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High-frequency (HF) skywave propagation relies on the ionosphere, making it susceptible to ionospheric variability. This study analyzes long-term Doppler residual measurements of a 10 MHz HF link between Fort Collins, CO, and Newark, NJ, to characterize the impact of ionospheric conditions on the link. We report that daytime measurements of Doppler variability exhibit Cauchy statistics, while nighttime measurements show a combination of exponential and log-normal statistics. These patterns correlate with solar activity and solar zenith angle. We also use PHaRLAP numerical ray tracing simulations through the IRI 2020 ionosphere to provide insights into signal ray paths and the altitudes of the ionosphere contributing to the observed Doppler shifts. By examining diurnal variations and statistical properties of Doppler residuals, this study aims to enhance our understanding of ionospheric dynamics and their influence on HF signal characteristics. 

This study describes a method to deduce the ionization layer virtual height and propagation path geometry responsible for communication between two HF radio stations a fixed distance apart. The method measures the Time Difference of Arrival (TDOA) between multipath propagation modes involving the active ionospheric layers and reconciles the data with a virtual height model of the ionosphere. The TDOA approach was implemented by transmitting audio signals that are sensitive to a time delay when summed together as happens in a receiver during multipath reception. The TDOA method eliminates the need for any absolute time references or extensive equipment calibration that would be required for an absolute time of flight (TOF) measurement. The audio waveforms used by the method included 1-cycle audio bursts, linear audio chirps of controlled sweep rate, and pseudorandom noise (PN) bursts. 

It has been shown that a proxy determination of the magnetospheric open–closed magnetic field line boundary (OCB) location can be made by examining the ultra-low-frequency (ULF) wave power in magnetometer data, with particular interest in the Pc5 ULF waves with periods of 3–10 min. In this study, we present a climatology of such Pc5 ULF waves using ground-based magnetometer data from the South Pole Station (SPA), McMurdo (MCM) station, and the Automatic Geophysical Observatories (AGOs) located across the Antarctic continent, to infer OCB behavior and variability during geomagnetically quiet times (i.e., Ap < 30 nT). For each season [i.e., austral fall (20 February 2017–20 April 2017), austral winter (20 May 2017–20 July 2017), austral spring (20 August 2017–20 October 2017), and austral summer (20 November 2017–20 January 2018)], north–south (i.e., H-component) magnetic field line residual power–spectral density (PSD) measurements taken during geomagnetically quiet periods within a 60-day window centered at the austral solstice/equinox are averaged in 10-min temporal bins to form the climatology at each station. These residual PSDs thus enable the analysis of Pc5 activity (and lower period “long-band” oscillations) and, thus, OCB location/variability as a function of season and magnetic latitude. The dawn and dusk transitions across the OCB are analyzed, with a discussion of dawn and dusk variability during nominally quiet geomagnetic periods. In addition, latitudinal dependencies of the OCB and peak Pc5 periods at each station are discussed, along with the empirical Tsyganenko model comparisons to our site measurements. 

As part of Ham Radio Science Citizen Investigation (HamSCI) Personal Space Weather Station (PSWS) project, a low-cost, commercial off-the-shelf magnetometer has been developed to provide quantitative and qualitative measurements of the geospace environment from the ground for both scientific and operational purposes at a cost that will allow for crowd-sourced data contributions. The PSWS magnetometers employ a magneto-inductive sensor technology to record three-axis magnetic field variations with a field resolution of ~3 nT at a 1 Hz sample rate. The measurement range of the sensor is +/-1.1e6 nT) and is valid over a temperature range of −40 °C to +85 °C. Data from the PSWS network will combine these magnetometer measurements with high frequency (HF, 3–30 MHz) radio observations to monitor large-scale current systems and ionospheric disturbances due to drivers from both space and the atmosphere. A densely-spaced magnetometer array, once established, will demonstrate their space weather monitoring capability to an unprecedented spatial extent. Magnetic field data obtained by the magnetometers installed at various locations in the US are presented and compared with the existing magnetometers nearby, demonstrating that the performance is very adequate for scientific investigations. 

Abstract Citizen science (also referred to as participatory science or community science), in which members of the general public contribute to scientific research, is not a new concept, as early examples of such studies can be found a couple of centuries ago. With the advancement of technology in an increasingly connected world, it has never been easier to engage citizen scientists in research projects. In this paper, we review citizen science initiatives and projects in the fields of atmosphere and space physics, including both early observation campaigns prior to the twenty-first century and recent projects. Ongoing initiatives take a broad range of forms, from the collection of data by citizen scientists to their involvement in the data analysis process and to the hosting of instruments in non-scientific public structures. We also discuss some of the challenges specific to citizen science, such as training citizen scientists, maintaining their engagement, ensuring reciprocity, managing citizen science data, interfacing the academic and citizen scientist communities, and funding citizen science. To these challenges we suggest possible solutions, and we highlight the unique opportunities offered by recent software and hardware developments. These game-changing opportunities are foreshadowing the dawn of a new era for citizen science – and hence for science in general and atmosphere and space physics in particular. 

Abstract In Vadas et al. (2024,https://doi.org/10.1029/2024ja032521), we modeled the atmospheric gravity waves (GWs) during 11–14 January 2016 using the HIAMCM, and found that the polar vortex jet generates medium to large‐scale, higher‐order GWs in the thermosphere. In this paper, we model the traveling ionospheric disturbances (TIDs) generated by these GWs using the HIAMCM‐SAMI3 and compare with ionospheric observations from ground‐based Global Navigation Satellite System (GNSS) receivers, Incoherent Scatter Radars (ISR) and the Super Dual Auroral Radar Network (SuperDARN). We find that medium to large‐scale TIDs are generated worldwide by the higher‐order GWs from this event. Many of the TIDs over Europe and Asia have concentric ring/arc‐like structure, and most of those over North/South America have planar wave structure and occur during the daytime. Those over North/South America propagate southward and are generated by higher‐order GWs from Europe/Asia which propagate over the Arctic. These latter TIDs can be misidentified as arising from geomagnetic forcing. We find that the higher‐order GWs that propagate to Africa and Brazil from Europe may aid in the formation of equatorial plasma bubbles (EPBs) there. We find that the simulated GWs, TIDs and EPBs agree with EISCAT, PFISR, GNSS, and SuperDARN measurements. We find that the higher‐order GWs are concentrated at N at 200 km, in agreement with GOCE and CHAMP data. Thus the polar vortex jet is important for generating TIDs in the northern winter ionosphere via multi‐step vertical coupling through GWs. 

The term “Medium-Scale Traveling Ionospheric Disturbances” is used to describe a number of different propagating phenomena in ionospheric plasma density with a scale size of hundreds of km. This includes multiple generation mechanisms, including ion-neutral collisions, plasma instabilities, and electromagnetic forcing. Observational limitations can impede characterization and identification of MSTID generation mechanisms. We discuss inconsistencies in the current terminology used to describe these and provide a set of recommendations for description and discussion. 

The objective of the Ham Radio Science Citizen Investigation (HamSCI) Personal Space Weather Station (PSWS) project is to develop a distributed array of ground-based multi-instrument nodes capable of remote sensing the geospace system. This system is being designed with the intention of distribution to a large number of amateur radio and citizen science observers. This will create an unprecedented opportunity to probe the ionosphere at finer resolution in both time and space as all measurements will be collected into a central database for coordinated analysis. Individual nodes are being designed to service the needs of the professional space science researcher while being cost-accessible and of interest to amateur radio operators and citizen scientists. At the heart of the HamSCI PSWS will be a high performance 0.1–60 MHz software defined radio (SDR) [1] with GNSS-based precision timestamping and frequency reference. This SDR is known as the TangerineSDR and is being developed by the Tucson Amateur Packet Radio (TAPR) amateur radio organization. The primary objective of PSWS system is to gather observations to understand the short term and small spatial scale ionospheric variabilities in the ionosphere-thermosphere system. These variabilities are important for understanding a variety of geophysical phenomena such as Traveling Ionospheric Disturbances (TIDs) [2], Ionospheric absorption events, geomagnetic storms and substorms. We present early results suggesting signature of Traveling Ionospheric Disturbances (TIDs) from an ionospheric sounding mode that we intend to implement on the PSWS system, currently implemented on an Ettus N200 Universal Software Radio Peripheral (USRP) using the open source GNU Chirpsounder data collection and analysis code.