GOLD reveals unexpected changes in Earth’s nighttime ionosphere

This October 15, 2018, GOLD image of daytime airglow clearly shows the equatorial ionization anomaly (EIA) as two arcs on either side of the magnetic equator, which extend across the nightside of the disk. The colors represent an increase in oxygen emissions from blue to red, with the left side of the Earth lit by the Sun, which has set over most of South America. (Courtesy GOLD)

NASA’s Global-scale Observations of the Limb and Disk (GOLD) mission has observed dramatic and unexplained shifts in the location of features in the Earth’s ionosphere surrounding the equator. Unanticipated changes in the nighttime ionosphere can lead to disruptions in communication and navigation that depend on satellites, such as GPS.

GOLD is an ultraviolet imaging spectrograph that was designed and built at the University of Colorado Boulder’s Laboratory for Atmospheric and Space Physics (LASP) and is hosted on the SES-14 communications satellite. The latest discoveries from the mission are challenging mission scientists and were published last week in Geophysical Research Letters.

Since reaching orbit in October 2018, GOLD has been making observations of the Equatorial Ionization Anomaly (EIA), regions of the ionosphere with enhanced electron density north and south of the magnetic equator. One of the primary goals of the mission is to better understand the behavior of the EIA and the instabilities within it. GOLD presents a new ability to image the variability of ionospheric plasma and, ultimately, to understand its causes.

“The variability of the nighttime ionosphere has been a puzzle that scientists have studied for more decades than most of us have lived,” said Richard Eastes, GOLD principal investigator and LASP research scientist. “Today it’s an important problem to solve because better forecasts are needed for reliable navigation and communication by airplanes and others.”

Density variations in the ionosphere can cause localized plasma depletions called “bubbles.”  Radio waves, including those used for communications and navigation, can be disrupted when they encounter these bubbles. The occurrence of bubbles and other ionospheric irregularities presents a critical challenge for efforts to predict how changes in solar and geomagnetic activity affect the nighttime ionosphere.

Because of GOLD’s unique perspective from geostationary orbit and its rapid imaging cadence (a complete scan of each hemisphere every 15 minutes), GOLD is providing new information that has not been available in previous EIA observations. From its geostationary vantage some 22,000 miles above the Earth, GOLD observes the same longitudes repeatedly every night and provides large scale images of the EIA.

GOLD has observed gaps occurring on a majority of the nights and has more irregularly detected abrupt changes in the location of the EIA. The team will rely on additional measurements before attempting to determine the cause of variability in the EIA and its changing location.

GOLD is a NASA mission of opportunity managed by the Goddard Space Flight Center in Greenbelt, MD. The GOLD principal investigator is based at LASP, which built the instrument, provides project management and systems engineering, as well as instrument operations for the GOLD mission. GOLD is a hosted payload on a commercial communications satellite, SES-14, built by Airbus for Luxembourg-based satellite operator, SES.

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