6. Van Allen Radiation Belts

6. Van Allen Radiation Belts. The Van Allen radiation belts are areas of charged particles originating mostly from the solar wind and other cosmic rays that are absorbed and retained by planets using the planet's magnetic field. The Earth has two Van Allen Belts from a height of 640 to 58,000 kilometers above the Earth's surface, namely the inner belt and the outer belt. These belts endanger satellites, so satellites require protection for sensitive components. Figure 17. Van Allen belt (Source : frontierscientists.com) The inner belt is located at a height of 0.2 to 2 times the radius of the earth, contains a high concentration of electrons and is trapped by a relatively strong magnetic field compared to the outer belt. Meanwhile, the outer belt consists of high-energy electrons trapped in the Earth's magnetosphere. The outer belt is more variable than the inner belt because the outer belt is more easily influenced by solar activity. The shape of the outer belt is toroidal with heights from 3 to 10 times the Earth's radius. 7. Aurora. Figure 18. Aurora (Source: quizizz.com) Aurora is a natural phenomenon that produces fiery rays of light in the night sky in the ionosphere layer of a planet. On Earth, Aurora occurs at the South Pole (Aurora Austrialis) and the North Pole (Aurora Borealis). Sometimes, Aurora can also appear on mountain peaks in tropical climates. The cause of Aurora is the sun. The Sun sends heat, light, energy and small particles to Earth and the magnetic field protects Earth from most of this energy and particles. However, the sun does not send energy constantly and when the sun releases electric gas that can move quickly in space, a solar storm called a coronal mass ejection will form. When a solar storm reaches Earth, some of the energy and particles move towards the magnetic fields at the North Pole and South Pole of the Earth. There, these particles interact with gases in the atmosphere, causing auroras to form. Figure 19. Aurora Formation Process (Source: researchgate.net - NASA) Auroras usually appear as luminous bands that can extend up to 200 miles high. Oxygen produces green and red colors, while nitrogen produces blue and purple colors. 8. Ionosphere The ionosphere layer is the upper atmospheric layer that is ionized from a height of 48 to 965 kilometers. In this layer there are quite a lot of free electrons which influence the propagation of electromagnetic waves through it. The ionosphere is ionized due to radiation and solar activity. The structure and maximum density of free electrons in this layer will vary significantly, namely with time (11-year, seasonal, and daily sunspot cycles), with geographic location (poles, auroral zones, mid-latitudes, and the equator), and with solar- related ionospheric disturbances. Figure 20. Ionosphere Layer (Source: Encyclopedia Britannica) The ionosphere layer is an important layer, especially in satellite geodesy. The ionosphere layer affects radio propagation on Earth. Based on the increase in height and electron density, the ionosphere layer is divided into: - Layer D Layer D is the lowest layer of the ionosphere with a height of 60 to 90 km above the earth's surface. This layer is only found in the morning. Ionization in this layer is Lyman-alpha series radiation. In this layer, high solar activity can create strong X-rays which can ionize N2 and O2 and the medium frequency (MF) and high frequency (HF) are significantly weakened. - Layer E Layer E is the middle layer in the ionosphere with a height of 90 to 150 km above the Earth's surface. Ionization of this layer occurs due to weak X-rays and far ultraviolet solar radiation. In normal times, this layer can only reflect radio frequencies lower than 10 MHz and may contribute to the absorption of frequencies above 10 MHz. - E5 layer The E5 layer is a layer characterized by small and thin intense ionization clouds and can help reflect radio waves. - F layer Layer F is the highest layer in the ionosphere with a height of 150 to more than 500 km above the Earth's surface. This layer has the highest electron density. Therefore, signals that penetrate this layer will be released into space. In the F layer, the number of oxygen ions decreases and light ions such as hydrogen are more dominant. Layer F consists of one layer at night (F2), but has two layers in the morning (F1 and F2). The F2 layer is responsible for sky wave propagation of radio waves and long-distance high-frequency radio communications. 9. Troposfer Figure 21. Troposphere (Source: www.skybrary.aero) The troposphere is the lowest layer of the atmosphere, starting from the earth's surface to an average height of 12 km. At the poles, the troposphere is at an altitude of 7 km with a thickness of around 17 km, while at the equator, the troposphere is at an altitude of 20 km with a thickness of 9 colometers. The troposphere is the layer where weather occurs, with 75%-80% of the mass of the atmosphere and 90% of the total mass of water vapor in this layer. The temperature, air pressure and air density in the troposphere will decrease as the layer's height increases, this is mostly caused by heating due to the transfer of energy from the Earth's surface. The troposphere layer influences the speed and direction of electromagnetic wave signals that pass through it. Temperature, pressure, and water vapor content in the troposphere layer affect signal propagation. The layer between the troposphere and the stratosphere is called the tropopause, which is when the temperature does not change drastically.