Passive all‐sky imaging radar in the HF regime with WWV and the first station of the Long Wavelength Array

2016

Ann. Geophys.

Abstract. This paper describes the results of a multiplatform observing campaign aimed at studying midlatitude sporadic E (E s ) and associated ionospheric phenomena. The assets used were the digisonde in Boulder, Colorado; the first station of the Long Wavelength Array, LWA1, in New Mexico; the transmitters of the radio station WWV in Colorado; and 61 continuously operating GPS receivers between LWA1 and WWV. The results show that southwestward-directed medium-scale traveling ionospheric disturbances (MSTIDs) were substantially more prevalent when E s was detected. The amplitudes of these correlate with a plasma frequency up to about 4.5 MHz. For f p 5 MHz, the MSTIDs become significantly weaker and basically vanish above ∼ 6.5 MHz. The prevalence of meteor trail reflections observed with LWA1 also correlates with f p up to about 4.5 MHz; above this limit, the relationship exhibits a significant turnover. The observed intensity of coherent backscatter from E s field-aligned irregularities (FAIs) also correlates with inferred plasma frequency. However, this trend continues to higher frequencies with a peak near 6 MHz, followed by a much more subtle turnover. The reflected power from E s structures observed with LWA1 is significantly more correlated on spatial scales between 10 and 40 km. The magnitude of this correlation increases with f p up to ∼ 6 MHz, above which it drops. These results are consistent with the following: (1) southwestwarddirected MSTIDs are produced via E-F coupling; (2) this coupling is stronger when the E s layer, seeded by meteor ablation, is more dense; (3) the coupling is substantially diminished for E s layers harboring extremely dense structures (f p 5 MHz).

Section: Lwa1 Wwv Fais and Meteor Trailsmentioning

confidence: 94%

Section: Lwa1 Wwv Fais and Meteor Trailsmentioning

confidence: 99%

Section: Lwa1 Wwv Fais and Meteor Trailsmentioning

confidence: 99%

Section: Lwa1 Wwv Fais and Meteor Trailsmentioning

confidence: 99%

Section: Sporadic-e Structure From Passive Radarmentioning

confidence: 99%

See 3 more Smart Citations

A multi-platform investigation of midlatitude sporadic E and its ties to E–F coupling and meteor activity

2016

Ann. Geophys.

Observations of the ionospheric impact of M‐class solar flares on local and hemispheric scales

Earth and Space Science

Kassim

Teare

2015

Self Cite

The ionospheric impact of a series of M-class solar flares that occurred on 12 March 2015 is described. A combination of data sets from GPS receivers and two different colocated radio telescopes, the very large array (VLA) and the long wavelength array (LWA), was used to detect and characterize flare-induced irregularities. The data demonstrate that each flare causes a rapid step-like increase in total electron content (TEC) of about 0.2 total electron content units (TECU), 1 TECU = 1016 el m −2 . The rise times of these steps are on the order of 1-3 min. The GPS data show signs of traveling ionospheric disturbances likely associated with gravity waves whose magnitudes were temporarily enhanced by the impact of two of the flares. Increased activity within the horizontal TEC gradients observed with the VLA was apparent for several minutes following the flare X-ray peak. The properties of these VLA-detected disturbances are strongly indicative of field-aligned irregularities within the plasmasphere. They initially form at two altitudes, approximately 2600 and 5600 km. Those that form higher quickly disappear, whereas those that form lower appear to descend over a period of ∼7 min to an altitude of roughly 1450 km before disappearing. LWA observations of ionospheric reflections of the HF radio station WWV show a significant and brief (∼few minutes) Doppler frequency disturbance near the onset of TEC enhancement, followed by a ∼5 min drop in received power, indicating increased ionization in the D region.

Ionospheric Detection of Explosive Events

Huang

Park

et al. 2019

Reviews of Geophysics

Self Cite

The ionospheric response to explosions which occur at or below the Earth's surface has been noted since the first detonations of nuclear devices during the early period of aboveground testing. Acoustic gravity waves and traveling ionospheric disturbances were detected in association with test explosions carried out by the Union of Soviet Socialist Republics in Novaya Zemlya in 1961. While research in this area has continued, the standards accepted by the Comprehensive Nuclear Test Ban Treaty for detection and confirmation of nuclear explosions have been based on (1) seismic, (2) hydroacoustic, (3) infrasound, and (4) radionuclide monitoring from ground detectors. We suggest that ionospheric sensing offers a complementary methodology that may allow for robust confirmation of explosive events. One method of ionospheric monitoring of explosive events is analysis of total electron content (TEC), available by processing data from Global Navigation Satellite System (GNSS) receivers distributed globally on land masses. Traveling ionospheric disturbances observed by their signature in TEC have been used to detect and confirm mine collapses, mine blasts, earthquakes, volcanic eruptions, and meteorite strikes as well as underground nuclear tests. While an integrated measurement like TEC is not as sensitive to small-amplitude density perturbations as other methods, the existence of large networks of continuously operating GNSS stations makes this an intriguing new monitoring asset. We report on the current capabilities for detection of explosions via the ionosphere, the outstanding challenges, and prospects for future developments that have potential to augment the current standards for detection and confirmation of nuclear detonations. By leveraging the worldwide network of GNSS receivers, robust confirmation of impulsive events is possible. This methodology complements existing technologies approved by the Comprehensive Test Ban Treaty. The article outlines background theory, new approaches to monitoring of explosions, and challenges that remain to be addressed.