We present 4-year study of the nighttime lower ionosphere height (h(N)) behavior for equatorial, low and middle latitudes over a region from 30 degrees E to 60 degrees E. The results show that hN oscillates with semiannual (SAO) and annual (AO) periodicity, being SAO dominant for low and equatorial latitudes, while AO seems to be significant for middle latitudes. For equatorial and middle latitudes, hN shows negative correlation with the mesospheric temperature variation, suggesting a close relation with the dynamics of the Mesosphere-Lower Thermosphere Region (MLT). For middle latitudes, the results shows no clear correlation, it can be due to the presence of planetary waves with periods around 10, 12, 16 days which might affect the seasonal behavior of the nighttime lower ionosphere. Since planetary waves are very predominantly of tropospheric origin, this result is an evidence of the vertical couplings in the atmosphere-ionosphere system.
