Northern and Southern Hemisphere Polar Cap Indices: To What Extent Do They Agree and to What Extent Should They Agree?

Abstract

The Polar Cap Indices (PCI) are compiled using data from one magnetometer station in each hemisphere, each close to the geomagnetic pole (Stauning, 2021a(Stauning, , 2021bTroshichev, 2022). The northern hemisphere index, PCN, is from observations made at the Thule (Qaanaaq) in Greenland (IAGA code THL: geographic coordinates 77.47°N, −69.23°E) and the southern hemisphere index, PCS, is from observations made at Vostok (IAGA code VOS: geographic coordinates −79.45°N, 106.87°E). (IAGA is the International Association of Geomagnetism and Aeronomy, one of the eight associations of the International Union of Geodesy and Geophysics). Over the years studied in this paper (1998-2018) there has been a relatively rapid motion of the Northern geomagnetic (eccentric dipole) pole toward the rotational axis and much slower motion of the Southern pole (Koochak & Fraser-Smith, 2017;Lockwood et al., 2021). This has resulted in different motions of the stations in geomagnetic coordinates. This paper employs the Altitude-Adjusted Corrected Geomagnetic Coordinate system AACGMv2 (Shepherd, 2014) and the magnetic coordinates of the two stations in this frame are given in Table 1 for the start, middle and end years of the period studied. This shows 1.50° equatorward motion of THL in the geomagnetic

Statistical Features of Polar Cap North and South Indices in Response to Interplanetary and Terrestrial Conditions: A Revisit

“…These studies have shown that the differences between these indices are results of the decoupling of solar wind and magnetospheric electric fields in association with the changes in the magnetosheath and magnetospheric magnetic fields (Lockwood, 2023a(Lockwood, , 2023b. In this regard, the distortion of the E KL -induced ionospheric current/convection system (Lockwood, 2023a(Lockwood, , 2023bO. A. Troshichev, 2022;O.…”

“…Troshichev et al, 2006). More recently, several studies have been conducted to statistically investigate the physical reasons that cause not only the occurrence of positive/negative values in PCN and PCS indices but also the difference in these indices (Lockwood, 2023a(Lockwood, , 2023bO. A. Troshichev, 2022;O.…”

“…A. Troshichev et al, 2023). Besides, the differences in the ionospheric conductance between the northern and southern polar caps can be a possible candidate because of their effects on the hemispheric differences in the ionospheric current system (Lockwood, 2023a(Lockwood, , 2023bLukianova et al, 2002;O. A. Troshichev, 2022;O.…”

Universal Time Effects on Substorm Growth Phases and Onsets

“…Lockwood and Milan (2023) have recently reviewed Universal Time ( UT ) variations in magnetospheric observations and indices. Their study included: the am planetary geomagnetic index (Lockwood et al., 2019; Mayaud, 1972); the SML auroral electrojet index (Newell & Gjerloev, 2011a, 2011b); the SMR partial ring current indices (Newell & Gjerloev, 2012); the polar cap indices (Lockwood, 2023; Stauning, 2007; Troshichev, 2022), transpolar voltage observations from Low‐Earth Orbit (LEO) spacecraft (e.g., Boyle et al., 1997; Hairston & Heelis, 1993), Φ PC ; field aligned‐current maps derived from measurements by magnetometers on the Iridium LEO satellites by the Active Magnetosphere and Planetary Electrodynamics Response Experiment project (Coxon et al., 2018); and substorm onset occurrence (Forsyth et al., 2015; Newell & Gjerloev, 2011a, 2011b). In addition, Lockwood et al.…”

Solar Wind‐Magnetosphere Coupling During High‐Intensity Long‐Duration Continuous AE Activity (HILDCAA)

“…The substorm electrojet produces an additional enhancement of AL—the substorm bay—often used as a signature of substorm onset. The PC index measures magnetic perturbations near the pole (Troshichev et al., 2006), which is determined by a combination of drift speed and ionospheric conductance in the central polar cap and hence can be used as a proxy for Φ PC (Lockwood, 2023; Milan et al., 2021).…”