Severe Space Weather Storms Affect GPS Meteorology Network

A network of ground-based Global Positioning System (GPS) receivers has been established by the NOAA Forecast Systems Laboratory in Boulder, Colorado to test a new weather observing and climate monitoring system for NOAA. Between March 30-31, the GPS-Met Demonstration Network was affected by a severe geomagnetic storm associated with major solar flare activity on the surface of the Sun. The storm, which caused auroral displays that were seen as far south as Fort Davis, Texas, was described in a recent NOAA Research Hot Item titled "Severe space weather storm-aurora widespread" by Joe Kunches of the NOAA Space Environment Center.

Although the impact of the storm was greatest on the GPS sites in Alaska, its effects were felt throughout the 70-station GPS-Met Network that extends from Central, Alaska to Key West, Florida.

Geomagnetic storms are known to cause a phenomenon called ionospheric scintillation. Scintillation, defined as small-scale variations in the plasma density of the ionosphere along the path followed by the GPS radio signal, causes the ground-based GPS receivers to "lose lock" momentarily on the GPS satellites. The resulting inability to track a satellite reduces the number of carrier phase and range observations that can be made in a 30-minute period. These observations are used by FSL to calculate the signal delays caused by water vapor in the atmosphere. As the number of GPS observations decreases, the uncertainty in the signal delay measurements increases. This uncertainty is expressed as an increase in the "formal error" in the tropospheric signal delay measurement from which the wet signal delays are derived.

We have discovered that the GPS-MET "formal error" is highly correlated with the estimated planetary K index prepared by SEC and updated every 15 minutes. The use of the "formal error" may provide space weather forecasters with an unanticipated independent near real-time verification of the space environment models.

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Name: Seth I Gutman
Tel: 303-497-7031