Abstract
Abstract. Ship tracks provide an ideal test bed for studying aerosol–cloud interactions (ACIs) and for evaluating their representation in model parameterisations. Regional modelling can be of particular use for this task, as this approach provides sufficient resolution to resolve the structure of the produced track including their meteorological environment whilst relying on the same formulations of parameterisations as many general circulation models. In this work we simulate a particular case of ship tracks embedded in an optically thin stratus cloud sheet which was observed by a polar orbiting satellite at 12:00 UTC on 26 January 2003 around the Bay of Biscay. The simulations, which include moving ship emissions, show that the model is indeed able to capture the structure of the track at a horizontal grid spacing of 2 km and to qualitatively capture the observed cloud response in all simulations performed. At least a doubling of the cloud optical thickness was simulated in all simulations together with an increase in cloud droplet number concentration by about 40 cm−3 (300%) and decrease in effective radius by about 5 μm (40%). Furthermore, the ship emissions lead to an increase in liquid water path in at least 25% of the track regions. We are confident in the model's ability to capture key processes of ship track formation. However, it was found that realistic ship emissions lead to unrealistic aerosol perturbations near the source regions within the simulated tracks due to grid-scale dilution and homogeneity. Combining the regional-modelling approach with comprehensive field studies could likely improve our understanding of the sensitivities and biases in ACI parameterisations, and could therefore help to constrain global ACI estimates, which strongly rely on these parameterisations.
Highlights
Combining the regional-modelling approach with comprehensive field studies could likely improve our understanding of the sensitivities and biases in ACI parameterisations, and could help to constrain global ACI estimates, which strongly rely on these parameterisations. Since their discovery in satellite imagery, ship tracks have been viewed as convincing evidence of aerosol–cloud interactions (ACIs) occurring in shallow, marine planetary boundary layers (PBLs)
Since marine shallow clouds are effective in modulating the radiative budget as well as the hydrological cycle (Stevens and Feingold, 2009), the role of anthropogenic emissions for these clouds is of particular interest for process understanding, and for climate impacts
In particular it has been shown in both satellite observations (Christensen and Stephens, 2011; Chen et al, 2012; Goren and Rosenfeld, 2012) and modelling studies (Wang et al, 2011; Kazil et al, 2011; Berner et al, 2013) that changes in the background aerosol and cloud condensation nuclei (CCN) concentrations affect the cloud albedo by producing more numerous and smaller cloud droplets (Twomey effect, 1974), but may induce transitions between cloud regimes, which fundamentally change the boundary layer state
Summary
Since their discovery in satellite imagery, ship tracks have been viewed as convincing evidence of aerosol–cloud interactions (ACIs) occurring in shallow, marine planetary boundary layers (PBLs). Since marine shallow clouds are effective in modulating the radiative budget as well as the hydrological cycle (Stevens and Feingold, 2009), the role of anthropogenic emissions for these clouds is of particular interest for process understanding, and for climate impacts In particular it has been shown in both satellite observations (Christensen and Stephens, 2011; Chen et al, 2012; Goren and Rosenfeld, 2012) and modelling studies (Wang et al, 2011; Kazil et al, 2011; Berner et al, 2013) that changes in the background aerosol and cloud condensation nuclei (CCN) concentrations affect the cloud albedo by producing more numerous and smaller cloud droplets (Twomey effect, 1974), but may induce transitions between cloud regimes, which fundamentally change the boundary layer state. Possner et al.: Ship track simulations over the Bay of Biscay
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
