New results on equatorial thermospheric winds and temperatures from Ethiopia, Africa
Measurements of equatorial thermospheric winds, temperatures, and 630 nm relative intensities were obtained using an imaging Fabry–Perot interferometer (FPI), which was recently deployed at Bahir Dar University in Ethiopia (11.6° N, 37.4° E, 3.7° N magnetic). The results obtained in this study c...
Main Authors: | , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-03-01
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Series: | Annales Geophysicae |
Online Access: | https://www.ann-geophys.net/35/333/2017/angeo-35-333-2017.pdf |
Summary: | Measurements of equatorial thermospheric winds, temperatures, and 630 nm
relative intensities were obtained using an imaging Fabry–Perot
interferometer (FPI), which was recently deployed at Bahir Dar University in
Ethiopia (11.6° N, 37.4° E, 3.7° N magnetic). The
results obtained in this study cover 6 months (53 nights of useable data)
between November 2015 and April 2016. The monthly-averaged values, which
include local winter and equinox seasons, show the magnitude of the maximum
monthly-averaged zonal wind is typically within the range of 70 to
90 ms<sup>−1</sup> and is eastward between 19:00 and 21:00 LT. Compared to prior
studies of the equatorial thermospheric wind for this local time period, the
magnitude is considerably weaker as compared to the maximum zonal wind speed
observed in the Peruvian sector but comparable to Brazilian FPI results.
During the early evening, the meridional wind speeds are 30 to 50 ms<sup>−1</sup>
poleward during the winter months and 10 to 25 ms<sup>−1</sup> equatorward in the
equinox months. The direction of the poleward wind during the winter months
is believed to be mainly caused by the existence of the interhemispheric
wind flow from the summer to winter hemispheres. An equatorial wind surge is
observed later in the evening and is shifted to later local times during the
winter months and to earlier local times during the equinox months.
Significant night-to-night variations are also observed in the maximum speed
of both zonal and meridional winds. The temperature observations show the
midnight temperature maximum (MTM) to be generally present between 00:30 and
02:00 LT. The amplitude of the MTM was ∼ 110 K in January 2016 with
values smaller than this in the other months. The local time difference
between the appearance of the MTM and a pre-midnight equatorial wind was
generally 60 to 180 min. A meridional wind reversal was also observed after
the appearance of the MTM (after 02:00 LT). Climatological models, HWM14 and
MSIS-00, were compared to the observations and the HWM14 model generally
predicted the zonal wind observations well with the exception of higher model
values by 25 ms<sup>−1</sup> in the winter months. The HWM14 model meridional wind
showed generally good agreement with the observations. Finally, the MSIS-00
model overestimated the temperature by 50 to 75 K during the early evening
hours of local winter months. Otherwise, the agreement was generally good,
although, in line with prior studies, the model failed to reproduce the MTM
peak for any of the 6 months compared with the FPI data. |
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ISSN: | 0992-7689 1432-0576 |