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Abstract Horizontals drifts of equatorial Spread F (ESF) at post-sunset and post-midnight are investigated by analyzing six ESF events observed during the period of November 2022–March 2023. Horizontal drift velocities of ESFs are calculated from the time lags between signals recorded by different transmitter–receiver pairs of a new Continuous Doppler Sounding (CDS) system operating at 6.80 MHz in a low latitude station, Tucumán, Argentina (26° 49’ S, 65° 13' W, mag. latitude ~ 13°) and by the older CDS system working at 4.63 MHz. A new method of time lags determination for spread structures is presented. In addition, the occurrence of airglow depletions associated with ESF events is verified using images of airglow emissions of atomic O red line, 630 nm. We found that the typical speeds of the ESF drift in the post-sunset hours (around 130 m/s) are about two times greater than the speeds of ESF occurring around midnight or in post-midnight hours (around 80 m/s). The drift speeds obtained using 4.63 and 6.80 MHz systems were practically the same with the exception of one event, which might have been due to wind shear. Azimuths obtained by 4.63 and 6.80 MHz systems are almost similar. No systematic dependence of the azimuth on the local time and sounding frequency was found. All ESF events drift roughly eastward with an average azimuth of about 105$$^\circ$$ with respect to the geographic north. Graphical Abstract
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Mean Zonal Drift Velocities of Plasma Bubbles Estimated from Keograms of Nightglow All-Sky Images from the Brazilian Sector
We present in this work a method for estimation of equatorial plasma bubble (EPB) mean zonal drift velocities using keograms generated from images of the OI 6300.0 nm nightglow emission collected from an equatorial station–Cariri (7.4° S, 36.5° W), and a mid-latitude station–Cachoeira Paulista (22.7° S, 45° W), both in the Brazilian sector. The mean zonal drift velocities were estimated for 239 events recorded from 2000 to 2003 in Cariri, and for 56 events recorded over Cachoeira Paulista from 1998 to 2000. It was found that EPB zonal drift velocities are smaller (≈60 ms−1) for events occurring later in the night compared to those occurring earlier (≈150 ms−1). The decreasing rate of the zonal drift velocity is ≈10 ms−1/h. We have also found that, in general, bubble events appearing first in the west-most region of the keograms are faster than those appearing first in the east-most region. Larger zonal drift velocities occur from 19 to 23 LT in a longitude range from −37° to −33°, which shows that the keogram method can be used to describe vertical gradients in the thermospheric wind, assuming that the EPBs drift eastward with the zonal wind. The method of velocity estimation using keograms compares favorably against the mosaic method developed by Arruda, D.C.S, 2005, but the standard deviation of the residuals for the zonal drift velocities from the two methods is not small (≈15 ms−1).
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- PAR ID:
- 10170728
- Date Published:
- Journal Name:
- Atmosphere
- Volume:
- 11
- Issue:
- 1
- ISSN:
- 2073-4433
- Page Range / eLocation ID:
- 69
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/atmos11010069
