Introducing a Disturbance Ionosphere Index (DIX)

Abstract

Although ionospheric perturbations such as Traveling Ionospheric Disturbances have a strong impact on Global Navigation Satellite Systems (GNSS) and other space based radio systems, the description of individual perturbations is difficult. This is due to the fact that our knowledge on the spatial and temporal variations of the ionosphere in particular during storms is rather poor. A pragmatic solution to overcome this problem is the use of information that describes the perturbation degree of the ionosphere in a less specific form e.g. as an index. Although such an index does not describe the exact propagation conditions at the measurement site, the estimated index number indicates the probability of a potential impact on radio systems used in communication, navigation and remote sensing. The definition of a perturbation index that might be used in operational applications must take into account the following major requirements: relevance to practical needs, objective measure of ionospheric conditions, easy and reproducible computation and availability of a reliable data base. Following these criteria, we propose an index which is specified in particular for use by GNSS customers. Since the Total Electron Content (TEC) has been shown in many publications to act as an outstanding parameter for quantifying the range error and also the strength of ionospheric perturbations, we propose the definition of a Disturbance Ionosphere indeX (DIX) that is based on GNSS measurements only. Following standard computational rules and depending on user needs the proposed DIX may be defined on local, regional and global scale. To illustrate the use of the index, recent storms monitored in 2011 and the Halloween storm are discussed. The proposed index is a robust and objective measure of the ionospheric state. Since DIX does not require any calibration procedure it can easily be calculated. The index is applicable to radio systems which are impacted by a highly variable perturbed ionosphere. If accepted by a broad community, the index could efficiently be used in operational ionosphere data services and GNSS augmentation systems.