We use a network of “high-rate” geodetic Global Navigation Satellite System (GNSS) receivers and Ionospheric Scintillation Monitoring Receivers (ISMR) to characterize ionospheric irregularities and scintillation at high-latitudes during the 2024 Gannon storm. We especially focus on the available data from American Longitude sector covering Alaska and Canada. We show that presence of L-band diffractive scintillation observed at L1, L2, and L5 bands, with fading exceeding 10 dB. The scintillation was observed during several local time sectors possible indicating the scintillation-producing irregularities residing in the SED plume, polar cap patches, and auroral structures. We analyze the strength of the observed scintillation in terms of elevation/filed-aligned aspect angle, TEC, TEC gradients, decorrelation times, and local time occurrence. The spatial localization of scintillation-producing structures is aided by High latitude Ionospheric Data Assimilation 4D (H-IDA4D) TEC outputs at 5-minute time resolution. H-IDA4D assimilated slant-TEC data from 250 high-latitude ground-based GNSS receivers into IRI and E-CHAIM background models.

The amateur radio community is a global, highly engaged, and technical community with an intense interest in space weather, its underlying physics, and how it impacts radio communications. The large-scale observational capabilities of distributed instrumentation fielded by amateur radio operators and radio science enthusiasts offers a tremendous opportunity to advance the fields of heliophysics, radio science, and space weather. Well-established amateur radio networks like the RBN, WSPRNet, and PSKReporter already provide rich, ever-growing, long-term data of bottomside ionospheric observations. Up-and-coming purpose-built citizen science networks, and their associated novel instruments, offer opportunities for citizen scientists, professional researchers, and industry to field networks for specific science questions and operational needs. Here, we discuss the scientific and technical capabilities of the global amateur radio community, review methods of collaboration between the amateur radio and professional scientific community, and review recent peer-reviewed studies that have made use of amateur radio data and methods. Finally, we present recommendations submitted to the U.S. National Academy of Science Decadal Survey for Solar and Space Physics (Heliophysics) 2024–2033 for using amateur radio to further advance heliophysics and for fostering deeper collaborations between the professional science and amateur radio communities. Technical recommendations include increasing support for distributed instrumentation fielded by amateur radio operators and citizen scientists, developing novel transmissions of RF signals that can be used in citizen science experiments, developing new amateur radio modes that simultaneously allow for communications and ionospheric sounding, and formally incorporating the amateur radio community and its observational assets into the Space Weather R2O2R framework. Collaborative recommendations include allocating resources for amateur radio citizen science research projects and activities, developing amateur radio research and educational activities in collaboration with leading organizations within the amateur radio community, facilitating communication and collegiality between professional researchers and amateurs, ensuring that proposed projects are of a mutual benefit to both the professional research and amateur radio communities, and working towards diverse, equitable, and inclusive communities.

The ionosphere can impair the accuracy, availability and reliability of satellite-based positioning, navigation and timing. The Arctic region is particularly affected by strong ionospheric gradients and phase scintillation, posing a safety issue for critical infrastructure and operations. Ionospheric warning and impact maps can provide support to Arctic operations, but to produce such maps threshold values have to be determined. This study investigates how such thresholds can be derived from the GPS and Galileo satellite signals. Rapid changes in total electron content (TEC) or scintillation-induced receiver tracking errors could result in cycle slips or even loss of lock. Cycle slips and data outages are used as a measure of impact on the receiver in this paper. For Galileo, 73.6% of the impacts were cycle slips and 26.4% were outages, while for GPS, 29.3% of the impacts were cycle slips and 70.7% were outages. Considering the sum of cycle slips and outages, it is worth noting that the sum of impacts for Galileo signals is larger than for GPS. A range of possible explanations have been examined through hardware-in-the-loop simulations. The simulations showed that the GPS L2 signal was not adequately tracked during rapid TEC changes and TEC changes were underestimated, thus the GPS cycle slips, derived from L1 and L2 derived TEC changes, were not all registered. These results are important in designing threshold values for TEC and for scintillation impact maps as well as for the operation of GNSS equipment in the Arctic. In particular, the results show that ionospheric changes could be underestimated if GPS L1 and L2 were used in isolation from other dual frequency combinations. It is the first time this analysis has been made for Greenland and the first time that the dual frequency derivation of ionospheric delay using GPS L1 and L2 has been shown to underestimate large TEC gradients. This has important implications for informing GNSS operations that rely on GPS to provide reliable estimates of the ionosphere.

At around 04:14 UTC on the 15th January 2022, a major volcanic eruption began beneath the Tongan islands of Hunga Tonga and Hunga Ha’apai (175.4W, 20.5S). Located under only a shallow depth of water, the volcano rapidly launched a plume of super-heated ash and vapourised water upwards into the atmosphere. Over the next few hours, satellite observations reveal unprecedented large-scale concentric waves in the mid-stratosphere (near 40km altitude) radiating away from the eruption across the entire Pacific Ocean. In this presentation, we show brightness temperature perturbations in the 4.3 micron bands of the AIRS/Aqua, CrIS/Suomi-NPP and CrIS/JPSS-1 instruments that reveal three groups of atmospheric waves of special interest. First, an initial concentric wave is found travelling near the stratospheric speed of sound, likely to be an acoustic compression wave. There then follows a gap, which corresponds to phase speeds not permitted by theory, then a second group of waves likely to be gravity waves. These gravity waves are shown to be travelling near the maximum phase speed permitted, and there is a suggestion that some may travel the whole way around the globe in the tropics. Third, we observe small-scale gravity waves that pervade many thousands of kilometres across almost the entire Pacific Ocean, suggesting an extremely consistent heating source. All three of these wave observations are unprecedented in more than 20 years of stratospheric satellite observations, and this eruption may potentially have produced the first observations of an acoustic wave in the mid-stratosphere that can be measured from space. Now that we have space-borne instruments to observe it, this volcanic eruption provides a unique test of theoretical predictions of atmospheric wave phase speeds on some of the largest scales possible.

The January 2022 Hunga Tonga–Hunga Ha’apai eruption was one of the most explosive volcanic events of the modern era 1 , 2 , producing a vertical plume that peaked more than 50 km above the Earth 3 . The initial explosion and subsequent plume triggered atmospheric waves that propagated around the world multiple times 4 . A global-scale wave response of this magnitude from a single source has not previously been observed. Here we show the details of this response, using a comprehensive set of satellite and ground-based observations to quantify it from surface to ionosphere. A broad spectrum of waves was triggered by the initial explosion, including Lamb waves 5 , 6 propagating at phase speeds of 318.2 ± 6 m s −1 at surface level and between 308 ± 5 to 319 ± 4 m s −1 in the stratosphere, and gravity waves 7 propagating at 238 ± 3 to 269 ± 3 m s −1 in the stratosphere. Gravity waves at sub-ionospheric heights have not previously been observed propagating at this speed or over the whole Earth from a single source 8 , 9 . Latent heat release from the plume remained the most significant individual gravity wave source worldwide for more than 12 h, producing circular wavefronts visible across the Pacific basin in satellite observations. A single source dominating such a large region is also unique in the observational record. The Hunga Tonga eruption represents a key natural experiment in how the atmosphere responds to a sudden point-source-driven state change, which will be of use for improving weather and climate models.

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.

A case study is presented which demonstrates the value and validity of a novel approach to the use of consolidated amateur (‘ham’) radio reception reports as indicators of the presence of intense ionospheric sporadic E (Es). It is shown that the use of amateur data can provide an important supplement to other techniques, allowing the detection and tracking of Es where no suitable ionosonde or other measurements are available. The effectiveness of the approach is demonstrated by reference to ionosonde data, and the advantages and limitations of the technique are discussed.

The January 2022 Hunga Tonga–Hunga Ha’apai eruption was one of the most explosive volcanic events of the modern era, producing a vertical plume which peaked > 50km above the Earth. The initial explosion and subsequent plume triggered atmospheric waves which propagated around the world multiple times. A global-scale wave response of this magnitude from a single source has not previously been observed. Here we show the details of this response, using a comprehensive set of satellite and ground-based observations to quantify it from surface to ionosphere. A broad spectrum of waves was triggered by the initial explosion, including Lamb waves5,6 propagating at phase speeds of 318.2+/-6 ms-1 at surface level and between 308+/-5 to 319+/-4 ms-1 in the stratosphere, and gravity waves propagating at 238+/-3 to 269+/-3 ms-1 in the stratosphere. Gravity waves at sub-ionospheric heights have not previously been observed propagating at this speed or over the whole Earth from a single source. Latent heat release from the plume remained the most significant individual gravity wave source worldwide for > 12 hours, producing circular wavefronts visible across the Pacific basin in satellite observations. A single source dominating such a large region is also unique in the observational record. The Hunga Tonga eruption represents a key natural experiment in how the atmosphere responds to a sudden point-source-driven state change, which will be of use for improving weather and climate models.

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.

Sue Bowler talks to organizers Carole Mundell, Cathryn Mitchell and Patricia Schady about the first fully virtual National Astronomy Meeting in July

Abstract Severe space weather was identified as a risk to the UK in 2010 as part of a wider review of natural hazards triggered by the societal disruption caused by the eruption of the Eyjafjallajökull volcano in April of that year. To support further risk assessment by government officials, and at their request, we developed a set of reasonable worst‐case scenarios and first published them as a technical report in 2012 (current version published in 2020). Each scenario focused on a space weather environment that could disrupt a particular national infrastructure such as electric power or satellites, thus, enabling officials to explore the resilience of that infrastructure against severe space weather through discussions with relevant experts from other parts of government and with the operators of that infrastructure. This approach also encouraged us to focus on the environmental features that are key to generating adverse impacts. In this paper, we outline the scientific evidence that we have used to develop these scenarios, and the refinements made to them as new evidence emerged. We show how these scenarios are also considered as an ensemble so that government officials can prepare for a severe space weather event, during which many or all of the different scenarios will materialize. Finally, we note that this ensemble also needs to include insights into how public behavior will play out during a severe space weather event and hence the importance of providing robust, evidence‐based information on space weather and its adverse impacts.

This Chapter considers space weather effects of the ionosphere on the propagation of radio frequencies classed by the International Telecommunications Union as HF (3-30 MHz), VHF (30-300 MHz) and UHF (300-3000 MHz). The ionosphere and its variation is important for these radio frequencies. The ionosphere is the part of the upper atmosphere above 70-80 km altitude, where the density of the neutral atmosphere is low and the ionisation is significant enough to affect radio propagation. Even though the amount of ionisation is still below 1% of the neutrals, it is sufficient to exert an important effect on radio signals. In this Chapter the ionosphere is introduced, then a description of the theory of radio propagation at HF, VHF and UHF is given. The effects of solar storms and space weather on the ionosphere and hence on radio propagation are outlined. Finally, anomalous propagation conditions and outstanding problems and questions are also discussed.

In the E-region of the ionosphere, at heights between 90 and 130 km, thin patches of enhanced ionization occur intermittently. The electron density in these sporadic-E (Es) clouds can sometimes be so high that radio waves with frequencies up to 150 MHz are obliquely reflected. While this phenomenon is well known, the reflection mechanism itself is not well understood. To investigate this question, an experimental system has been developed for accurate polarimetric and fading measurements of 50 MHz radio waves obliquely reflected by mid-latitude Es layers. The overall sensitivity of the system is optimized by reducing environmental electromagnetic noise, giving the ability to observe weak, short-lived 50 MHz Es propagation events. The effect of the ground reflection on observed polarization is analyzed and the induced amplitude and phase biases are compensated. It is found that accurate measurements are only possible below the pseudo-Brewster angle. To demonstrate the effectiveness of the system, initial empirical results are presented which provide clear evidence of magneto-ionic double refraction.

In Global Navigation Satellite (GNSS)-based positioning, a user within a region covered by a network of reference stations can take advantage of the network-estimated parameters. The use of State Space Representation (SSR) parameters as GNSS-augmentation is valuable for Network-Real Time Kinematic (N-RTK) positioning and enables the ambiguity resolution for Precise Point Positioning (PPP) in the so-called PPP-RTK. SSR atmospheric corrections, i.e. tropospheric and ionospheric delays, are commonly estimated for the approximate user position by interpolation from values estimated for the reference stations. Widely used techniques are Inverse Distance Weighted, Ordinary Kriging and Weighted Least Squares (WLS). In this work, we analyze the interpolation quality of such techniques during severe weather events and Traveling Ionospheric Disturbances (TID). Furthermore, we propose modified WLS methods taking advantage of the physical atmospheric behavior during such events. Here, we exploit the use of Numerical Weather Models for tropospheric horizontal gradients information, and estimated TID parameters like wavelength and direction of propagation. Firstly, the interpolation is assessed using simulations considering artificial and real network geometries. Secondly, the proposed techniques are evaluated in post-processing using real SSR parameters generated by network computation of GNSS measurements. As examples, two severe weather events in North Europe in 2017, and one TID event over Japan in 2019 have been analyzed. The interpolation of SSR tropospheric and ionospheric parameters is evaluated. Considering the reference station positions as rover locations, the application of the modified WLS approach reduces the root mean square error in up to 80% of the cases during sharp weather fluctuations. Also, the average error can be decreased in 64% of the cases during the TID event investigated. Improvements up to factors larger than two are observed. Furthermore, specific cases are isolated showing particular tropospheric variations where significant errors (e.g. larger than 1 cm) can be reduced up to 20% of the total amount. Finally, tropospheric and ionospheric messages are proposed to transmit to the user the information needed to implement the suggested interpolation properly. (C) 2021 COSPAR. Published by Elsevier B.V. All rights reserved.

The UK's Defence Science and Technology Laboratory (Dstl) is partnering with the US Naval Research Laboratory (NRL) on a joint mission to launch miniature sensors that will advance space weather measurement and modelling capabilities. The Coordinated Ionospheric Reconstruction Cubesat Experiment (CIRCE) comprises two 6U cube-satellites that will be launched into a near-polar low earth orbit (LEO), targeting 500 km altitude, in 2021. The UK contribution to CIRCE is the In situ and Remote Ionospheric Sensing (IRIS) suite, complementary to NRL sensors, and comprising three highly miniaturised payloads provided to Dstl by University College London (UCL), University of Bath, and University of Surrey/Surrey Satellite Technology Ltd (SSTL). One IRIS suite will be flown on each satellite, and incorporates an ion/neutral mass spectrometer, a tri-band global positioning system (GPS) receiver for ionospheric remote sensing, and a radiation environment monitor. From the US, NRL have provided two 1U Triple Tiny Ionospheric Photometers (Tri-TIPs) on each satellite (Nicholas et al., 2019), observing the ultraviolet 135.6 nm emission of atomic oxygen at night-time to characterize the two-dimensional distribution of electrons.

Abstract. The most intense ionospheric storm observed in recent times occurred between 29–31 October 2003. The disturbances to the high-latitude regions set off several Large-Scale Travelling Ionospheric Disturbances (LSTIDs), wavelike perturbations in the ionospheric electron density. This paper investigates one particular Travelling Ionospheric Disturbance (TID) on 31 October 2003 using North American Global Positioning System (GPS) receiver network data and a tomographic imaging technique. The TID has an estimated period of 30 min, an estimated horizontal wavelength of 700 km and propagates South-Westward over North America. The tomographic reconstruction of the wave is validated using a simulation of the observations and with independent observations from ionosondes and the CHAMP Planar Langmuir Probe. The results are discussed in the context of the magnetic and ionospheric conditions that may have contributed to the launch of the wave. Large-scale TIDs are challenging to study over large regions of the Earth, and the GPS network here is shown to offer a unique perspective on the spatial and temporal variation of the TID. The experimental results are backed up by simulations that show a denser network of receivers, as is available in more recent years, would produce improved accuracy in the TID imaging.