The layer of very rare air above the mesosphere is called the thermosphere. High-energy X-rays and UV radiation from the Sun are absorbed in the thermosphere, raising its temperature to hundreds or at times thousands of degrees. The thermosphere has the highest temperatures due to the fact that it receives a lot of the UV radiation from the sun. Light from the Sun heats the ground. The warm ground gives off the heat as infrared "light". The IR energy heats the troposphere. The lowest part of the troposphere is the warmest because it is closest to the ground, where the heat is coming from. Light from the Sun heats the ground. The warm ground gives off the heat as infrared "light". The IR energy heats the troposphere. The lowest part of the troposphere is the warmest because it is closest to the ground, where the heat is coming from. Light from the Sun heats the ground. The warm ground gives off the heat as infrared "light". The IR energy heats the troposphere. The lowest part of the troposphere is the warmest because it is closest to the ground, where the heat is coming from.

Air is warmest at the bottom of the troposphere near ground level. Air gets colder as one rises through the troposphere. That's why the peaks of tall mountains can be snow-covered even in the summertime. Air pressure and the density of the air also decrease with altitude. The lowest part of the troposphere is the warmest because it is closest to the ground, where the heat is coming from. Light from the Sun heats the ground. The warm ground gives off the heat as infrared "light". The IR energy heats the troposphere. Since temperature decreases upwards in troposphere at the rate of 1°C for every 165 m of height, it is natural that temperature at the height of 17 km over the equator (–80°C) becomes much lower that at the height of 9-10 km over the poles (–45°C). That layer absorbs the highest amount of solar energy making it the hottest. The Troposphere- It is the lowest part of the atmosphere, the part where we live. In this region the temperature increases with height. Heat is produced in the process of the formation of Ozone and this heat is responsible for temperature increases from an average -60°F (-51°C) at tropopause to a maximum of about 5°F (-15°C) at the top of the stratosphere. The thermosphere lies between the exosphere and the mesosphere. “Thermo” means heat, and the temperature in this layer can reach up to 4,500 degrees Fahrenheit. If you were to hang out in the thermosphere, though, you would be very cold because there aren't enough gas molecules to transfer the heat to you. Temperatures in the upper thermosphere can range from about 500° C (932° F) to 2,000° C (3,632° F) or higher. The boundary between the thermosphere and the exosphere above it is called the thermopause. At the bottom of the thermosphere is the mesopause, the boundary between the thermosphere and the mesosphere below. The temperature of the thermosphere increases with height due to absorption of solar radiation within the ionosphere, which is concentrated in the upper thermosphere. There is very little to absorb solar radiation in the mesosphere, and it receives very little heat from below, hence the thermosphere is much warmer. The temperature of the thermosphere gradually increases with height. Unlike the stratosphere beneath it, wherein a temperature inversion is due to the absorption of radiation by ozone, the inversion in the thermosphere occurs due to the extremely low density of its molecules.