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Global monsoon in ICON: the scale-dependent response of Northern Hemisphere monsoons
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DOI：10.5194/wcd-7-979-2026.png)
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Abstract
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Abstract. The global monsoon system is a lifeline for two-thirds of the world's population; as it is essential for tropical water security; food; and agriculture. However; its complex multiscale interactions challenge weather and climate models. This study investigates how horizontal grid spacing (80; 40; and 10 km) in the ICOsahedral Non-hydrostatic (ICON) model affects both the mean and the variability of Northern Hemisphere monsoons across diurnal; intraseasonal; and interannual timescales. All simulations show substantial skill in capturing the global monsoon system domain and its mean annual range of precipitation with a pattern correlation of > 0.7 and RMSE < 3 mm d−1. For the key Northern Hemisphere regional monsoons; South Asia (SAsiaM); West Africa (WAfriM) and North America (NAmerM); ICON achieves an accuracy > 80 % in capturing the observed monsoon domain. Crucially; the impact of grid spacing is strongly region-dependent and non-systematic. The finer grid spacing induces higher mean precipitation biases over continental SAsiaM; and WAfriM. Some of these biases are related to the intensity and location of moist monsoonal low-level jets; as well as their sensitivity to grid spacing. Furthermore; the fine grid spacing overestimates monsoon precipitation variability at interannual and intraseasonal scales; including intense precipitation frequency (> 10 mm d−1). This amplification stems primarily from enhanced grid-scale precipitation resulting from efficient microphysical processes; while convective precipitation exhibits limited sensitivity to grid spacing. Over NAmerM; biases are smaller and show minimal sensitivity to model grid spacing. Increased intraseasonal variance (2–30 d band) in the 10 km simulation is linked to more intense low-pressure synoptic systems over SAsiaM and intense African easterly wave activity over WAfriM. All simulations agree on the diurnal precipitation peak timing; with the 10 km simulation marginally performing better over continents. Our results demonstrate that fine grid spacing alone does not uniformly improve monsoon simulations. Some features; such as the precipitation diurnal cycle; are improved while existing biases in mean precipitation and variability are enhanced. This underscores the role of region-dependent sensitivity of grid spacing governing monsoon dynamics.
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