Soft X-rays or XUV (10 nm to 30 nm.

Usually associated with solar coronal phenomena, flares, million-degree temperatures, and atomic dissociation. The corona extends from about 21,000 km to 1,400,000 km above the photosphere. X-ray flares are responsible for enhancements in the D and E regions of the Earth's ionosphere. Real-time solar X-ray emissions at shorter wavelengths that are representitve of hard X-ray variations are measured by the GOES satellites, and can be viewed at the NOAA/SEC web site

Extreme ultraviolet or EUV (30 nm to 120 nm).

EUV has emission lines that come from the upper chromosphere (near-coronal temperatures), transition region, and lower corona. This spectral band is responsible for ionization and heating in the Eand fregionof the ionosphere.

Ultraviolet or UV (120 nm to 400 nm).

UV solar flux comes primarily from the base of the sun's chromosphere layer, and has components due to active and quiet solar conditions. This band is responsible for only 1% of the total solar irradiance, but it is important because below 300 nm, it is completely absorbed by ozone and diatomic oxygen atoms in the eart's upper atmosphere.

Visible, optical or VIS (400 nm to 700 nm).

Visible light comes from the solar photosphere, which is only about 400 km thick, has a temperature of approximately 5,000 to 6,000 degrees Kelvin, and yet is responsible for the greatest percentage of the total solar radiation.

Infrared or IR (0.70 mm to 10 mm).

Solar infrared in this range is responsible for the direct heating of the Earth's lower atmosphere, through absorbtion by H2O, and has an effect on minor species constituents in the Earth's mesosphere and thermosphere.

Atmospheric Nomenclature - The Thermosphere and Ionosphere

The thermosphere and ionosphere are terms that describe regions of the Earth's upper-atmosphere from about 100 to 500 km. The thermosphere describes that part of the neutral atmosphere dominated by exponential temperature increases to a maximum temperature plateau, and include atomic or molecular species in diffusive equilibrium. The ionosphere, on the other hand, describes the part of the atmosphere governed by electrons and ions and that is formed by solar ionizing radiation and other electromagnetic processes. In either case, the upper and lower boundaries vary as a function of solar-terrestrial processes, e.g., with solar irradiance variation and with electric field strength as modulated by the magnetosphere.

Thermosphere

The thermosphere lies above approximately 90 km, the point at which the mesopause is defined. Above this point the temperature changes from decreasing to increasing. The thermosphere ends at the boundary with the exosphere, approximately 500-700 km, where atoms are in free escape from the atmosphere. The thermosphere is heated by solar UV and EUV wavelengths where photons are absorbed by atoms and molecules leading to their dissociation or ionization. This photoabsorption process effectively transfers the energy of a photon into kinetic energy of an atom or molecule; the source of heating. The effect is direct, i.e., more photons during high solar activity lead to more heating. From solar minimum to maximum the temperature at the top of the thermosphere (700 km), the exospheric temperature can vary from (900 to 1500 degrees Kelvin). Night to day differences are on the order of 30 percent. Since satellites have orbits as low as about 120 km, the lower thermosphere can have a dramatic effect on satellite drag; the increased density causes satellites to lose altitude. Although the atmosphere densities at these altitudes are still a vacuum from a human perspective, from a satellite perspective the density is very significant since a satellite is traveling thousands of kilometers per hour and the integrated resistance becomes significant very quickly. Satellites lose altitude at different rates depending on their areal cross-section, altitude, and mass as well as the varying atmospheric density.

Ionosphere

The ionosphere contains charged particles of ions and electrons that are formed from solar ionizing radiation, predominately the solar EUV and X-ray irradiances. To a large degree, photoionization of oxygen and nitrogen, in combination with photochemistry, produces the ions and electrons in the E and F regions. Usually, the assumption is made that the ionosphere is neutrally charged, i.e., that there are equal numbers of electrons and ions. The electron density is low at 50 km, rises rapidly to a maximum between 100-250 km (the exact altitude of the peak layer is dependent on solar activity), and then gradually decreases for thousands of km. The regions and layers of the ionosphere are roughly described in the following table:

Ionospheric Layer

Height Range (km) Region / Layer D  50 - 90 Km

Height Range (km) Region / Layer E  120-140 Km

Height Range (km) Region / Layer F1,F2  over 120-140 km

One dramatic effect of the ionosphere is how it affects radio communication. Depending on solar activity, some radio frequencies are totally blocked, while others are enhanced and under disturbed conditions; this can change by the minute, particularly during large geomagnetic storms that come from the solar wind carrying charged ions. Another interesting effect is that spacecraft experience "charging" as a result of the large numbers of available electrons that become attached to the spacecraft and, under the right conditions, electrical arcs can occur within the satellite that sometimes damage electronic components.