The coherence between the IMF and high-latitude ionospheric flows: The dayside magnetosphere–ionosphere low-pass filter

• Published in: Journal of atmospheric and solar-terrestrial physics Vol. 69; no. 3; pp. 223 - 233
• Main Authors: Murr, D.L., Hughes, W.J.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 01.03.2007; Elsevier
• Subjects: Earth, ocean, space; Exact sciences and technology; External geophysics; Ionospheric dynamics; Magnetosphere/ionosphere interactions; Magnetospheric configuration and dynamics; Physics of the high neutral atmosphere; Physics of the ionosphere; Physics of the magnetosphere; Plasma convection; Ionospheric dynamics; Magnetosphere/ionosphere interactions; Magnetospheric configuration and dynamics; Plasma convection; Interplanetary magnetic field; High latitude; Cut off low; Magnetopause; Time series; Convection flow; Ionosphere magnetosphere coupling; North south component; dynamics; magnetosphere; fluctuations
• ISSN: 1364-6826; 1879-1824
• DOI: 10.1016/j.jastp.2006.07.019

This study seeks to establish a new system characteristic describing dayside convective flows in the coupled magnetosphere–ionosphere: the low-pass filter function through which interplanetary magnetic field (IMF) fluctuations are processed as they are communicated from the magnetopause to the high-latitude ionosphere near local noon. In doing so, this study confirms that variations in the ionospheric flows at high-latitudes near local noon are well correlated with variations in the IMF orientation and magnitude on short timescales. We construct the filter function by comparing time series of the ionospheric equivalent flows at a fixed location at magnetic local noon and 80° latitude with time series of the IMF. The coherence spectra of these two parameters—averaged over 330 h of comparison—indicate that there is a low-pass cutoff in the ionospheric response to IMF driving at a periods shorter than 20 min (frequencies higher than 0.8 mHz). When there is sufficient power in the IMF fluctuations, this cutoff is relatively sharp—the coherence drops by roughly a factor of three between the periods 32 and 21 min (0.5 and 0.8 mHz). The results also show that on average the coherence between the east–west component of the equivalent flows and IMF B y tends to be less than the coherence between the north–south component of the equivalent flows and IMF B z .