The influence of transformed Reynolds number suppression on gas transfer parameterizations and global DMS and CO2 fluxes

Eddy covariance measurements show gas transfer velocity suppression at medium to high wind speed. A wind-wave interaction described by the transformed Reynolds number is used to characterize environmental conditions favoring this suppression. We take the transformed Reynolds number parameterization to review the two most cited wind speed gas transfer velocity parameterizations: Nightingale et al. (2000) and Wanninkhof (1992, 2014). We propose an algorithm to adjust k values for the effect of gas transfer suppression and validate it with two directly measured dimethyl sulfide (DMS) gas transfer velocity data sets that experienced gas transfer suppression. We also show that the data set used in the Nightingale 2000 parameterization experienced gas transfer suppression. A compensation of the suppression effect leads to an average increase of 22% in the k vs. u relationship. Performing the same correction for Wanninkhof 2014 leads to an increase of 9.85 %. Additionally, we applied our gas transfer suppression algorithm to global air-sea flux climatologies of CO2 and DMS. The global application of gas transfer suppression leads to a decrease of 11% in DMS outgassing. We expect the magnitude of Reynolds suppression on any global air-sea gas exchange to be about 10

Eddy covariance air-sea gas flux measurements: Regional sources and gas transfer limitation

Eddy covariance is a technique to measure air-sea gas exchange directly. A direct flux measurement has the advantage that, without parameterizations or major simplifications of processes. Section 3 focuses on the efflux of these aerosol predecessors together with aerosol numbers in the atmosphere. The oceanic emissions are tracked using the FLEXPART forward trajectory model, which provides the locations and the times for the satellite remote sensing. The averaged satellite aerosol numbers along the 12 h downwind trajectory were correlated with the magnitude of the oceanic sources, which was found to be a significant positive correlation. The results point to a local influence of air-sea fluxes on the aerosol number, which could give rise to local feedbacks. My investigation in Section 4 uses gas transfer velocities derived from DMS and CO2 eddy covariance measurements to describe gas transfer limitations which is caused by a wind-wave interaction. This process is parameterized using the transformed Reynolds number Retr. Below a threshold of |Retr| <6.7·105, flow separation develops at the wave’s lee side and causes a decoupling between the flow above the wave and the ocean surface. The gas exchange is then highly likely to be suppressed. In Section 5, the impact of gas transfer limitation on gas transfer parameterizations and global climatologies of DMS and CO2 is calculated. The data sets of two highly cited gas transfer parameterizations are investigated with respect to gas transfer limitation. Based on these algorithms the Nightingale 2000 parameterization is found to be heavily gas transfer limited and its gas transfer velocity will increase on average by 22% if the correction is applied. The Wanninkhoff 2014 parameterization increases by 9.85% after correction. The correction is applied to the global air-sea flux climatologies of DMS and CO2 for the year 2014

Eddy Kovarianz Gastransfermessungen. Regionale Quellen und Limitierungen

Eddy covariance is a technique to measure air-sea gas exchange directly. A direct flux measurement has the advantage that, without parameterizations or major simplifications of processes. Section 3 focuses on the efflux of these aerosol predecessors together with aerosol numbers in the atmosphere. The oceanic emissions are tracked using the FLEXPART forward trajectory model, which provides the locations and the times for the satellite remote sensing. The averaged satellite aerosol numbers along the 12 h downwind trajectory were correlated with the magnitude of the oceanic sources, which was found to be a significant positive correlation. The results point to a local influence of air-sea fluxes on the aerosol number, which could give rise to local feedbacks. My investigation in Section 4 uses gas transfer velocities derived from DMS and CO2 eddy covariance measurements to describe gas transfer limitations which is caused by a wind-wave interaction. This process is parameterized using the transformed Reynolds number Retr. Below a threshold of |Retr| <6.7·105, flow separation develops at the wave’s lee side and causes a decoupling between the flow above the wave and the ocean surface. The gas exchange is then highly likely to be suppressed. In Section 5, the impact of gas transfer limitation on gas transfer parameterizations and global climatologies of DMS and CO2 is calculated. The data sets of two highly cited gas transfer parameterizations are investigated with respect to gas transfer limitation. Based on these algorithms the Nightingale 2000 parameterization is found to be heavily gas transfer limited and its gas transfer velocity will increase on average by 22% if the correction is applied. The Wanninkhoff 2014 parameterization increases by 9.85% after correction. The correction is applied to the global air-sea flux climatologies of DMS and CO2 for the year 2014.Die Eddy-Kovarianz-Methode ist eine Technik zur direkten Messung des Gasaustauschs zwischen Atmosphäre und Ozean. DMS, Isopren und Gischt sind in der marinen Atmosphäre Ausgangsstoffe für Schwefelaerosole, sekundäre organischen Aerosole und primäre organische/anorganische Aerosole. In Kapitel 3 wird der Einfluss dieser Aerosolquellen auf Aerosolkonzentrationen in der Atmosphäre untersucht. Die Emissionen werden mit Hilfe des FLEXPART-Transportmodells in Windrichtung verfolgt. Die gemittelten Aerosolkonzentrationen entlang der Trajektorie wurden dann mit der Größe der Quelle korreliert. Die Ergebnisse deuten auf einen lokalen Einfluss des Gasaustauschs auf die Aerosolkonzentration hin. Der Gasaustausch zwischen Atmosphäre und Ozean kann durch die Gasaustauschgeschwindigkeit k beschrieben und modelliert werden. Diese Geschwindigkeit k ist normalerweise von der Windgeschwindigkeit anhängig und bezogen auf diese monoton ansteigend. Messungen haben gezeigt, dass die Relation zwischen k und Windgeschwindigkeit bei mittlerer bis hoher Windgeschwindigkeit jedoch abnehmen kann. In Kapitel 4 werden Gasaustauschgeschwindigkeiten verwendet um einen Prozess zu beschreiben, der eine Begrenzung des Gastransfers bewirkt. Dieser Prozess ist eine Wind-Wellen-Interaktion und wird mit Hilfe der transformierten Reynoldszahl Retr beschrieben. In Kapitel 5 wird die Auswirkungen der Limitierung des Gasaustausches auf den Gasaustausch von globalen DMS und CO2 Klimatologien berechnet. Zwei häufig verwendete Parametrisierungen des Gasaustauschs werden auf das Auftreten von Limitierung in Ihren Datensätzen untersucht. Basierend auf diesen Berechnungen sind die Nightingale 2000 und die Wanninkhoff 2014 Parametrisierungen einer sehr starken Limitierung ausgesetzt. Der Korrekturalgorithmus für das Jahr 2014 wird dann auf die globalen Klimatologien von DMS und CO2 angewendet

Mixing and Circulation in the Tropical Atlantic Cruise No. M98

July 01 – July 28, 2013 Fortaleza (Brazil) – Walvis Bay (Namibia

Van der Pauw resistivity measurement and thermoelectric properties of Ba(8)Zn(x)Ni(y)Ge(46-x-y)

In the present diploma thesis thermoelectric properties of type I clathrates Ba(8)Zn(x)Ni(y)Ge46-x-y are investigated. In addition a van der Pauw resistivity measurement system is designed, constructed and calibrated.Transport properties such as electrical resistivity, thermal conductivity and Seebeck coefficient were measured from 4 K to 600 K to assess the material's thermoelectric performance. This performance is scaled using the figure of merit ZT, which reaches 0.75 at 900 K for some samples.To measure resistivity of thin samples van der Pauw invented a new method. A sample holder was designed and constructed. Based on the graphical programming language LabView an automated measurement program was developed. Using the standard resistivity measurement system employed at the TU Wien, samples were gauged and used to asses the accuracy of the van der Pauw system.8

Eddy covariance data for CO2 and sensible and latent heat flux during SONNE cruises SO234/2 and SO235 (OASIS)

Direct CO2/DMS flux measurements were done aboard the RV Sonne sailing from Durban, SA to Port Louis, MU (SO 234-2, 8–20 July 2014) and from Port Louis, MU to Malé, MV (SO 235, 23 July to 8 August 2014). Additionally, bulk air and seawater concentrations of CO2 and DMS were recorded. Basic meteorological observations were done by the ship's automated weather station. The wind speed is measured by the ship's meteorological station and then recalculated by stability parameters of COARE to u10n

Global Synthesis of Air-Sea CO2 Transfer Velocity Estimates From Ship-Based Eddy Covariance Measurements

The air-sea gas transfer velocity (K-660) is typically assessed as a function of the 10-m neutral wind speed (U-10n), but there remains substantial uncertainty in this relationship. Here K-660 of CO2 derived with the eddy covariance (EC) technique from eight datasets (11 research cruises) are reevaluated with consistent consideration of solubility and Schmidt number and inclusion of the ocean cool skin effect. K-660 shows an approximately linear dependence with the friction velocity (u*) in moderate winds, with an overall relative standard deviation (relative standard error) of about 20% (7%). The largest relative uncertainty in K-660 occurs at low wind speeds, while the largest absolute uncertainty in K-660 occurs at high wind speeds. There is an apparent regional variation in the steepness of the K-660-u* relationships: North Atlantic >= Southern Ocean > other regions (Arctic, Tropics). Accounting for sea state helps to collapse some of this regional variability in K-660 using the wave Reynolds number in very large seas and the mean squared slope of the waves in small to moderate seas. The grand average of EC-derived K-660 ( - 1.47 + 76.67 u * + 20.48 u *(2) o r 0.36 + 1.203 U-10n + 0.167 U (2)(10n) ) is similar at moderate to high winds to widely used dual tracer-based K-660 parametrization, but consistently exceeds the dual tracer estimate in low winds, possibly in part due to the chemical enhancement in air-sea CO2 exchange. Combining the grand average of EC-derived K-660 with the global distribution of wind speed yields a global average transfer velocity that is comparable with the global radiocarbon (C-14) disequilibrium, but is similar to 20% higher than what is implied by dual tracer parametrizations. This analysis suggests that CO2 fluxes computed using a U-10n (2) dependence with zero intercept (e.g., dual tracer) are likely underestimated at relatively low wind speeds