Publications

Jack Townshend, geophysicist and dedicated public servant, died on 13 August 2012 in Fairbanks, Alaska. He was 85. Jack's career with the federal government, most of it with the national magnetic observatory program, spanned more than six solar cycles of time, and he retired only days before his death. The duration of Jack's career encompassed an important period in the history of the advancement

In this paper, the effects of the assumptions made in the calculation of the Dst index with regard to longitude sampling, hemisphere bias, and latitude correction are explored. The insights gained from this study will allow operational users to better understand the local implications of the Dst index and will lead to future index formulations that are more physically motivated. We recompute the i

Statistical analysis is made of rare, extreme geophysical events recorded in historical data -- counting the number of events $k$ with sizes that exceed chosen thresholds during specific durations of time $\tau$. Under transformations that stabilize data and model-parameter variances, the most likely Poisson-event occurrence rate, $k/\tau$, applies for frequentist inference and, also, for Bayesian

Thematic maps are arrays of labels, or "themes", associated with discrete locations in space and time. Borrowing heavily from the terrestrial remote sensing discipline, a numerical technique based on Bayes' theorem captures operational expertise in the form of trained theme statistics, then uses this to automatically assign labels to solar image pixels. Ultimately, regular thematic maps of the sol

We study the seasonal variation of substorms, geomagnetic activity and their solar wind drivers in 1993–2008. The number of substorms and substorm mean duration depict an annual variation with maxima in Winter and Summer, respectively, reflecting the annual change of the local ionosphere. In contradiction, substorm mean amplitude, substorm total efficiency and global geomagnetic activity show a do

The operational version of the United States Geological Survey one-minute Dst index (a global geomagnetic disturbance-intensity index for scientific studies and definition of space-weather effects) uses either four- or three-station input (including Honolulu, Hawaii; San Juan, Puerto Rico; Hermanus, South Africa; and Kakioka, Japan; or Honolulu, San Juan and Guam) and a method based on the U.S. Ge

We produce a 1-min time resolution storm-time disturbance index, the USGS Dst, called Dst8507-4SM. This index is based on minute resolution horizontal magnetic field intensity from low-latitude observatories in Honolulu, Kakioka, San Juan and Hermanus, for the years 1985–2007. The method used to produce the index uses a combination of time- and frequency-domain techniques, which more clearly ident

Analysis is made of the geomagnetic-activity aa index and its source K-index data from groups of ground-based observatories in Britain, and Australia, 1868.0–2009.0, solar cycles 11–23. The K data show persistent biases, especially for high (low) K-activity levels at British (Australian) observatories. From examination of multiple subsets of the K data we infer that the biases are not predominantl

Magnetic storms result from the dynamic interaction of the solar wind with the coupled magnetospheric-ionospheric system. Large storms represent a potential hazard for the activities and infrastructure of a modern, technologically based society [Baker et al., 2008]; they can cause the loss of radio communications, reduce the accuracy of global positioning systems, damage satellite electronics and

The Gamburtsev Subglacial Mountains are the least understood tectonic feature on Earth, because they are completely hidden beneath the East Antarctic Ice Sheet. Their high elevation and youthful Alpine topography, combined with their location on the East Antarctic craton, creates a paradox that has puzzled researchers since the mountains were discovered in 1958. The preservation of Alpine topograp

Recent paleomagnetic work has highlighted a common and shallow inclination bias in continental redbeds. The Permian and Triassic paleomagnetic records from Laurentia are almost entirely derived from such sedimentary rocks, so a pervasive inclination error will expectedly bias the apparent polar wander path of Laurentia in a significant way. The long-standing discrepancy between the apparent polar

We study the seasonal variation of substorms, geomagnetic activity and their solar wind drivers in 1993–2008. The number of substorms and substorm mean duration depict an annual variation with maxima in Winter and Summer, respectively, reflecting the annual change of the local ionosphere. In contradiction, substorm mean amplitude, substorm total efficiency and global geomagnetic activity show a do