The ionosphere is located in the upper atmosphere, specifically between 50 to 1,000 kilometers (31 to 621 miles) above Earth's surface.

Here's a breakdown:

* Lower limit: The ionosphere starts at around 50 km, which is within the mesosphere and overlaps with the thermosphere.

* Upper limit: It extends up to about 1,000 km, well into the thermosphere.

Keep in mind that the ionosphere is not a distinct layer with sharp boundaries. Rather, it's a region where the atmosphere is ionized due to solar radiation, creating a complex and dynamic environment.