On the application of ensemble modeling techniques to improve ambient solar wind models

Abstract

Ensemble modeling is a method of prediction based on the use of a representative sample of possible future states. Global models of the solar corona and inner heliosphere are now maturing to the point of becoming predictive tools; thus, it is both meaningful and necessary to quantitatively assess their uncertainty and limitations. In this study, we apply simple ensemble modeling techniques as a first step towards these goals. We focus on one relatively quiescent time period, Carrington rotation 2062, which occurred during the late declining phase of solar cycle 23. To illustrate and assess the sensitivity of the model results to variations in boundary conditions, we compute solutions using synoptic magnetograms from seven solar observatories. Model sensitivity is explored using (1) different combinations of models, (2) perturbations in the base coronal temperature (a free parameter in one of the model approximations), and (3) the spatial resolution of the numerical grid. We present variance maps, “whisker” plots, and “Taylor” diagrams to summarize the accuracy of the solutions and compute skill scores, which demonstrate that the ensemble mean solution outperforms any of the individual realizations. Our results provide a baseline against which future model improvements can be compared.