Final answer:
The jet stream helps identify the beginning of the stratosphere, which starts at the tropopause and is marked by the ozone layer absorbing UV radiation, leading to a temperature increase.
Step-by-step explanation:
The jet stream is a significant atmospheric feature that, among other things, helps to indicate the beginning of the stratosphere. The transition between the troposphere and the stratosphere is marked by a boundary called the tropopause, which is the coldest part of the atmosphere. The defining characteristic that attaches to the jet stream and marks the beginning of the stratosphere is the presence of the ozone layer. This layer, which is composed of ozone (O3), absorbs ultraviolet (UV) radiation from the Sun, leading to a temperature increase that reverses the cooling trend seen in the troposphere. The absorption of UV radiation by ozone not only defines the start of the stratosphere but also provides critical protection against the Sun's harmful ultraviolet rays, essential for life on Earth.