Near Earth spacecraft can be used not only to predict the occurrence of sun-caused magnetic storms but also the time they will occur and their magnitude, Jet Propulsion Laboratory scientist said Wednesday.

Dr. Bruce Tsurutani prepared paper for presentation before the 1989 Fall Meeting of the American Geophysical Union at San Francisco.

The paper, entitled "The Interplanetary Features Causing Magnetic Storms and Substorms: How Can We Forecast Them?" was co authored by Drs. Edward J. Smith, also of JPL, and Walter D. Gonzalez of the Instituto de Pesquisas Espaciais, Sao Paulo, Brazil, and Frances Tang of the California Institute of Technology, Pasadena, Calif.

Plasma and field data from near-Earth spacecraft can be used to predict major and moderate storms, Tsurutani said.

Magnetic storms arising from interaction of the sun's solar wind with the Earth's magnetic field cause radio blackouts and prevent the use of over-the-horizon radar by interfering with the ionosphere. They also cause power surges which can be damaging to power installations.

Additionally, the Van Allen belt of charged particles becomes more intense as the result of increased solar wind activity and that presents hazard to orbiting satellites and manned space flight.

Tsurutani said solar radiation reaches levels during solar surges sufficiently high to be harmful to astronauts or to interfere with spacecraft and space shuttle computers.

Magnetic storms also are associated with the colorful auroras. During intense magnetic storms the auroras can be seen as far south as Mexico.

The ability to predict such solar activity diminishes with the distance of the spacecraft from Earth, however, Tsurutani said. But spacecraft at about four times the distance of the moon's orbit, such as the NASA/ESA International Sun Earth Explorer (ISEE-3) can still predict storms accurately.

Remote sensing from Earth also can be used, he said. As one example, high solar wind streams close to the sun can be detected from Earth by radio scintillation techniques -- such as looking at radio emissions by spacecraft on the other side of the sun, or looking at the fluctuations of radio emissions from some stars to determine velocity and density of the solar stream interfering with those emissions.

While such measurements can be used to indicate when there will be statistically higher percentage of storms, they are not sufficient to determine if storm will occur or not, he said.

To accurately forecast the magnitude of impending solar storms, scientists need the prediction of the interplanetary field and the velocity of the solar stream as it strikes the Earth's magnetic field.

To be able to use ground-based or near-Earth satellite observations of the solar corona and sun, he said, computer modeling will be necessary to determine the effects of the normal solar wind stream and the intense surges of activity as they interact and propagate to the distance of Earth's orbit.

The study was performed at JPL under contract with the National Aeronautics and Space Administration.

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