The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation.
It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth
The Ionosphere represents the space from an altitude of about 50km to 2000km where the ionization plays a very important physical parameter. It can be divided into C, D, E, F1, F2 layer by electron density distribution and the main source of the ionization is the x-ray and UV-like electromagnetic radiation from the Sun.
Other than these, energetic particles and cosmic rays also give huge effects on ionosphere ionization. Because the radiation from the Sun is absorbed as they pass through the atmosphere and it depends on the length of the atmospheric path, overall, it depends on the zenith angle (χ).
Maximum ionization rate occurs when the Sun is on top of us (χ=0), but the degree of ionization differs by location and time variation (daily, seasonal, annual). The degree of ionization by solar radiation and charged particles are balanced by degree of ionization loss caused by events like collision re-bonding between the electron and the proton, and the electron bonding to a neutral gas atoms or molecules. Structure of the ionosphere can be expressed in mathematical model by using solar ionization flux, vertical distribution and absorption efficiency of neutral gas, and solar zenith angle. At 1931, Chapman developed ionosphere model that appears by monochromatic solar radiation for isothermal, single component gas. It appears that it is approaching reasonably for creation of E layer and F1 layer, but it’s poor for explaining D and F2 layer. Especially in an altitude lower than 90km, where the lowest part of the ionosphere, the absolute source is galactic cosmic ray, as a result, the variation of the electron density does not depend on the solar zenith angle.
The D layer is usually distributed in range of 50∼90km; the electron density here increases rapidly as height increases. The D layer has huge variation in electron density between during the day and night that shows maximum variation altitude between 70~90km and the maximum electron density becomes generally 108∼109electrons/㎥. Also the electron density in D layer varies significantly by seasonal variation, and its maximum value appears at summer and minimum value at winter. At an altitude of 70∼90km, the rate of ionization becomes maximum state because the solar x-ray contributes most to the ionization.
The E layer, a region between altitudes of 90∼130km, is a regular layer similarly follows Chapman model that the electron density varies with solar zenith angle, and maximum electron density appears near at noon. The maximum electron density altitude is about 110km, and shows density value of about 1011electrons/㎥ satisfies maximum plasma frequency of about 3MHz, and plasma frequency drops to 0.4~0.6 MHz. Also, E layer appears to have maximum layer density during solar maximum. In this part of region, the phenomenon that the electron density increases few times than its surround, which is called sporadic E, appears and occurs frequently on mid-latitude at summer daytimes.
The F layer indicates the region with an altitude higher than 130km. The F layer can be divided into F1 layer and F2 layer which division only appears at daytime. The F1 layer has an altitude range of 130~210km with a maximum electron density of 2×1011/㎥, like the E layer, the F1 layer similarly follows Chapman model, but the dependence of the solar zenith angle differs from the E layer. The F2 layer is a region where the electron density appears largest from 1012/㎥ at daytime to 5×1010/㎥ at night time, and since F2 layer is largely effected by wind, diffusion and other mechanical effect, it cannot be well described by Chapman’s equation.
Ionospheric Event Ionospheric Event Feature Cause Sporadic E Layer HF Communication interruption,
VHF Communication Interruption.
Concentrated on late spring to early fall, Frequent on daytime
High density electron clouds at the E layer of the ionosphere. Fade out of short wave radios (Dellinger Phenomenon) HF Communication Fade Out from a few minutes to a few hours.
Frequent during solar maximum
Strong x-ray accompanied by flare Ionosphere Storm Few days duration, U/VHF Communication Interruption
Related with rapid solar activity
Geomagnetic Perturbation, Coronal Hole Scintillation Maximum at midnight related with the F layer events
Satellite Communication Interruption, Main cause of the radio fade out
Irregular Electron Density Distribution
The data observed every 15 minutes interval are transferred to RRA.
The observed data also delivered to SWPC.