Scientists call the ionosphere an extension or a part of the thermosphere. So technically, the ionosphere is not another atmospheric layer, but a region of the atmosphere. The ionosphere represents less than 0.1% of the total mass of the Earth's atmosphere. Even so, it is extremely important!

The upper atmosphere is ionized by solar radiation. Under normal conditions free electrons and ions tend to recombine and a balance is established between electron and ion production and loss.

Ionization processes release energy which heat up the upper atmosphere. So temperature increases with height in the ionosphere region to the extent that by 150-200km, the Earth's atmosphere is extremely hot compared to surface temperatures.

Different regions of the ionosphere make long distance radio communication possible by reflecting the radio waves back to Earth. It is also home to auroras and the mega-ampere currents that heat the atmosphere at high latitudes during geomagnetically active times. During storms, depletions and enhancements of ionization occur depending on the local time and geographical location.

Aeronomy is a term of recent origin which is applied to the processes, both physical and chemical, of the ionosphere.

The correct answer is option 'A': The temperature in the Ionosphere layer of the atmosphere starts increasing with height.

The Ionosphere is a region of the Earth's atmosphere that is ionized by solar radiation. It is located between the mesosphere and the exosphere, extending from about 60 km to 1,000 km above the Earth's surface. The Ionosphere is an important layer as it plays a crucial role in various atmospheric phenomena and communication systems.

Temperature Variation in the Ionosphere:
The temperature variation in the Ionosphere is unique compared to other layers of the atmosphere. While the temperature typically decreases with increasing altitude in the troposphere, stratosphere, and mesosphere, it starts to increase with height in the Ionosphere. This is primarily due to the absorption of high-energy solar radiation by the ionized gases present in this region.

Reasons for Temperature Increase:
1. Ionization: The Ionosphere is formed due to the ionization of neutral atoms and molecules by high-energy solar radiation. This ionization process releases a significant amount of energy, which leads to an increase in temperature.
2. Absorption of Solar Radiation: The ionized gases in the Ionosphere absorb a substantial portion of the incoming solar radiation, particularly in the ultraviolet and X-ray regions of the electromagnetic spectrum. This absorption contributes to the heating of the region, resulting in an increase in temperature with height.

Importance of the Ionosphere:
1. Radio Wave Propagation: The Ionosphere plays a crucial role in the propagation of radio waves. The ionized gases present in this layer can reflect, refract, and scatter radio waves, allowing long-distance communication through the reflection of signals back to the Earth's surface.
2. Aurora Borealis and Aurora Australis: The Ionosphere is also responsible for the phenomenon of auroras. When charged particles from the solar wind interact with the ionized gases in the Ionosphere, they emit light, creating the beautiful aurora borealis (Northern Lights) and aurora australis (Southern Lights).
3. Ionospheric Storms: Variations in the ionization levels and other factors in the Ionosphere can lead to ionospheric storms, which can disrupt communication and navigation systems that rely on signals passing through this layer.

Conclusion:
The Ionosphere is a unique layer of the atmosphere where the temperature increases with height. This temperature variation is primarily due to the absorption of high-energy solar radiation and the ionization of gases in this region. Understanding the properties and dynamics of the Ionosphere is crucial for various scientific studies, communication systems, and space weather forecasting.