Observing the open‐closed boundary using cusp‐latitude magnetometers

Abstract

[1] A new ground-based diagnostic of reconnection at the magnetopause using ULF waves is presented, and we give an example day in which the dynamics of the open-closed boundary (OCB) are clearly observed. The diagnostic is based on data from two close ($110 km), magnetic azimuthally spaced magnetometer sites (Davis and Zhongshan, Antarctica). During average IMF conditions Davis passes just equatorward of the last closed field lines in the dayside magnetosphere, and cross-phase measurements indicate propagation away from local magnetic noon (LMN) as expected for the Kelvin-Helmholtz Instability (KHI) acting at the magnetopause. During times when IMF B z < À2 nT intervals of broadband activity appear, with the azimuthal component of propagation directed towards noon. Statistical analysis shows a correlation between the negative magnitude of IMF B z and cross-phase measurements ±2 -6 hours from LMN. We conclude that under the right conditions, reconnection signatures can be identified in magnetometer data superimposed on the KHI-like propagation signatures of the last closed field lines.Citation: Ables, S. T., and B. J. Fraser (2005), Observing the open-closed boundary using cusp-latitude magnetometers,

The annual and longitudinal variations in plasmaspheric ion density

“…In order to ensure consistency across the data set by eliminating, as far as possible, subjective human intervention in analyzing spectra, the entire data set was then reexamined using automated algorithms to determine the resonant frequencies. Following the work by Ables and Fraser [2005], individual whole‐day spectra were generated using a 256‐point fast Fourier transform (FFT) with 50% overlap and using a pure state filter to determine spectral estimates and the degree of polarization for each estimate. Depending on availability, data for each station or station pair spanning up to 30 contiguous days for each of June and December 2001 were averaged to produce whole‐day spectra for both seasons.…”

Investigation of a low-cost magneto-inductive magnetometer for space science applications

“…In a similar manner, the observation of field line resonances has been used to infer other properties of the magnetosphere such as location (Dent et al, 2006), density (Berube et al, 2003) and composition of the plasmapause or also the location of the openclosed field line boundary (Ables and Fraser, 2005).…”

Reply to reviewer comment 2 by Prasanna Mahavarkar

“…In addition, and due to the dependence of the Alfvén velocity on the local plasma density, ground magnetometers can be used to infer low-energy populations that are difficult to measure in space due to spacecraft charging effects (Menk et al, 1999). In a similar manner, the observation of field line resonances has been used to infer other properties of the magnetosphere such as location (Dent et al, 2006), density (Berube et al, 2003) and composition of the plasmapause or also the location of the openclosed field line boundary (Ables and Fraser, 2005).…”

“…A similar approach was taken by the AMPERE project (Anderson et al, 2000), making use of the engineering magnetometers on board the commercial satellites of the IRID-IUM constellation. With a resolution of 48 nT, they are able to capture signals above the noise level of the instruments at high latitude that correspond to perturbations coming from FAC.…”