NOAA / Space Weather Prediction Center

A Primer on Space Weather

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Aurora

The aurora is a dynamic and visually delicate manifestation of solar-induced geomagnetic storms. The solar wind energizes electrons and ions in the magnetosphere. These particles usually enter the Earth’s upper atmosphere near the polar regions. When the particles strike the molecules and atoms of the thin, high atmosphere, some of them start to glow in different colors. Aurora begin between 60 and 80 degrees latitude. As a storm intensifies, the aurora spread toward the equator. During an unusually large storm in 1909, an aurora was visible at

Singapore, on the geomagnetic equator. The aurora provide pretty displays, but they are just a visible sign of atmospheric changes that may wreak havoc on technological systems.

     
Communications
Many communication systems utilize the ionosphere to reflect radio signals over long distances. Ionospheric storms can affect High Frequency (HF) radio communication at all latitudes. Some radio frequencies are absorbed and others are reflected, leading to rapidly fluctuating signals and unexpected propagation paths. TV and commercial radio stations are little affected by solar activity, but ground-to-air, ship-to-shore, Voice of America, Radio Free Europe, and amateur radio are frequently disrupted. Radio operators using high frequencies rely upon solar and

geomagnetic alerts to keep theircommunication circuits up and running.

Some military detection or early-warning systems are also affected by solar activity. The Over-the-Horizon Radar bounces signals off the ionosphere in order to monitor the launch of aircraft and missiles from long distances. During geomagnetic storms, this system can be severely hampered by radio clutter. Some submarine detection systems use the magnetic signatures of submarines as one input to their locating schemes. Geomagnetic storms can mask and distort these signals.

The Federal Aviation Administration routinely receives alerts of solar radio bursts so that they can recognize communication problems and forego unnecessary maintenance. When an aircraft and a ground station are aligned with the Sun, jamming of air-control radio frequencies can occur. This can also happen when an Earth station, a satellite, and the Sun are in alignment.

Radiation storms, also known as solar particle events or proton events can affect the lower regions of the polar ionosphere. This region can become ionized and severe HF and VHF signal absorption may occur. This is called a polar cap absorption (PCA) event. PCA events may last for days or weeks and polar HF radio propagation often becomes impossible during these events.

     
Navigation Systems
Systems such as LORAN and OMEGA are adversely affected when solar activity disrupts their signal propagation. The OMEGA system consists of eight transmitters located through out the world. Airplanes and ships use the very low frequency signals from these transmitters to determine their positions. During solar events and geomagnetic storms, the system can give navigators information that is inaccurate by as much as several miles. If navigators are alerted that a radiation storm or geomagnetic storm is in progress, they can switch to a backup system. GPS signals are
affected when solar activity causes sudden variations in the density of the ionosphere. Global Positioning Systems are being used for ever more precise applications, including mapping of coastlines, surveying for highway construction, landing airplanes, and oil drilling.
     
Satellites
Geomagnetic storms and increased solar ultraviolet emission heat the Earth’s upper atmosphere, causing it to expand. The heated air rises, and the density at the orbit of satellites up to about 1000 km increases significantly. This results in increased drag on satellites in space, causing them to slow and change orbit slightly. Unless low-Earth-orbit satellites are routinely boosted to higher orbits, they slowly fall, and eventually burn up in the Earth’s atmosphere. Skylab is an example of a spacecraft re-entering the Earth’s atmosphere prematurely as a result
of higher-than-expected solar activity. During the great geomagnetic storm of March 1989, four Navy navigational satellites had to be taken out of service for up to a week.

As technology has allowed spacecraft components to become smaller, their miniaturized systems have become increasingly vulnerable to the more energetic solar particles. These particles can cause single event upsets which often cause physical damage to microchips and change software commands in satellite-borne computers.

Another problem for satellite operators is differential charging. During geomagnetic storms, the number and energy of electrons and ions increase. When a satellite travels through this energized environment, the charged particles striking the spacecraft cause different portions of the spacecraft to be differentially charged. Eventually, electrical discharges can arc across spacecraft components, harming and possibly disabling them.

Bulk Charging. Bulk charging (also called deep charging) occurs when energetic particles, primarily electrons, penetrate the outer covering of a satellite and deposit their charge in its internal parts. If sufficient charge accumulates in any one component, it may attempt to neutralize by discharging to other components. This discharge is potentially hazardous to the electronic systems of the satellite.

     
Geologic Exploration
The Earth’s magnetic field is used by geologists to determine subterranean rock structures. For the most part, these geodetic surveyors are searching for oil, gas, or mineral deposits. They can accomplish this only when Earth’s magnetic field is quiet, so that true magnetic signatures can be detected. Other surveyors prefer to work during geomagnetic storms, when the variations to normal subsurface electric currents help them to see subsurface oil or mineral structures. For these reasons many surveyors use geomagnetic alerts and predictions to schedule their mapping activities
     
Main Primer | Versión en Español | Effects of Space Weather Storms: Page 1 | Page 2 | Back to Education | Home