@conference {542, title = {Sources of Large Scale Traveling Ionospheric Disturbances Observed using HamSCI Amateur Radio, SuperDARN, and GNSS TEC}, booktitle = {NSF CEDAR (Coupling, Energetics, and Dynamics of Atmospheric Regions)}, year = {2021}, month = {06/2021}, publisher = {CEDAR}, organization = {CEDAR}, address = {Virtual}, abstract = {

Large Scale Traveling Ionospheric Disturbances (LSTIDs) are quasi-periodic variations in F region electron density with horizontal wavelengths \> 1000 km and periods between 30 to 180 min. On 3 November 2017, LSTID signatures were detected in simultaneously over the continental United States in observations made by global High Frequency (HF) amateur (ham) radio observing networks and the Blackstone (BKS) SuperDARN radar. The amateur radio LSTIDs were observed on the 7 and 14 MHz amateur radio bands as changes in average propagation path length with time, while the LSTIDs were observed by SuperDARN as oscillations of average scatter range. LSTID period lengthened from T ~ 1.5 hr at 12 UT to T ~ 2.25 hr by 21 UT. The amateur radio and BKS SuperDARN radar observations corresponded with Global Navigation Satellite System differential Total Electron Content (GNSS dTEC) measurements. dTEC was used to estimate LSTID parameters: horizontal wavelength 1136 km, phase velocity 1280 km/hr, period 53 min, and propagation azimuth 167{\textdegree}. The LSTID signatures were observed throughout the day following ~400 to 800 nT surges in the Auroral Electrojet (AE) index. As a contrast, 16 May 2017 was identified as a period with significant amateur radio coverage but no LSTID signatures in spite of similar geomagnetic conditions and AE activity as the 3 November event. We hypothesize that atmospheric gravity wave (AGW) sources triggered by auroral electrojet intensifications and associated Joule heating are the source of the LSTIDs, and that seasonal neutral atmospheric conditions may play a role in preventing AGW propagation in May but not in November.

}, author = {Nathaniel A. Frissell and Diego F. Sanchez and Gareth W. Perry and Dev Joshi and William D. Engelke and Evan G. Thomas and Anthea Coster and Philip J. Erickson and J. Michael Ruohoniemi and Joseph B. H. Baker} } @proceedings {505, title = {Survey of ionospheric F2 region variability from the lower atmosphere: drivers and responses - Part 1}, year = {2021}, month = {03/2021}, abstract = {

Carl Luetzelschwab, K9LA, will review the factors that cause the F2 region of the ionosphere to vary in the short-term, on day-to-day and even shorter time scales. These factors can directly affect amateur radio operators through their influence on electron density and therefore on HF propagation. Ionospheric variability drivers will be sorted into three broad categories: 1) solar radiation 2) geomagnetic activity and 3) meteorological sources (neutral atmosphere). Carl will also assess how much F2 ionospheric parameters vary in the short-term during both day and night, and he will also review the contribution of each of the factors to observed F2 region variability.

}, author = {R. Carl Luetzelschwab and Philip J. Erickson} } @proceedings {506, title = {Survey of ionospheric F2 region variability from the lower atmosphere: drivers and responses - Part 2}, year = {2021}, month = {03/2021}, publisher = {HamSCI}, address = {Scranton, PA (Virtual)}, abstract = {

Phil Erickson, W1PJE, will follow with a condensed summary of recent community research on the types of physical processes that produce F2 layer ionospheric variations from waves, heating, and other sources in the lower neutral atmosphere (space weather {\textquotedblleft}from below{\textquotedblright}). Examples will include acoustic waves, gravity waves, planetary waves, TADs (traveling atmospheric disturbances), and their influence on TIDs (travelling ionospheric disturbances). Numerical estimates of the various forcing terms provide a useful gauge of the relative importance and impact of these processes. Phil will close by specifically focusing on estimates of the magnitude of electron density variations in the F2 region of the ionosphere due to earthquake effects. In particular, ionospheric density observations from sources such as the global satellite navigation system (GNSS) allow a quantitative, numerate discussion of earthquake drivers in both time and space dimensions as compared to other known lower atmosphere ionospheric variability drivers.\  Phil will conclude with a discussion of the implications for earthquake associated HF propagation effects in the face of observed day-to-day ionospheric density variability.

}, author = {Philip J. Erickson and R. Carl Luetzelschwab} } @conference {325, title = {Sounding the Ionosphere with Signals of Opportunity in the High-Frequency (HF) Band}, booktitle = {HamSCI Workshop 2019}, year = {2019}, month = {03/2019}, publisher = {HamSCI}, organization = {HamSCI}, address = {Cleveland, OH}, abstract = {

The explosion of commercial off-the-shelf (COTS) education- and consumer-grade hardware supporting software-defined radio (SDR) over the past two decades has revolutionized many aspects of radio science, bringing the cost and calibration of traditionally complex receiver hardware within the grasp of even advanced amateur experimenters. Transmission has now become the limiter of access in many cases, particularly through spectrum management and licensing considerations. Fortunately, several classes of signals endemic to the HF band lend themselves to processing for ionospheric characteristics: time and frequency standard broadcasters, surface-wave oceanographic radars, amateur radio transmissions, and ionospheric sounders.

This presentation is a tour of these signals of opportunity and techniques for collecting and processing them into ionospheric characteristics, with emphasis on distributed receivers collecting on a small number (four or fewer) of coherent channels. Receiving techniques will be discussed for near-vertical ({\textquotedblleft}quasi-vertical{\textquotedblright}) incidence skywave (NVIS or QVI), long-distance oblique soundings, and transionospheric sounding. Soundings will be demonstrated from space-based, ground-based, and maritime platforms.

Binary, Doppler, delay, cone angle of arrival, and polarization observations will be exploited, depending on the signal type and capability of the collector. Each of these techniques conveys different, but not always {\textquotedblleft}orthogonal,{\textquotedblright} information about the ionospheric skywave channel. The information content of each datum will be discussed with respect to the implications for inverting the local or regional ionosphere from the observations. More importantly than inverting the full ionosphere, some of these techniques are sensitive indicators of ionospheric irregularities, structures, and instabilities, that might otherwise be difficult to study due to limited geographic coverage with larger, more exquisite instrumentation.

}, author = {Ethan S. Miller and Gary S. Bust and Gareth W. Perry and Stephen R. Kaeppler and Juha Vierinen and Nathaniel A. Frissell and A. A. Knuth and Philip J. Erickson and Romina Nikoukar and Alexander T. Chartier and P. Santos and C. Brum and J. T. Fentzke and T. R. Hanley and Andrew J. Gerrard} }