Uncertainties in space weather forecasting using coupled physics models

Abstract:

Although probabilistic forecasts are issued for some space weather phenomenologies, most magnetospheric prediction systems yield deterministic forecasts. To address the needs of users it is desirable to not just issue a single forecast, but to report likely outcomes or probabilities of different results. This need arises not just in forecasting, but also in defining extreme event scenarios for benchmarking purposes. Errors in forecasts typically arise through inaccurate specification of initial conditions or boundary conditions, as well as model uncertainties that arise because the model only approximates the system it simulates. As part of a large, interdisciplinary project studying the impacts of extreme space weather events on power grid infrastructure we have recently developed a method to assess the effect of uncertainties in solar wind driving on the predictions of geomagnetic indices (Sym-H, Kp), and geomagnetic disturbances (dB/dt) at selected observatories within a modeling framework. We used operational configuration of the Space Weather Modeling Framework and simulated a test event using a 40 member perturbed input ensemble. This ensemble method also allows us to identify intervals of activity that cannot be explained by uncertainty in the solar wind driver, highlighting areas for further model development. We now extend this work to examine the uncertainty in predicted field quantities such as magnetic perturbations and geoelectric field. Finally, we examine the challenges associated with developing uncertainties and confidence in likely scenarios for extreme, as-yet-unobserved events.