An energy balance study of the lower topside ionosphere using the Arecibo incoherent scatter radar and heating facilities

Abstract

In this paper we describe the results of an experiment to study electron and ion temperature enhancements during an HF modification experiment at the Arecibo Observatory. This experiment is unique in that we pointed the radar away from the interaction region in the F region in order to study heat conduction along the field lines. Although electron temperature enhancements have been frequently observed when high‐power radio waves are injected into the ionosphere, observations generally have occurred in the interaction region and the regions of elevated electron temperatures have been accompanied by small ion temperature increases (50–200 K). Like many such experiments, this one was conducted during winter solar minimum, when f0F2 is low during the night at midlatitudes, but this experiment also had the advantage of the upgraded Arecibo HF facility, first used in 1997. The electron temperature enhancements were accompanied by a significant increase in the ion temperature (nearly 500 K). The observation away from the interaction region allowed the application of the time‐dependent heating equation without having to estimate local heating effects (i.e., by keeping the conduction and loss terms in the energy balance calculation and neglecting the source term). More specifically, the heating rate of conduction was quantified by manipulating the heat equation. Thus the primary purpose was to observe the temperatures as the heat was conducted away from the F region ionosphere. We have observed the gradients in the electron temperature caused by the heater, estimated the conduction along the field lines, and studied the transfer of energy from the hot electrons to the ions and neutrals. At lower altitudes, near the electron‐temperature peak, we show that O+ cooling is dominant, whereas in the lower topside H+ cooling is the most important. Experiments of the type described here could be enhanced with the new dual‐beam system at Arecibo in conjunction with a heating facility.