We have studied the zonal drift velocity of nighttime ionospheric irregularities from Cachoeira Paulista (22.41°S,45°W, dip latitude −17.43°), a station under the Equatorial Anomaly, from December 1998 to February 1999 using L1 band GPS receivers and OI all-sky images. The average decimetric solar flux index for this period of increasing solar activity was about 145 and magnetically quiet days with ΣKp<24 were selected. The GPS technique used receivers spaced in the magnetic east–west direction and probed small scale plasma structures (scale size about ) at altitudes near . The zonal irregularity drift velocities measured by this technique were eastward with values of about at 20 LT, about around midnight, and decreased further in the post-midnight sector. The variability of these drifts decreased significantly after midnight. The zonal velocities of large scale plasma structure were obtained using OI all-sky images from a region located about 24.1°S and 45°W at a nominal height of which corresponds to the bubble projection along the magnetic field lines to over Cachoeira Paulista. These all-sky imager derived zonal drifts are also eastward, but have magnitudes smaller than the spaced GPS eastward drifts, particularly in the pre-midnight sector. We will discuss these two drift measurement techniques and the interpretation of our results.
"The climatological model of Fejer et al.  reveals the zonal drifts to vary from 100 m/s to 170 m/s. The peak drift velocities calculated from optical measurements over American sector are found to be ~120 m/s to ~150 m/s [e.g., de Paula et al., 2002; Martinis et al., 2003; Pimenta et al., 2003]. Over Indian sector, using VHF scintillation data, Kumar et al.  reported the drift velocities to decrease from ~200 m/s at 2000 h IST to ~60 m/s at 0400 h IST. "
[Show abstract][Hide abstract] ABSTRACT:  We report the east-west velocity measurements of the equatorial plasma depletion (EPD) from Gadanki (13.5°N, 79.2°E, dip latitude 6.5°N) estimated using the airglow imaging of O(1D) 630 nm airglow emission during the years 2012–2013. Our measured EPD velocity values are significantly smaller than earlier reported values from low-latitude stations in India. The measured nocturnal EPD velocity variations are compared with recent empirical model given by England and Immel (2012). We note that during March–April months, our measurements agree very well with the empirical model while minor differences are noted in other months. We also note the differences between our measurements and horizontal wind model. We believe that these differences suggest the deviation of electrodynamics associated with EPD from the one occurring in the background thermospheric altitudes.
Journal of Geophysical Research Atmospheres 01/2014; 119(1-6). DOI:10.1002/2013JA019465 · 3.43 Impact Factor
"Although there are a number of papers on the zonal plasma drift, a large number of those studies are restricted to local nighttime because they used equatorial plasma bubbles (EPBs) as a tracer for estimating the zonal plasma drift (e.g. Kil et al., 2002; de Paula et al., 2002; Martinis et al., 2003; England and Immel, 2012). Some of the other extensive studies , which covered the dayside climatology, used groundbased instrumentation at a fixed geographic location (e.g. "
[Show abstract][Hide abstract] ABSTRACT: In this paper we estimate zonal plasma drift in the equatorial
ionospheric F region without counting on ion drift meters. From June
2001 to June 2004 zonal plasma drift velocity is estimated from
electron, neutral, and magnetic field observations of Challenging
Mini-satellite Payload (CHAMP) in the 09:00-20:00 LT sector. The
estimated velocities are validated against ion drift measurements by the
Republic of China Satellite-1/Ionospheric Plasma and Electrodynamics
Instrument (ROCSAT-1/IPEI) during the same period. The correlation
between the CHAMP (altitude ~ 400 km) estimates and ROCSAT-1 (altitude ~
600 km) observations is reasonably high (R ≈ 0.8). The slope of the
linear regression is close to unity. However, the maximum westward drift
and the westward-to-eastward reversal occur earlier for CHAMP estimates
than for ROCSAT-1 measurements. In the equatorial F region both zonal
wind and plasma drift have the same direction. Both generate vertical
currents but with opposite signs. The wind effect (F region wind dynamo)
is generally larger in magnitude than the plasma drift effect (Pedersen
current generated by vertical E field), thus determining the direction
of the F region vertical current.
"A gradual decrease is observed in the zonal drift velocity from between 100 and 200 m/s at around 22:00 LT to below 50 m/s after local midnight [Mendillo and Baumgardner, 1982; Mendillo et al., 1997; Taylor et al., 1997; Sinha and Raizada, 2000; Pimenta et al., 2003b]. However, other researchers have seen a slight increase in the drift velocity near local midnight [Tinsley et al., 1997; Santana et al., 2001; de Paula et al., 2002; Makela and Kelley, 2003; Mukherjee, 2003]. Still others have at times seen zonal drift velocities as fast as 400 m/s [Fagundes et al., 1997]. "
[Show abstract][Hide abstract] ABSTRACT: The propagation of electromagnetic waves through the turbulent ionosphere produces scintillations through diffraction, and understanding the physical nature of scintillations is important for engineers and technologists as well as for scientists. In recent years, the establishment of the Global Positioning System (GPS) provided a new technique that can be used to study ionospheric scintillations. The usual way of doing that is the deployment of GPS receivers closely spaced in east-west magnetic direction and then estimating the zonal drift velocities based on the signal power observations. One of the weaknesses of this method is that high-rate sampling such as 20 Hz is required for close-spaced stations and generally no such data are available for studying ionospheric scintillation in the past years. In this research work, a scintillation monitoring method based on slant TEC (STEC) observations of local GPS Continuously Operating Reference Station (CORS) network is proposed. First, the past research works on the equatorial ionospheric drift velocities are summarized. Then, by comparing the scintillation pattern of the signal power and STEC observations of California local GPS reference network, we find that the STEC is a good choice for estimating the ionospheric zonal drift velocity. Then it is illustrated how to calculate the ionospheric scintillation velocity based on STEC. Finally, the proposed method is applied to Hong Kong GPS reference network and several cases of the calculated ionospheric zonal velocities are given.
Journal of Geophysical Research Atmospheres 08/2011; 116(A8). DOI:10.1029/2010JA015993 · 3.43 Impact Factor
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