J. Matzka | Geology Reports

USGS2010

Geomagnetic observations on tristan da cunha, south atlantic ocean

Few geomagnetic ground observations exist of the Earth's strongest core field anomaly, the South Atlantic Anomaly (SAA). The geomagnetic repeat station on the island Tristan da Cunha, located half-way between South Africa and South America at 37?? 05' S, 12?? 18' W, is therefore of crucial importance. We have conducted several sets of repeat station measurements during magnetically quiet conditions (Kp 2o or less) in 2004. The procedures are described and the results are compared to those from earlier campaigns and to the predictions of various global field models. Features of the local crustal bias field and the solar quiet daily variation are discussed. We also evaluate the benefit of continuous magnetic field recordings from Tristan da Cunha, and argue that such a data set is a very valuable addition to geomagnetic satellite data. Recently, funds were set up to establish and operate a magnetometer station on Tristan da Cunha during the Swarm magnetic satellite mission (2011-2014).

Annals of Geophysics↗

USGS2009

New substorm index derived from high-resolution geomagnetic field data at low latitude and its comparison with AE and ASY indices

High-resolution geomagnetic field data (i.e., ≤5 seconds) have recently become more commonly used by space physicists. The data permit the identification of Pi2 pulsations, having periods of 40-150 seconds and irregular waveforms. Pulsations of this type appear clearly in time series from mid- and low-latitude ground stations on the nightside at substorm onset. Therefore, with data from multiple observatories, substorm genesis and evolution can be monitored. Here we propose a new substorm index, the Wp index (Wavelet and planetary), which measures Pi2 spectral power at low-latitude. This index is derived from geomagnetic field data obtained from observatories arranged in longitude around the Earth’s circumference. Presently, data from 5 ground stations (Fürstenfeldbruck, Iznik, Urumqi, Kakioka, and Teoloyucan) are used, but future work will include data from other sites as well (Honolulu, Tucson, San Juan, Tristan da Cunha, and Ebro). Here we compare substorm occurrence estimated from the Wp index and those from the AE and ASY indices. We show that Wp index is a good indicator of substorm onset.

Conference Paper↗