Assessing Precipitation Over the Amazon Basin as Simulated by a Storm-Resolving Model

In this study, we investigate whether a better representation of precipitation in the Amazon basin arises through an explicit representation of convection and whether it is related to the representation of organized systems. In addition to satellite data, we use ensemble simulations of the ICON-NWP model at storm-resolving (2.5-5.0 km) scales with explicit convection (E-CON) and coarse resolutions, with parameterized convection (P-CON). The main improvements in the representation of Amazon precipitation by E-CON are in the distribution of precipitation intensity and the spatial distribution in the diurnal cycle. By isolating precipitation from organized convective systems (OCS), it is shown that many of the well simulated precipitation features in the Amazon arise from the distribution of these systems. The simulated and observed OCS are classified into 6 clusters which distinguish nocturnal and diurnal OCS. While the E-CON ensembles capture the OCS, especially their diurnal cycle, their frequency is reduced compared to observations. Diurnal clusters are influenced by surface processes such as cold pools, which aid to the propagation of OCS. Nocturnal clusters are rather associated with strong low-level easterlies, possibly related to the Amazonian low-level jet. Our results also show no systematic improvement with a twofold grid refinement and remaining biases related to stratiform features of OCS suggest that yet unresolved processes play an important role for correctly representing precipitating systems in the Amazon.

Automated summary

This study investigates the representation of precipitation in the Amazon basin through explicit convection and its relation to organized systems. Ensemble simulations of the ICON-NWP model at different resolutions with explicit and parameterized convection are used, alongside satellite data. The improvements in precipitation representation by explicit convection are shown to be in intensity distribution and spatial distribution. The well-simulated precipitation features in the Amazon are predominantly driven by the distribution of organized convective systems. However, further research is needed to address unresolved processes that affect the representation of precipitation systems in the Amazon.