Sep 27, 2010
Insight: marine clouds are sensitive to surface wind speed
Greenhouse gases affect Earth's climate but aerosol particles are also important for our planet's radiation budget. This is because these particles directly scatter solar radiation back into space or absorb it, and indirectly influence the properties of clouds by acting as cloud-condensation nuclei. When predicting how the climate will respond to an enhanced greenhouse effect, a big challenge is also to figure out how wind-generated marine aerosols will amplify or reduce global warming. The outcome is uncertain because of surface wind-speed predictions.
We can investigate marine clouds using satellite observations. Figure 1 shows the correlation between satellite cloud optical thickness (COT) and model surface wind speed (U10m), obtained in the sub-arctic marine atmosphere over the Norwegian Sea and Barents Sea (this area is shown in figure 2). The movement of marine air masses, before they arrive in the area being investigated, are represented by the light solid lines in figure 2. The relationship shown in figure 1 allows a very simple but powerful way to incorporate climate forcing in model predictions, and highlight how marine sea-spray influences COT and the way that it affects the global climate.
We will evaluate results from these optical property measurements on low-level clouds, as well as on estimated cloud-droplet numbers, based on model simulations. To this end, a process model will be developed that can accurately handle both predictions of vertical mixing of water vapour and clouds, together with the number of sea-salt particles – which are greatly affected by wind speeds – and descriptions of gas-phase chemistry and aerosol-cloud interactions.
About the author
Paul Glantz is an associate research scientist at the Department of Applied Environment Science at Stockholm University, Sweden. His work focuses on understanding aerosol cloud interactions in the lower background atmosphere and in anthropogenic-influenced air masses.