What is the Ionosphere?

The ionosphere (Ionosphere) is an ionized region of the Earth's atmosphere. Ionosphere An upper layer of the atmosphere that is ionized by high-energy solar radiation and cosmic rays. The entire earth's atmosphere over 60 kilometers is in a partially ionized or fully ionized state. The ionosphere is a partially ionized atmospheric area. The fully ionized atmospheric area is called the magnetic layer. Some people also call the entire ionized atmosphere the ionosphere, so the magnetic layer is regarded as a part of the ionosphere. Apart from Earth, Venus, Mars, and Jupiter all have ionosphere. The ionosphere extends from about 50 kilometers above the ground to the high-level atmosphere of the earth's upper atmosphere. There are quite a lot of free electrons and ions, which can change the propagation speed of radio waves, cause refraction, reflection and scattering, and generate polarization. The rotation of the surface is absorbed to varying degrees.

Ionosphere

The ionosphere (Ionosphere) is an ionized region of the Earth's atmosphere. Ionosphere An upper layer of the atmosphere that is ionized by high-energy solar radiation and cosmic rays. The entire earth's atmosphere over 60 kilometers is in a partially ionized or fully ionized state. The ionosphere is a partially ionized atmospheric area. The fully ionized atmospheric area is called the magnetic layer. Some people also call the entire ionized atmosphere the ionosphere, so the magnetic layer is regarded as a part of the ionosphere. Apart from Earth, Venus, Mars, and Jupiter all have ionosphere. The ionosphere extends from about 50 kilometers above the ground to the high-level atmosphere of the earth's upper atmosphere. There are quite a lot of free electrons and ions, which can change the propagation speed of radio waves, cause refraction, reflection and scattering, and generate polarization. The rotation of the surface is absorbed to varying degrees.

Chinese name

Ionosphere

Foreign name

Ionosphere

Area

Partially ionized area of the atmosphere above 60 kilometers

Research object

Distribution of electron density with height

Existing stars

Earth, Venus, Mars, etc.

Upper level

Magnetosphere

Due to the ionization of neutral, atomic and air molecules by rays outside the earth (mainly solar radiation), the entire earth's atmosphere more than 60 kilometers from the surface is partially or completely ionized. The ionosphere is a partially ionized atmosphere Area, the completely ionized area of the atmosphere is called the magnetosphere. Some people also call the entire ionized atmosphere the ionosphere, so the magnetic layer is regarded as a part of the ionosphere. In addition to Earth, Venus, Mars, and Jupiter also have ionospheres.

In 1899 Nikola Tesla attempted to use the ionosphere for long-range wireless energy transfer. He sends extremely low-frequency waves between the ground and the so-called Konorial Heaviside in the ionosphere. Based on his experiments, he performed mathematical calculations, and his calculation of the resonance frequency in this region was less than 15% of the results of today's experiments. Scholars in the 1950s confirmed that this resonance frequency was 6.8 Hz.

Atmospheric ionization is mainly caused by ultraviolet and X-rays in solar radiation. In addition, solar high-energy charged particles and galactic cosmic rays also play an important role. The molecules and atoms in the upper atmosphere of the earth are ionized under the action of solar ultraviolet rays, X-rays, and high-energy particles, generating free electrons and positive and negative ions, forming a plasma region, which is the ionosphere. The ionosphere is neutral from a macro perspective. The change of the ionosphere is mainly manifested in the change of the electron density with time. The conditions for the electron density to reach equilibrium mainly depend on the electron generation rate and the electron disappearance rate.

Solar radiation ionizes some neutral molecules and atoms into free electrons and positive ions. The deeper it penetrates in the atmosphere, the less the intensity (the ability to generate ionization), and the density of the atmosphere gradually increases, so it appears at a certain height. Ionization maximum. Different components of the atmosphere, such as molecular oxygen, atomic oxygen, and molecular nitrogen, are unevenly distributed in space. They are ionized by radiation in different wavelength bands, forming their respective extreme regions, which results in a layered structure of the ionosphere. The ionosphere has a layered structure in the vertical direction, and is generally divided into D, E, and F layers, and F layer is further divided into F1 and F2 layers. The maximum electron density is about 10 cm, which is about 300 kilometers in height. In addition to the regular layers, there are heterogeneous structures in the ionosphere area, such as the occasional E layer (Es) and extended F. Occasional E-layers are more common and are uneven structures that appear in the E-layer area. The thickness ranges from several hundred meters to one to two kilometers, the horizontal extension generally ranges from 0.1 to 10 kilometers, the height is about 110 kilometers, and the maximum electron density can reach 10 cm. The extended F is an uneven structure that appears in the F layer. In the equatorial region, it often extends along the geomagnetic direction and is distributed in the ionospheric region of 250 to 1000 kilometers or higher.

Ionospheric mode is a mathematical description of ionospheric parameters as a function of height. This change is related to geographic location, season, local time, and solar and geomagnetic activity. The complex ionospheric morphology brings great difficulties to practical applications. Therefore, based on a large amount of measured data, people describe the ionospheric morphology and structure with a simpler mathematical model in order to apply it to engineering designs such as radio communications and space navigation. . The most studied are the electron density modes that have a direct impact on radio wave propagation.

Where N (h) is the electron density at the height h from the ground; h0 is the starting height; is a constant; is the half thickness of the layer. These modes can only describe a certain part of the ionospheric electron density profile. In order to describe the profile completely, different mathematical expressions must be used in different parts.

For the electron density profile below the F-layer peak, different combination modes can be adopted according to different practical applications. The Bradley-Dudner mode recommended by the International Radio Advisory Committee for short-wave field strength calculation is a combination mode of parabolic mode (F2 layer)-linear mode (F1 layer)-parabolic mode (E layer). The mode parameters can be deduced from the characteristic parameters obtained from the ionospheric observation station. In general, the height difference between the obtained electron density distribution and the actual distribution is less than 20 kilometers. Other modes are: a combination mode of cosine mode (layer F2)-secant mode (EF layer)-parabolic mode (layer E), which can be used for ray tracing calculations with higher accuracy requirements; parabolic mode (F2) layer and polynomials The combined mode is convenient for calculating the peak height, the elevation at the peak, and the equivalent plate thickness under the peak of the F2 layer from the frequency-altitude map of the ionospheric plummetometer.

Electron density, electron temperature, and ion temperature profiles given in the International Reference Ionosphere (IRI, 1979).

In the electron density profile including the F-layer peak region, the more typical are the Bent mode and the Pennsylvania 1 ionosphere mode. The altitude range of this special mode is from 150 km to 2000 km. Below the peak height is the parabolic square mode, and above the peak height is the parabolic mode; at higher altitudes, there are three consecutive exponential modes. This special mode ignores the details of the section (especially the F area) and focuses on accurately expressing the ionosphere electron content. It is suitable for calculating the delay and direction change of radio waves due to refraction. The Pennsylvania Ionosphere Model (120-1250 km) is a simulation of the physical and chemical processes of the ionosphere within an empirical height range, and the electron density is calculated by adjusting the ionization reaction speed and vertical electron flow. This model is mainly used to study theoretical issues such as transport processes and wind attenuation.

The International Radio Science Union and the United States Space Research Commission compiled the International Reference Ionospheric according to the measured data of the ionosphere. It is a set of specialized computer programs. The input data is geographic longitude and latitude, month, local time, and sunspot number. The output data is the vertical distribution of the parameters of the ionosphere. Figure 3 shows an example of the output profile.

Due to the excitation of various disturbance sources from outer space, the sun and the Earth's atmosphere itself, the ionosphere will also generate corresponding disturbance changes and irregular structures, showing a variety of different forms (see ionospheric disturbances, ionospheric heterogeneous bodies, Ionospheric modulation)

Due to the effects of thermal motion and electromagnetic force, the electrons escaping from one molecule may collide with another cation that has lost electrons, and may also be temporarily combined with a neutral molecule to form an anion. In the ionosphere, ionization and recombination are always ongoing, but in a region, the concentration of free electrons and anions is basically the same as the concentration of cations, so it is generally electrically neutral. This is the fourth state of matter, called the plasma state. The temperature of the ionosphere does not exceed 1000K, which belongs to cold and weak plasma.

Various components of solar radiation have different effects on the atmosphere. Short ultraviolet rays and X-rays ionize the atmosphere. Longer ultraviolet rays decompose atmospheric molecules into single atoms. Longer ultraviolet rays cause O2 to O3. Particle flow can cause a variety of effects such as atmospheric ionization and elevated temperature. As solar radiation passes through the atmosphere, it is attenuated by absorption. The shorter the wavelength of radiation, the more attenuation it traverses through the same layer of gas. Therefore, only ultraviolet rays with longer wavelengths can reach the ground, and the composition of the atmosphere also changes with altitude due to absorption of ultraviolet rays.

Studies and actual rocket measurements have shown that there is no significant change in the molecular weight of the atmosphere below about 90 km altitude, but the percentage of O3 content in the range of heights from 10 to 50 km is large, with the maximum at about 20 to 35 km. NO appears over 35 to 40 km. Above 90km, O2 begins to decompose into oxygen atoms, and N2 also begins to decompose at higher places. Above about 100km, the main components of the atmosphere are O, N2, and N. Above about 500 km, N2 and O2 are no longer present, and the percentages of He and H content gradually increase. Above 2000 km, there are only these two atoms.

Atmospheric molecules tend to diffuse outward. As a result of this confrontation with the gravity of the earth, atmospheric pressure decays exponentially with altitude. The number of ions contained in various components may have a maximum value at a certain height, but due to the simultaneous effect of various factors (including the geomagnetic field) on the ionosphere and the migration and dissipation of charged particles, the actual ion concentration varies with the height. Change is not a superposition of the theoretical distribution of several components. In general, anions only exist below 70km (day) or 90km (night), and the cations and free electrons are mainly the same concentration. The distribution curve of concentration with height appears at certain heights, and these heights play an important role in the reflection of electromagnetic waves. Each area is named from the bottom to the D layer (about 40 to 90 km above the ground), the E layer (about 90 to 160 km), and the F layer (stretching thousands of kilometers away).

The distribution of electron concentration with height is greatly affected by time, season, and solar activity. The concentration value and the range of each area are not fixed. At night, because it is not exposed to the sun, and the density of the lower atmosphere is larger, the recombination is stronger, the D layer will disappear, and the electron concentration of the E and F layers will decrease by one or two orders of magnitude. Occasionally, the E layer will appear in the E layer. The electron concentration range is high, and it can even reflect electromagnetic waves of about 50 MHz. Its life is only a few hours or less. When there are many sunspots on the surface of the sun and a large number of particle streams are ejected, the concentration of the F layer may be greatly reduced due to thermal expansion, so that short-wave communication is interrupted for several hours or even tens of hours. This situation is more serious in high latitudes.

The ionosphere is a dispersive medium. When the refractive index becomes an imaginary number, the electromagnetic wave is attenuated by the cutoff and cannot propagate.

Under the action of an electric field, the free electrons in the ionosphere move in a way that random thermal motion is superimposed with regular vibration. When colliding with other heavier particles, the vibrational kinetic energy is absorbed by the collided particles, and this kinetic energy is converted from the electromagnetic field energy flow that exerts force on the electrons, so the collision causes the electromagnetic waves to be absorbed and attenuated. In layer D, due to the high atmospheric density, the collision frequency is about 8 × 107 times / second. In layer F, collisions are almost negligible except when the sun erupts (heat turbulence). The motion of free electrons in the ionosphere is also affected by the geomagnetic field. The trajectory of the electronic thermal motion is not a straight line. When there is an external electromagnetic field in the ionosphere, due to the weak degree of ionization, the interaction between the charges and the magnetic field in the electromagnetic wave have a relatively weak effect on the electrons. The force that determines the regular movement of the electrons comes from the electric and geomagnetic fields of the electromagnetic wave. The direction of the geomagnetic field force is orthogonal to the plane common to the geomagnetic field and the velocity of the electrons, so that the electrons get lateral acceleration at any time, so the regular vibration of the electrons is not co-linear with the electric field, so the equivalent electrode strength vector is not parallel to the electric field intensity vector . The ionosphere becomes a magnetically anisotropic medium under the influence of the geomagnetic field. The equivalent refractive index of the ionosphere has double values n1 and n2 and is related to the angle between the wave propagation direction and the geomagnetic direction. In the case where n1 and n2 are both real numbers, n1 <n2. When the wave propagation direction is perpendicular to the geomagnetic direction, n2 has nothing to do with the geomagnetic field, so it is called ordinary refractive index and n1 is called abnormal refractive index.

The ionosphere is not entirely static, and there are also random flows there. The distribution of charged particles is superimposed with random fluctuations on the average value. In some areas, there may be high-concentration clumps, and the fluctuations and clumps all change with time. The detection and analysis of the fine structure of the ionosphere are attracting many people's attention.