As we know, in many references (Farmer et al., 1975; Schmidt et al., 2018; Austin, 2019), the harmonic analysis on the individual thermistor temperature records was applied, especially for the high-frequency water temperature data. I think this method is helpful for water temperature analysis, but I still do not fully understand the physical significance of this method. Can anyone make a clear explanation for this?
After a harmonic analysis, we can obtain a signal. It is easy to understand that the magnitude of the signal decreases with water depth. But some researchers assume that it can be fitted with an offset exponential equation (Austin, 2019). In this way, I can not understand. Hope some warm-hearted can help to explain it.
Thanks very much!
Reference:
[1] Farmer D M. Penetrative convection in the absence of mean shear[J]. Quarterly Journal of the Royal Meteorological Society, 1975, 101(430): 869-891.
[2] Austin J A. Observations of radiatively driven convection in a deep lake[J]. Limnology and Oceanography, 2019, 64(5): 2152-2160.
[3] Schmidt S R, Gerten D, Hintze T, et al. Temporal and spatial scales of water temperature variability as an indicator for mixing in a polymictic lake[J]. Inland Waters, 2018, 8(1): 82-95.
I don't know about harmonic analysis, but in water there can be internal waves. The phenomenon is called seiche, and is explained here: https://en.wikipedia.org/wiki/Seiche This can cause the temperature at one point to fluctuate in line with the water. Especially around the thermocline.
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