Field measurements of water temperatures in two turbulent streams in interior Alaska have been made during periods of frazil-ice production. The measured equilibrium temperature of the water Te-0.005°C agrees with the value calculated from the electrical conductivity of the water. Average cooling rates of the streams during the summer-to-fall stream cooling period were on the order of several tenths of a degree per day with average surface heat losses of -5 to -18 W m−2. Just prior to a frazil-ice event, the water-cooling rates were -1 to -3 mK min−1 with surface heat losses of -47 to -140 M m−2Supercooling at the water surface of a stream prior to and during frazil-ice production does not exceed 0.2°C as shown by measurements of air-water temperature profiles and by radiometer measurements. Mater supercooling at the time of frazil-ice nucleation was <10 mK. These measurements show that frazil-ice nuclei in streams must be other ice particles, cold organic materials, cold soil particles, or a combination of these, that may be introduced into the stream by mass exchange processes at the air-water interface.
The maximum observed supercooling was ΔTm 40 mK. Two measured values for the residual supercooling were 3 and 9 mK. Frazil growth rates calculated from the observed values of supercooling show that, unless the period of residual supercooling is very long, most of the frazil-ice production during one night of supercooling occurred in the transient thermal period from the time of nucleation to the time that the water became residually supercooled.