Why ionosphere important

It lies km miles above the Earth. The ionized electrons behave as free particles. The Sun's upper atmosphere, the corona , is very hot and produces a constant stream of plasma and UV and X-rays that flow out from the Sun and affect, or ionize, the Earth's ionosphere. During the night, without interference from the Sun, cosmic rays ionize the ionosphere, though not nearly as strongly as the Sun.

These high energy rays originate from sources throughout our own galaxy and the universe -- rotating neutron stars , supernovae , radio galaxies , quasars and black holes.

Thus the ionosphere is much less charged at nighttime, which is why a lot of ionospheric effects are easier to spot at night — it takes a smaller change to notice them. The ionosphere has major importance to us because, among other functions, it influences radio propagation to distant places on the Earth, and between satellites and Earth. Image courtesy Morris Cohen, Stanford University.

The ionosphere is composed of three main parts, named for obscure historical reasons: the D, E, and F regions. The electron density is highest in the upper, or F region.

The F region exists during both daytime and nighttime. During the day it is ionized by solar radiation, during the night by cosmic rays. The D region disappears during the night compared to the daytime, and the E region becomes weakened.

Back to top. The amount of energy photon flux at EUV and x-ray wavelengths varies by nearly a factor of ten over the 11 year solar cycle. The density of the ionosphere changes accordingly.

Due to spectral variability of the solar radiation and the density of various constituents in the atmosphere, there are layers are created within the ionosphere, called the D, E, and F-layers. Other solar phenomena, such as flares, and changes in the solar wind and geomagnetic storms also effect the charging of the ionosphere. Radio waves generally travel in straight lines, so unless a tall transmission tower can "see" the top of a receiver tower, the curvature of the Earth limits the range of radio transmissions to stations that are not over the horizon.

However, some frequencies of radio waves bounce or reflect off of the electrically charged particles in certain ionosphere layers.

Pre-satellite radio communications often took advantage of this phenomenon, bouncing radio waves off of the "sky" to extend the range of the signals. Radio operators had to account for the constant changes in the ionosphere, particularly the shifts or disappearance of the layers between day and night, to effectively take advantage of these mirror-like reflections of radio waves.

The ionosphere regions can absorb or dampen radio signals, or they can bend radio waves, as well as reflecting the signals as described above. The specific behavior depends on both the frequency of the radio signal as well as the characteristics of the ionosphere region involved.

Since Global Positioning System GPS satellites use radio signals to determine locations, the accuracy of GPS can be severely reduced when those signals bend as they pass through ionosphere regions.

Similarly, some radio communications can be disrupted if the frequency used is one that an ionosphere layer dampens or absorbs entirely, resulting in a weakened signal or even total loss of communications. Scientists constantly measure and produce computer models of the ever-changing ionosphere so that people in charge of radio communications can anticipate disruptions.

Scientists use radio waves in various ways to probe and monitor the otherwise invisible ionosphere. Various radio antennas and radar systems, on the ground and on satellites, are used to monitor the constantly evolving ionosphere. Radio antennas "listen" for radio signals generated by the ionosphere itself, radar systems bounce signals of the different layers, and pairs of transmitters and receivers shoot signals through the ionosphere to determine how much those signals are dampened or redirected.

Along with the daily fluctuations in the ionosphere, there are also seasonal and longer-term variations in this complex set of regions. Different latitudes warm and cool with the seasons as the intensity of sunlight varies from place to place due to the tilt of Earth's axis.

Similarly, the ionosphere varies seasonally as the location of the peak intensity of solar X-rays and UV light, which drive the rate of formation of ions, moves around on the globe.