Comparisons of thermospheric wind and temperature measurements in equatorial Brazil to Whole Atmosphere Model Predictions

Abstract

The results from the Whole Atmosphere Model (WAM) at 240km are compared with measurements of equatorial thermospheric winds and temperatures acquired by nearly continual nighttime Fabry–Perot interferometer (FPI) measurements made in northeastern Brazil from September 2009 to August 2012. These comparisons show generally good agreement for the zonal winds with only slight differences seen in regard to the early morning period. For the evening period of 21–23 LT the observed meridional winds differed from the WAM predictions in two respects. First, while the flow direction was generally correct, the speeds of observed cross-hemispheric flow from the summer to the winter hemisphere were generally somewhat greater by 25 to 35ms−1 than the predicted speeds from WAM. In contrast, the observed meridional winds are found to be weaker than the WAM results for winter months for all three years. Second, although the observations and predictions both show similar timing and amplitude for a 3-h period of northward flow in September and October, the observations indicate a shift in the timing of this flow of about 1h, from ∼22 LT in September and October to ∼21 LT in December. The WAM predictions show a systematic shift in phase from 21–00 LT in September to 18–21 LT in December. Regarding temperature, the WAM predictions show a midnight temperature maximum (MTM) with a peak amplitude of 50–65K, in agreement with the observations. However, the WAM results also show a systematic shift in timing of the MTM occurrence, with the MTM peak seen at ∼22 LT in summer and at 00 LT in winter. In contrast, the FPI monthly climatology data show the timing of the MTM peak to be 00±0.5 LT for all months except winter, when the MTM peak is not clearly evident.