Ionosphere
The ionosphere ( from Ancient Greek ἰών or ἰόν ión, going ' and Greek σφαίρα sfära, ball ') is that part of the atmosphere of a celestial body, containing large amounts of ions and free electrons.
The planets of the solar system, the ionosphere makes each of the majority of the upper atmosphere. Ionisation of the gas molecules is performed by high-energy portions of the solar radiation ( ultraviolet and hard X-rays ). The range of the radiation determines the transition to neutrosphere.
The ionosphere of the Earth acquired its practical significance for worldwide radio communications because they reflected shortwave and thus allows worldwide connections and because their electrons and ions increasingly dampen the propagation of radio waves with increasing wavelength.
It begins above the mesosphere at an altitude of about 80 km, reaching its greatest electron density at 300 km and goes ultimately into interplanetary space. As a boundary between the ionosphere and plasmasphere the transition altitude between O and H at an altitude of 1000 km can be considered. There, the scale height of decrease of the particle density increased exponentially. The ionosphere is thus mostly within the thermosphere defined with a view to neutral.
- 3.1 Radio waves
- 3.2 energy
- 3.3 earthquake prediction
- 4.1 characteristics 4.1.1 plasma frequency
- 4.1.2 Schumann resonances
- 4.2.1 ionosondes
- 4.2.2 riometer
- 4.2.3 sounding rockets
- 4.2.4 satellite
- 4.2.5 Incoherent Scatter Radar
- 5.1 The geomagnetic anomaly
- 5.2 The D -layer winter anomaly
- 6.1 Ionosphärenstörungen by ray bursts 6.1.1 Electromagnetic radiation: Sudden Ionospheric Disturbance ( SID)
- 6.1.2 particle: Polar cap absorption ( PCA)
- 6.2.1 The sporadic E layer ( ES)
- 6.2.2 Ionosphärenstürme
Emergence of the ionosphere
The ionosphere is caused by absorption of ionizing solar radiation, especially by high-energy electromagnetic waves ( ultraviolet and X-rays ) but also by particle ( corpuscular ) mainly electrons and protons. However afford the cosmic background radiation and meteor streams that burn constantly in the atmosphere, also a certain contribution to ionization. The solar radiation to be solved by the valence atoms: are created positive ions and free electrons, and thus an electrically conductive region of the atmosphere. A ( at least partially ) ionized gas is also referred to as plasma.
On their way down the solar ultraviolet and X-ray radiation is more and more absorbed. At high altitudes ( exosphere ) is the radiation with the highest energy, however, only applies to a few ionizable gas molecules. The denser the atmosphere down, the larger first local ionization. However, by absorbing the radiation intensity decreases. Also the mean free path of the gas, leading to an accelerated reunion of electrons and positive ions is reduced by the increase of atmospheric density ( recombination). The balance between ionization and recombination determines the local electron density. This describes in the simplest form Sydney Chapman theory. But because dependent molecular composition of the height and both required for ionization energy and the possible recombination of the nature of the neutral gas, usually forming between exosphere and lower ionosphere during day three maxima of ionization ( D-, E-and F- region ) from.
The height of these layers depends on the density distribution of the (majority ) from neutrals, but also by the elevation-dependent occurrence of the various atomic and molecular species. The intensity of the solar radiation only influences the local density of the electrons is not the height of the maxima of the electron density.
The degree of ionization depends primarily on the intensity of the solar radiation on, but also by the recombination and annealing processes. Consequently, there is a diurnal (daily ), a seasonal ( seasonal ) and a current (local ) dependency. In the F region, the situation is more complicated, which is why working with empirical ionization cards. An important role is also played by the solar activity in the eleven-year sunspot cycle, sometimes events such as solar storms.
The ionospheric
Within the ionosphere, there are three local Ionisationsmaxima, which is why it is divided into three regions: D, E and F.
Ionisationsmaxima the energy absorption can be assigned by certain Gasteilchenarten. About an altitude of 100 km, the mixing of the air in an even distribution of the gases is not enough, it turns a heterogeneous distribution. This region is referred to as hetero sphere. The absorption of radiation that ionizes a particular gas, preferably takes place where it is present highly concentrated.
The D layer
The D layer is the layer closest to the Earth and exists only during the day in an altitude range between 70 and 90 km. Ionization takes place by radiation of the Lyman - series instead of 121.6 nm, is absorbed by the nitrogen monoxide (NO). In times of sufficiently high sunspot number also hard X- rays ionize (wavelength < 1 nm), the air molecules (N2, O2). On the night remains by cosmic radiation a small residual ionization.
Because of the high rate of air density on the one hand, recombination size, which is why the layer dissolves almost at sunset within a few minutes, on the other hand is the collision frequency between electrons and other particles during the day is very high (about 10 million collisions per second). This means a strong attenuation which increases with increasing wavelength of radio waves. In long-distance traffic, this prevents the use of the space wave radio frequencies less than about 10 MHz ( ionospheric wave guide ). FM signals may be scattered at the D layer ( Ionoscatter ).
The E layer
The E layer is the mean ionospheric layer that forms at a height between 90 and 130 km. Ionization takes place due to soft X-rays (wavelength 1-10 nm) and ultraviolet ( 80 to 102.7 nm) of atomic oxygen (O ), and nitrogen and oxygen molecules (N2, O2) instead. It has an average electron concentration of about 100,000 per cm3, so that only 0.1% of the atoms present are ionized.
The E- layer forms on the dayside of the Earth, reaches its Ionisationsmaximum at lunchtime and after sunset disappears almost completely within an hour. In the sunspot maximum, the layer is higher than in the minimum. Within the E- layer, there is often, but not regularly, severe local ionizations in a few kilometers thick layer, referred to as sporadic E layer.
For short-wave reflection is interesting about the E- layer maximum in the transport, since its critical frequency is only 2-4 MHz.
The E layer is also called the Heaviside layer, or shorter than Heaviside layer. The name goes back to Arthur Edwin Kennelly and Oliver Heaviside, who almost simultaneously predicted its existence independently in 1902. The E- layer was detected as the first ionospheric layers in 1924 by Edward Victor Appleton, who first designated in 1927 as E ( dielectric ) layer. The later discovered further layers was then designated according to their relative altitude as D- and F- layer. ( See also History ).
The F- layer
The F layer is 200 to 400 km at its highest and is the most heavily ionized layer. It is ionized by extreme ultraviolet rays (EUV, wavelength of 14 to 80 nm), which meets the atomic oxygen or nitrogen molecules. It is a broad region of maximum ionization of up to a million of free electrons per cm3.
In the F- layer electron collisions will find mostly elastic ( non-contact) with positive ions instead of what is called the Coulomb collision. In contrast, predominate in the denser D and E layers inelastic collisions of electrons with the neutral gas. [ This is the Earth's ionosphere is an exception - in most astrophysical plasmas outweigh the Coulomb collisions. ]
The F- layer persists even at night, because the free electrons recombine very slowly because of the large mean free path. The day is reflected in the profile of the F layer often a deformation. the so-called F1 - layer, the peak of the profile, however, lies in the F2 layer. The F1 layer is the place of greatest ion production that goes back much without sunlight. The strongest ion concentration, however, is to be found but in the F2 layer due to there weaker recombination. The F1 layer, which appears only during the day, is located in a photochemical equilibrium in which the losses done by rapidly occurring recombination. In contrast, the predominant loss process in the F2 layer with the conversion of O ions into NO - linked and O2 ions. This loss process is slower. In summer, the peak of the F2 layer is higher than in winter. For short waves, it is the most important layer because radio traffic over 3500 km comes only through repeated reflection at this layer about.
The F- layer is referred to as Appleton layer. The name goes back to Edward Victor Appleton, the 1924 could prove the existence of the Heaviside layer (see History ).
Use of the ionosphere
Radio waves
Higher layers of the ionosphere can be ionized by the solar radiation partially and therefore contain free electrons that can be excited by the electric field of radio waves of the frequency f of oscillations. The oscillating electrons in turn send out waves ( 2-7 MHz ) are strongly shifted in phase in the vicinity of the plasma frequency fP and overlap with the original wave. Since the ionosphere is penetrated by the magnetic field of the earth, the free electrons can be excited by the radio wave in addition to a circular motion about the field lines. This cyclotron frequency fB is over central Europe about 1.3 MHz. The direction of rotation of the circularly polarized radio wave with the movement of electrons may be the same or not, and therefore the ionosphere is circularly birefringent. Linearly polarized waves must therefore be interpreted as a superposition of two circular waves with opposite sense of rotation, and they have different refractive indices n. Runs the propagation direction parallel to the magnetic field lines, the following approximations are valid for f > 1 MHz:
The difference between both formulas is in the VHF range is negligible and vanishes if the wave vector with the direction of the magnetic field forms a right angle, because then fB = 0 ( anisotropy ). The two circularly polarized radio waves travel at different phase velocity ( phase velocity corresponds to a greater refractive index smaller ) through the material and can be differently attenuated. Upon receipt, both portions are superimposed to an elliptically polarized wave whose main direction is usually rotated ( Faraday effect).
For f < fP, the refractive index is purely imaginary, so all lower frequencies are reflected. As with the excess of the cutoff frequency of a waveguide can - with sufficient layer thickness - the waves do not penetrate the ionosphere, but not absorbed. So long and medium wave signals can always go back to the ground, as well as radio frequencies below the plasma frequency of the F2 layer, which is usually about 7 MHz. Radio signals above this critical frequency can penetrate the ionosphere at normal incidence. For an oblique incident wave, the corresponding cut-off frequency, the maximum usable frequency ( MUF abbreviated ) is higher than the critical, even more so the flatter the incident takes place. They may be made of the critical frequency approximately be determined as follows:
= angle with the shaft relative to the horizon, = distance between the transmitting and the receiving location = virtual height of reflection.
Make flat radiated wave after the total reflection at an ionospheric layer at some distance back to the ground. If the bump has shorter range, is created around the transmitter a dead zone where no reception is possible, but probably at a greater distance. The term "reach" loses its meaning here.
The minimum usable frequency (English: lowest usable frequency, LUF ) is the lower cut-off frequency in the shortwave range, which can be used for the transmission of a signal between two points at a given time. It depends on the electron density and the frequency of collisions in absorbing lower ionospheric layers and is generally highest at noon. These considerations do not apply to the FM band, whose frequencies are above the plasma frequency.
Energy
The Propulsive Small Expendable Deployer System ( ProSEDS ) is a cable- based energy recovery system for spacecraft that operates according to the principle of a Space Tethers. Its launch was postponed several times and is currently uncertain. A previous system ( Tethered Satellite System ( TSS )) was successfully tested in 1996 during the space shuttle mission STS -75.
Earthquake prediction
It is believed that there is during and before earthquakes effects in the ionosphere. Possible causes include chemical, acoustic and electromagnetic mechanisms are discussed. For example, the release of charge carriers from the oxide minerals is cited by tectonic stresses, but also items such as the excitation of atmospheric gravity waves by outgassing (Fig. 12 ). Although the ionosphere is monitored for a long time from the ground and satellites, is a coupling to be considered not currently proven to be sustainable.
Satellites that study this phenomenon in more detail, are Demeter ( Detection of Electro- Magnetic Emissions Transmitted from Earthquake Regions) of the French Space Agency CNES in 2004 and launched in 2006 Russian Kompas 2
Parameters of the ionosphere
Parameters
The following proposed sizes can be divided into local physical quantities and characteristics of the layers. [ The latter measurement from the outside and are directly accessible for applications usually sufficient. ] The practical application of the definitions is the URSI Handbook explains.
Plasma frequency
For applications related to electromagnetic waves, the plasma frequency is a key parameter. It indicates down to what frequencies the waves propagate in the plasma. The plasma frequency is mainly dependent on the number density of the electrons since these are easier to follow the alternating field as the inert ions. Neglecting the ion is the plasma frequency
This includes e and me the charge and mass of the electron and the permittivity of the vacuum. Substituting these constants, we obtain
Depending on the density of free electrons increasing the plasma frequency of about 1.5 MHz to about 100 km altitude is 7 MHz to about 800 km altitude.
A similar size is dependent on the magnetic field gyration. Apart from solar storms, the magnetic field is the earthly and the Gyrofrequenz close to 1 MHz.
Schumann resonances
The space between the ground and can act as a cavity resonator of the ionosphere. Schumann resonances are called those frequencies where the wavelength of an electromagnetic wave in the waveguide between the earth surface and the ionosphere is an integral part of the circumference of the earth. The excitation with electromagnetic oscillations such frequencies standing waves occur, the Schumann waves so-called. The energy for the low-frequency excitation comes from the global thunderstorm activity. The fundamental harmonic of the Schumann resonance is 7.8 Hz, plus get different harmonics 14-45 Hz Due to atmospheric turbulence occur volatility of these values .
Measurement
Ionosondes
An ionosonde is a radar system for the active investigation of the ionosphere. Ionosondes monitor the level and the critical frequency of the ionospheric layers. For this purpose they send short wave radar pulses of different frequencies against the ionosphere and mainly measure the duration of the received echoes, from which the magnitude of the reflection can be determined.
As the frequency increases, the signal is less sharply broken and thus penetrates more deeply into the ionosphere, before it is reflected. By the deeper penetration of the measured changes, so-called virtual height of the reflective layer. When the critical frequency is exceeded, the ionosphere is no longer in a position to reflect the signal. Can each be explored to the maximum electron density is only half of the ionosphere. The measuring systems are usually on the ground to study the bottom ("bottom side" ) or on satellites for the top ( " topside ").
With the probe records the signal propagation time or calculated from reflection height can be created on the frequency, the so-called ionograms.
Riometer
A Relative Ionospheric Opacity meter or short riometer is a device for passive observation of the ionospheric absorption capacity.
It measures the reception level of the cosmic background radiation in the range of the radio waves emitted by stars or galaxies resistant and after passing through the ionosphere, the Earth reaches (Radio window). Although the strength varies with the Earth's rotation, it is nevertheless sufficiently constant and therefore predictable, depending on the region of the sky for earthly standards. It is up to 110 km is measured, in particular the absorption heights, since the major part of the absorption in the lower layers of the ionosphere occurs as the D layer.
Sounding rockets
Sounding rockets (English Sounding Rockets ) are equipped with measuring instruments sounding rockets, which are preferably used for creating profiles of the ion distribution in the ionosphere. They are inexpensive and allow measurements to heights above the maximum height of the balloon ( ≈ 40 km) and below the minimum altitude of the satellite ( ~ 120 km) are. Moreover, they achieve not possible with other methods of measurement spatial resolution in the centimeter range.
Satellite
Satellites are used for two purposes of Ionosphärenmessung. For a complete satellite ionograms ( topside shots), the measured data of the ground stations ( Bottom Side recordings ), on the other hand, the measured variables are not affected as with ground stations from the atmosphere. For example, the solar X-ray flux from GOES is measured. The solar flux at 10.7 cm wavelength, however, is not changed by the atmosphere and measured daily from ground stations.
The measurement method of the satellite can be divided into passive (receive only sensors) and active ( signal transmission and reception ). In the active method, transmitter and receiver are usually like a radar spatially close together ( in the same satellite ), but need not necessarily be the way. Examples are the radio Okkultationsverfahren or the GPS-based Ionosphärentomographie, be used in the dual-frequency measurements to determine the along the signal path integrated electron content (TEC, Total electron content ).
One of the first satellite, which was used to study the ionosphere, was next to the 1958 launched Explorer 1, the United States which started in 1962, Canadian satellite Alouette 1 (French lark ). After ten years of his mission, he was off schedule. He is still in orbit (as of January 2006) and its senior engineers see even a slight chance that he could be reactivated. He was followed by other ionospheric satellites of the International Satellites for Ionospheric Studies (ISIS) program. The measurement program of the German - American Aeros satellites arose in the context of international project International Reference Ionosphere and has made important contributions to it.
One of the recent satellites for ionospheric research is Demeter ( Detection of Electro- Magnetic Emissions Transmitted from Earthquake Regions) in 2004, the French CNES has sent among other things, to investigate the possibilities for earthquake predictions.
Incoherent Scatter Radar
This one technique is referred to, the erdgestützt sends radar waves against the ionosphere. This valence electrons are there in isolation, their echo is evaluated. From the Echo out information to the electron density, ion and electron temperature, ion composition and plasma velocity can be derived.
The word here means of phase incoherent and refers to the fact that the medium to be examined in relation to the monitoring capabilities of the radar is to be regarded as unstable, ie the medium is changing so fast that these changes can not be observed in detail with the radar.
Currently, worldwide there are nine such facilities.
Models
The exact knowledge of the parameters of the ionosphere, in particular the electron density is essential for many applications such as radio communications, the tracking of satellites and earth observation weltallseitige. For this reason, models have been developed that are used for the description and analysis of the ionosphere.
The view of its development time and number of the most mature at sizes derived model is the International Reference Ionosphere (IRI). The IRI is a joint project of the Committee of Space Research ( COSPAR ) and the International Union of Radio Science ( URSI ), which is developed on annual workshops. This model is since 1999 the world standard for the terrestrial ionosphere.
Other models focus on specific ionospheric electron density as, maximum electron density in the F2 - layer electron temperature and drift and strength of the electric field (see links). In addition to global and regional models are used to describe more precisely to geographical details.
Ionosphärenanomalien
A model of the ionosphere goes out due to its simplistic nature of a structurally homogeneous ionosphere. In reality, this is but messy and does not regular Ionisationsstrukturen on. Ionosphärenanomalien are deviations from the expected general behavior of the ionosphere. These anomalies are resistant observable and demarcate the anomalies of the Ionosphärenstörungen spontaneously occurring, short-term.
Some of the known anomalies are discussed next.
The geomagnetic anomaly
The maximum of the electron density is not more than the equator. Rather, there is a strip with decreased ionization. The so-called fountain effect to the true magnetic equator arises there because the free electrons of the F layer are pushed to greater heights through a combination of electric and magnetic fields ( ExB drift), from where they then along the north - south running magnetic field lines of the Earth's magnetic field to the north and south are moved. Thus, the electron density is increased on both sides of the magnetic equator. The geomagnetic abnormality is also referred to as anomaly equatorial.
The causative electric field generated by thermospheric tidal winds that are directed westward during the day and the relatively large ion swept by shock friction, electrons have only a little. Since the field lines in the electric field pointing in the direction of the force acting on a positive test charge, this is directed to the east ( dynamo ionospheric layer). In the magnetic field, the field lines in the outer region of each magnet from magnetic north to the south pole, that is northward during Earth's magnetic field. According to the three-finger rule, the Lorentz force acting on the free electrons in the ionosphere at the equator upward.
The D -layer winter anomaly
The D -layer winter anomaly was discovered in 1937 by Edward Victor Appleton, and describes the phenomenon that above 35 ° latitude (Berlin ≈ 52.5 ° ) on many winter days, the absorption capacity of the D- layer is much higher than the would justify angle of incidence of solar radiation, often even higher still than on summer days at noon. The anomaly typically achieves a stretch of several thousand kilometers, so a meteorological component is suspected as the cause. The exact causes are not developed until today with certainty.
Furthermore, the day - to-day variance of the absorption capacity in the winter is much higher than in summer and seems to increase with increasing latitude, but this trend is superimposed to the poles of other Ionisationseinflüssen. Although not affected by solar special effects, the absorption within two days may increase by a factor of 5, on average, about 80 % increase in attenuation are likely.
Ionosphärenstörungen
As Ionosphärenstörungen is any irregularities occurring spontaneously in the structure of the ionosphere. The cause of Ionosphärenstörung is usually directly or indirectly, to see the solar radiation activity, but can also affect their ionization meteorites. The direct factors include increased solar ultraviolet, X-ray and / or particle ( corpuscular radiation ) due to a disturbed increased solar activity, to include the indirect atmospheric and electromagnetic processes that can occur in an undisturbed sun.
Ionosphärenstörungen only of short-term nature, and can last from a few minutes to several days. The best known and probably also aesthetically valuable expression of a Ionosphärenstörung is the aurora, aurora borealis, which is triggered by high-energy solar wind particles. In contrast, triggered by their effect on global short wave radio communications is undesirable.
Ionosphärenstörungen should not be confused with Ionosphärenanomalien. The latter not occur spontaneously but are subject to a regularity and describe deviations from the expected general behavior of the ionosphere.
Ionosphärenstörungen by ray bursts
The ionosphere is created by light emitted by the sun radiations of various kinds, charged particles ( also called corpuscles ) or light waves, and a direct impact on their state. A very intense short duration disturbance occurs as a result of an eruption on the sun's surface, which is referred to as a flare (English: flare = bright, flickering light ). On the sun, the light outbreak affects only a small area in the often particularly active radiation outskirts of sunspots (called flare areas). It comes often to the ejection of charged particles, which is called a coronal mass ejection.
Eruptions of charged ponds travel as a cloud of plasma from the Sun to Earth, where they are guided by the magnetic field of the earth in the near polar regions ( spherical magneto- electric convection field ). There they change the ionosphere significantly, often for days, resulting in radio communications to many failures. While the electromagnetic radiation travels the path to ground in about eight minutes, the particle requires up to 40 hours. The Ionosphärenstörung caused by it occurs temporally offset to interference, which are due to electromagnetic radiation. For radio operation longer-term disorders are serious.
Electromagnetic radiation: Sudden Ionospheric Disturbance ( SID)
Sudden Ionospheric Disturbances (SIDs ) have their origin in an elevated X-ray and ultraviolet radiation from the sun. It is absorbed by the ionosphere and carries there, especially in the D layer to a strong increase of the ionization. SIDs are most frequently observed in the sunspot maximum and occur only on the dayside of the Earth.
Due to the high plasma density increases the ability of the D layer, to absorb short-wave to their full extinction, which is referred to as Mögel - Dellinger effect. At the same time an improvement in the propagation of long waves (English Very Low Frequency, VLF ) can be observed, because the D layer can serve long waves as a reflector. Increased ionization enhances this reflection property. The sudden increase in the signal strength of VLF transmitters is used as an indicator of SIDs.
Particle: Polar cap absorption ( PCA)
Associated with solar flares of high -energy protons ( ≈ 10 MeV) ejected, which then penetrate along the magnetic field lines of the earth near the magnetic poles in the atmosphere and greatly increase the electron density in the lower ionosphere (D - layer, E layer ).
The additional charge carriers short waves are so strongly damped that it can come to a complete failure of wireless links whose propagation path passes over the polar caps. Radio waves with a lower frequency, which would normally be reflected from the ionosphere are lower, then reflected at a very much lower amount, such that the propagation paths vary significantly. This phenomenon is referred to as polar cap absorption (PCA).
PCA effects are usually only short-lived nature. During the Rothammel called as average duration of PCA effects 2-3 days, Kenneth Davies speaks only of up to 5-6 hours.
More Ionosphärenstörungen
As already mentioned, are not due to solar flares all the disturbances of the ionosphere. One such example is the so-called equatorial spread -F (English: Equatorial Spread -F ), an unequal distribution of the electron density of the F layer in the equatorial region. This is caused by electric currents in the ionosphere due to rotational differences between free electrons and ions, but since the latter are subjected to mechanical friction, the former do not. These are not sun -induced events are divided into two types, and in terms of the spatial structure of the interference. Following are the transient phenomena ( Transient Phenomena ) and migratory ionospheric disturbances ( Travelling Ionic Disturbances, TIDs ).
As their name suggests are the transient phenomena only by short-lived, volatile nature. Furthermore, they performed locally in cloud -like expression and move horizontally, ie the same height through the ionosphere. This type, for example, sporadic E events and Equatorial Spread -F.
In contrast, TIDs wave -like fluctuations of the electron density with a front width of up to several hundred kilometers. You can take a few minutes to several hours, and express themselves in strong fluctuations of the reflection height and the MUF. On the short- wave propagation, this TID effects affect not serious. The largest TIDs begin in the area of auroras and spread towards the equator from.
Thunderstorms can cause minor TID fronts that travel 200 km before they disperse. Thunderstorms are also the cause of a designated as Elves luminous phenomenon in the ionosphere, but only less than a thousandth of a second lasts and therefore no TID is. Another thunderstorm phenomenon are those referred to as Whistler low frequency electromagnetic signals that travel through the ionosphere and others.
The sporadic E layer ( ES)
The sporadic E layer (English Sporadic -E) is in the range of the E- layer and occurs only sporadically. It is strongly ionized and can cover all higher layers. Their structure is often cloud-like, but may be homogeneous in a wide range. It can lead to unexpectedly high ranges.
Normally radio signals penetrate above the normal cut-off frequency of the E layer this. During a sporadic E event, the signals are reflected there, but what long-range connections deteriorated, but leads for better reception within the Erstsprungzone or dead zone.
There are several theories about the origin of the ES layer, but it is not completely clarified.
Ionosphärenstürme
In the course of Ionosphärenstürmen may cause both a decrease as well as abnormal to the electron density. The former case is referred to as positive Ionosphärensturm, the latter as a negative Ionosphärensturm.
Ionosphärenstürme can have solar or terrestrial causes. For example, an increased particle radiation of the sun, the electron density decrease: Surrounded by a flare ejected solar plasma consisting of protons and electrons affects the Earth's magnetic field, and penetrates into the atmosphere. This results in a decrease in the critical frequency of the F2 layer down to half their normal value, and an increase in the D layer absorption. Thus, the usable for the shortwave radio spectrum at both sides concentrated ago. Intensive Ionosphärenstürme can cause complete blackouts for long distance connections. This is referred to as a so-called short - wave Fade ( out).
Ionosphärenstürme can also atmospheric causes: Today it is believed that increases in electron density are often due to thermospheric winds, while decreases mainly caused by changes in the neutral gas composition, for example by removing elemental oxygen and thus reduced ion production rate. Bubbles with a reduced plasma density can be seen as a cause for the trans- equatorial propagation (trans Equitorial propagation, short- TEP).