EARTH’S ATMOSPHERE- TROPOSPHERE

What is the troposphere?

Troposphere extends from the Earth’s surface to about 12 kilometres in height. Its height is the lowest at the two poles and the highest at the equator. This very shallow layer is essential as it holds all the air that the plants need for photosynthesis and animals need to breathe. 

The composition of the troposphere includes nitrogen (78%), oxygen (21%), argon (0.93%), carbon dioxide (0.04%), water vapour, and other gases. It also contains about 99% of all the water vapour and aerosols (minute solid or liquid particles suspended in the atmosphere). Since most of the heat found in the troposphere is generated by transfer of energy from the Earth’s surface, the temperatures typically fall with an increase in altitude. Therefore, the troposphere is also known as an inversion layer. 

The troposphere is the densest atmospheric layer, compressed by the weight of the rest of the atmosphere above it. Except for large magellanic thunder clouds, whose tops can ascend into the lowest sections of the surrounding stratosphere, most of the Earth’s climate occurs in the troposphere which also contains practically all clouds formed by weather. Aeroplanes fly in the region between this layer of atmosphere and the stratosphere.

Propagations of electromagnetic waves

The influence of atmospheric refraction on the propagation of electromagnetic waves has been studied from the initial stages of radio wave technology. It is clarified that the route of EM waves can bend due to the irregular structure and distribution of the reflective index of air, causing problems. These include multipath fading and interference, attenuation due to diffraction on the terrain obstacles, or so-called radio holes. These effects significantly damage radio communication, navigation, and radar systems. The atmospheric reflectivity is dependent on physical parameters of air such as pressure, temperature, and water content.

1.      Tropospheric propagation:

When the earth’s lower layer is bending, scattering, and/or reflecting due to electromagnetic fields, EM radiation spreads through the sphere. Tropospheric propagation is the name given to all of such phenomena. Wireless transmission can be affected by this propagation, which can sometimes increase the effective range while also increasing interruptions.

The most well-known form of tropospheric propagation is called bending. It is a process which reduces radio-wave propagation speed compared with the speed in a vacuum. The greater the air density, the more the air slows the waves, and thus the greater is the index of refraction. The volume and refractive index of the troposphere are the greatest closer to the surface and start decreasing with elevation. Electromagnetic radiation at very high frequencies ( 30 to 300 Megahertz) and ultra-high frequencies (300 Megahertz to 3 Gigahertz) are reflected toward the earth as a result of this. A horizontally emitted wave can travel hundreds of kilometres along the Earth’s curvature.

2.      Tropospheric scattering

The troposphere scatters EM waves in a wide variety of wavelengths, including radio signals. Tropospheric scatter is the name given to this phenomenon, or troposcatter. In general, tropospheric scatter is most utilised at ultra-high and EM wave frequency (300 Megahertz and over). A signal transmitted above the horizon is scattered at altitudes up to several miles, making over-the-horizon communication possible. The greatest communications range can be realised over flat land or water. Scattered waves are weak, so high-power transmitters and sensitive receivers are necessary.

3.      Ducting

A less common, but often dramatic, form of tropo is called ducting or duct effect. The duct effect occurs when there is a defined, horizontal boundary between air masses having different densities. When a cool air mass is overlain by a warm air mass, as is the case along and near warm fronts and cold fronts, transmissions at very high and ultra high frequency are reflected at the edge, and they hit at an angle of incidence from beneath. Because radio waves are also reflected from the Earth’s surface, the result can be efficient propagation for hundreds or, in some cases, upwards of 1,000 miles (ca. 1,609 km), as the waves alternately bounce off the frontal boundary and the surface. Ducting can allow long-distance radio reception in the frequency-modulation (FM) broadcast band between 88 and 108 MHz. 

Conclusion

The troposphere contains about 85% of the atmosphere’s total mass. Tropospheric processes, such as the water or hydrologic cycle (the formation of clouds and rain) and the greenhouse effect, have a great influence on meteorology and the climate of this planet. The chemical composition of the troposphere determines the air quality. There are certain components, even if they are only present in small amounts, that may harm health and vegetation. Therefore, it is of utmost importance to understand the composition of the troposphere.