Neutral atmospheric density profiles between 135 and 225 km obtained from a cold cathode ion gauge onboard the Atmosphere Explorer-C spacecraft frequently exhibit considerable wave-like structure, which is interpreted to be internal gravity waves. We have attempted to correlate the occurrence probability and amplitude of these waves with several parameters of geophysical importance. Only weak correlations are found with common parameters, suh as Kp, for which strong correlations with the neutral atmospheric density are known to exist. However, the waves do appear over certain preferred geographical locations which tend to coincide with regions of high wind speeds and windshear in the upper troposphere. This relationship leads us to suggest that the majority of the waves observed in our data originate in the troposphere and subsequently propagate upwards into the thermosphere.