Lower Map:
CRS
(Congressional Research Service)
Report For Congress
High Altitude Electromagnetic Pulse (HEMP) and
High Power Microwave (HPM) Devices:
Threat Assessments
Updated March 26, 2008
https://www.wired.com/images_blogs/dangerroom/files/Ebomb.pdf
Electromagnetic Pulse (EMP) is an instantaneous, intense energy field that can overload or disrupt at a distance numerous electrical systems and high technology microcircuits, which are especially sensitive to power surges. A large scale EMP effect can be produced by a single nuclear explosion detonated high in the atmosphere.
---
More here:
Chinese Balloon Over The Center of the United States
imgflip.com/i/7a6jlf