A case study of air‐sea interaction during swell conditions

Smedman, Ann‐Sofi; Högström, Ulf; Bergström, Hans; Rutgersson, Anna; Kahma, Kimmo K.; Pettersson, Heidi

doi:10.1029/1999jc900213

Cited by 146 publications

(130 citation statements)

References 26 publications

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“…Smedman et al (1999) found that, although the phase speed of the relatively long waves was indeed influenced by shallow water effects, little effect on the turbulence structure in the atmospheric surface layer was observed. In Smedman et al (2003) a comparison was made of roughness length z 0 (m) for pure wind sea conditions (young waves) fromÖstergarnsholm and from deep sea expeditions.…”

Section: The Measurement Sitementioning

confidence: 99%

“…At about 10 km from the peninsula the water depth is 50 m, reaching below 100 m farther out. In Smedman et al (1999) the possible influence of limited water depth on the tower measurements was studied in detail. Flux footprint calculations were done, showing that the turbulence instruments 'see' areas far upstream of the island.…”

Section: The Measurement Sitementioning

confidence: 99%

“…Taking the 'footprint weighting function' F (z) from Equation (A7) of appendix A of Smedman et al (1999), it is possible to calculate a weighted mean phase speed…”

Section: The Measurement Sitementioning

confidence: 99%

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Critical re‐evaluation of the bulk transfer coefficient for sensible heat over the ocean during unstable and neutral conditions

Smedman

Erik

Johansson

2007

Quart J Royal Meteoro Soc

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ABSTRACT:A new analysis of the neutral heat transfer coefficient C HN on data fromÖstergarnsholm is presented, which is primarily based on a limited set of measurements with the very accurate MIUU (Meteorological Institute of the University of Uppsala) instrument, but with additional information from an extensive set of measurements with Solent sonic R2. Sonic data are, however, used with great caution, since for wind speed U above 10 m s −1 , a strongly windspeed-dependent correction is shown to be required. This error is roughly proportional to (U − 10) for sea-air temperature differences less than 4-5 K. For a larger temperature difference, no correction appears to be necessary in the wind speed range 10-15 m s −1 .We infer from our data that for conditions when unstable and near-neutral conditions prevail, measurements of the sea surface -air temperature difference are accurate to within 0.1 K at our site. This means that data for a range of relatively small temperature differences (0.5-1.5 K) which were often rejected in previous studies could be retained. It is observed that a rapid increase of C H and C HN occurs in that range.For wind speed above 10 m s −1 , C HN is observed to increase rapidly with U 10 . During those conditions, the wave field at the site is known to have characteristics very similar to those in deep-sea conditions. In a previous analysis of data fromÖstergarnsholm, it was speculated that observed high C HN values could be due to spray. Calculations with a spray model showed, however, conclusively that for wind speeds less than 14 m s −1 , the spray effect on the sensible heat flux is expected to be small. The high C HN values must instead be due to dynamic effects.It is demonstrated that when the Obukhov length L is less than about −150 m a regime with very specific characteristics ensues. This regime is dominated by surface-layer scale eddies, which cause Monin-Obukhov relations for the exchange of sensible heat to break down. The characteristics of this surface-layer regime are treated in detail in the companion paper.The rise of C HN with wind speed is shown to be closely related to a corresponding increase of z 0T with roughness Reynolds number for winds above 10 m s −1 . This means that during those conditions, traditional surface renewal theory for heat is no longer valid. It is suggested that this, in turn, is a result of increasing importance of wave-breaking with increasing wind and with a possible link to processes in near-surface atmospheric layers in the regime with −L > 150 m.

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Section: The Measurement Sitementioning

confidence: 99%

Section: The Measurement Sitementioning

confidence: 99%

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Critical re‐evaluation of the bulk transfer coefficient for sensible heat over the ocean during unstable and neutral conditions

Smedman

Erik

Johansson

2007

Quart J Royal Meteoro Soc

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“…Swell loses energy to the atmosphere as it gradually decays [2,23], accelerating the airflow at lower altitudes, in the form of the so called "wave-driven wind", inducing a departure from the logarithmic wind profile [15,21]. For this reason swell has a consistent influence on the overall turbulence structure of the boundary layer, since it reduces the wind shear in the MABL and consequently the mechanical production of turbulence [14,15,18,22,23]. Under the wave-growing process, energy is transferred to the ocean throughout vertical transport of horizontal momentum via momentum flux, which drives currents, generates waves, and triggers wave breaking.…”

Section: Introductionmentioning

confidence: 99%

“…For example, as swell waves propagate into light wind areas they perform work on the overlying atmosphere, inducing a pressure perturbation in the first few meters of the marine atmospheric boundary layer (MABL), producing a forward thrust on the flow [14,17,21,22]]. Swell loses energy to the atmosphere as it gradually decays [2,23], accelerating the airflow at lower altitudes, in the form of the so called "wave-driven wind", inducing a departure from the logarithmic wind profile [15,21]. For this reason swell has a consistent influence on the overall turbulence structure of the boundary layer, since it reduces the wind shear in the MABL and consequently the mechanical production of turbulence [14,15,18,22,23].…”

Section: Introductionmentioning

confidence: 99%

Seasonal Variability of Wind Sea and Swell Waves Climate along the Canary Current: The Local Wind Effect

Semedo

2018

JMSE

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A climatology of wind sea and swell waves along the Canary eastern boundary current area, from west Iberia to Mauritania, is presented. The study is based on the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis ERA-Interim. The wind regime along the Canary Current, along west Iberia and north-west Africa, varies significantly from winter to summer. High summer wind speeds generate high wind sea waves, particularly along the coasts of Morocco and Western Sahara. Lower winter wind speeds, along with stronger extratropical storms crossing the North Atlantic sub-basin up north lead to a predominance of swell waves in the area during from December to February. In summer, the coast parallel wind interacts with the coastal headlands, increasing the wind speed and the locally generated waves. The spatial patterns of the wind sea or swell regional wave fields are shown to be different from the open ocean, due to coastal geometry, fetch dimensions, and island sheltering.

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Swell impact on wind stress and atmospheric mixing in a regional coupled atmosphere‐wave model

Rutgersson

Larsén³

2016

JGR Oceans

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Over the ocean, the atmospheric turbulence can be significantly affected by swell waves.Change in the atmospheric turbulence affects the wind stress and atmospheric mixing over swell waves. In this study, the influence of swell on atmospheric mixing and wind stress is introduced into an atmospherewave-coupled regional climate model, separately and combined. The swell influence on atmospheric mixing is introduced into the atmospheric mixing length formula by adding a swell-induced contribution to the mixing. The swell influence on the wind stress under wind-following swell, moderate-range wind, and nearneutral and unstable stratification conditions is introduced by changing the roughness length. Five year simulation results indicate that adding the swell influence on atmospheric mixing has limited influence, only slightly increasing the near-surface wind speed; in contrast, adding the swell influence on wind stress reduces the near-surface wind speed. Introducing the wave influence roughness length has a larger influence than does adding the swell influence on mixing. Compared with measurements, adding the swell influence on both atmospheric mixing and wind stress gives the best model performance for the wind speed. The influence varies with wave characteristics for different sea basins. Swell occurs infrequently in the studied area, and one could expect more influence in high-swell-frequency areas (i.e., low-latitude ocean). We conclude that the influence of swell on atmospheric mixing and wind stress should be considered when developing climate models.

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A case study of air‐sea interaction during swell conditions

Cited by 146 publications

References 26 publications

Critical re‐evaluation of the bulk transfer coefficient for sensible heat over the ocean during unstable and neutral conditions

Critical re‐evaluation of the bulk transfer coefficient for sensible heat over the ocean during unstable and neutral conditions

Seasonal Variability of Wind Sea and Swell Waves Climate along the Canary Current: The Local Wind Effect

Swell impact on wind stress and atmospheric mixing in a regional coupled atmosphere‐wave model

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