Sensitivity of the simulated atmospheric rivers over East Asia to horizontal resolution in the HadGEM3-GC3.1 general circulation model

This study evaluates the performance of the Met Office Hadley Centre Global Environment Model 3-Global Coupled version 3.1 (HadGEM3-GC3.1) in simulating the climatology of atmospheric rivers (ARs) over East Asia during the period 1951-2014. Compared to a high-resolution climate reanalysis dataset and three different precipitation observation datasets, better performances in simulating the characteristics of ARs, including the frequency of occurrences, intensity of moisture transport, meridional heat transport and contributions to precipitation, are demonstrated by the simulation at the N512 (0.35 degrees x 0.23 degrees, similar to 25-km) horizontal resolution compared to those at the N96 (1.875 degrees x 1.25 degrees, similar to 135-km) and N216 (0.83 degrees x 0.56 degrees, similar to 65-km) resolutions. Also, the N512 experiment is more capable of representing the significant increase in AR frequency for the years with preceding El Nino events. However, the N512 experiment still presents an underestimation of AR frequency in different seasons. In contrast to the N96 and N216 simulations, it overestimates the AR-associated extreme precipitation amount over most of the study region, which is partly explained by the more precipitation-favorable thermodynamic conditions along the simulated AR axes. Overall, a sufficiently high horizontal resolution is crucial for the GCM to realistically represent the observed characteristics of ARs over East Asia and to robustly project their potential changes in a warming climate, although the systematic errors still affect the realism of the simulated ARs.