HiRO-ACE: Fast and skillful AI emulation and downscaling trained on a 3 km global storm-resolving model

TL;DR

HiRO-ACE is a novel two-stage AI framework that efficiently emulates high-resolution global atmospheric simulations, accurately reproducing extreme precipitation events and atmospheric features from coarse inputs, enabling rapid climate and weather analysis.

Contribution

The paper introduces HiRO-ACE, combining a stochastic climate emulator with diffusion-based downscaling to generate high-resolution precipitation fields from coarse data, trained on a decade of storm-resolving model outputs.

Findings

Accurately reproduces extreme precipitation distribution up to the 99.99th percentile.

Achieves less than 10% bias in time-mean precipitation across most regions.

Generates plausible atmospheric phenomena like cyclones and fronts from coarse inputs.

Abstract

Kilometer-scale simulations of the atmosphere are an important tool for assessing local weather extremes and climate impacts, but computational expense limits their use to small regions, short periods, and limited ensembles. Machine learning offers a pathway to efficiently emulate these high-resolution simulations. Here we introduce HiRO-ACE, a two-stage AI modeling framework combining a stochastic version of the Ai2 Climate Emulator (ACE2S) with diffusion-based downscaling (HiRO) to generate 3 km precipitation fields over arbitrary regions of the globe. Both components are trained on data derived from a decade of atmospheric simulation by X-SHiELD, a 3 km global storm-resolving model. HiRO performs a 32x downscaling--generating 3 km 6-hourly precipitation from coarse 100 km inputs by training on paired high-resolution and coarsened X-SHiELD outputs. ACE2S is a $1^\circ \times 1^\circ$ ($\sim$100 km) stochastic autoregressive global atmosphere emulator that maintains grid-scale precipitation variability consistent with coarsened X-SHiELD, enabling its outputs to be ingested by HiRO without additional tuning. HiRO-ACE reproduces the distribution of extreme precipitation rates through the 99.99th percentile, with time-mean precipitation biases below 10% almost everywhere. The framework generates plausible tropical cyclones, fronts, and convective events from poorly resolved coarse inputs. Its computational efficiency allows generation of 6-hourly high-resolution regional precipitation for decades of simulated climate within a single day using one H100 GPU, while the probabilistic design enables ensemble generation for quantifying uncertainty. This establishes an AI-enabled pathway for affordably leveraging the realism of expensive km-scale simulations to support local climate adaptation planning and extreme event risk assessment.