Atmospheric noise
![CCIR 322 atmospheric noise relationship. The standard has tables and maps that determine the noise figure at 1 MHz according to the season and the time of day. This graph converts that noise figure to other frequencies. Notice that the plotted lines are spaced in 10 dB increments at 1 MHz.](/Images/godic/202412/15/Atmosphericnoise1948.PNG")
![Replica of Jansky's radio telescope, now at the National Radio Astronomy Observatory. 38°25′54″N 79°48′59″W / 38.431659°N 79.816253°W / 38.431659; -79.816253](/Images/godic/202412/15/Janksy_Karl_radio_telescope1948.jpg")
Atmospheric noise is radio noise caused by natural atmospheric processes, primarily lightning discharges in thunderstorms. On a worldwide scale, there are about 40 lightning flashes per second – ≈3.5 million lightning discharges per day.