The coupled ocean-atmosphere climate system in temperature-salinity-humidity space

Project leader

Funding source

Swedish Research Council - Vetenskapsrådet (VR)

Project Details

Start date: 01/01/2016
End date: 31/12/2019
Funding: 3285000 SEK


The main purpose of this project is to study to what extent the global atmospheric hydrothermal cycle is connected to the ocean thermohaline circulation in temperature-humidity-salinity space. We will explore to which degree the water-mass conversion in temperature-salinity space can directly be linked to the air-mass conversion in humidity-temperature space along a "line" corresponding to the Clausius-Clapeyron relationship. The oceanic thermohaline circulation and the atmospheric hydrothermal circulation are generally analysed as two separate systems, although they interact with each other at the sea surface through heat exchange and evaporation-precipitation. We will in the present project analyse and visualise how the ocean and atmosphere act as a number of overturning cells, expressing the mixing of air- and water-masses. In order to do so we will use two recently introduced stream functions, one for the ocean and one for the atmosphere.

The oceanic thermohaline stream function makes it possible to analyse and quantify the entire world-ocean conversion rate between cold/warm and fresh/saline waters in one single representation. The atmospheric analogue is the hydrothermal stream function that instead captures the conversion rate between cold/warm and dry/humid air in one single representation. We will in the present project superimpose the overturning analyses of the ocean and atmosphere in order to explore and relate the salinity of the ocean and the humidity of the atmosphere, where we not only set the heat and freshwater transports equal in the two stream functions but also the impact of evaporation-precipitation on the salinity and humidity. We intend to produce what we denote the hydrothermohaline stream function of the coupled ocean-atmosphere overturning circulation in one single picture. Geographical descriptions will be searched for in order to link the thermohaline and hydrothermal space to real space.

Our preliminary results show that the connecting line between the oceanic and atmospheric cells is to a large extent set by the Clausius-Clapeyron relationship and that any climate change will shift these cells along this line. This since most of the conversion in the oceanic temperature-salinity space takes place at the sea surface. The climate model to be used in the present project is the Earth system model EC-Earth, which is based on the modelling systems of the European Centre for Medium-Range Weather Forecasts and the NEMO global ocean circulation model. As part of the EC-EARTH consortium, we at the Bert Bolin Centre for Climate Research, in collaboration with the Rossby Centre at SMHI, have developed the EC-Earth model and have made a number of historic runs and scenarios of future possible climates.

The project is thematically organised, where the common thread is how the coupling of the ocean with the atmosphere can be understood in temperature-salinity-humidity space. The first theme will consist of merging successfully the hydrothermal and thermohaline stream functions for the present climate and how they are connected to each other according to what we intend to name the hydrothermohaline relationship. In the second theme, we will explore how a climate change will move both the atmospheric and oceanic cells along the Clausius-Clapeyron relationship for both the atmosphere and the ocean. The following four themes will explore various aspects of the ocean and atmosphere circulation, making use of the results from themes one and two such as turn-over time of the ocean, Lagrangian decomposition of the stream functions and their projection back into geographical space.

A successful outcome of the present project will 1) give new insights on how the ocean and atmosphere is coupled to each other, 2) show how the ocean and atmosphere reacts on a climate change, 3) provide a better understanding of how the ocean can be both rapid and slow in its response to a climate change, 4) give powerful tools to analyse the coupled ocean-atmosphere circulation in one singe representation.

External Partners

Last updated on 2017-01-06 at 13:49