Figure 11: (a) Monthly sensible
heat flux (red), latent heat flux (blue) and net radiation (black) from
June 2018 to December 2021. Bars indicate monthly minimum and maximum
average values. (b) Monthly Bowen ratio. The error bars indicate the
maximum and minimum values observed for each month.
The Bowen ratios exhibited high negative values during the first seven
months of each year due to low LE values. After the onset of the
heat release period (end of July), it stayed around zero before
gradually increasing to about 1.5 in December. This indicates that the
reservoir was mostly releasing heat through sensible heat flux, as
evaporation was constrained by the small vapour pressure deficit induced
by the cold air temperatures.
The energy state of the reservoir is closely tied to the stability
regime of the overlying atmosphere. During heat release (August to early
January), the overlying atmosphere was unstable, while it remained
mostly stable during the heat storage (mid-May to August) and ice-cover
periods. Figure 12 explores the relationship between daily LE and
atmospheric stability ζ for heat storage and release. The figure
confirms that larger daily evaporation occurs under near-neutral
(ζ ≈ 0) and unstable conditions (ζ < 0), and
that stable conditions (ζ > 0) are related to low
evaporation rates. Note that condensation occurred primarily under
near-neutral and stable conditions.