Winds near the top of the atmosphere are expected to be the same at all heights for a given location by assuming high viscosity in rarefied gases. However, wind measurements from satellite drag at 350–400 km altitude were found to be up to 2 times larger than optical measurements at ∼240 km. Satellites provide global measurements, and ground-based FPIs provide long-term monitoring at single sites. So we must understand this inconsistency to model and predict atmospheric behaviour correctly.