Abstract
AbstractAtmospheric science relies on numerical models to simulate the complex multiscale nature of atmospheric variability, but our confidence in weather and climate predictions relies on theory and simplified models that describe scale interactions at a mechanistic level and can provide causal accounts of atmospheric behaviour. Global simulations at kilometre‐scale resolution are now feasible and offer new opportunities to the atmospheric science community for testing and expanding our understanding of climate variability and change. Taking full advantage of this new tool requires smart strategies for evaluating and analysing the output, especially as kilometre‐scale climate modelling will be limited to relatively short simulations with a rather small number of realizations. We here review some of the available tools for diagnosing and studying the dynamics of waves, coherent flows, and the interactions between them in terms of their ability to provide causal accounts of the behaviour seen in observations and in comprehensive simulation models. We describe their successes but also some of their limitations. The limitations are seen to be especially pronounced in the Tropics, where clouds, convection and atmospheric circulation are inextricably linked. The lack of a natural spatial truncation scale in the Tropics has given rise to many theoretical challenges, but it is for precisely this reason that the Tropics are where we might expect the largest gain from global kilometre‐scale models.
Highlights
The atmosphere exhibits a rich spectrum of variability in both space and time
Since the real world is non-stationary, we are interested in how the non-stationarity plays out, on a variety of time-scales ranging from probabilistic weather prediction to climate change
For extratropical dynamics, where the Coriolis parameter is bounded away from zero, the frequencies of the eastward- and westward-propagating inertia-gravity wave (IGW) solutions are well separated from the frequencies of the Rossby wave solutions, as discussed
Summary
The atmosphere exhibits a rich spectrum of variability in both space and time. Our knowledge of this variability comes first and foremost from observations. Much of the excitement about global kilometre-scale models derives from the idea that the newly resolved small scales are of immediate relevance for a realistic simulation of larger-scale processes (Schär et al, 2019) These simulations can serve as a tool to test and expand our understanding of climate variability and change. We here review some of the ways those concepts have been used to understand atmospheric behaviour, based on atmospheric reanalysis data, numerical models, and observations In this we bring together three strands of knowledge – large-scale dynamics, normal modes, and tropical convection and gravity waves (GWs) – which have historically represented rather distinct communities of researchers, with an eye to their application to the emerging first generation of kilometre-scale global atmospheric models, and with a particular focus on the Tropics.
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