Climatology of the nighttime equatorial thermospheric winds and temperatures over Brazil near solar minimum

Abstract

[1] We report on the climatology of equatorial thermospheric winds and temperatures based on Fabry-Perot interferometer measurements of Doppler shifts and Doppler broadenings of the 630.0 nm spectral emission from the Cajazeiras observatory located in the northeastern part of Brazil (6.89°S, 38.56°W). These results apply to the lower thermosphere region near 240 km and were obtained during a period of weak solar activity with the solar flux typically within the range of 72 and 82 solar flux units. Examination of the monthly averaged meridional thermospheric winds for 1 year of measurement from October 2009 to September 2010 found the wind direction to be equatorward during summer months throughout the early evening hours with maximum speeds reaching ∼65 ms −1 . During winter months, the early evening meridional wind direction reversed to poleward with similar speeds. This result is attributed to the cross-hemispheric flow from the summer to winter hemisphere. Superimposed upon this wintertime meridional wind flow was an equatorward surge shortly before midnight. This surge shifted to earlier local times in the transition from the vernal equinox to summer and to later local times between the summer solstice and the autumnal equinox; this flow feature is attributed to tidal wave forcing. The temperature observations exhibited the expected behavior, with the midnight temperature maximum showing a greater amplitude, ∼120 K, in the vernal equinox with somewhat weaker amplitudes, ∼75 K, seen at earlier local times during the summer. Also observed was a phase lag of 60 to 90 min between the appearance of the equatorward meridional wind flow and occurrence of the midnight temperature maximum peak.

Thermospheric zonal mean winds and tides revealed by CHAMP

“…The time mean and diurnal components in the CHAMP zonal wind agree fairly well with the WAM. Meriwether et al [2011] have presented interferometerbased winds over Brazil obtained for solar minimum conditions. The behavior of CHAMP nighttime winds at 5 ı S (not shown) is quite consistent with the winds reported for Brazil.…”

Characteristics of equatorial plasma bubbles observed by TEC map based on ground-based GNSS receivers over South America

“…Figure 9 shows the monthly averaged zonal drift velocities of the EPBs at 5 • S and the monthly averaged thermospheric zonal wind measured by a OI 630 nm FPI near the Equator during the months when we observed a large occurrence of EPBs. The FPI is able to measure thermospheric zonal and meridional neutral winds by measuring Doppler shift of OI 630 nm emission line at 250 km altitude with an accuracy of 5 to 10 m s −1 Meriwether et al, 2011). The FPI is located at São João do Cariri (7.4…”

Calibration and validation of the advanced E-Region Wind Interferometer

“…In a recent paper on multiple order Fabry-Perot wind observations (Shiokawa et al, 2012) (similar to the observation technique used by Makela et al, 2011 andMeriwether et al, 2011) random errors ranging from 2 to 13 m s −1 are quoted for a single wind observation with an exposure time of 60 s. Assuming that observing conditions in the middle of this range correspond to those for ERWIN II, it would take this instrument ∼ 5 min to observe the same five velocities with a precision of ∼ 7 m s −1 .…”

“…For this approach, a non-linear least-mean-squares analysis using the Levenberg Marquardt method (as described in Press et al, 2007) is implemented. The variation in photons detected per integration time for a step during the k-th 8-point scan is modelled according to the following equation:…”