The Ionosphere

The ionosphere is an electrified region in the upper atmosphere where large quantities of free electrons, charged atoms and molecules exist. The ionosphere lies in a region 60-1000 km (37-621 miles) and beyond the atmosphere and is entirely ionized by the radiation coming from the Sun. The ionosphere extends along portions of the mesosphere, thermosphere and exosphere and it is divided into three layers; the F layer, the D layer and the E layer. The ionosphere helps propagate radio waves on Earth and is where Auroras, colorful light displays at the poles, occur, as well.

What is ionization?

Ionization is the process by which an atom or molecule obtains a positive or negative charge by adding or removing electrons. Ionization in the atmosphere occurs when the solar wind, which is the sun’s radiation, interacts with the Earth’s magnetosphere, ionosphere and magnetic field. A positively charged ion is created when an electron absorbs sufficient amounts of energy to be able to escape the electric potential barrier that confines it to an atom or molecule, while a negatively charged ion is produced when a free electron collides with an atom or molecule and is caught into the electric potential barrier, while releasing an excess of energy.

The ionosphere is a layer in the Earth’s atmosphere that, when ionized, conducts electricity. The atoms and molecules in this layer are ionized by the Sun’s ultraviolet and X-rays. Ionization varies greatly depending on the amount of radiation received. There is more ionization during the day than at night. Radiation varies depending on geographical location and the yearly season, thus, there is less radiation received during winter than in the summer season.  The radiation received in the ionosphere is also determined by the activity of the Sun, with more ionization occurring during times when there is more sunspot activity.

Layers of the ionosphere

The ionosphere consists of three distinct regions called the D, E, and F layers. The D layer is the lowest layer situated at about 60-90 km (37- 56 miles) above the surface of the Earth. This layer absorbs high frequency radio waves. The D layer is more prominent during the day, weakening as the day gradually progresses from day to night, during which it allows radio waves to penetrate higher into the ionosphere. Above the D layer is the E layer at about 90-120 km (56-75 miles) above the surface of the Earth. This layer was first thought to exist in 1902 and is known as the Kennelly-Heaviside Layer.

The E layer prevails during the day and usually starts to disappear with the approach of night. Ionization in the E layer is produced by X-rays and ultraviolet rays and it contains a higher concentration of ions. During Es (Sporadic E events), the E layer can reflect higher radio wave frequencies 50 MHz or higher. The F layer extends from approximately 200-500 km (120-310 miles) above the Earth’s surface. This is the layer of the ionosphere that has the highest concentration of ions. The F layer consists of two sections; the F1 layer and the F2 layer. In the F2 layer, the propagation of radio waves occur.

The ionosphere comprises less than one percent of the Earth’s atmosphere, yet, it is of great importance in communication, as it propagates radio waves. Most of the ionosphere is electrically neutral; however, when solar radiation interacts with the atoms and molecules, it becomes electrically charged. The F2 layer is of great importance for navigation and radio communication, as it is here where the concentrations of electrons are the highest. According to noaa, the free electrons in the ionosphere permit the propagation of electromagnetic waves for radio communication and it also is where Aurora, which are bright displays of light at the poles occur.