Altitude‐adjusted corrected geomagnetic coordinates: Definition and functional approximations

Abstract

Analysis of the functional approximations used to transform between geographic and Altitude‐Adjusted Corrected Geomagnetic (AACGM) coordinates reveals that errors of >50 km can occur in the auroral and polar regions. These errors are the result of efforts to better approximate AACGM coordinates near the magnetic equator and the South Atlantic Anomaly. In these regions AACGM coordinates are not defined and alternate coordinates have been used. This augmentation and emphasis on the solution in regions near the equator result in spherical harmonic approximating functions that are less accurate than need be in the auroral and polar regions. In response, a new set of spherical harmonic coefficients have been derived that better represent AACGM coordinates in these regions. These new AACGM coefficients are limited to below 2000 km in altitude in order to ensure accuracy. For altitudes above 2000 km, a magnetic field‐line tracing solution is recommended. A software package developed to take advantage of the new AACGM coefficients provides the capability of tracing magnetic field lines at any altitude, for improved accuracy. In addition, linear interpolation between 5 year epochs is used to produce coordinates that vary smoothly over the entire period from 1965 to present. The intent of this work is to provide a more accurate procedure for determining AACGM coordinates in the auroral and polar regions for the study of magnetospheric and ionospheric processes.

Climatology of GPS phase scintillation at northern high latitudes for the period from 2008 to 2013

“…The phase scintillation occurrence is represented as a function of magnetic local time (MLT) and the altitude-adjusted corrected geomagnetic (AACGM) latitude (Baker and Wing, 1989;Shepherd et al, 2014). In this paper, the scintillation data are merged on a grid with bins of 1 h MLT × 2.5 • CGM latitude.…”

The AUTUMNX magnetometer meridian chain in Québec, Canada

“…Using best field models, geomagnetic coordinates can be defined, such as the Corrected Geomagnetic Coordinates or CGM updated by Gustafsson (1984) and presented as a table allowing conversion between geodetic and geomagnetic coordinates. Updated coordinate systems such as PACE (Baker and Wing 1989) and its modification AACGM (Shepherd 2014) usually use a series representation and attempt to overcome issues of poorly defined magnetic coordinates near the equator. The latter is of little concern here due to our focus on the auroral zone.…”

Large-scale coordinated observations of Pc5 pulsation events

“…The corresponding map for event 1 is shown in Paper 1. The solid lines indicate the AACGM (Altitude Adjusted Corrected Geomagnetic Coordinates) magnetic latitudes (Baker and Wing, 1989;Shepherd, 2014).…”

“…The earliest of these was the Kelvin-Helmholtz instability (Southwood, 1968;Walker, 1981). This is an instability of the fast wave as a result of the shear across the magnetopause.…”

“…When observed in the meridian plane the oscillation appears to be standing. There is generally phase advance in the azimuthal direction, which is characterized by the azimuthal wave number m. Various sources have been identified such as Kelvin-Helmholtz oscillations at the magnetopause (Southwood, 1968), excitation of cavity or waveguide modes (Kivelson and Southwood, 1985;Samson et al, 1992), direct control by oscillations in the solar wind (Stephenson and Walker, 2002), and more recently fluctuating field-aligned currents in the auroral zone (Pilipenko et al, 2016). Pulsations can also be generated by drift-bounce resonance with ring current particles (Dungey, 1965).…”