Timescale separation in the solar wind-magnetosphere coupling during St. Patrick's Day storms in 2013 and 2015

In this work, we present a case study of the relevant timescales responsible for coupling between the solar wind changes and the magnetospheric response during the St. Patrick's DayGeomagnetic Storms in 2013 and 2015. We investigate the behavior of the Interplanetary Magnetic Field (IMF) component Bz, the Perreault-Akasofu coupling function and the AE,AL and Sym-H geomagnetic indices at different timescales by using the Empirical Mode Decomposition (EMD) method and the Delayed Mutual Information (DMI). The EMD allowsto extract the intrinsic oscillations (modes) present into the different datasets, while the DMI, which provides a measure of the total linear and nonlinear correlation degree, allows to investigate the relevance of the different timescales in the solar wind-magnetosphere coupling. The results show the existence of a relevant timescale separation in the solar wind-magnetosphere coupling. Indeed, while long-timescales (τ > 200 min) show a large degree of correlationbetween solar wind parameters and magnetospheric dynamics proxies, at short-timescales (τ < 200 min) this correlation is missed. This result indicates an internal origin of timescaleslower than 200 min, while the magnetospheric response to the solar wind driver occurs on timescales related to solar wind structure periodicities. This results can be relevant in theframework of Space Weather forecasting.