Assume I have a "1D"-column of 50 m sand. At the top the surface air temperature is -25°C.
At the beginning of the experiment the sediment column is almost completely filled with tap water, resulting in a saturated sediment of 49 m. Tap water is kept constantly at a temperature of 10 °C.
During the experiment I decrease step wise the water level in the column by 5 m; let's say 5 times. At the same time I am measuring the resulting equilibrium temperature at the top of the air-column-interface (temperature at column surface). At the end of the experiment the resulting saturated sediment column is 24 m and the isolating sediment layer is 26 m.
Now my questions concerning that experiment are:
1. Is during the experiment the resulting equilibrium surface temperature dropping linearly or exponentially or otherwise? Why?
2. Does the thickness of the increasing isolating sediment layer play a role in the time equilibrium temperatures are achieved at the column surface? How long will it take approx. until equilibrium conditions are reached?
3. Is the expected behaviour the same if the air temperature is for example 25°C?

Please help.

I didn't find the right solution from the Internet.

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