Which characteristic is most associated with the D layer of the ionosphere?

The characteristic most associated with the D layer of the ionosphere is low ionization density. The D layer, which exists at altitudes of approximately 30 to 90 miles (48 to 144 kilometers) above the Earth's surface, experiences a relatively low level of ionization compared to other layers of the ionosphere, such as the E and F layers. This lower ionization density is primarily due to the absorption of higher frequency UV and X-ray radiation from the sun, which reduces the number of free electrons present in this layer.

Low ionization density in the D layer results in its limited ability to reflect radio waves, particularly those of higher frequencies. Its primary function includes absorbing radio waves, which can lead to increased signal absorption during the daytime when solar radiation is much more intense. Understanding this characteristic is vital for grasping how different layers of the ionosphere interact with radio frequency signals, influencing communication and navigation systems.