Drift and aspect sensitivity of scattering irregularities in the upper equatorial <i>E</i> region

Røyrvik, O.

doi:10.1029/ja087ia10p08338

Cited by 23 publications

(24 citation statements)

References 10 publications

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“…Such echoes, called 150-km echoes, were first reported by Balsley (1964) and later associated to fieldaligned irregularities (FAIs) by Røyrvik and Miller (1981) and Røyrvik (1982). Very little attention was given to these echoes until the very high-resolution observations were reported by Kudeki and Fawcett (1993).…”

Section: Introductionmentioning

confidence: 98%

Naturally enhanced ion-line spectra around the equatorial 150-km region

et al. 2009

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Abstract. For many years strong radar echoes coming from 140-170 km altitudes at low latitudes have been associated to the existence of field-aligned irregularities (FAIs) (the so called 150-km echoes). In this work, we present frequency spectra as well as angular distribution of 150-km echoes. When the 150-km region is observed with beams perpendicular to the magnetic field (B) the observed radar spectra are very narrow with spectral widths between 3-12 m/s. On the other hand, when few-degrees off-perpendicular beams are used, the radar spectra are wide with spectral widths comparable to those expected from ion-acoustic waves at these altitudes (>1000 m/s). Moreover the off-perpendicular spectral width increases with increasing altitude. The strength of the received echoes is one to two orders of magnitude stronger than the expected level of waves in thermal equilibrium at these altitudes. Such enhancement is not due to an increase in electron density. Except for the enhancement in power, the spectra characteristics of off-perpendicular and perpendicular echoes are in reasonable agreement with expected incoherent scatter spectra at these angles and altitudes. 150-km echoes are usually observed in narrow layers (2 to 5). Bistatic common volume observations as well as observations made few kilometers apart show that, for most of the layers, there is very high correlation on power fluctuations without a noticeable time separation between simultaneous echoes observed with Off-perpendicular and Perpendicular beams. However, in one of the central layers, the echoes are the strongest in the perpendicular beam and absent or very weak in the offperpendicular beams, suggesting that they are generated by a plasma instability. Our results indicate that most echoes around 150-km region are not as aspect sensitive as originally thought, and they come from waves that have been enhanced above waves in thermal equilibrium.

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Section: Introductionmentioning

confidence: 98%

Naturally enhanced ion-line spectra around the equatorial 150-km region

et al. 2009

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“…The so‐called 150 km echoes, the coherent radar echoes coming from the 140–180 km region during daytime, first detected using the Jicamarca radar nearly four and half decades ago [ Balsley , 1964], continue to puzzle researchers till the free energy sources and the generation mechanism of the echoing phenomenon are identified. They were found to exhibit narrow spectral width (<15 m s −1 ) [e.g., Røyrvik and Miller , 1981] and were associated to field‐aligned irregularities (FAI) [ Røyrvik , 1982]. Fascinating details of these echoes, revealed through high‐resolution observations made using the Jicamarca radar [ Kudeki and Fawcett , 1993] are (1) height‐time variation of the echoing region displaying forenoon descent and afternoon ascent indicating the role of solar zenith angle on the echoing process, (2) quasiperiodic variation in the echo power indicating the possible role of gravity waves in the echoing process, and (3) good correlation of the radial Doppler velocities to ground magnetic field variation suggesting their usefulness in estimating F region E × B drift.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of 150 km echoes linked with solar eclipse and their implications to the echoing phenomenon

Patra

Chaitanya

Tiwari³

2011

J. Geophys. Res.

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[1] This paper presents a study based on Gadanki radar observations of 150 km echoes made during the solar eclipse of 15 January 2010 that occurred during 1122-1515 IST. Radar echoes were observed only during 1150-1215 IST and 1344-1356 IST linked with the entry and recovery phases of the eclipse, respectively. The most striking observation found is the unusual ascending and descending features of the echoing regions observed during these two time periods. Although these echoes occurred at higher altitudes than those of control days, SNR and spectral width of these echoes are similar to those of the lower echoing region observed on the control days. Further, Doppler velocities suggest the presence of westward electric field unlike those of the control days. Concurrent ionosonde observations showed ascent and descent of the F 1 layer very similar to those observed in the 150 km echoes. These observations and related analysis suggest that the observed echoes were due to the combined action of the electron density gradients and the reduced recombination rate linked with the solar eclipse effect. These observations are first of its kind and elucidate the role of density gradient and recombination rate in the 150 km echoing process.

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“…Surprisingly, the generation mechanism for these echoes continues to be elusive since a suitable free energy source for their generation has not been identified. While many of the characteristics of these echoes were revealed by Jicamarca radar observations [ Royrvik and Miller , 1981; Royrvik , 1982; Kudeki and Fawcett , 1993; Hysell et al , 1997; Chau and Woodman , 2004; Chau , 2004; Chau and Kudeki , 2006], important additional characteristics of these echoes came from Pohnpei wind profiler radar (6.9°N, 158.2°E, 1° magnetic dip angle) observations [ Kudeki et al , 1998; Tsunoda and Ecklund , 2000, 2004]. The characteristic diurnal pattern in echo occurrence resembling a necklace shape and mean velocity representing the daytime vertical plasma drift have been the most important results revealed from the Jicamarca observations.…”

Section: Introductionmentioning

confidence: 99%

Further investigations on 150‐km echoing riddle using simultaneous observations of 150‐km and E region echoes from off‐electrojet location Gadanki

Patra

Rao

2007

J. Geophys. Res.

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[1] In this paper we present a detailed study of the off-electrojet daytime 150-km echoes based on simultaneous observations of daytime 150-km and E region echoes made on a few days per month during July 2005 to August 2006 using the Gadanki radar. Daytime 150-km echoes are found to occur in all seasons over Gadanki. Although echo occurrence is found to be maximum in equinoxes and minimum in summer, no clear seasonal preference over Gadanki has been observed. In contrast, E region echo occurrence made simultaneously shows a strong seasonal dependence with remarkably low occurrence in winter as compared to other seasons. Interestingly, the 150-km echoes show a distinctly different morphology in winter as compared to other seasons. Echoes are observed in two distinct height regions in winter as compared to one broad region in other seasons. Also the strongest echo and the lowest altitude of echo occurrence are found to be associated with winter. Further, a significant share of Doppler velocities is found to be downward in winter as compared to predominantly upward velocities observed in other seasons. No seasonal dependence in the spectral width of 150-km echoes, however, has been observed. Seasonally averaged Doppler velocities are quite similar to those of the F region drifts reported from Jicamarca. Again seasonally averaged drifts are found to be downward in winter afternoon as compared to upward velocities observed in other seasons. Notwithstanding the seasonal differences observed in the 150-km echoes, echo occurrence is found to have a common feature of strong forenoonafternoon asymmetry with forenoon occurrence being greater. These observations are discussed in the light of present understanding on the daytime 150-km echoing phenomenon.Citation: Patra, A. K., and N. V. Rao (2007), Further investigations on 150-km echoing riddle using simultaneous observations of 150-km and E region echoes from off-electrojet location Gadanki,

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Drift and aspect sensitivity of scattering irregularities in the upper equatorial E region

Cited by 23 publications

References 10 publications

Naturally enhanced ion-line spectra around the equatorial 150-km region

Naturally enhanced ion-line spectra around the equatorial 150-km region

Characteristics of 150 km echoes linked with solar eclipse and their implications to the echoing phenomenon

Further investigations on 150‐km echoing riddle using simultaneous observations of 150‐km and E region echoes from off‐electrojet location Gadanki

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