The Earth’s atmosphere differs in density and composition as the altitude increases above the surface. The lowest part of the atmosphereis called the trosposphere and extends from the surface to 10 km . The gases in this region are predominately molecular oxygen (O₂) and molecular nitrogen (N₂). All weather is confined to the troposhpere as is 90% of the Earth’s atmosphere and 99% of the water vapor. All mountains are within the troposhpere and all of our daily activities occur here as well.

Above the troposphere is the stratosphere, which extends from 10 km to about 50 km above the Earth’s surface. The gas is still dense enough for hot air balloons to ascend 15-20 km. It is within the stratophere that incoming solar radiation breaks up the molecular O_{2 into separate individual oxygen atoms. Each individual oxygen atom} may combine with an oxygen molecule to form a molecule of ozone (O₃).

At heights above 80 km, the gas is so thin that free electrons can exist for short periods of time before they are captured by a positive ion. The location of these charged particles indicates the beginning of the ionosphere. The ionosphere is a region with the properties of a gas and of a plasma that has charged particles surrounding the Earth and is created by the ultraviolet radiation from the sun.

Plasma, formed at high temperatures when electrons are stripped from neutral atoms, consists of freely moving charged particles; electrons and positively charged ions. Because of its unique physical properties, plasma is the fourth state of matter. Plasma is common in nature. On Earth, lightning, fluorescent light bulbs and neon signs are common examples of plasma. The ionosphere affects our modern society in many ways. International broadcasters use the ionosphere to reflect radio signals back to Earth so that entertainment and information programs can be heard around the world. The ionosphere provides long range capabilities for commercial ship-to-ship and ship-to-shore communications, for trans- oceanic aircraft links, and military communication and surveillance systems. But the sun has a major effect on the ionosphere. Solar events such as solar wind, solar flares, and coronal mass ejections cause enormous variability and turbulence to occur in the ionosphere. Since signals transmitted to and from satellites for communication and navigation must pass through the ionosphere, any irregularities in the ionosphere will impact system performance and reliabilty. How do solar events such as the solar wind, affect the ionosphere? The solar corona, the outermost layer of the sun, is constantly losing particles. Protons and electrons evaporate off the sun, and reach the Earth traveling at velocities up to 500 km/sec. Since the corona is a plasma, it is an excellent electrical conductor. As a result of this electrical conductivity, the coronal plasma moves along magnetic field lines. There are two types of magnetic field lines- “open” and “closed”. Closed field lines are anchored at two points in the sun’s photosphere and extend into the corona as a loop or arch (solar prominance is one example). Open field lines are anchored at one point in the photosphere and extend into interplanetary space. It is along the open field lines that the coronal plasma can expand outward in the form of solar wind. When the solar wind comes to Earth it meets an obstacle more than 10 times the size of the Earth- the magnetosphere. The magnetosphere is the region in space where the Earth’s magnetic field balances the pressure of the solar wind. The solar magnetic field is carried outward from the sun by the solar wind. The magnetosphere encloses the Earth and causes particles coming from the sun to be deflected around the Earth. This compresses the Earth’s magnetic field on the side that faces the sun (dayside) and stretches out the “tail” to a length over 100 times the radius of the Earth, on the side opposite the sun (nightside) creating a shock wave called the “Bow Shock”. As particles pass through the curved “Bow Shock”, a surface that slows, heats, and deflects particles around the Earth, they enter a region called the magnetosheath and for the most part they remain there as they flow around another barrier called the magnetopause. The magnetopause separates the Earth’s magnetic field from the sun’s magnetic field.

Most particles travel down the length of the tail and out into interplanetary space. However, some solar wind particles pass through funnel-like openings at the North and South poles, releasing tremendous energy into the ionosphere. We see this energy release displayed as the auroras, but enhanced fluxes of energetic particles and ionospheric disturbances can cause communications “blackouts” and induced current in power lines and pipe lines. Since there is a correlation between the sun’s activity (sunspots, solar flares, coronal mass ejections) and the sun’s varying energy output, which occur more frequently at the peak of the 11 year solar cycle, any variations over the 11 year solar cycle in the intensity of the sun’s electromagnetic output significantly affects the chemistry, structure and dynamics of the Earth’s ionosphere.

One Internet-based data retrieval interface from which you can find the sun’s energy output and make a prediction about what the possible affects would be on Earth is OMNIWeb. OMNIWeb is a WWW-based data retrieval and analysis interface to the National Space Science Data Center’s OMNI data which consist of one hour resolution “near-Earth” solar wind magnetic fields and plasma data, energetic proton fluxes (1-60 MeV), and geomagnetic and solar activity indices. It allows you to select a subset from the availble OMNI data to view as a plot or to retrieve. OMNIWeb also has a graphical browsing capability to analyze and preview the data as time series plots.

OMNIWeb’s data sets come from a variety of spacecrafts including IMP 8 which provide data about the sun’s magnetic field. The Interplanetary Monitoring Platform (IMP 8) which was launched on October 26, 1973 on a Delta rocket was built at and is managed by NASA/Goddard Space Flight Center. IMP 8 is in a near-circular 35 Earth radii 12 day orbit in the Earth’s magnetosphere of which 4-5 days it is not in the solar wind and therefore not collecting data. There are 11 instruments on IMP 8 that measure solar wind magnetic fields, plasmas and energetic particles. On October 26, 1995, the IMP 8 spacecraft had measured solar wind magnetic fields and plasmas through one complete 22 year solar magnetic cycle, during which a reversal of polarity of the sun’s magnetic field occured. The IMP 8 spacecraft continues to be an important part of NASA’s active space plasms physics missions, complimenting the observations of WIND, GEOTAIL, and other spacecraft.