Evolution and dynamics of ionospheric intermediate layers above Arecibo Observatory

The research presented in this dissertation focuses on the formation, evolution, and morphology of midlatitude intermediate layers. This work explores layer morphology using three distinct techniques: in-situ rocket measurements, incoherent scatter radar observations, and a first principles numerical model. The rocket and radar data are from the 1998 Coqui II rocket campaign. This data set is then used in conjunction with the numerical model, which was conceived, developed, and validated as a tool for studying nighttime ionospheric E-region dynamics during the course of this research. The first portion of the research utilizes data provided by instruments aboard a sounding rocket. Neutral wind and plasma density measurements of a weak layer allow the first exploration of the density structure and wind field morphology of an intermediate layer. Coupled with simultaneous data from the Arecibo Observatory (AO), the upleg and downleg density profiles enable the first detailed investigation of the horizontal extent and variation of an intermediate layer. Next, the nightly variability of intermediate layer structure is examined using data from the Arecibo Observatory taken during the three month period of the Coqui II rocket campaign. The numerous layer observations permit a study of the effects of geomagnetic activity on layer development, and provide a qualitative understanding of nightly variability in the lower ionosphere. A numerical model, consisting of three independent phases, explores specific aspects of layer morphology. Phase I calculates the apparent nighttime E-region vertical ion velocities from a time sequence of density profiles. Phase II investigates layer formation due to a static neutral wind field. In-situ measured winds are used to initialize the model and the results are compared to the observed density profiles. Phase III employs time-varying neutral winds to explore the coupling between metallic ion transport and local neutral wind variations. For the first time, the relative metallic ion transport efficiency of meridional versus zonal neutral winds is explored as a function of wave parameters and time. Phase III also investigates layer morphology resulting from the application of the complete horizontal wind field as specified by the empirical model known as the Horizontal Wind Model, HWM-93.