Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 35, 333-344, 2017
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Regular paper
03 Mar 2017
New results on equatorial thermospheric winds and temperatures from Ethiopia, Africa
Fasil Tesema1,2,5, Rafael Mesquita2, John Meriwether2, Baylie Damtie1, Melessew Nigussie1, Jonathan Makela3, Daniel Fisher3, Brian Harding3, Endawoke Yizengaw4, and Samuel Sanders2 1Washera Geospace and Radar Science Laboratory, Bahir Dar University, Bahir Dar, Ethiopia
2Department of Physics and Astronomy, Clemson University, Clemson, South Carolina, USA
3Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
4Institute for Scientific Research, Boston College, Boston, Massachusetts, USA
5Department of Physics, Wollo University, Dessie, Ethiopia
Abstract. 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−1 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−1 poleward during the winter months and 10 to 25 ms−1 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−1 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.

Citation: Tesema, F., Mesquita, R., Meriwether, J., Damtie, B., Nigussie, M., Makela, J., Fisher, D., Harding, B., Yizengaw, E., and Sanders, S.: New results on equatorial thermospheric winds and temperatures from Ethiopia, Africa, Ann. Geophys., 35, 333-344, doi:10.5194/angeo-35-333-2017, 2017.
Publications Copernicus
Short summary
Measurements of equatorial thermospheric winds obtained from an optical instrument called a Fabry–Perot interferometer in Ethiopia show a significance difference as compared with other longitudinal sectors. The zonal wind in this sector is small and shows a gradual decrease through out the night. Application of climatological wind and temperature models shows good agreement with the observations over Ethiopia.
Measurements of equatorial thermospheric winds obtained from an optical instrument called a...