How do clouds influence climate change?

One of the main sources of uncertainty in computer model projections of future climate change is due to a lack of knowledge of how clouds will change in a changing climate. At present, different models suggest that cloud changes could either enhance or limit the amount of future warming (Figure 1). Scientists at RSMAS are using both modelling and field studies to gain understanding of cloud systems so that estimates of climate sensitivity can be improved. Figure 2 shows an example of an observational study of clouds in the Eastern equatorial Pacific, and Figure 3 shows an example of a high resolution model simulation.

Figure 1: One climate problem of interest to both modelers and observationalists is the response of convection to the atmospheric moisture profile. A recent field experiment to the eastern tropical Pacific documented the cloud vertical structure through a cloud radar, the wind divergences with a Doppler precipitation radar, the surface rainfall rates, and the atmospheric relative humidity, all shown in this figure for 5 days. A strong dry air intrusion, originating from the equator, is apparent at 6-7 km. This not only suppresses surface-based convection, but sublimates the overlying cirrus anvil. The precipitation radar wind divergences are averages over ~100 km area, yet are consistent with the point measurement of the cloud radar. Measurements such as these improve our understanding of the cloud processes influencing the tropical climate. Figure 2: a picture of an observation station. Contact: Paquita Zuidema, Bruce Albrecht.

Figure 3: This figure shows a cross section from a global model with a 3km mesh, run on the Japanese Earth Simulator. The top panel of relative humidity (color), cloud (white) and rain (blue). Contact: Brian Mapes (Click thumbnails for larger images)