Interpreting vertical plasma drift in the mid-lattitude ionosphere using ionosonde measurements

Measurements of the density at the F₂ peak (N_mF₂) were obtained by the Boulder, Colorado, ionosonde as part of the SUNDIAL-86 campaign. The measurements were made during a period of low to moderate geomagnetic activity following a “disturbed” day. These measurements were then used to estimate the height of the F₂ peak (h_mF₂). A three-dimensional time-dependent model of Earth's ionosphere was used to calculate N_mF₂ and h_mF₂ using the vertical plasma drift as a free parameter. Since the plasmasphere-ionosphere exchange flux can remain upward during the night for these conditions, different feasible flux scenarios were inputed to the ionospheric model. These different flux scenarios had a large effect on the “induced” vertical plasma drifts required to match the measurements (i.e. at times greater than a factor of 2 in speed or a difference in direction). Futhermore, uncertainty in the O⁺---O collision frequency changes the required vertical plasma drift at night. Despite knowledge of h_mF₂, interpretation of the vertical plasma drifts as meridional neutral winds is compromised by a lack of knowledge of the plasmasphere-ionosphere exchange flux following disturbed days.