Ionospheric irregularity zonal velocities over Cachoeira Paulista
ABSTRACT 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.
- SourceAvailable from: A. Taori
[Show abstract] [Hide abstract]
- "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. "
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 · 3.44 Impact Factor
[Show abstract] [Hide abstract]
- "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. "
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.Annales Geophysicae 06/2013; 31(6):1035-1044. DOI:10.5194/angeo-31-1035-2013 · 1.68 Impact Factor
[Show abstract] [Hide abstract]
- "dip angle at 300 km$ 201S). The large-scale plasma depletions/ irregularities have been widely reported to move eastward as measured by different techniques (Sobral et al., 1980a,1980b, 1985, 2009; Mendillo and Baumgardner, 1982; Abdu et al., 1985, 1987; Taylor et al., 1997; Rohrbaugh et al., 1989; Fejer et al., 1981, 1985, 1991, 2005; Sobral and Abdu, 1990; Basu et al., 1996, 2004; Valladares et al., 1996; Fagundes et al., 1996, 1997, 1998; Kudeki and Bhattacharyya, 1999; Kil et al., 2000; Bhattacharyya et al., 2001; Pimenta et al., 2001, 2003a, 2003b; de Paula et al., 2002; Otsuka et al., 2002, 2004; Immel et al., 2003, 2004; Kelley et al., 2003; Martinis et al., 2003; Makela, 2003, 2006 Abalde et al., 2004; Sheehan and Valladares, 2004; Lin et al., 2005; Ogawa et al., 2005; Park et al., 2007). However in considerably less frequent cases westward zonal motions have been observed, almost all of which being related to disturbance dynamo electric fields that are formed during geomagnetically disturbed time. "
ABSTRACT: In an effort to better understand the dynamics of westward velocities of the nocturnal F-region plasma, the climatology of the westward traveling plasma bubbles – WTB – occurring during quiettime is studied here. The climatology of the WTB is analyzed here based on airglow images obtained during 14 quiet days between 2001 and 2006 at the Brazilian station São João do Cariri (Geographic 7.45°S, 36.5°W, dip ∼20°S). The frequency of occurrence of the WTB maximizes in the descending phase of the solar cycle. The WTB velocities ranged between ∼20 and 40 ms−1. The frequency of occurrence had a peak value of only 3.65% at 2345 LT. The maximum occurrence of the WTB was in July–September. No WTB have been observed from November until April in all years 2001–2006. We show for the first time theoretically that the WTB dominant forcing mechanisms during geomagnetically quiet days are westward thermospheric winds.Research highlights► This paper presents for the first time midnight reversals of the zonal motion of plasma bubbles. ► It also presents calculated field-line integrated plasma zonal velocities. ► Airglow data to calculate the zonal speeds of the ionospheric plasma has been used.Journal of Atmospheric and Solar-Terrestrial Physics 07/2011; 73(11-12):1520-1528. DOI:10.1016/j.jastp.2010.11.031 · 1.75 Impact Factor