Geomagnetic Monitoring in the Mid-Atlantic United States

Near Civil War battlefields southeast of Fredericksburg, Virginia, in a secluded, grassy glade ringed by forest, a specially designed observatory records Earth's changing magnetic field. The Fredericksburg Magnetic Observatory is one of 14 run by the U.S. Geological Survey's Geomagnetism Program across the United States and its territories, serving government, academic and commercial science.

A history of the mid-Atlantic record

Cheltenham was the CGS Geomagnetism Program's headquarters and ran reliably for more than half a century, until the site's physical limits blocked needed modernisation.

Figure 1. The Cheltenham Magnetic Observatory in 1926. Photograph from the USGS archive.

Fredericksburg in turn became the program's headquarters. Besides long-term monitoring, the site trained American and foreign geomagneticians, calibrated magnetometers — including for satellites — made geodetic measurements, and supported seismic, weather and cosmic-ray monitoring.

Changing hands

• 1965: the CGS's services, the Geomagnetism Program among them, moved to the Environmental Science Services Administration.
• 1970: many of them moved to the National Oceanic and Atmospheric Administration (NOAA).
• 1973: the Geomagnetism and Earthquake Programs moved to the USGS. NOAA's National Geodetic Survey shared the Fredericksburg site until 2006, when it was divided so the two agencies could work and administer independently.

From photographs to near real time

• Late 1970s: staff began installing digital electronic systems to record 1-minute data.
• November 1982: Fredericksburg's first 1-minute digital data were reported.
• 2012: 1-second data began to be reported routinely from Fredericksburg and the other USGS observatories.
• Today: 1-minute and 1-second data from every USGS observatory are available in near real time.

Since 1991 all USGS observatories have belonged to INTERMAGNET, an international consortium promoting modern magnetic observatories and sharing their data. The network is now part of national efforts to monitor and assess hazardous magnetic storms and electromagnetic pulses.

What the record shows

The observatories record magnetic signals from inside Earth and from the space around it. Figure 2 shows the field's horizontal intensity at Cheltenham and Fredericksburg from 1901 to 2018, hour by hour and as yearly means.

Figure 2. Horizontal intensity at the Cheltenham (CLH) and Fredericksburg (FRD) observatories, 1901–2018. The move in 1956 introduced a discontinuity. Intense magnetic storms appear as brief spikes, including the great Québec storm of March 1989.

• Slow change. For more than a century, horizontal intensity in the mid-Atlantic fell and then rose, driven by dynamic processes in Earth's core.
• The 1956 step. The offset between the two stations comes from a local difference in the permanent magnetisation of the crust.
• Spikes. Brief periods of rapid disturbance are magnetic storms — temporary disturbances of near-Earth space caused by bursts and concentrated streams of solar-wind plasma from the Sun.

The storm of March 1989

During the great storm of March 1989, electric fields induced in Earth's conducting crust collapsed the high-voltage grid of Québec, Canada, blacking out the province. The same storm caused many problems in northeastern U.S. grids, including damage to a high-voltage transformer at a nuclear power plant in Salem, New Jersey.

USGS researchers are using Fredericksburg data — including from the 1989 storm — to estimate and map geoelectric hazards across the mid-Atlantic. This work, and the observatory data generally, help utilities and regulators judge how vulnerable power grids are to magnetic storms and make them more resilient.

Who uses the data

• Space weather. Fredericksburg is one of several observatories worldwide that supply data for the standard indices of geomagnetic disturbance. Its data are used by NOAA's Space Weather Prediction Center, the U.S. Air Force and NASA.
• Navigation. They feed the International Geomagnetic Reference Field, used for navigation, orientation and research.
• Research into Earth's interior.
• Industry.

Sources

• Love, J.J., and Lewis, K.A., 2021, Geomagnetic monitoring in the mid-Atlantic United States: U.S. Geological Survey Fact Sheet 2021–3001. https://pubs.usgs.gov/publication/fs20213001
• The web version runs the introduction into the middle of the history; the figures and captions come from the fact sheet's PDF.
• Rewritten in hubnx's own words.