Tropical convection in ERA5 has partly shifted from parameterized to resolved

Abstract

AbstractIn a recent study, Benestad and colleagues found that the distribution of global precipitation variability in ERA5 appears to have shifted towards smaller spatial scales over the course of the twentieth century. Using an alternative wavelet‐based analysis, we demonstrate that the trends are located almost entirely over the tropical oceans. The phenomenon can be explained by a remarkable shift from parameterized to explicitly resolved convection in this region. The slightly coarser resolved JRA‐55 reanalysis data set exhibits no such trend. A comparison with the conventional data‐only version JRA‐55C reveals that assimilated satellite data can introduce an additional trend in tropical precipitation amount, but does not, on its own, alter the characteristics of tropical precipitation in JRA‐55. An artificial dual‐diurnal cycle in ERA5 total precipitation and convective available potential energy (CAPE) leads us to the conclusion that the unexpected regime shift is induced primarily by changes in the observation system and not real‐world climate change.