By Jeffrey J. Love and Carol A. Finn, U.S. Geological Survey, and Yesenia C. Gamez Valdez and Don Swann, National Park Service
The Tucson magnetic observatory in Saguaro National Park. USGS.
A small station with a big job
On a sandy plain near the park's Rincon Mountain Visitor Center, among brittlebush, creosote and other desert plants, stands an unusual observatory: a small, unmanned station that monitors Earth's changing magnetic field. Named for nearby Tucson, Arizona, it is 1 of 14 operated by the USGS Geomagnetism Program across the United States and its territories.
Data from USGS observatories — and from observatories in other countries — record signals from processes deep in Earth's interior and in the space environment around it. They are used for:
- geomagnetic mapping and surveying;
- basic scientific research;
- assessing magnetic storms, which can threaten technology and infrastructure (Love and others, 2008).
The observatories are part of a national effort to monitor and assess space weather hazards (National Science and Technology Council, 2015).
The observatory's electronics building, among the desert plants. USGS.
History
| Year | |
|---|---|
| June 1909 | President William H. Taft sets aside federal land outside Tucson for a Coast and Geodetic Survey magnetic observatory (Hazard, 1913); offices and analog magnetometers follow |
| November 1909 | the first hourly measurements of magnetic variation are reported |
| 1970s | federal reorganizations hand the observatories to the USGS |
| 1989 | as Tucson's growth surrounds the site and interferes with the instruments, the city agrees to help the USGS find a new one |
| January 1996 | the first data come from the new site in Saguaro National Park, operating under a special use permit from the Park Service |
The old site is now part of Tucson's Udall Park.
What the data show
A compass measures the horizontal direction of Earth's magnetic field. One quantity an observatory records is declination — the angle between the compass needle and true north — and it changes over time.
Hourly (gray) and annual (blue) magnetic declination at the Tucson observatory, 1909–2013. USGS.
- Slow change (blue) comes from fluid motion in Earth's deep interior — the dynamo that makes most of the magnetic field.
- Rapid change (gray) comes from the space-weather environment, especially during magnetic storms.
- The jump in 1996 reflects the move to Saguaro: the rock beneath the new site is magnetized differently.
More: USGS Geomagnetism Program · Saguaro National Park
Sources
Based on Magnetic Monitoring in Saguaro National Park, by Jeffrey J. Love, Carol A. Finn, Yesenia C. Gamez Valdez and Don Swann, USGS Fact Sheet 2017–3035, U.S. Geological Survey; a work of the United States government in the public domain. The photographs and the declination chart are taken from the fact sheet's PDF, which the import had left out.
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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