In reply to Dave Cumberland:
Hi,
Rest assured there is no conspiracy theory
I placed the sensors in N.Wales.
The probes are pushed into ground on mixed terrain. Not on a climbing route or high on a crag, but on reasonably accessible ledges, at the stated altitude near to climbing crags. The probes are within a few inches of each other, and certainly not sheltered.
They are stainless steel probes pushed in the ground on stakes to mark the depth.
Although 30cm is too deep for an ice tool, it shows the long term effects of prolonged cold spells etc, and the much slower rate of change as the air temp fluctuates, which serves as a
Often in winter conditions in North Wales, the ground probes have been insulated under snow; in those cicumstances they never get below 1degC.
It's possible that in other times with no insulation from snow cover, the surface may well be frozen but the frost has not penetrated below to where wind-chill will have a diminished effect.
Out of interest, next time your garden is bullet hard, go at it with your ice axe and have a look how deep it is frozen.
What's missing is the temperature gradient for the surface vegetation and the first couple of inches of earth.
Placing them closer to the surface would be tricky because of the persistent issue of rodents, sheep, goats, hungry climbers nibbling at the gear and disloging the wires, but worth considering.
Post edited at 00:14