Joint Seminar: Cloud energy balance models
Stratocumulus (St) clouds have high impact on the climate system because of their strong cooling effect (albedo). They naturally break up into cumulus (Cu) as environmental conditions change, resulting in drastic decrease of cooling due to reduction in cloud cover. Such a transition may be triggered sooner rather than later due to climate change. However, even in the most accurate climate models representation of stratocumulus can be inaccurate, which makes studying the transition ambiguous.
Here we take a fundamentally different approach to better understand the factors influencing most this transition, an approach akin to theoretical physics. We develop a conceptual boundary layer model with dynamic cloudiness and sea surface temperature (SST) and study this physical system in isolation. In this model St and Cu states are two alternative attractors of the dynamics, or, two ends of a limit cycle. We tested various different parameterizations of processes with unclear theoretical representation, and in most configurations the model broadly reproduces observed variability in cloud fraction, SST, radiation balance, heat fluxes, and many other aspects. In this isolated system we show that transitions between St and Cu are most sensitive to changes in circulation rather than direct CO2-induced warning. This result is robust across a wide range of parameter variability or different parameterizations. This hints that when examining St-Cu transitions in the context of global warming, attention should be given to indirect effects of changing circulation, or changes in the pattern of warming, both of which are difficult to capture in isolated models. We conclude with an extensive analysis of the dynamics of the system, including its property to robustly sustain periodic dynamics without any periodic solar forcing. Our work is accompanied by a flexible and easy-to-use codebase that allows performing further studies with similar or derived conceptual frameworks based on the DynamicalSystems.jl software library.
Datum
17.07.2024
Uhrzeit
13:30–15:00 Uhr
Ort
- Bundesstr. 53, room 101/102
- Seminar Room 101/102, 1st floor, Bundesstr. 53, 20146 Hamburg, Hamburg