More Like this

1. History of the Super Dual Auroral Radar Network (SuperDARN)-I: pre-SuperDARN developments in high frequency radar technology for ionospheric research and selected scientific results

   https://doi.org/10.5194/hgss-12-77-2021  

   Greenwald, Raymond A. (January 2021, History of Geo- and Space Sciences)

   Abstract. Part I of this history describes the motivations for developing radars in the high frequency (HF) band to study plasma density irregularities in the F region of the auroral zone and polar cap ionospheres. French and Swedish scientists were the first to use HF frequencies to study the Doppler velocities of HF radar backscatter from F-region plasma density irregularities over northern Sweden. These observations encouraged the author of this paper to pursue similar measurements over northeastern Alaska, and this eventually led to the construction of a large HF-phased-array radar at Goose Bay, Labrador, Canada. This radar utilized frequencies from 8–20 MHz and could be electronically steered over 16 beam directions, covering a 52∘ azimuth sector. Subsequently, similar radars were constructed at Schefferville, Quebec, and Halley Station, Antarctica. Observations with these radars showed that F-region backscatter often exhibited Doppler velocities that were significantly above and below the ion-acoustic velocity. This distinguished HF Doppler measurements from prior measurements of E-region irregularities that were obtained with radars operating at very high frequency (VHF) and ultra-high frequency (UHF). Results obtained with these early HF radars are also presented. They include comparisons of Doppler velocities observed with HF radars and incoherent scatter radars, comparisons of plasma convection patterns observed simultaneously in conjugate hemispheres, and the response of these patterns to changes in the interplanetary magnetic field, transient velocity enhancements in the dayside cusp, preferred frequencies for geomagnetic pulsations, and observations of medium-scale atmospheric gravity waves with HF radars. 

   more » « less
2. Predicting Equatorial Ionospheric Convective Instability Using Machine Learning

   https://doi.org/10.1029/2023SW003505  

   Garcia, D.; Rojas, E. L.; Hysell, D. L. (December 2023, Space Weather)

   Abstract The numerical forecast methods used to predict ionospheric convective plasma instabilities associated with Equatorial Spread‐F(ESF) have limited accuracy and are often computationally expensive. We test whether it is possible to bypass first‐principle numeric simulations and forecast irregularities using machine learning models. The data are obtained from the incoherent scatter radar at the Jicamarca Radio Observatory located in Lima, Peru. Our models map vertical plasma drifts, time, and solar activity to the occurrence and location of clusters of echoes telltale of ionospheric irregularities. Our results show that these models are capable of identifying the predictive power of the tested inputs, obtaining accuracies around 75%. 

   more » « less
3. On the Role of Mild Substorms and Enhanced Hall Conductivity in the Plasma Irregularities Onset and Zonal Drift Reversals: Experimental Evidence at Distinct Longitudes Over South America

   https://doi.org/10.1029/2023EA003071  

   Sousasantos, J.; Rodrigues, F. S.; Fejer, B. G.; Abdu, M. A.; Massoud, A. A.; Valladares, C. E. (November 2023, Earth and Space Science)

   Abstract The 14‐panel Advanced Modular Incoherent Scatter Radar (AMISR‐14) system deployed at Jicamarca observed equatorial spread F plumes on two consecutive nights under unfavorable seasonal and solar flux conditions during a period that can be categorized as geomagnetically quiet. The AMISR‐14 capability of observing in multiple pointing directions allowed the characterization of the irregularity zonal drifts revealing that, in addition to their atypical occurrence, the zonal drifts of these plumes/irregularities also presented distinct patterns from one night to another, reversing from east to west on the second night. This work addresses two main subjects: (a) the mechanisms that may have led to the generation of these irregularities, despite the unfavorable conditions, and (b) the mechanisms that possibly led to the reversal (east‐to‐west) in the zonal plasma drift on the second night. To do so a multi‐instrumented and multi‐location investigation was performed. The results indicate the occurrence of simultaneous spread‐F events over the Peruvian and the Brazilian regions, evidencing a non‐local process favoring the development of the irregularities. The results also suggest that, even under very mild geomagnetic perturbation conditions, the recurring penetration of electric fields in the equatorial ionosphere can occur promptly, modifying the equatorial electrodynamics and providing favorable conditions for the plume development. Moreover, the results confirm that the eastward penetration electric fields, combined with the upsurge of Hall conductivity in the nighttime typically associated with the presence of sporadic‐E layers, are likely to be the mechanism leading to the reversal in the irregularity zonal drifts over these regions. 

   more » « less
4. Equatorial F ‐Region Plasma Waves and Instabilities Observed Near Midnight at Solar Minimum During the NASA Too WINDY Sounding Rocket Experiment

   https://doi.org/10.1029/2020JA028408  

   Hysell, D_L; Rao, S.; Larsen, M_F (September 2020, Journal of Geophysical Research: Space Physics)

   Abstract Radar and sounding rocket observations of plasma irregularities in theF‐region ionosphere acquired on 19 June 2019 during NASA experiment Too WINDY on Kwajalein Atoll are presented. The experiment was conducted near local midnight during a period of low solar flux and quiet geomagnetic conditions. Plasma density irregularities were seen by the rocket and also in the incoherent scatter radar data to emerge and persist mainly in the topside. Density irregularities in the bottomside remained very small by comparison throughout the observations. Zonal plasma drifts measured by the rocket were highly structured in the topside. Patches of coherent scatter entrained in the large‐scale topside density irregularities appeared to propagate slowly westward in a narrow flow channel detected by the rocket. Broadband ELF emissions were also detected in the topside. Some of the characteristics of the topside irregularities are typical of postsunset equatorialF‐region irregularities observed frequently by coherent scatter radars, and some of the common features in the coherent scatter database are reviewed. Two scenarios that have been proposed to account for postmidnight spreadFare tested computationally. One involves unseasonably large background zonal electric fields, and the other involves forcing from below by neutral waves and turbulence. Neither scenario appears to be able to account for the Too WINDY observations and the preponderance of topside irregularities without bottomside precursors in particular. 

   more » « less
5. Bistatic Observations With SuperDARN HF Radars: First Results

   https://doi.org/10.1029/2020RS007121  

   Shepherd, S. G.; Sterne, K. T.; Thomas, E. G.; Ruohoniemi, J. M.; Baker, J. B. H.; Parris, R. T.; Pedersen, T. R.; Holmes, J. M. (August 2020, Radio Science)

   Abstract Super Dual Auroral Radar Network (SuperDARN) radars operate in a coordinated but monostatic configuration whereby high‐frequency (HF) signals scattered from ionospheric density irregularities or from the surface of the Earth return to the transmitting radar where Doppler parameters are then acquired. A bistatic arrangement has been developed for SuperDARN radars in which HF signals transmitted from one radar are received and analyzed by another radar that is separated by a large distance (>1,000 km). This new capability was developed and tested on radars located in Oregon and Kansas. Numerous 3‐day bistatic campaigns have been conducted over a period extending from September 2019 through March 2020. During these campaigns three distinct bistatic propagation modes have been identified including a direct mode in which signals are transmitted and received through the radar side lobes. Direct mode signals propagate along the great‐circle arc connecting the two bistatic radar sites, reflecting from the ionosphere at bothEregion andFregion altitudes. Two additional modes are observed in which HF signals transmitted from one radar scatter from either ionospheric density irregularities or from the surface of the Earth before propagating to the bistatic receiving radar. Ray tracing simulations performed for examples of each mode show good agreement with observations and confirm our understanding of these three bistatic propagation modes. Bistatic campaigns continue to be scheduled in order to improve technical aspects of this new capability, to further explore the physical processes involved in the propagation and scattering of HF bistatic signals and to expand the coverage of ionospheric effects that is possible with SuperDARN. 

   more » « less