On the coexistence of kilometer‐ and meter‐scale irregularities in the nighttime equatorial F region

Abstract

Nighttime multifrequency scintillation and 50-MHz radar backscatter observations simultaneously performed over a nearly common ionospheric volume at the dip equator in Peru during March 1977 were used to study the relationship between the large-scale irregularities (-•0.1-1 km) giving rise to scintillations and small-scale irregularities (3 m) causing 50-MHz backscatter. It is shown that during the generation phase of equatorial irregularities in the evening hours, the kilometer-and meter-scale irregularities coexist, whereas in the later phase, approximately an hour after the onset, the meter-scale irregularities decay but the large-scale ones continue to retain their high spectral intensities. Further, multistation scintillation observations from a host of geostationary satellites as well as from the Wideband satellite indicate that eastward-drifting irregularity structures detected around midnight cause significant scintillations at UHF and L band but generally fail to give rise to appreciable backscatter. Thus, contrary to expectations, it is possible to have even L band scintillations without any plume structure on backscatter maps. This indicates that at later local time a cutoff of the spectral intensity probably occurs at some scale length between 100 and 3 m. These observational results are discussed in the context of current theories of plasma instability in the equatorial ionosphere.• Emmanuel Col}ege, Boston, Massachusetts 02115. •' Air Force Geophysics Laboratory, Hanscom Air Force Base, Bedford, M assach usetts 01731.

Simultaneous radar and spaced receiver VHF scintillation observations of ESF irregularities

“…In the initial phase, the radar measured vertical irregularity drift velocity also has large values, with the corresponding spectral widths also being larger. It is interesting to note that although the backscattering structures were absent after 20:55 IST, a high level of scintillations was observed until 01:00 IST, similar to earlier observations reported elsewhere (Basu et al, 1978;Rodrigues et al, 2004). This is due to the decay of 8.3-m irregularities, while the longer scale length (>100 m) irregularities which formed earlier to the west of the observation point remained intact while they drifted eastward on to the signal path, to produce the recorded scintillations.…”

Climatology of GPS phase scintillation and HF radar backscatter for the high-latitude ionosphere under solar minimum conditions

“…On the other hand, the cusp scintillation is dominated by an annual cycle maximizing in late autumn and in winter with lower occurrence in spring and summer. A comparison between the occurrence of phase scintillation and HF radar backscatter from fieldaligned irregularities is addressing the question of coexistence of kilometer-and meter-scale irregularities, which was first raised for equatorial latitudes (Basu et al, 1978) and followed up at high latitudes (Milan et al, 2005). We found a statistical collocation of the phase scintillation and HF radar backscatter occurrence in the auroral oval and cusp.…”

“…These larger irregularities may coexist with small-scale fieldaligned irregularities produced by plasma instabilities such as the gradient-drift instability. Using multifrequency scintillation and 50-MHz radar observations Basu et al (1978) studied such coexistence of large-and small-scale irregularities in the nighttime equatorial F-region. HF radar backscatter from decameter-size irregularities drifting with E × B velocity is routinely observed with SuperDARN.…”

A comparison of the equatorial spread F derived by the International Reference Ionosphere and the S 4 index observed by FORMOSAT-3/COSMIC during the solar minimum period of 2007–2009

“…These rising bubbles with the passage of time can bifurcate to form small-scale irregularities by cascade, or two step, mechanisms (Ossakow, 1981). Such smaller-scale irregularities effectively produce scintillations at the L-band (Basu et al, 1978;DasGupta et al, 1982).…”