Air-water interactions

The interactions between air and water are complex, highly nonlinear processes due to the differences between the two mediums in terms of heat capacity, turbulence, etc. Air-water interactions play a crucial role in weather and climate systems since they control the fluxes of momentum, heat,as well as mass and gases. However, the limited understanding of the air-water interaction processes poses a significant uncertainty in weather and climate sciences.

Air-water interaction have been our research focuses for decades, including ocean waves, turbulent fluxes, carbon dioxide (CO₂) and methane (CH₄), marine aerosols and upper ocean turbulence. The research goal is to more accurately describe those processes and represent them in weather and climate models. In situ measurements, remote sensing, and numerical simulations are used in our group to achieve the research goals. The observation platforms include the permanent stations Östergarnsholm, Erken and various temporary platforms during dedicated field experiments. The numerical models include Large-Eddy simulations, regional models and Earth System models. Two sub research themes are included, which are air-sea interaction and air-lake interaction.

Air-Sea interaction studies:

The interaction between atmosphere and ocean is a crucial link in the climate system as it represents the interface between the dominating spheres. Exchange of momentum, heat, humidity as well as mass, influences the energy, water and carbon cycles as well as the biochemical and chemical composition both in the atmosphere and the ocean.

Ocean surface waves can significant affect air-sea interaction processes, such as momentum, heat, mass and boundary layer mixing. However, they have been neglected in climate models for decades due to their small scales compared to atmospheric and oceanic dynamics. In addition, waves and air-sea interaction are crucial when modelling the climate system since they represent the boundary between the two dominating spheres, the atmosphere and the ocean. Waves interact with the atmosphere and ocean in numerous ways. Here, the focus is on the impact of waves on turbulence in the atmosphere and ocean, due to swell impact on mixing in the atmosphere and Langmuir turbulence in the ocean, and on the impact of swell waves on surface friction. These mechanisms have recently been shown by our group and others to act in a different way than previously expected and have significant impact in models due to the importance of secondary processes.
Primary marine aerosols from the bursting of air bubbles produced by breaking waves is the largest global aerosol source and influences the properties of the atmosphere and the climate over the Oceans and a large part of the continental landmasses. The marine aerosols both act as cloud condensation nuclei and reflect the incoming solar radiation.

We use data from several experiments to cover a variety of wave conditions when developing improved parameterization. A state-of-the-art atmosphere-wave-ocean-ice regional coupled model (Uppsala University-Coupled Model, UU-CM) has been developed in our group, in which we are introducing a correct response of the wave forcing of the atmosphere and ocean/ice. The coupling methodology is also being implemented in the global model EC-Earth.

Ongoing projects

Persons: Leonie Esters, Lucia Gutierrez Loza, Monica Mårtensson, Anna Rutgersson, Lichuan Wu

Experimental lake studies:

The role of lakes in the global cycle of coal has received much attention in the scientific literature in recent times. It has been shown that lakes and other freshwater systems, which cover <1% of the earth's surface, naturally emit very large amounts of carbon dioxide (CO2) and methane (CH4) into the atmosphere. It has been estimated that the amount of these natural emissions is of the same order of magnitude as the net uptake of the world's oceans, which covers a considerably larger part of the Earth's surface, about 70%. These estimates justify more studies on the subject.

The research goal is to try to more accurately determine the amount of these greenhouse gases emitted to the atmosphere from lakes and to understand the processes that control the lakes' exchange of gas with the atmosphere. We do this by conducting field measurements. Our studies also include evaluating the methodology for how best to make these measurements.

Since 2010, we have operated a measuring station with instruments to directly measure the amount of CO2 and CH4 emitted from lakes. The instrumentation is specially adapted to be able to measure the flow driven by the turbulent vortices that are in the atmosphere closest to the Earth's surface. In order to be able to link the measured flows to relevant processes, we also measure other things such as meteorological parameters (e.g. air temperature and wind speed) and the properties of the water, e.g. the amount of dissolved CO2 in the water and the water temperature. During special measurement campaigns, we add additional instrumentation, e.g. measurements of water movement, waves and turbulence. These are parameters that are probably important when determining how much greenhouses move between the air and the water.

The measurements have been carried out on three different lakes: 2010-2012 on Tämnaren, a relatively large (38 km2) and shallow (maximum depth approx. 2 m) lake located 50 km north of Uppsala. 2012-2015 on Erssjön in the Skogaryd area, a small forest lake (0.07 km2) located 100 km north of Gothenburg. From September 2014, we perform the measurements at Erken (23.7 km2), 50 km east of Uppsala. Erken is part of the Swedish national infrastructure for ecosystem research SITES.

Persons: Leonie Esters, Erik Sahlée