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https://doi.org/10.5194/gmd-2024-66
https://doi.org/10.5194/gmd-2024-66
Submitted as: model evaluation paper
 | 
10 Jun 2024
Submitted as: model evaluation paper |  | 10 Jun 2024
Status: this preprint is currently under review for the journal GMD.

Impact of horizontal resolution and model time step on European precipitation extremes in the OpenIFS 43r3 atmosphere model

Yingxue Liu, Joakim Kjellsson, Abhishek Savita, and Wonsun Park

Abstract. Events of extreme precipitation pose a hazard to many parts of Europe but are typically not well represented in climate models. Here, we evaluate daily extreme precipitation over Europe during 1982–2019 in observations (GPCC), reanalysis (ERA5) and a set of atmosphere-only simulations at low- (100 km), medium- (50 km) and high- (25 km) horizontal resolution with identical vertical resolutions using OpenIFS (version 43r3). We find that both OpenIFS simulations and reanalysis underestimate the rates of extreme precipitation compared to observations. The biases are largest for the lowest resolution (100 km) and decrease with increasing horizontal resolution (50 and 25 km) simulations in all seasons. The sensitivity to horizontal resolution is particularly high in mountain regions (such as the Alps, Scandinavia, Iberian Peninsula), likely linked to the sensitivity of vertical velocity to the representation of topography. The sensitivity of precipitation to model resolution increases dramatically with increasing percentiles, with modest biases in the 70th–80thpercentile range and large biases above the 99th percentile range. We also find that precipitation above the 99th percentile mostly consists of large-scale precipitation (~80 %) in winter, while in summer it is mostly large-scale precipitation in Northern Europe (~70 %) and convective precipitation in Southern Europe (~70 %). Compared to ERA5, the OpenIFS overestimates large-scale precipitation extremes in winter, but underestimates in summer. The discrepancy between OpenIFS and ERA5 decreases with increasing horizontal resolutions. We also examine the sensitivity of extreme precipitation to model time step and find that the convective contribution to extreme precipitation is more sensitive to the model time step than the horizontal resolution. This is likely due to the sensitivity of convective activity to model time step. On the other hand, the large-scale contribution to extreme precipitation is more sensitive to horizontal resolution than the model time step, which may be due to sharper fronts and steeper topography at higher horizontal resolution.

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Yingxue Liu, Joakim Kjellsson, Abhishek Savita, and Wonsun Park

Status: open (until 05 Aug 2024)

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Yingxue Liu, Joakim Kjellsson, Abhishek Savita, and Wonsun Park
Yingxue Liu, Joakim Kjellsson, Abhishek Savita, and Wonsun Park

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Short summary
The impact of horizontal resolution and model time step on extreme precipitation over Europe is examined in OpenIFS. We find that the biases are reduced with increasing horizontal resolution, but not with reducing time step. The large-scale precipitation is more sensitive to the horizontal resolution, however, the convective precipitation is more sensitive to the model time step. Increasing horizontal resolution is more important for extreme precipitation simulation that reducing time step.