Modeling the Arecibo nighttime F2 layer: 1. Overhead properties

Abstract

The servo model of Rishbeth et al. (1978) is extended and applied to fit the height and plasma density of the nighttime F2 layer, as measured from the Arecibo Observatory in Puerto Rico during solar maximum by Burnside (1984). The model equations are integrated numerically to fit the observed peak height and density. Specifically, the fitting is made by applying a theoretical zonal current (or drift), as needed so as to match the observed F2 peak. Moreover, the applied current/drift employs the measured ion velocity, whereas the component due to the neutral wind is freely adjusted. An improvement over previous servo‐model fits is made by considering the time variations in all the model neutral and plasma densities and temperatures. All the background neutral densities are obtained from the MSIS model (Hedin, 1987). The following results are obtained: (1) the model adequately reproduces the observed behavior of the F2 layer; (2) the additional terms in the extended servo‐height equation affect the peak height computation by no more than 10% on average; (3) the applied current is generally eastward though it becomes westward during the postmidnight collapse or descent of the layer; (4) differences between model and optically measured meridional wind speeds appear to be related to the presence of large vertical shears in the wind; (5) the observed peak density can be reproduced to within 20% to 40% accuracy; and (6) variable plasmaspheric fluxes of the order of 1013 (m−2 s−1) contribute to the maintenance and variability of the nighttime peak density. Also, horizontally divergent plasma fluxes remove plasma away from the local F2 peak; however, this is relatively minor. The overall model fit to the data is improved with the ion‐neutral collision frequency increased by 70% (Burnside et al., 1987).