First in situ observations of equatorial ionospheric bubbles by Indian satellite SROSS‐C2 and simultaneous multisatellite scintillations
TL;DR: The first observation of equatorial ionospheric irregularities by the RPA probe of the Indian low Earth orbiting satellite SROSS-C2 is presented in this paper, where scintillation measurements of medium Earth orbiting Global Positioning System (GPS) satellites and geostationary FLEETSATCOM (244 MHz, 73°E) and INMARSAT (1.5 GHz, 65°E), recorded simultaneously at Calcutta (lat: 22.97° N, long: 88.50°E geographic; dip: 32°N) are
Abstract: [1] The first observation of equatorial ionospheric irregularities by RPA probe of the Indian low Earth orbiting satellite SROSS-C2 is presented in this paper. Amplitude scintillations of medium Earth orbiting Global Positioning System (GPS) satellites and geostationary FLEETSATCOM (244 MHz, 73°E) and INMARSAT (1.5 GHz, 65°E) signals recorded simultaneously at Calcutta (lat: 22.97° N, long: 88.50°E geographic; dip: 32°N) are used for a coordinated study of equatorial F region irregularities in the Indian zone. Cases of ionospheric irregularities identified from the SROSS-C2 records obtained during the initial one-and-a-half years since its launch in May 1994 have been analyzed. Some events of in situ ion density irregularities are compared with scintillations simultaneously observed on the transionospheric satellite links. Intense bite-outs of ion density (maximum relative irregularity amplitude ΔN/N ∼ 65%) were detected on one occasion (October 29, 1994) coupled with deep fadings (S4 ∼ 1 at VHF, ∼0.52 at L-band, and ∼0.69 at GPS L1 frequency) on ground-based satellite links. An estimate of scintillation indices from the observed in situ density deviations compares well with the ground-based measurements. The development of intense equatorial bubbles even on a day like October 29, 1994, under low solar activity conditions, may be attributed to a prompt penetration of magnetospheric electric field equatorwards during the main phase of a magnetic storm in progress [maximum negative excursion of Dst ∼ −127 nT at 1600UT (2100MLT) with a dDst/dt rate −37 nT/hr at 1300–1400UT (1800–1900MLT)]. The drift velocity and spatial extent of these irregularities have been estimated from ground-based observations.
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TL;DR: In this article, a long-term study of scintillations at 15 GHz observed from Calcutta extending from minimum to high sunspot number (1996-2000) was presented.
36 citations
TL;DR: In this paper, a multistation and multi-technique observation of equatorial ionospheric irregularities from locations over the magnetic equator through the northern crest of the Equatorial Ionization Anomaly (EIA) and beyond is one of the important objectives of the Indian CAWSES program.
10 citations
TL;DR: In this article, the authors have used weak scattering theory and assumed the plasma density fluctuations to behave like phase changing diffraction screen and derived appropriate relations for scintillation index S 4, and phase variance δϕ are derived and computed for different parameters of the plasminar irregularities of the ionosphere.
9 citations
TL;DR: The morphological features of initial ionospheric scintillations on 3.925 GHz beacon signal from geostationary satellite Intelsat (701) at Suva (Lat., 18.08° S, Long., 178.3° E, Geom. Lat., 22.1° S), Fiji, a low latitude station in the South Pacific region have been studied during the period of December 2003 to June 2004 as mentioned in this paper.
Abstract: The morphological features of initial ionospheric scintillations on 3.925 GHz beacon signal from geostationary satellite Intelsat (701) at Suva (Lat., 18.08° S, Long., 178.3° E, Geom. Lat., 22.1° S), Fiji, a low latitude station in the South Pacific region have been studied during the period of December 2003 to June 2004. Scintillations were, in general, sparse, of which activity was more pronounced in the daytime. Scintillation occurrence was less in general, showing a peak value of about 2.5% at 09 h LT and a secondary peak of about 2% at around 16 h LT. Scintillations were weak (S4 index ≤ 0.25) and occurred mostly in patches of short duration of 2–5 min. It is reported here that weak and short duration scintillations with more daytime occurrence are mainly due to (i) the higher frequency beacon signal used, (ii) the recording station being situated off the equatorial ionisation anomaly belt, and (iii) the period of observation falling in the low solar activity phase of the current solar cycle.
7 citations
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TL;DR: In this paper, the results of backscatter observations of the F region irregularities made with the large 50MHz radar at Jicamarca, Peru, during a few days of observations are presented.
Abstract: The paper presents some results of backscatter observations of the F region irregularities made with the large 50-MHz radar at Jicamarca, Peru, during a few days of observations. The results were obtained by using three observational techniques: the modified range-time-intensity technique, the digital power mapping technique, and the digital raw data recording technique. Backscatter intensity maps as a function of altitude and time are presented, which can be interpreted as radar pictures of F region irregularities. A classification of spread F spectral signatures resulting from approximately 30,000 spectra obtained in sets of 64 simultaneous heights under a variety of conditions is also given.
917 citations
TL;DR: In this article, the weak scatter scintillation theory is reformulated to show explicitly the ramifications of an arbitrarily large ionospheric outer scale, which is applied to representative data sets from the Wideband satellite.
Abstract: In this paper the weak scatter scintillation theory is reformulated to show explicitly the ramifications of an arbitrarily large ionospheric outer scale. The measured temporal phase spectrum, for example, is effectively truncated at a fixed frequency corresponding to the detrend time or the length of the data interval over which it is measured (whichever is smaller). As a consequence, the rms phase exhibits a complicated dependence on the relative irregularity drift velocity and the propagation geometry. This effect has not been included in previous analyses. By comparison, intensity scintillation data are intrinsically high-pass filtered by the diffraction process. By taking advantage of this fact a simple closed form expression for the S4 intensity scintillation index has been derived. The theory is applied to representative data sets from the Wideband satellite. The interpretation of the ionospheric parameters deduced from the analysis is also discussed.
443 citations
TL;DR: This paper observed large-scale (10 to 200-km) irregular biteouts of up to three orders of magnitude in the ion concentration in the nighttime equatorial F region associated with small-scale inhomogeneities in ion concentration.
Abstract: The Atmosphere Explorer satellite observed large-scale (10 to 200-km) irregular biteouts of up to three orders of magnitude in the ion concentration in the nighttime equatorial F region associated with small-scale inhomogeneities in the ion concentration. Simultaneous plasma velocity observations show irregular upward and westward motion of the order of 150 m/s associated with some of these 'bubbles', while others move more slowly or move with approximately the velocity of the background plasma. The plasma composition signatures indicate that most of the bubbles observed have recently moved upward. Several features of recent VHF radar observations can be understood as resulting from these plasma bubbles, e.g., the 'plume' features and very high apparent velocities seen on range-time-intensity spread F maps and the very complex and/or wide spectral features observed using such radars.
386 citations
TL;DR: In this paper, the authors present theoretical and numerical simulation studies supporting these ideas on equatorial spread-F (ESF) phenomena and show that these irregularities are formed by a two-step process in which they are driven by the steep plasma density gradients created by the primary long wavelength Rayleigh-Taylor type plasma fluid instabilities.
375 citations
TL;DR: The theory of the variation of the depth of amplitude scintillations with the zenith angle of the source is considered in this article, for radio waves received from a star or a satellite.
367 citations