A Laboratory Study of the Effect of Surface Waves on Heat and Momentum Transfer at High Wind Speeds. Issue 7 (6th July 2020)

• Record Type: Journal Article
• Authors: Troitskaya, Yuliya; Sergeev, Daniil; Vdovin, Maksim; Kandaurov, Alexander; Ermakova, Olga; Takagaki, Naohisa
• Is Part Of: Journal of geophysical research. Volume 125:Issue 7(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-07-06
• Subjects: air‐sea fluxes -- waves -- whitecapping -- sea storm; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2020JC016276
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: This paper describes laboratory experiments (using a high‐speed wind‐wave flume) of the effects of water waves on heat and momentum exchange in the near‐water atmospheric boundary layer at high wind speeds. Different from previous experiments of this type, the parameters of waves were controlled by a net stretched along the entire channel to effectively decrease the fetch. This helped to achieve dependency of the transfer coefficients on two independent parameters, namely, the wind speed and fetch (expressed via variations of the wavefield). Another key to the experiment was using a stable temperature stratification of the air flow, with the temperature of the air entering the flume 15–25° higher than the water. The experiments showed a sharp increase in the heat exchange coefficient at winds exceeding 33–35 m/s, similar to that observed earlier in the high‐speed wind‐wave flume of Kyoto University with conditions of unstable temperature stratification of the air flow. The joint analysis of the data obtained in the high‐speed wind‐wave flumes of IAP RAS and Kyoto University yields the universal dependency of the exchange coefficients and the temperature roughness on the peak wave number of surface wave spectra. This is independent of the type of temperature stratification of the atmospheric boundary layer, either stable or unstable. The sharp increase in the heat exchange coefficient is shown to be associated with increased whitecapping. Key Points: The sharp increase of the heat exchange at air‐water interface at winds exceeding 33–35 m/s for stable and unstable air flow stratification was observed The universal dependency of the exchange coefficients and the temperature roughness on the peak wave number of surface wave spectra was found The correlation of the sharp increase in the air‐water heat exchange with increased whitecapping was observed Plain Language Summary: The heat‐moisture ocean‐atmosphere exchange, forces acting at the air‐water interface, are critical factors determining weather and climate. They are quantified by fluxes, the amounts of heat, moisture, or momentum entering the atmosphere from a unit ocean surface in a unit time. The fluxes are entered directly into atmosphere‐ocean circulation models used for climate studies and weather prediction. One of the important questions is the effect of wind waves on air‐sea fluxes, especially on the heat exchange, while the largest uncertainties occur at high winds, where reliable data are needed for the prediction of sea storms. This paper describes laboratory experiments in a high‐speed wind‐wave flume, where the effects of water waves on heat and momentum exchange in the near‐water atmospheric boundary layer at high winds were studied. The experiments were conducted in stable atmospheric stratification when water is colder than air. We observed sharp increase in water‐air heat transfer correlated with increased whitecapping at wind speeds exceeding 30–35 m/s, similar to that previously observed in experiments at unstable air stratification when the water was warmer than air. The increase in ocean‐atmosphere heat transfer caused by the presence of whitecapping may be a mechanism of rapid intensification of ocean storms.