Observations of condensate profiles over arctic leads with a hot‐film anemometer

During the AIDJEX Lead Experiment on the Arctic Ocean large‐amplitude, high‐frequency spikes were observed on the voltage signals of hot‐film sensors being used for turbulent velocity measurements near the water surface. Because over leads in winter temperature gradients are very steep and the super‐saturation extreme, condensate droplets can form and grow to measurable size even in the few seconds the air is over the lead. the voltage spikes resulted when these condensate droplets struck the hot‐films. We could, therefore, use the hot‐film information to determine not only turbulence quantities but also condensate concentration profiles and the flux of condensate droplets at the surface of leads. Condensate droplets were roughly 10 μm in diameter, concentrations within 20cm of the surface were usually 20‐80mg kg −1 (50‐220 droplets cm −3 ), and the condensate flux was of order 3mgm −2 s −1 . Non‐dimensional condensate profiles are well modelled by\documentclass{article}\pagestyle{empty}\begin{document}$$ \left\{{- C\left(z \right)/c_*} \right\}^{{\textstyle{1 \over 2}}} = - 0.34\ln (z/h) $$\end{document}where c * is a concentration scale and h , an estimator of the internal boundary layer height, is fetch dependent. the condensate flux is related to average quantities through the Nusselt number, Nu c , and the fetch Reynolds number, R x : NU c\documentclass{article}\pagestyle{empty}\begin{document}$$ Nu_c = 0.14R_x ^{0.72}. $$\end{document}Because c* also depends on the condensate flux, the simplicity of the profile relation and this Nusselt number equation suggest two alternative ways to estimate condensate flux at the surface of leads from the measurement of bulk environmental parameters.