Highlights of Ionospheric Response

to the April 10-11, 1997, Geomagnetic Storm

  • Global Maps of Ionospheric Total Electron Content

    This map displays the global distribution of electron content in the Earth's ionosphere during the large geomagnetic storm of April 10-11, 1997, using techniques developed at JPL. The ionosphere is a tenuous atmosphere of electrically charged gas (plasma) that surrounds the Earth at altitudes between 100-1000 km. It refracts (bends), reflects and absorbs radio frequency radiation and is an important element (either constructively or destructively) in a variety of advanced technology systems. For example, ground to ground short-wave radio communications over large distances and over-the-horizon radar systems depend on reflections of radio signals off the ionospheric layer. Satellite-based radio navigation systems are affected by the significant delays (10-100 meters effective length) that can be introduced. When the ionosphere becomes disturbed by solar eruptions traveling to Earth, communications and navigation systems can become disrupted and spacecraft within the plasma layer can be harmed.

    Global snapshots of ionospheric "weather" can be made in real time using data from extensive networks of receivers tracking the dual-frequency transmissions of Global Positioning System (GPS) satellites, a satellite navigation system. Small and inexpensive, the receivers can be connected to Internet and automatically relay ionospheric data in real-time from around the world. These snapshots can be used to warn radio-frequency users of trouble spots in the ionosphere, so that mitigating action can be taken. This global GPS data set comes into JPL on a near-real time and daily basis.

    The global map shown above is plotted in terms of local time and geographic latitude. It clearly shows that the ionosphere is "charged" up by the solar ultra-violet radiation: the red areas representing the largest numbers of electrons appear in the afternoon and in equatorial climates. Ionospheric electrons are minimized at night (particularly 0300-0500) when the electrons can recombine with the positively charged atmospheric atoms and molecules. During disturbed conditions, rapid changes and significant enhancements or depletions can occur relative to normal quiet conditions. In this plot, a rapidly developing enhancement can be seen extending over a broad region covering Australia and New Zealand. Other areas, such as in North America, were also severely affected (this can be more clearly seen on the US real-time plot shown elsewhere on this page).

  • Regional Ionospheric Disturbances


    JPL is currently receiving real-time GPS tracking data from a network of 14 GPS receivers deployed across the continental U.S. This data is being provided by SATLOC, Inc. with a latency of less than 2 seconds. This data allows JPL to produce maps of the current ionospheric electron content over the U.S. within minutes. Images shown above and below are ionosphere maps over the U.S. produced by this real-time system at 3:15 AM Greenwich Mean Time on April 10 and 11 1997 respectively. The April 10 map shows the "quiet" ionosphere before the onset of the ionospheric storm. The April 11 map shows the effects of the storm: Note the strong depletion of free electrons over southern Canada and an enhancement of electron content over much of the US. These disturbances likely contributed to the development of smaller-scale ionospheric irregularities, which caused short-wave communications loss during the storm.

  • Ionospheric Differential Map


    This map displays the change in the total electron content (TEC) over North America due to the impact of the ionospheric storm of April 10-11, 1997. Enhancements of electron content appear in red; depletions of electron content appear in blue. This map has been generated from real time data provided by SATLOC, Inc., by subtracting a quiet-time average TEC map from the TEC map representing the state of the ionosphere at approximately 2:00 UT on April 11. The quiet time map was produced by averaging the TEC maps at the same UT time over the previous four days. The depletion just south of Hudson Bay and the enhancement over the central United States were also observed in a global difference map produced from an independent set of GPS measurements from the International GPS Service for Geodynamics (IGS) network.

  • Global Ionospheric Irregularities


    The irregularly structured ionosphere can cause random fluctuations in both amplitude and phase of trans-ionospheric radio signals received at an antenna. The phenomenon is known as ionospheric scintillation, which degrades the quality of satellite-based navigation systems, such as GPS, and disrupts short-wave radio communications. Using the techniques developed at JPL, global ionospheric irregularities can be monitored through the global GPS network by measuring phase fluctuations in the GPS signals. The snapshot of the irregularities shown above is produced using GPS data collected from 70+ globally distributed stations during the April 10-11 geomagnetic storm. These irregularities were enhanced (higher ROTI values) at high latitudes and expanded to middle latitudes in the North American region, where disruptions in short-wave radio communications were also reported during the storm.

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