A study of the undisturbed mid-latitude ionosphere using simultaneous multiple site ionosonde measurements during the Sundial-86 campaign

The Sundial-86 campaign obtained simultaneous ionosonde measurements of NmF2 from 41 mid-latitude sites geographically dispersed around the world from September 21 to October 5, 1986. A three-dimensional, time-dependent model of Earth's ionoshpere has been used to fit the variations in NmF2 obtained from these sites. The model successfully reproduced the measurements in both the northern and southern hemispheres using the vertical plasma drift as a free parameter. During geomagnetically quiet conditions this drift is primarily due to the meridional neutral wind. The vertical plasma drift required to fit the data is consistent from location to location and the deduced meridional neutral wind is also consistent with previous neutral wind measurements and models. However, it is shown that a lack of knowledge of the variation of the O+ flux at the top of the atmosphere introduces a large uncertainty in the deduced thermospheric winds