The time from sunspot maximum (lots of sunspots) to sunspot minimum (very few spots) then back again to sunspot maximum averages approximately 11 years. The last sunspot maximum was around 2012 - 2013. We experienced a particularly long and deep sunspot minimum from 2018 to 2020. If you click on "SKETCHES" in the header, I have sketches from 2012 - 2013 and 2018 that illustrate the difference.
The chart on the left shows the number of days with no sunspots on the solar disk each year since 2012. The graph on the right shows the sunspot numbers for each year since 2010.
2012 - 0 days
2013 - 0 days
2014 - 1 day
2015 - 0 days
2016 - 32 days
2017 - 104 days
2018 - 221 days
2019 - 281 days
2020 - 208 days
2021 - 64 days
2022 - 1 day
2023 - 0 days
The current spotless streak: 0 days
Part of the work being done by Kjell Inge Malde and the astronomers at CV-Helios is using statistical analysis to make more accurate predictions of when the next maxima and minima will occur. It is important because during sunspot maximum, the increase in solar flares and coronal mass ejections can impact communications, power grids, GPS systems, satellite orbits and many other things here on Earth. During sunspot minima, the outward pressure of the solar radiation is lower, therefore more radiation from beyond the heliopause, such as cosmic rays and gamma ray bursts, are able to reach the inner part of the solar system where the Earth resides.
The graph below from the Earth to Sky Calculus group illustrates the increase in in-coming radiation from beyond the solar system beginning in 2015 as the Sun became less active. The measurements were taken by high-altitude balloon launches from California at the location indicated on the map inset.
Here is a summary of their findings:
Radiation always increases with altitude, with dose rates doubling every 5000 to 6000 feet. This make sense: The closer you get to space, the more cosmic rays you absorb.
At typical commercial airlines cruising altitudes, cosmic radiation is 40 to 60 times greater than natural sources at sea level.
Passengers on cross-country flights across the USA typically absorb a whole body dose equal to 1 or 2 dental X-rays.
On international flights, the total dose can increase ~five-fold with passengers racking up 5 to 6 dental X-rays.
Cosmic rays in the atmosphere are rapidly subsiding. In the past year alone, radiation levels in the air high above California have plummeted more than 15%, according to regular launches of cosmic ray balloons by Spaceweather.com and Earth to Sky Calculus. The latest measurement on July 23, 2022, registered a 6 year low:
This development, while sudden, is not unexpected. Cosmic rays from deep space are repelled by solar activity; when one goes up, the other goes down. Since 2021, Solar Cycle 25 has roared to life faster than forecasters expected. The onset of the new solar cycle has naturally led to a decrease in cosmic radiation reaching Earth.