Time-scale dependence of solar wind-based regression models of ionospheric electrodynamics

Abstract

The solar wind influence on geospace can be described as the sum of a directly driven component, or dayside reconnection, and an unloading component, associated with the release of magnetic energy via nightside reconnection. The two processes are poorly correlated on short time scales, but exactly equal when averaged over long time windows. Because of this peculiar property, regression models of ionospheric electrodynamics that are based on solar wind data are time scale specific: Models derived from 1 min resolution data will be different from models derived from hourly, daily, or monthly data. We explain and quantify this effect on simple linear regression models of various geomagnetic indices. We also derive a time scale-dependent correction factor that can be used with the Average Magnetic field and Polar current System model. Finally, we show how absolute estimates of the nightside reconnection rate can be calculated from solar wind measurements and geomagnetic indices.

A Survey of 25 Years' Transpolar Voltage Data From the SuperDARN Radar Network and the Expanding‐Contracting Polar Cap Model

“…The variation of Φ N inferred from time‐constants by Laundal et al. (2020) shows a strong variation with − AL , as does the analysis of the polar cap boundary location by Aikio et al. (2013).…”

“…), Hubert, Palmroth, et al (2006), and Milan et al (2009 used auroral images to also infer the loss of open flux during substorm expansion phases, which also implies a relationship between −AL and Φ N . The variation of Φ N inferred from time-constants by Laundal et al (2020) shows a strong variation with −AL, as does the analysis of the polar cap boundary location by Aikio et al (2013).…”

Dependence of the global dayside reconnection rate on interplanetary magnetic field By and the earth’s dipole tilt

“…These findings further indicate that the explicit B y -effect is a global phenomenon, which is likely related to a type A or B mechanism (or both) as mentioned above. Since dayside and nightside reconnection are the processes that allow for opening and closure of magnetic flux; the steady state, in which we interpret the long-term averages to represent (Laundal et al, 2020), must represent a balance of the two. The observed changes of the steady state open flux content depending on IMF B y /Ψ polarity must therefore either be due to a type A or B mechanism (or both).…”

Possible Ionospheric Influence on Substorm Onset Location

“…That IMF B z is not strongly related to the onset MLT, while the AL index is, is counter‐intuitive because the IMF B z and AL are correlated. However, the AL index is not a simple function of the simultaneous B z , but also depends on the delayed response of the magnetotail to energy transfer from the solar wind to the magnetosphere (Laundal et al., 2020). Our results therefore indicate that the possible ionospheric influence on substorm onset location depends more on the time‐delayed magnetotail component.…”