Accounting for the 3D Earth in a space weather forecasting workflow: Methods of real-time geoelectric field estimation

Abstract:

In the context of an operational Geospace model, ionospheric currents and ground-level geomagnetic fields are estimated and forecast in real time. While accurate actionable predictions of geomagnetic fields are at present an aspirational goal, the scientific community is striving for model improvements (including, possibly, data assimilation techniques) that would employ real time satellite observations to enable accurate prediction of these quantities with enough lead time for action to be taken on the ground. These predictions, once available, could be expanded to also include ground-level geoelectric fields. Indeed, accurate forecasting of ground-level geoelectric fields is a critical long-term goal of Sun-to-Earth space weather modeling. If achieved, this would allow power grid operators sufficient lead time to redistribute the load and/or switch off those transformers that would be most affected by an upcoming storm, thus mitigating the damage.

Here, we review the full range of methods that could use an operational forecast of ionospheric currents or ground-level geomagnetic fields to model geoelectric fields in real time. We discuss (but do not implement) full physics modeling of ground level geoelectric fields in the time domain, as well as an efficient variant of physics-based modeling that is based on utilizing the linear relationship between geoelectric fields and ionospheric sources (e.g., Püthe & Kuvshinov, 2013; Honkonen et al, 2018). We compare that with an alternative approach that forgoes real-time Earth modeling altogether, utilizing instead the empirical or pre-computed Earth impedances (e.g., Bonner & Schultz, 2017; Lucas et al, 2018), or the equivalent impulse responses (e.g., Kelbert et al, 2017), for real-time geoelectric field estimation. We review the methods and the related research questions and provide a progress update.