The occurrences of nighttime 'ledges' in the total electron content (TEC) measurements at Arecibo are discussed and related, via a model calculation, to the rise and fall of the height of the peak density (hmax) around local midnight. The model behavior of hmax is consistent with observations and with reported changes in flow directions of the meridional nighttime neutral wind system deduced from incoherent scatter measurements. The results suggest that nighttime TEC data might be used to give indirect evidence for thermospheric wind flow directions.