资源环境科技发展态势分析平台

Tropical convective clouds evolve over a wide range of temporal and spatial scales, which makes them difficult to simulate numerically. Here we propose that cloud statistical properties can be derived within a simplified time-independent coordinate system of cloud number n, saturated static energy h*, and cloud perimeter lambda. Under the constraint that circulations around cloud edge compete with each other for total buoyant energy and air, we show that the product of cloud number and cloud perimeter n lambda is invariant with lambda and that cloud number follows a negative exponential with respect to cloud-edge deviations of h* with respect to the mean. Overall, the summed perimeter of all clouds scales as the square root of the atmospheric static stability. These theoretical results suggest that the complexity of cloud field structures can be viewed statistically as an emergent property of atmospheric bulk thermodynamics. Comparison with a detailed tropical cloud field simulation shows general agreement to within <= 13%. For the sake of developing hypotheses about cloud temporal evolution that are testable in high resolution simulations, the shapes of tropical cloud perimeter distributions are predicted to be invariant as climate warms, although with a modest increase in total cloud amount.

Plain Language Summary Narrowing uncertainty in forecasts of climate change has been hindered by the difficulty of representing the extraordinary complexity of clouds. Here we show how the numbers and sizes of clouds, and their total amount, can be derived thermodynamically from the atmospheric temperature and humidity profile. Our theoretical predictions are closely reproduced within a detailed full-day dynamic cloud simulation of one billion grid points. Thus, simple methods from statistical thermodynamics may provide constrained solutions for cloud complexity to complement much more detailed computational simulations. For the purpose of developing hypotheses about future climate states, we suggest that any tropical surface warming will lead to a slight increase in the total cloud cover but that there will be no change in how the clouds are spatially distributed. In this case, the net impact of tropical clouds on surface temperatures may remain quite small.