Cross-linking lab and field measurements and numerical modeling to identify and quantify the mechanisms of air-sea gas transfer
Workshop, 5 – 6 September 2022, Heidelberg University
Organizers: Bernd Jähne1,2, Kerstin Krall1, Christa Marandino3
1 Institute of Environmental Physics, Heidelberg University, Germany
2 Interdisciplinary Center for Scientific Computing (IWR), Heidelberg University, Germany
3 GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany
Start: Monday, September 5th 1 pm
End: Tuesday, September 6th 3 pm
Location: Mathematikon, Im Neuenheimer Feld 205, 69120 Heidelberg
Conference Room 5.104 and Common Room 5.303, 5th floor
Book of Abstracts and Program
Field measurements showed to be useful for finding empirical gas transfer velocity - wind speed relations. However, identifying and quantifying the mechanisms of the small-scale mass exchange processes from field measurements alone remains challenging. This is due to many factors influencing the gas transfer velocity besides the wind speed, including buoyancy effects at low wind speeds, the state of the wind wave field (wave age, swell), rain, bubbles and spray and last but not least surface films. In addition, measurements both at very low wind speeds and high wind speeds are fundamentally difficult. Thus, fully resolving the mechanisms of air-sea gas exchange even with a significant effort towards more and larger field campaigns only is not to be expected to be successful in the near future.
In contrast, systematic studies isolating individual influencing factors are easy to perform in wind-wave tank facilities. However, the question remains how to simulate realistic oceanic conditions. In linear facilities measurements can be conducted at very low fetch conditions only, and even in annular facilities, high wave ages are not possible because of the limited water depth. No lab facility is currently available to perform measurements with large oceanic gravity waves. Still, in recent years, major advances in understanding the small scale physical processes governing air-sea interactions have been made in wind-wave tank studies, e. g. the equivalency of heat and gas transfer (Nagel et al. 2015), the structure of the airflow above water waves (Buckley and Veron, 2016), the identification of the dominant mechanism of spray production at high wind speeds (Troitskaya, 2017), the enhancement of heat transfer at low fetch conditions (Kunz and Jähne, 2018) and gas transfer at extremely high wind speeds up to 85 m/s (Krall et al. 2019).
Finally, there are many conceptual models to relate the gas transfer to driving parameters. Most of them are not based on first principles but simplified concepts or empirical findings. Therefore the questions arises about the range of environmental conditions under which they can be applied. Another serious challenge is how the parameters of these models can be measured in lab facilities and the field.
The many conceptual models arise from the simple fact that it is still not possible to derive a universal relation for the gas transfer velocity from first principles, i.e., the Navier-Stokes equation. Therefore another promising approach is direct numerical simulation (DNS). However, this approach faces also serious challenges, which are the simulation of coupled flows in air and water close to the interface including wind-wave generation and the high Schmidt number.
Goal of the workshop
It is the goal of workshop is to bring together researchers from the different communities in order to inform each other about the current state in their field and to discuss what is the best research strategy to identify and quantify the mechanisms of air-sea gas transfer.
Therefore, we call for contributions to the following four sessions:
Session I: Status of Field Measurements (DT, EC, floating chamber as mainly used techniques, but also others such as active and passive thermography)
Under which environmental conditions are measurements possible at all, which conditions are missed? How frequently have those conditions been sampled by measurements? The conditions do not only include wind speed but all other environmental parameters known to influence the gas transfer velocity.
What is the statistical uncertainty of the measured transfer velocity under which conditions?
What systematic biases are possible? Are there means to detect and/or to correct them?
Which environmental parameters have been measured in previous field measurements?
How has the Schmidt number dependency be handled?
SESSION II: Status of Wind-Wave Tunnel Studies
How closely could the conditions in wind wave tunnels simulate oceanic conditions with respect to the goal to quantify the mechanisms of gas exchange from first principles?
What conditions can never be simulated?
Are there environmental conditions which can be measured in wind-wave facilities but not in the field because of the limitations of current field measurements?
What can be learned from wind-wave facilities that cannot be measured in the field? (Possible example is the Schmidt number dependency)
SESSION III: Status of Conceptual Models and Direct Numerical Simulation
Which conceptual models are available, how do they compare and where do they differ?
How can conceptual models be verified or falsified by field or lab measurements?
What are the current capabilities and limits of direct numerical simulations? What progress can be expected in the near future?
SESSION IV: Discussion Session
The workshop will close with a discussion session about the best possible research strategy
Where is it necessary to improve field measuring techniques? Or more radical: is it necessary to invent entirely new field measuring techniques and what requirements for new techniques to measure the gas transfer velocity and the parameters driving it?
Which environmental parameters are necessary to be measured and how can this be achieved with minimal effort?
Which are the environmental conditions for further field and lab measurements under which most can be learned about the mechanisms of air-sea gas exchange?
How could an approach look like that closely links laboratory and field measurements?
How could an approach look like that closely links direct numerical modeling and measurements?
Abstract Submission, Deadlines
Abstract submission has closed. If you would like to attend (in person or online) without giving a presentation please contact GasExchangeWorkshop2022@iup.uni-heidelberg.de
Attendance is free of charge. Participants have to cover their travel and accomodation expenses.
The workshop will be held in a hybrid format, however, we strongly recommend attendance in person to facilitate discussions.
Travel & Accomodation
If you come by public transport:
at Heidelberg main station take tram number 21, direction Hans-Thoma-Platz or tram number 24 direction Handschuhsheim Nord or Schriesheim. Due to some tram track construction work going on, the tram lines have changed slightly. From the main station take tram number 24 direction Heiligenbergschule. Get off at stop Bunsengymnasium. The Mathematikon is the three large tan colored buildings across the street from the tram stop. Use the south entrance of the southern building to get to the workshop venue.
Please be aware that you need to wear an FFP2/N95 or surgical mask to ride on public transport in Germany!
If you come by car: Parking is available here:
- P8 (approx. 10 Euros per day, but 5 Minute walk to Mathematikon) enter "Im Neuenheimer Feld 535, 69120 Heidelberg" into your navigation system
- Parkhaus im Mathematikon (approx. 2 Euros per hour, in the basement of the workshop venue), enter "Im Neuenheimer Feld 235, 69120 Heidelberg" into your navigation system
Hotel Cafe Frisch is within easy walking distance of the workshop venue
ibis Heidelberg Hauptbahnhof very convenient budget option located right at the main station.
Hotel Panorama Heidelberg right in the middle of the historic town center at the Neckar river
Staycity Heidelberg a brand new hotel located in Heidelbergs newest city quarter, Bahnstadt, right behind the main station
L. Nagel, K. E. Krall, and B. Jähne, “Comparative heat and gas exchange measurements in the Heidelberg Aeolotron, a large annular wind-wave tank,” Ocean Sci., vol. 11, pp. 111–120, 2015, doi: 10.5194/os-11-111-2015.
M. P. Buckley and F. Veron, “Structure of the airflow above surface waves,” J. Phys. Oceanogr., vol. 46, no. 5, Art. no. 5, 2016, doi: 10.1175/JPO-D-15-0135.1.
Y. Troitskaya, A. Kandaurov, O. Ermakova, D. Kozlov, D. Sergeev, and S. Zilitinkevich, “Bag-breakup fragmentation as the dominant mechanism of sea-spray production in high winds,” Sci. Rep., vol. 7, p. 1614, 2017, doi: 10.1038/s41598-017-01673-9.
J. Kunz and B. Jähne, “Investigating small scale air-sea exchange processes via thermography,” Front. Mech. Eng., vol. 4, p. 4, 2018, doi: 10.3389/fmech.2018.00004.
K. E. Krall, A. W. Smith, N. Takagaki, and B. Jähne, “Air–sea gas exchange at wind speeds up to 85 m/s,” Ocean Sci., vol. 15, pp. 1783–1799, 2019, doi: 10.5194/os-15-1783-2019.