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Ionosphere, an area of the atmosphere that is not part of the classic list of layers of the earth's atmosphere like the stratosphere or mesosphere, for example, it is a particular area that plays, as we shall see, a very important in balance of our planet, if we can now call it balance!
Hundreds of kilometers thick, it is extremely rarefied, in it we find only 1% of the total atmospheric gas mass, this also affects its temperature which, during the day, varies from 200 K, in the innermost part, to 1500 K if we go to measure it in the states furthest from the Earth and more exposed to the Sun. The Sun itself, and its rays, interact gas we find in the ionosphere, so their properties can change from day to night.
The ionosphere is so called because it is the zone where ionization takes place. Let's see better: this band is very close to the Sun which, hitting the particles of the gases present in it, ionizes them. Some ionization is also due to cosmic rays coming from space but to a lesser extent.
It is found partly in the mesosphere and partly in the thermosphere, this particular band, we can locate it between 60 km away from the earth's crust and 450 km. If we look at the electrical properties of the ionosphere, we notice that they are not the same everywhere but they vary when changes the composition and intensity of solar radiation received. For this reason, in this perspective, we could also define ionosphere substrates.
When we talk about ionospheric propagation we are talking about radio waves because this area of the atmosphere shows an important role in some applications that concern them.
When a radiofrequency wave affects an ionized layer, it can happen that it is totally reflected, if particular conditions occur. This does not happen in other areas of the atmosphere that are not ionized. The phenomenon just described opens up the possibility of use a propagation model based on multiple reflections between the earth's surface and the ionosphere, a model that is efficient for short waves (with frequencies below 30 MHz), those of amateur radio broadcasts.
Ionosphere and earthquakes
Studies are underway investigating how earthquakes can affect the distribution of electrons in the ionosphere. Some data were also collected following the earthquake of 25 April 2015, which occurred in Nepal with an intensity of magnitude 7.8. The wave of energy generated, unfortunately, managed to spread into the atmosphere even going to "disturb ”the electrons in the ionosphere.
To record these variations in the distribution of electrons were employed GPS satellites who were above Nepal at the time of the earthquake, NASA then developed a system called Vtec, from "vertical electron content", specifically to record the disturbances produced by the distribution of electrons in the upper atmosphere.
We call it Northern Lights or Southern Lights, depending on whether it occurs at the south or north pole, but it is the polar aurora, caused by the interaction of protons and electrons of solar origin with the earth's ionosphere. These charged particles are able to excite the atoms of the atmosphere which, to de-energize, they emit light of various wavelengths.
We just have to admire the many colors produced in the sky, changing over time and space. Red-green-blue prevail, usually, but each time it's a different and unpredictable spectacle.
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