Assessing the added value of the Intermediate Complexity Atmospheric Research Model (ICAR) for precipitation in complex topography

Modeling the state of the atmosphere with traditional numerical weather prediction techniques on the scale of alpine valleys and peaks is a computationally expensive task. Efficient statistics based methods, on the other hand, require measurements which are rare or non-existent in remote alpine regions such as glaciers. ICAR is an atmospheric model that uses a simplified model of the atmosphere to calculate the wind field and transport atmospheric quantities such as moisture within it. This keeps ICAR computationally frugal and requires no measurements as input while still ensuring a degree of physical consistency in the generated atmospheric fields. While a basic evaluation has been carried out, a more thorough investigation of the capabilities and weaknesses of ICAR is desirable to improve the understanding of this novel model.

Our study constitutes a first step in closing this gap by analyzing ICAR generated precipitation fields for the South Island of New Zealand. In particular we focus on the mountain range of the Southern Alps where data from eleven alpine weather stations is available for evaluation. ICAR performs better than its coarse driving global model ERA-Interim at nine out of eleven weather stations in the Southern Alps, and shows the highest performance for days with linear, cross-alpine atmospheric flow. The precipitation patterns generated by ICAR capture most of the characteristic features found on the South Island of New Zealand, such as the precipitation maximum in the Southern Alps and the ensuing precipitation shadow downwind.

Nonetheless, currently ICAR systematically underestimates the precipitation amounts observed at the weather stations, and the skill of the model decreases with higher model top settings. While ICAR shows great potential as a tool to generate atmospheric fields on a fine temporal and spatial grid, these open questions remain and require further research.


Mean daily precipitation over New Zealand

Horak, J., Hofer, M., Maussion, F., Gutmann, E., Gohm, A., and Rotach, M. W.: Assessing the added value of the Intermediate Complexity Atmospheric Research Model (ICAR) for precipitation in complex topography, Hydrol. Earth Syst. Sci.,  23, 2715-2734,, 2019.

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