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Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.3/207053
- Change of regime of air-sea interactions in extreme weather conditions
- Babanin, Alexander V.
- The paper discusses two new results, essentially linked. The first one is based on data analysis conducted in the present study and the second outcome follows from literature review. The first topic is dedicated to wave breaking probability. This issue, important across a great variety of oceanographic, meteorological and engineering applications, has been difficult to comprehensively address because of lack of observations of the breaking and difficulties of respective measurements in the field conditions. In the meantime, vast amounts of wave records are available, which undoubtedly contain the breaking events embedded, but there have been no reliable means to quantify numbers of such events within the records. Here, we suggest a parameterisation of the breaking probability based on average asymmetry of wave profiles (with respect to the vertical axis). Such asymmetry is due to waves breaking at a certain phase of their evolution caused by modulational instability, which is argued to be the main physical mechanism responsible for the breaking of typical waves. Larger values of the average asymmetry correspond to waves breaking more frequently. In literature, however, there are indications that the magnitude of wave asymmetry tends to saturate at wind speeds of U10 ≈34m/s. That is the waves either do not break more frequently as the wind grows over this limit, or mechanism of the breaking changes, or both. This limit is the subject of the second topic. It is also approximately the wind speed at which the drag coefficient was found to saturate in the recent field observations (U10 ≈32-33m/s). Below the surface, change of the upper-ocean mixing mechanism and of bubble dynamics, supersaturation with gases is known to occur at U10 >35m/s. As a reference point for the extreme weather conditions, the hurricane-scale classification can be used: that is a tropical storm becomes a hurricane if the wind speed reaches U~33m/s (119km/h). As seen above, such classification is not arbitrary, and indeed signifies change of the physical regimes in all environments near the air-sea interface: in the atmospheric boundary layer, at the surface and through the upper ocean. Apparently, this cannot be coincidental, and consequences of the regime change for the air-sea interaction modelling are discussed.
- Publication type
- Conference paper
- Research centre
- Swinburne University of Technology
- Proceedings of 'Coasts and ports 2011: diverse and developing', the 20th Australasian Coastal and Ocean Engineering Conference and the 13th Australasian Port and Harbour Engineering Conference, Perth, Western Australia, Australia, 28-30 September 2011 / C. Pattiaratchi (ed.)
- Publication year
- Air-sea interactions; Extreme weather conditions; Upper-ocean mixing; Wave asymmetry; Wave-breaking probability
- Engineers Australia
- Publisher URL
- Copyright © 2011.
- Peer reviewed