Stations in sync

I have the fortune to have a number of different counters, with varying collection method, tubes and firmware...

I recently went on holiday for ~2 weeks (31st August - 15th September) - during this time I saw a remarkable sync-up of the counters in my house.

Whilst there are commonalities between some of these, the number of different combinations is what has me convinced that this phenomenon is real... for example GC10Next count collection via UART and Pulse counting on others. Old firmware I haven't touched in years and recent firmware I've written....ESP8266 and ESP32, counters from various places and controlled by different mechanisms.. so what is it?

I'm in a 5-10% Radon area, could it be because there were no doors or windows open during this time?

steadramon
Pulse counter with SMB-20. ESP8266. Firmware from several years ago, bit flakey, submission by node-red
Note: only counter in a case. crashed ~13th September
 

steadramonbu
Pulse counter ESP32 CAJOE unit with M4011 tube. A very basic firmware from about a year ago. Submitted by ESP
 

steadramongc10
ESP32 connected to GC10next, ESPGeiger, collecting data via serial UART value
 

steadramonespghw
Hardware version 1 of ESPGeiger-HW with STS-5 tube (pulse counter, no voltage feedback) with ESPGeiger firmware
 

steadramonespghw2
Hardware version 2 of ESPGeiger-HW with J305 tube (pulse counter, voltage feedback) with ESPGeiger firmware
Note: the spike on the morning of 20th is me "playing" with some pendants
 

I looked into this some years ago, after seeing similar results at Netc.com. I didn't see it often, but from the research articles I read, this is how it can be explained:  Radon is more or less constantly produced by local Uranium decay underground, and the gas percolates through ground layers depending on porosity, which depends in part on water content.  Another variable is air pressure which changes with temperature, and wind.  Daily increases in CPM sometimes occur, which could be caused by warm surface air drawing cooler, more dense ground gases upward (more so if the ground is dry), and when the sun rises on quiet mornings, resultant breezes waft pools of heavier Radon-laden air to the sensor location.  The ground water effect on Radon seepage can also explain seasonal variations shown on some multi-year charts.

--Bert