Abstract
Abstract. The high-latitude atmosphere is a dynamic region with processes that respond to forcing from the Sun, magnetosphere, neutral atmosphere, and ionosphere. Historically, the dominance of magnetosphere–ionosphere interactions has motivated upper atmospheric studies to use magnetic coordinates when examining magnetosphere–ionosphere–thermosphere coupling processes. However, there are significant differences between the dominant interactions within the polar cap, auroral oval, and equatorward of the auroral oval. Organising data relative to these boundaries has been shown to improve climatological and statistical studies, but the process of doing so is complicated by the shifting nature of the auroral oval and the difficulty in measuring its poleward and equatorward boundaries. This study presents a new set of open–closed magnetic field line boundaries (OCBs) obtained from Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) magnetic perturbation data. AMPERE observations of field-aligned currents (FACs) are used to determine the location of the boundary between the Region 1 (R1) and Region 2 (R2) FAC systems. This current boundary is thought to typically lie a few degrees equatorward of the OCB, making it a good candidate for obtaining OCB locations. The AMPERE R1–R2 boundaries are compared to the Defense Meteorological Satellite Program Special Sensor J (DMSP SSJ) electron energy flux boundaries to test this hypothesis and determine the best estimate of the systematic offset between the R1–R2 boundary and the OCB as a function of magnetic local time. These calibrated boundaries, as well as OCBs obtained from the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) observations, are validated using simultaneous observations of the convection reversal boundary measured by DMSP. The validation shows that the OCBs from IMAGE and AMPERE may be used together in statistical studies, providing the basis of a long-term data set that can be used to separate observations originating inside and outside of the polar cap.
Highlights
The high-latitude atmosphere is a dynamic region with processes that respond to forcing from the Sun, magnetosphere, neutral atmosphere, and ionosphere
This study investigates the relationship between the AMPERE Region 1 (R1)–Region 2 (R2) boundary and the open–closed magnetic field line boundaries (OCBs) inferred from particle precipitation measurements made by the Defense Meteorological Satellite Program Special Sensor J (DMSP SSJ) electron energy flux boundaries
This study follows the process outlined in Boakes et al (2008), which determined the offset between the Imager for Magnetopauseto-Aurora Global Exploration (IMAGE) far ultraviolet (FUV) poleward auroral boundaries and DMSP OCBs, to obtain a correction between the AMPERE R1–R2 boundary and the DMSP SSJ OCBs
Summary
The high-latitude atmosphere is a dynamic region with processes that respond to forcing from the Sun, magnetosphere, neutral atmosphere, and ionosphere. Due to these and other differences in MIT coupling processes in the auroral oval and the polar cap, it is desirable to have a coordinate system that indicates where (in which region) measurements were taken This type of adaptive, highlatitude gridding has been performed with various data sets (Redmon et al, 2010; Chisham, 2017b; Kilcommons et al, 2017). CRBs were chosen as a validation data set because the direction of convective plasma drifts are strongly tied to the motion and state (i.e. open or closed) of the magnetic field lines This means that the CRB is typically located at or just equatorward of the OCB (Newell et al, 2004; Drake et al, 2009), except for regions of the dayside and nightside ionosphere that map to regions of ongoing magnetic reconnection.
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