4 ms·

Got to admit I too thought that claim merited a [citation needed] so I tried some internet googling to try and find something that backed up those numbers and d

by Pick-A-Hill2019 6y ago

Got to admit I too thought that claim merited a [citation needed] so I tried some internet googling to try and find something that backed up those numbers and drew a blank. I have never seen a ~100v per vertical metre potential difference in any cables or equipment that I've run. That includes a long SWA cable from a buildings' floor level to the roof-top end point (roughly 40 metres - so that would equal 40x 100v = 4kV). [Edit to add - Longest vertical cable run I have dealt with was 180m / 41 floors for a four-core fire rated comms cable] [Double Edit, Sorry.] The only source I was able to find was this "Or, if we suspend a metal object outdoors, we’ll find that it spontaneously charges up to a certain voltage: about +100VDC for every meter of altitude above the ground." from https://www.quora.com/Can-electric-current-charge-flow-through-air https://www.quora.com/Can-electric-current-charge-flow-throu...?

mncharity 6y ago
> googling [...] drew a blank Global atmospheric electric circuit; atmospheric electric field (or potential gradient); Carnegie curve; electric field mill sensor. > those numbers It varies a lot. Time of day, location, conditions. Perhaps usually more than -100 V/m, and less than 200 V/m or so? Nothing compared to the 10 kV of zapping doorknobs in winter. > never seen [in...] buildings' The e-field contours follow the outside of a building, rather than cutting through it. And of a person. And more inconveniently, sometimes of a sensor pole. It's long seemed to me a pity this isn't used more in intro physics E&M. Been known for one or two+ centuries. Maybe with drone-sized less-expensive e-field sensors it will get more visibility?
- Pick-A-Hill2019 6y ago
  Have an upvote for the rabbit hole although I still don't see any solid evidence backing up the 100v per metre claim unless scaled to ground vs. a theoretical probe placed 5+ kilometres up in the clouds.
  - mncharity 6y ago
    You can watch it live[1] at UK Reading's Atmospheric Observatory. Currently (00-ish UTC), the last 12-ish hours there, have been between 100 and 150 V/m. Preceded by 6-ish hours of high-variability, say -50 to 100 with excursions down by -200 V/m. And then 6-ish hours of 50 to 100 V/m. Aside from the 6 hrs of variability, which look like a front coming in, the shape seems stereotypical Carnegie curve. [1] http://www.met.reading.ac.uk/weatherdata/Reading_daily_AWS_graphs.html#8 http://www.met.reading.ac.uk/weatherdata/Reading_daily_AWS_g...
    - BlueTemplar 6y ago
      Right, the voltage is huge compared to household electronics, however the amperage is tiny...

mncharity 6y ago

> googling [...] drew a blank Global atmospheric electric circuit; atmospheric electric field (or potential gradient); Carnegie curve; electric field mill sensor. > those numbers It varies a lot. Time of day, location, conditions. Perhaps usually more than -100 V/m, and less than 200 V/m or so? Nothing compared to the 10 kV of zapping doorknobs in winter. > never seen [in...] buildings' The e-field contours follow the outside of a building, rather than cutting through it. And of a person. And more inconveniently, sometimes of a sensor pole. It's long seemed to me a pity this isn't used more in intro physics E&M. Been known for one or two+ centuries. Maybe with drone-sized less-expensive e-field sensors it will get more visibility?

Pick-A-Hill2019 6y ago
Have an upvote for the rabbit hole although I still don't see any solid evidence backing up the 100v per metre claim unless scaled to ground vs. a theoretical probe placed 5+ kilometres up in the clouds.
- mncharity 6y ago
  You can watch it live[1] at UK Reading's Atmospheric Observatory. Currently (00-ish UTC), the last 12-ish hours there, have been between 100 and 150 V/m. Preceded by 6-ish hours of high-variability, say -50 to 100 with excursions down by -200 V/m. And then 6-ish hours of 50 to 100 V/m. Aside from the 6 hrs of variability, which look like a front coming in, the shape seems stereotypical Carnegie curve. [1] http://www.met.reading.ac.uk/weatherdata/Reading_daily_AWS_graphs.html#8 http://www.met.reading.ac.uk/weatherdata/Reading_daily_AWS_g...
  - BlueTemplar 6y ago
    Right, the voltage is huge compared to household electronics, however the amperage is tiny...