Post tagged Large-eddy Simulation

Challenges and Solutions in LES of Stratocumulus Clouds

In a recent article in JAMES (Pressel et al., 2017), we explore how numerical error and subgrid-scale modeling in LES interact to determine the quality of LES of stratocumulus clouds and show that a technique called implicit large eddy simulation provides particularly high fidelity LES. Here we offer a bit of background and a discussion of that work. If you are not familiar with stratocumulus clouds you can see a high resolution LES of stratocumulus here.
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Cloud Simulations Set in Stone

How much does a cloud weigh? That was the question Karen LaMonte asked us in an email a year and a half ago. LaMonte—an artist who lives in Prague and is known for monumental sculptures in ceramic, bronze, and glass—wanted to create a marble cloud sculpture of similar weight as a real cloud. What resulted is LaMonte’s sculpture Cumulus, which is an accurate visualization, in marble, of a numerically simulated tropical cumulus cloud. Cumulus is currently on display during the Biennale in Venice.

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Paris and the future of clouds

How low clouds respond to warming remains the greatest source of uncertainty in climate projections. Climate models projecting that much less sunlight will be reflected by low clouds when the climate warms indicate that CO2 concentrations can only reach 470 ppm before the 2℃ warming threshold of the Paris agreement is crossed—a CO2 concentration that will probably be reached in the 2030s. By contrast, models projecting a weak decrease or increase in low-cloud reflection indicate that CO2 concentrations may reach almost 600 ppm before the Paris threshold is crossed. In a new paper, we outline how new computational and observational tools enable us to reduce these vast uncertainties.

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The role of the surface energy balance in the low-cloud response to global warming

Figure 1: Top-right: ISCCP low cloud cover (%) climatology for June-July-August, with the GPCI transect and the three locations used in our study (adapted from Teixeira et al. 2011). Bottom-left: schematic of cloud regimes in the tropical overturning circulations (Stevens 2005, adapted from Arakawa 1975).

Large-eddy simulation (LES) of clouds can help resolve one of the most important and challenging question in climate dynamics, namely, how subtropical low clouds respond to global warming. However, earlier LES studies have generally prescribed large-scale conditions (e.g., surface temperatures) in a way that does not guarantee energy balance. We have developed an energetically consistent framework for driving LES, in which the LES domain is coupled to a simple slab ocean. In this framework, the cloud responses to global warming can be very different than in the traditional frameworks that prescribe surface temperatures.

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