Timescales of Birkeland Currents Driven by the IMF

Abstract

We obtain current densities from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), alongside By and Bz from the Interplanetary Magnetic Field (IMF) for March 2010. For each AMPERE spatial coordinate, we cross‐correlate current density with By and Bz, finding the maximum correlation for lags up to 360 min. The patterns of maximum correlation contain large‐scale structures consistent with the literature. For the correlation with By, the lags on the dayside are 10 min at high latitudes but up to 240 min at lower latitudes. Lags on the nightside are 90–150 min. For Bz, the shortest lags on the dayside are 10–20 min; on the equatorward edge of the current oval, 60–90 min; and on the nightside, predominantly 90–150 min. This novel approach enables us to see statistically the timescales on which information is electrodynamically communicated to the ionosphere after magnetic field lines reconnect on the dayside and nightside.

Magnetospheric Flux Throughput in the Dungey Cycle: Identification of Convection State During 2010

“…The ECPC has been modeled numerically (e.g., Freeman & Morley, 2004; Lockwood & Morley, 2004; Lockwood et al., 2006; Milan, 2013), allowing the ionospheric flows associated with expansions and contractions of the polar cap to be quantified (subject to reasonable assumptions). A significant body of work has confirmed that the flows and timescales predicted by the ECPC are consistent with observations (e.g., Coxon et al., 2019; Lockwood et al., 2009; Snekvik et al., 2017; Walach et al., 2017). The ECPC has been employed to investigate the response of the magnetosphere to solar wind driving, either as case studies of a limited number of events (e.g., Hubert et al., 2017, 2006; Milan, 2004; Milan et al., 2008, 2003), or as statistics of many events (e.g., Clausen, Milan et al., 2013; Coxon et al., 2014; Milan, Grocott et al., 2009; Milan, Hutchinson et al., 2009; Milan et al., 2019; Walach & Milan, 2015).…”

The Evolution of Long‐Duration Cusp Spot Emission During Lobe Reconnection With Respect to Field‐Aligned Currents

“…The dayside polar cap responds quickly to changes in the magnitude and orientation of the IMF. The fast response of the polar cap FACs to changes in IMF orientation was recently demonstrated by Taguchi et al (2015) during a transition from a IMF B Z -dominated to IMF B Y -dominated scenario in approximately 10 min, and again by Coxon et al (2019) following a statistical study of FACs, which also showed a 10-min response at high latitude. The IMF turns briefly southward twice after 20 hr UT on 16 June 2012 and each time for 4 min in duration.…”

The Impact of Sudden Commencements on Ground Magnetic Field Variability: Immediate and Delayed Consequences

“…Studies have shown that high-latitude surface magnetic field perturbations, and the field-aligned currents that drive them, react to the solar wind on different characteristic time scales: ranging between 10 and 150 minutes depending on location (e.g. Coxon et al, 2019;Shore et al, 2019).…”