How different are deterministic physics suites when coupled to fixed model dynamics and why?

TL;DR

This study compares different atmospheric physics suites coupled with fixed large-scale dynamics, revealing high similarity in precipitation and tendencies across suites but notable differences from a high-resolution benchmark, highlighting model overconfidence.

Contribution

It provides a systematic comparison of physics suites with prescribed dynamics using a common dataset, revealing their similarities and differences relative to a high-resolution benchmark.

Findings

Physics suites produce similar precipitation amounts with correlations >0.95.

The benchmark is more dissimilar from physics suites, with correlations around 0.80.

Water vapour sink closely linked with precipitation across suites.

Abstract

It is often difficult to attribute uncertainty and errors in atmospheric models to designated model components. This is because sub-grid parameterised processes interact strongly with the large-scale transport represented by the explicit model dynamics. We carry out experiments with prescribed large-scale dynamics and different sub-grid physics suites. This dataset has been constructed for the Model Uncertainty Model Intercomparison Project (MUMIP), in which each suite forecasts sub-grid tendencies at a 22km grid. The common dynamics is derived from a convection-permitting benchmark: an ICON DYAMOND experiment (2.5km grid). We compare four different physics suites for atmospheric models in an Indian Ocean experiment. We analyse their joint PDFs of precipitation and associated physics tendencies for a full month. Precipitation is selected because it is a dominant uncertainty in the models that redistributes large amounts of heat. We find that all physics suites produce very similar precipitation amounts, with very high correlations between models, which exceed 0.95 at the native grid. However, the convection-permitting benchmark is more dissimilar from each of the physics suites, with correlations of $\approx$0.80. Similarly, we show that the vertically averaged physics tendencies in the free-troposphere are highly similar between the four physics suites, yet different if reconstructed for the benchmark. The water vapour sink is very closely linked with precipitation in the four physics suites. This suggests that the coarse-grid models are overconfident. We hypothese is that variation in unresolved convective structures can lead to variation in the dynamics, following a given amount of latent heating at fine grids, but not in our physics suites. The abstract length limit of ArXiv requires you to proceed in the PDF.