The Sun

The Sun is an average star, similar to millions of others in the Universe. It is a prodigious energy machine, manufacturing about 3.8 x 1023 kiloWatts (or kiloJoules/sec). In other words, if the total output of the Sun was gathered for one second it would provide the U.S. with enough energy, at its current usage rate, for the next 9,000,000 years. The basic energy source for the Sun is nuclear fusion, which uses the high temperatures and densities within the core to fuse hydrogen, producing energy and creating helium as a byproduct. The core is so dense and the size of the Sun so great that energy released at the center of the Sun takes about 50,000,000 years to make its way to the surface, undergoing countless absorptions and re-emissions in the process. If the Sun were to stop producing energy today, it would take 50,000,000 years for significant effects to be felt at Earth!

The Sun has been producing its radiant and thermal energies for the past four or five billion years. It has enough hydrogen to continue producing for another hundred billion years. However, in about ten to twenty billion years the surface of the Sun will begin to expand, enveloping the inner planets (including Earth). At that time, our Sun will be known as a red giant star. If the Sun were more massive, it would collapse and re-ignite as a helium-burning star. Due to its average size, however, the Sun is expected to merely contract into a relatively small, cool star known as a white dwarf.

Some Effects of Space Weather Storms

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, short wave broadcastings, 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.

Electric Power

When magnetic fields move about in the vicinity of a conductor such as a wire, an electric current is induced into the conductor. This happens on a grand scale during geomagnetic storms. Power companies transmit alternating current to their customers via long transmission lines. The nearly direct currents induced in these lines from geomagnetic storms are harmful to electrical transmission equipment. On March 13, 1989, in Montreal, Quebec, 6 million people were without commercial electric power for 9 hours as a result of a huge geomagnetic storm. Some areas in the northeastern U.S. and in Sweden also lost power. By receiving geomagnetic storm alerts and warnings, power companies can minimize damage and power outages.

Pipelines

Rapidly fluctuating geomagnetic fields can induce currents into pipelines. During these times, several problems can arise for pipeline engineers. Flow meters in the pipeline can transmit erroneous flow information, and the corrosion rate of the pipeline is dramatically increased. If engineers unwittingly attempt to balance the current during a geomagnetic storm, corrosion rates may increase even more. Pipeline managers routinely receive alerts and warnings to help them provide an efficient and long-lived system.

Climate

The Sun is the heat engine that drives the circulation of our atmosphere. Although it has long been assumed to be a constant source of energy, recent measurements of this solar constant have shown that the base output of the Sun can have temporary decreases of up to one-half percent. Atmospheric scientists say that this variation is significant and that it can modify climate over time. Plant growth has been shown to vary over the 11-year sunspot and 22-year magnetic cycles of the Sun, as evidenced in tree-ring records. While the solar cycle has been nearly regular during the last 300 years, there was a period of 70 years during the 17th and 18th centuries when very few sunspots were seen. This drop in sunspot number coincided with the timing of the Little Ice Age in Europe, implying a Sun-climate connection. Recently, a more direct link between climate and solar variability has been speculated. Stratospheric winds near the equator blow in different directions, depending on the time in the solar cycle. Studies are under way to determine how this wind reversal affects global circulation patterns and weather. During proton events, many more energetic particles reach the Earth’s middle atmosphere. There they cause molecular ionization, creating chemicals that destroy atmospheric ozone and allow increased amounts of harmful solar ultraviolet radiation to reach the surface of the Earth. A solar proton event in 1982 resulted in a temporary 70% decrease in ozone densities.

Source: NOAA Space Weather Prediction Center - http://www.swpc.noaa.gov.

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