime fluctuation method” (NFM), the “terminator time method” (TTM), and the “natural time” (NT) analysis method. These methods have satisfactorily been applied in the past in a series of other studies leading to interesting results. Moreover, we additionally used two more analysis techniques focusing on the signal’s amplitude characteristics. The first is the wavelet analysis of the nighttime part of the signal’s amplitude. It is based on the Morlet wavelet function, aiming to unveil the possible existence of atmospheric gravity waves (AGWs) before EQ. The second is named “long wavelength propagation capability” (LWPC), which simulates the amplitude of the signal and is based on the reflection parameters of ionosphere and by searching for increases or decreases of the electron density profile of the ionospheric D layer concerning the shifts of the minima of terminator times (TTs) in the diurnal variation of the signal. Finally, in this work, we summarize our findings and discuss possible “pre-”, “co-”, and “post-” seismic effects as observed from all the work. Full article

(This article belongs to the Special Issue Recent Advances in Ionosphere Observation and Investigation)

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19 pages, 5395 KiB

Open AccessEditor’s ChoiceArticle

A Statistical Analysis of Sporadic-E Characteristics Associated with GNSS Radio Occultation Phase and Amplitude Scintillations

by Daniel J. Emmons, Dong L. Wu and Nimalan Swarnalingam

Atmosphere 2022, 13(12), 2098; https://doi.org/10.3390/atmos13122098 - 14 Dec 2022

Cited by 5 | Viewed by 1963

Abstract

Statistical GNSS-RO measurements of phase and amplitude scintillation are analyzed at the mid-latitudes in the local summer for a 100 km altitude. These conditions are known to contain frequent sporadic-E, and the S

_{4}

-

σ_{ϕ}

trends provide insight into the statistical [...] Read more.

Statistical GNSS-RO measurements of phase and amplitude scintillation are analyzed at the mid-latitudes in the local summer for a 100 km altitude. These conditions are known to contain frequent sporadic-E, and the S

_{4}

-

σ_{ϕ}

trends provide insight into the statistical distributions of the sporadic-E parameters. Joint two-dimensional S

_{4}

-

σ_{ϕ}

histograms are presented, showing roughly linear trends until the S

_{4}

saturates near 0.8. To interpret the measurements and understand the sporadic-E contributions, 10,000 simulations of RO signals perturbed by sporadic-E layers are performed using length, intensity, and vertical thickness distributions from previous studies, with the assumption that the sporadic-E layer acts as a Gaussian lens. Many of the key trends observed in the measurement histograms are present in the simulations, providing a key for understanding the complex mapping between layer characteristics and impacts on the GNSS-RO signals. Additionally, the inclusion of Kolmogorov turbulence and a diffusion-limited threshold on the lens strength/(vertical thickness)

^{2}

ratio helps to make the layers more physically realistic and improves agreement with the observations. Full article

(This article belongs to the Special Issue Recent Advances in Ionosphere Observation and Investigation)

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Graphical abstract

12 pages, 5228 KiB

Open AccessArticle

Ionospheric Disturbances after the 2022 Hunga Tonga-Hunga Ha’apai Eruption above Indonesia from GNSS-TEC Observations

by Ihsan Naufal Muafiry, Irwan Meilano, Kosuke Heki, Dudy D. Wijaya and Kris Adi Nugraha

Atmosphere 2022, 13(10), 1615; https://doi.org/10.3390/atmos13101615 - 03 Oct 2022

Cited by 9 | Viewed by 2056

Abstract

On 15 January 2022, a VEI 5 eruption occurred at the submarine Hunga Tonga-Hunga Ha’apai (HTHH) Volcano in the Southwest Pacific, causing an ash plume reaching a height of 50–55 km. The eruption generated strong acoustic-gravity waves in the near-field and stations all [...] Read more.

On 15 January 2022, a VEI 5 eruption occurred at the submarine Hunga Tonga-Hunga Ha’apai (HTHH) Volcano in the Southwest Pacific, causing an ash plume reaching a height of 50–55 km. The eruption generated strong acoustic-gravity waves in the near-field and stations all over the world recorded Lamb waves (LW) that travelled around the earth multiple times at a speed of ~0.3 km/s. Here we report ionospheric anomalies due to the LW over Indonesian islands, 5000–10,000 km away from the volcano, in terms of changes in total electron contents (TEC) using the nationwide network of GNSS stations. We detected ionospheric anomalies travelling above Indonesia several times both westward and eastward. The first passage of LW over Java caused strong TEC increases of >12 TECU. The wave circled the earth and returned to Java on subsequent days. The second passage was recorded early 1/17, the anomaly decayed to 6 TECU. We also detected the passage of long-path waves propagating from west to east. In addition to such anomalies, we examined the existence of ionospheric disturbances apparently propagating from the geomagnetic conjugate point of the volcano that could possibly emerge in Indonesia. However, their signatures in Indonesia were not clear. Full article

(This article belongs to the Special Issue Recent Advances in Ionosphere Observation and Investigation)

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21 pages, 15981 KiB

Open AccessArticle

A Systematic Study of 7 MHz Greyline Propagation Using Amateur Radio Beacon Signals

by Sam Lo, Nikola Rankov, Cathryn Mitchell, Benjamin Axel Witvliet, Talini Pinto Jayawardena, Gary Bust, William Liles and Gwyn Griffiths

Atmosphere 2022, 13(8), 1340; https://doi.org/10.3390/atmos13081340 - 22 Aug 2022

Cited by 3 | Viewed by 2320

Abstract

This paper investigates 7 MHz ionospheric radio wave propagation between pairs of distant countries that simultaneously lie on the terminator. This is known as greyline propagation. Observations of amateur radio beacon transmitters recorded in the Weak Signal Propagation Reporter (WSPR) database are used [...] Read more.

This paper investigates 7 MHz ionospheric radio wave propagation between pairs of distant countries that simultaneously lie on the terminator. This is known as greyline propagation. Observations of amateur radio beacon transmitters recorded in the Weak Signal Propagation Reporter (WSPR) database are used to investigate the times of day that beacon signals were observed during the year 2017. The WSPR beacon network consists of thousands of automated beacon transmitters and observers distributed over the globe. The WSPR database is a very useful resource for radio science as it offers the date and time at which a propagation path was available between two radio stations, as well as their precise locations. This paper provides the first systematic study of grey-line propagation between New Zealand/Eastern Australia and UK/Europe. The study shows that communications were predominantly made from the United Kingdom (UK) to New Zealand at around both sunset and sunrise times, whereas from New Zealand to the UK, communication links occurred mainly during UK sunrise hours. The lack of observations at the UK sunset time was particularly evident during the UK summer. The same pattern was found in the observations of propagation from Eastern Australia to UK, and from New Zealand and Eastern Australia to Italy and the surrounding regions in Europe. The observed asymmetry in reception pattern could possibly be due to the increase in electromagnetic noise across Europe in the summer afternoon/evening from thunderstorms. Full article

(This article belongs to the Special Issue Recent Advances in Ionosphere Observation and Investigation)

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