X-rays degrade solar panels and are part of the charging problem. Solar cells convert solar photons into electrical energy. Flare X-rays can damage the solar cells, reducing their power output and aging a satellite. Electrons flow onto and off orbiting satellites. X-rays from a solar flare knock the electrons off satellites. If too much charge is removed a discharge can damage the satellite.

Atmospheric drag. The solar irradiance at FUV wavelengths between 122 and 200 nm creates atomic oxygen that flows up to form the thermosphere and ozone that flows down to form the ozone layer. The solar irradiance at X-ray & EUV wavelengths (between 1 and 122 nm) creates the ionosphere. When X-rays from a solar flare are absorbed in the atmosphere the thermosphere heats and expands, increasing the atmospheric density at the altitudes of low-Earth orbits. Higher density & temperature leads to more frictional drag.

Deep-Dielectric Charging and Single Event Upsets The energetic particles of an SEP event and those produced during a geomagnetic storm are among the most damaging radiation of SWx.

The radiation belts are a region of trapped energetic charged particles located inside the Earth's magnetosphere between altitudes of 6000 to 40,000 km. Unfortunately for satellite operators and users this is also a region where many satellites orbit. Large scale increases in the energy and flux of relativistic "killer" electrons in the Earth's radiation belts are an important space weather effect.

Often associated with magnetic storms, the high intensity of relativistic electrons cause deep-dielectric charging and single event upsets (SEUs) in electronic satellite components. Past relativistic electron flux enhancements have been blamed for damaging and sometimes for the complete failure of satellites. The Living With a Star RBSP mission will study the acceleration of these electrons.

Surface Charging and the Aurora Aurora are a beautiful manifestation of space weather. They are caused by the flow of magnetospheric electrons along field lines into the upper atmosphere. These energetic charged particles interact with oxygen and nitrogen molecules in the atmosphere causing them to emit the colorful red and green lights of the aurora. Electrons flowing along a field look like an electrical current to orbiting satellites. If the charge buildup caused by increased auroral electrons is not removed a dangerous spark can occur in the satellite.

Many small particles strike the Earth every day. They also strike satellites in orbit around the Earth. Most of these impacts cause minor damage and their impact craters are used to measure the number of hits. A more recent problem has been what happens after satellites fall apart in orbit. The remaining pieces are called orbital debris. The orbits of orbital debris is monitored so as to avoid collisions. Space weather increases the atmospheric drag on the debris, changing the orbits and making the tracking more difficult, but also removing the debris by causing them to re-enter the atmosphere.

Some solar images from Skylab's soft x-ray telescope, S-056. This grazing incidence telescope produced images of the Sun in x-rays with wavelengths from 6 to 49 Å. Coronal holes are the dark regions where the hot coronal material is very thin. Coronal holes were observed to rotate fairly rigidly and maintain their shape through several 27-day solar rotations. A movie of these images can be seen at NASA Marshall Space Flight Center.

Even when flares are not occurring the Sun is brighter at X-ray and EUV wavelengths at solar maximum then at minimum. It is already known that changes in the energy output of the sun can affect the climate here on earth. During solar maximum, the peak of the 11-year cycle, the sun shines a tiny bit brighter (up to one half of a percent). Studies of tree-ring thickness show that plant growth follows the ups and downs of the solar cycle. Another example is a historical event called the Maunder Minimum, a 65-year dip in solar activity that caused a period of global cooling on earth in the late seventeenth century. During this time, known as the Little Ice Age, temperatures plunged and the Baltic Sea froze over regularly.

Scientists speculate that GCRs may also affect our climate. GCRs create ions (charged particles) as they are stopped in our atmosphere. Because ions act as "seeds" (nucleation centers) for clouds, GCRs may be involved with cloud formation in our atmosphere. The solar cycle modulation of GCRs would then become a solar cycle modulation of clouds, relating our climate to solar activity.

IBM has made an extensive effort to understand how sensitive computer components are to GCR radiation. Volume 40 of IBM's research journal, Terrestrial Cosmic Rays and Soft Errors, is devoted to an examination of these problems.

Forbush Decrease, a Reduction in GCRs by CMEs A Forbush Decrease (FD) is a reduction in the GCR intensity at the Earth's surface caused by the passage of a CME. The complex and enhanced magnetic field that expands out into the solar system during a CME scatters away the incoming GCRs. Ground level neutron monitors on Earth can measure a 30% decrease in the observed GCR intensity. The effect is more enhanced at higher latitudes (due to the shape of the magnetosphere.) Typically FDs last for several days, while the GCR intensity returns to normal background levels.

SEP events can increase the level of atmospheric radiation. Severe SEP events that cause an increase in radiation at ground level are known as Ground Level Events (GLEs). To produce a noticeable increase in radiation at ground level usually requires particles with energies greater than 100 MeV at the top of the atmosphere. The intensity of the event will ultimately depend on the higher energy range of the SEP spectrum.

The radiation dose you receive from a SEP event depends your altitude, your magnetic latitude, and on the energy of the solar particles. When you move to higher altitude you have less shielding from the atmosphere, increasing your dose. When you move to higher latitudes (towards the polar regions) the protection provided by the Earth's magnetic field becomes less, also increasing your dose. During SEP events the risk of increased radiation exposure is highest during the first few hours while the most energetic of the SEPs arrive at Earth. However, the intensity of these particles quickly decreases and the danger is reduced. It should be noted however, that many SEP events coincide with CMEs which often result in a Forbush Decrease, an overall decrease in the background cosmic ray intensity. This decrease in the background GCR intensity may more than compensate for the increase in radiation due to the SEPs. Therefore many factors must be taken into account when assessing the increase in radiation dose due to SEP events.

Increased Galactic Cosmic Ray Intensity Like SEP events, the radiation dose you receive GCRs depends your magnetic latitude and altitude. The protection provided by the Earth's magnetic field becomes less as you move towards the polar regions (higher latitudes). As you move to higher altitude you receive less shielding from the atmosphere, again increasing your GCR dose. During solar minimum the solar magnetic field is smaller and less contorted, allowing more GCRs into the solar system and increasing the radiation dose. The intensity of GCRs decreases as solar activity increases.

HF Communication Degradation. High Frequency (HF) radio signals use frequencies around 30 MHz that pass through the ionospheric D-region (at ~80 km) but are reflected by the F-region (at ~300 km). You can use the reflection to increase the range of the signal by bouncing it off the ionosphere (called skip). Large X-ray fluxes during a solar flare increase the ionization of the D-region resulting in increased absorption of the radio signal. The reduced signal strength can cause degradation of the radio communications. This can be partially mitigated by increasing the frequency but this only works until the signal also passes through the F-region at which point any communication relying on skip is completely lost.

Energetic particles from SEP events, CMEs, and high-speed streams enter the upper atmosphere near the magnetic poles. As a result, the lower levels of the polar ionosphere become more ionized, with severe absorption of HF and VHF (100 MHz) radio signals. Such an event is known as a polar cap absorption (PCA) event and may last from days to weeks, depending on the strength of the stream of solar particles and the location of the source region on the Sun. HF radio communication in polar regions is often impossible during PCA events.

These HF communication dropouts are the most important SWx problem for airline pilots.

HF Communication Degradation. The ionosphere's F region can become depleted of electrons during magnetic storms, degrading HF radio communications. Unlike the flare effect, this communications problem comes from the removal of the reflecting layer.

Scintillations cause GPS dropouts and navigation errors A GPS receiver uses radio signals from several orbiting satellites to determine the range, or distance, from each satellite, and uses those ranges to determine the position of the receiver. Because the radio signals must pass through the ionosphere, they are affected by the variations in the electron density of the ionosphere. Changes in the electron density due to space weather can change the speed at which the radio waves travel, introducing a propagation delay in the GPS signal. The propagation delay can vary from minute to minute, and such intervals of rapid change can last for several hours, especially in the polar and auroral regions. Changing propagation delays cause errors in the determination of the range.

• Scintillations are small fluctuations in the electron density. They deflect the radio waves moving from the satellite to your receiver. Much like a stick stuck in water appears bent when you look near the surface (even though the stick is still straight) this deflection causes your receiver to misjudge the location of the GPS transmitter.
• Position errors for single frequency GPS can range to the tens of meters, while dual frequency or differential GPS can reduce these errors to 1-2 meters. These GPS errors can be both horizontal and vertical in nature.

Magnetospheric electric fields cause GPS dropouts and navigation errors During a magnetic storms large electric fields are generated in the magnetosphere that move the electrons and ions in the ionosphere. The new pattern of ionization affects the GPS radio signals and causes navigation errors. This effect is seen over the USA, unlike other SWx effects that are primarily over the poles and equator.

Powerlines. One of the most dramatic effects on ground systems during geomagnetic storms is the disruption of power systems. Ionospheric currents can reach tens of thousands of amperes during a geomagnetic storm, producing fluctuations in the Earth's magnetic field. Such disturbances can generate low-frequency (DC) ground induced currents (GICs) in long power lines that can overload transformers and cause power outages. For instance, during the March 13, 1989, storm, GICs caused a complete shutdown of the Hydro-Quebec power grid resulting in a nine-hour power outage for 6 million people. The power pools that served the entire northeastern United States came uncomfortably close to a cascading system collapse. With warning from space weather forecasters, power companies can take steps to minimize failures.

Pipelines. Just like wires, the pipelines that carry oil and other materials are made of conducting material. Geomagnetic storms can also induce electric currents in these pipelines. Where pipelines pass through rock that doesn't conduct electricity well (such as igneous rocks) the currents follow the path of least resistance and become concentrated in man-made conductors like pipelines. The currents flow between the Earth and the pipeline causing increased corrosion of the pipeline.