You can detect it by use of a barometer but you're not going to detect it in a massive overall amount on the seas, other than to know the pressure changes by using a barometer.
The best one to visually use is the simplest one.
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You can if you cared to measure it with a float over a period of time.
However, the barometer (above) should give you a massive clue.
Are you on about getting to the centre to measure it directly?
If so then I explained all that.
If that's not what you mean then can you elaborate?
It does melt but minimally as the reflected energy passes over the area of dome.
The melt would be so minor due to extreme low pressure and much less dense matter, meaning much much less friction of that matter.
You can ask why there's snow on mountains.
Similar reason but much lower down from the dome.
Extreme low pressure does not allow for mass agitation of matter higher above but the reflected energy hits lower and lower as the atmosphere becomes more dense which allows more denser agitated molecules which we feel on our skin.