Analysis on the Visibility of the O-mode and X-mode in SuperDARN Data

Abstract

The anisotropic nature of the ionosphere, caused by the Earth's magnetic field, causes the decomposition of HF radio waves into two component po larizations. These components, known as the Ordinary(O) mode and Ex traordinary(X) mode, each have a slightly different refractive index leading to a divergence in the paths taken by each mode. This divergence is well known by space weather and upper atmosphere researchers but doesn't al ways get the same interest as other phenomena. One example of this is with the Super Dual Auroral Radar Network (SuperDARN). SuperDARN is a global network of HF radars designed to study the Earth's ionosphere, but little research into the effects these two modes have on their data has been done. To rectify this, the raytracing program known as PHaRLAP is used to model SuperDARNs data output and investigate the effect of the O and X modes. This is done by using the density of rays in the raytracing model as a proxy for the power of the backscatter returned to the radar, so Range Time Intensity (RTI) plots can be formed. Once in this form, comparisons can be made between simulations including the Earth's magnetic field and simulations that ignore the Earth's magnetic field. This comparison shows the expected effect the O and X mode have on SuperDARN data, that being, a duplication of the peak ground scatter power near the skip distance. The distance between the duplications is then quantified to act as a metric for the impact the separation of the modes has on SuperDARN data. To better understand the effect, an analysis is conducted where key parameters, like frequency, bearing, and time of day, are varied to determine how the distance between the modes is affected. Once the analysis is completed an investiga tion of SuperDARN data can confirm the existence of the effect while also determining that the effect can be left out of most analysis of SuperDARN data due to the spatial scale of the effect being less than the normal range resolution of the radars.