Air-sea gas exchange at hurricane wind speeds

Krall, Kerstin E.; Jähne, Bernd

doi:10.5194/os-2019-72

Cited by 4 publications

(4 citation statements)

References 34 publications

(51 reference statements)

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“…For example, gas transfer is typically parametrised solely by wind speed with the proposed dependencies ranging from nearly linear, (e.g. Krall and Jähne, 2019), over quadratic (e.g. Ho et al, 2006) to cubic (Wanninkhof and McGillis, 1999).…”

Section: Introductionmentioning

confidence: 99%

Using global reanalysis data to quantify and correct airflow distortion bias in shipborne wind speed measurements

Landwehr¹,

Thurnherr²,

Cassar³

et al. 2019

Preprint

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Abstract. At sea, wind forcing is responsible for the formation and development of surface waves and represents an important source of near surface turbulence. Therefore, processes related to near surface turbulence and wave breaking, such as sea spray emission and air-sea gas exchange are often parametrised with wind speed. Shipborne wind speed measurements thus provide highly relevant observations. They can, however, be compromised by flow distortion due to the ship's structure and objects nearby the anemometer that modify the airflow, leading to a deflection of the apparent wind direction and positive or negative acceleration of the apparent wind speed. The resulting errors in the estimated true wind speed can be greatly magnified at low wind speeds. For some research ships, correction factors have been derived from computational fluid dynamic models or through direct comparison with wind speed measurements from buoys. These correction factors can, however, loose their validity due to changes of the structures nearby the anemometer and thus require frequent re-evaluation, which is costly in either computational power or ship time. Here we evaluate if global weather forecast model data can be used to quantify the flow distortion bias in shipborne wind speed measurements. The method is tested on data from the Antarctic Circumnavigation Expedition (ACE) on board the R/V Akademik Tryoshnikov, which are compared with ERA-5 reanalysis wind speeds. We find that, depending on the relative wind direction, the relative wind speed and direction measurements are biased by −37 % to +20 % and −13° to +15°, respectively. The resulting error in the true wind speed is +11 % on average but ranges from −5 % to +40 % (5th and 95th percentile). After applying the bias correction, the uncertainty in the true wind speed is reduced to 5 % and depends mainly on the average accuracy of the ERA-5 data over the period of the experiment. The obvious drawback of this approach is the potential intrusion of model bias in the correction factors. We show that this problem can be somewhat mediated when the error propagation in the true wind correction is accounted for and used to weight the observations. We discuss the potential caveats and limitations of this approach and conclude that it can be used to quantify flow distortion bias for ships that operate on a global scale. The method can also be valuable to verify Computational Fluid Dynamic studies of airflow distortion on research vessels.

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Section: Introductionmentioning

confidence: 99%

Using global reanalysis data to quantify and correct airflow distortion bias in shipborne wind speed measurements

Landwehr¹,

Thurnherr²,

Cassar³

et al. 2019

Preprint

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“…Later, Wanninkhof (2014) updated the parameterization equation using revised global ocean 14 C inventories and improved wind speed products while keeping the quadratic dependence intact. Studies of gas transfer across the air‐sea boundary in very high wind regimes show that bubbles and increased near surface turbulence may cause a strong increase in gas transfer at such high winds giving rise to uncertainties in parameterizations of the transfer velocities (Asher et al., 1996; Gu et al., 2021a; Iwano et al., 2013; Krall and Jahne 2019; McNeil and D’Asaro 2007). In our study, the uncertainty in the computed air‐sea flux of CO 2 is nearly 20% and is found to be majorly determined by the uncertainty of

k

.…”

Section: Methodsmentioning

confidence: 99%

Response of Surface Ocean pCO₂ to Tropical Cyclones in Two Contrasting Basins of the Northern Indian Ocean

et al. 2023

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Although situated on the same geographical latitude, the two ocean basins (the Bay of Bengal (BoB) and the Arabian Sea (AS)) of the northern Indian Ocean (NIO) experience diverse met-ocean conditions. These ocean basins are the warmest world oceans exhibiting high sea surface temperatures (SST) year-round. Conducive SST, its gradient and coupled interactions of vertical wind shear, absolute vorticity, relative humidity, and potential intensity lead to NIO being host to 7%-10% of all the tropical cyclones (TCs) in the world (Gray, 1979(Gray, , 1998. However, compared to the AS, the BoB witnesses more cyclones, a majority of which propagate in the west-northwest/north-northwest direction (Evan & Camargo 2011;Mohanty 1994). The National Cyclone Risk Mitigation Project (NCRMP) report of India states that during 1891-2000 nearly 308 TCs (out of which 103 were severe) affected the east coast of India. In contrast, only 48 TCs affected the west coast (of which 24 were severe) within the same period. Cyclones in BoB are known to be stronger and more destructive than those in AS (Singh Abstract This study examines the impact of two very severe tropical cyclonic events, Phailin (over the Bay of Bengal) and Ockhi (over the Arabian Sea), on surface ocean pCO 2 and the associated changes in the upper ocean structure using a coupled biogeochemical ROMS model. The primary productivity averaged over the mixed layer is increased from 6.9 to 12.0 (7.2-45.6) mgCm − 3 d −1 in response to Phailin (Ockhi). A decomposition analysis reveals that the mean contribution of temperature-driven changes in inducing pCO 2 variability in response to pre-and post-cyclonic conditions, in case of Phailin (Ockhi), are 5.4 (−8.8) and −7.6 (−58.8) μatm whereas dissolved inorganic carbon (DIC) driven changes are 23.6 (19.5) and 27.8 (78.0) μatm. Although salinity and total alkalinity have a relatively lesser control in inducing pCO 2 variability, salinity's response to the post-Phailin conditions is significant owing to strong salinity stratification in the Bay of Bengal. The enhancement of DIC is more in the near-surface waters than its removal by net biological processes resulting in the dominance of cyclone-induced upwelling and associated vertical mixing driven changes over the enhanced biology-driven changes in controlling pCO 2 variability during both cyclones. Despite comparable magnitudes of environmental forcing during both cyclones, the oceanic response to Phailin is comparatively short-lived and subdued due to stronger stratification in the Bay of Bengal. A relatively large ratio of DIC to total alkalinity in the upper layers of Arabian Sea facilitates a higher pCO 2 response to Ockhi. This makes Ockhi a greater source of CO 2 to the atmosphere.Plain Language Summary Tropical cyclones dissipate large amounts of energy into the upper ocean, enhancing vertical mixing under the influence of strong winds. The enrichment of nutrients and carbon due to upwelling of deeper waters enhance pCO 2 levels making a favorable environment for biological pr...

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“…Wave breaking that entrains air rarely occurs in lighter wind regimes with a crude threshold of U 10 ≈ 5-8 m s -1 . Gas transfer enhancement by bubbles has been studied in laboratory experiments (Woolf, 1993;Rhee et al, 2007;Krall et al, 2019) and with numerical models (Woolf and Thorpe, 1991;Liang et al, 2013;Deike et al, 2017). The laboratory studies quoted here conflict somewhat on the importance of bubbles.…”

Section: Atmospheric and Ocean Side Turbulent-molecular Diffusion And...mentioning

confidence: 97%

Air-Sea Trace Gas Fluxes: Direct and Indirect Measurements

Fairall

Yang²,

Brumer³

et al. 2022

Front. Mar. Sci.

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The past decade has seen significant technological advance in the observation of trace gas fluxes over the open ocean, most notably CO2, but also an impressive list of other gases. Here we will emphasize flux observations from the air-side of the interface including both turbulent covariance (direct) and surface-layer similarity-based (indirect) bulk transfer velocity methods. Most applications of direct covariance observations have been from ships but recently work has intensified on buoy-based implementation. The principal use of direct methods is to quantify empirical coefficients in bulk estimates of the gas transfer velocity. Advances in direct measurements and some recent field programs that capture a considerable range of conditions with wind speeds exceeding 20 ms-1 are discussed. We use coincident direct flux measurements of CO2 and dimethylsulfide (DMS) to infer the scaling of interfacial viscous and bubble-mediated (whitecap driven) gas transfer mechanisms. This analysis suggests modest chemical enhancement of CO2 flux at low wind speed. We include some updates to the theoretical structure of bulk parameterizations (including chemical enhancement) as framed in the COAREG gas transfer algorithm.

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Air-sea gas exchange at hurricane wind speeds

Cited by 4 publications

References 34 publications

Using global reanalysis data to quantify and correct airflow distortion bias in shipborne wind speed measurements

Using global reanalysis data to quantify and correct airflow distortion bias in shipborne wind speed measurements

Response of Surface Ocean pCO₂ to Tropical Cyclones in Two Contrasting Basins of the Northern Indian Ocean

Air-Sea Trace Gas Fluxes: Direct and Indirect Measurements

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Air-sea gas exchange at hurricane wind speeds

Cited by 4 publications

References 34 publications

Using global reanalysis data to quantify and correct airflow distortion bias in shipborne wind speed measurements

Using global reanalysis data to quantify and correct airflow distortion bias in shipborne wind speed measurements

Response of Surface Ocean pCO2 to Tropical Cyclones in Two Contrasting Basins of the Northern Indian Ocean

Air-Sea Trace Gas Fluxes: Direct and Indirect Measurements

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Response of Surface Ocean pCO₂ to Tropical Cyclones in Two Contrasting Basins of the Northern Indian Ocean