Introduction

This case study examines the major Saharan dust outbreak that crossed the tropical Atlantic and affected Barbados during August 2023. The event formed part of a strong Saharan Air Layer (SAL) episode and was investigated in detail by Rushley et al. (2026), who analysed its impact on the atmospheric environment over Barbados using observations, reanalyses and numerical modelling. The study identified a pronounced dust intrusion during 14–16 August 2023, associated with elevated aerosol optical depth (AOD), a deep Saharan Air Layer extending several kilometres above the surface, and substantial changes in temperature, humidity and wind profiles.
Here, the event is reproduced using OpenIFS 48r1 with the CAMS aerosol and atmospheric composition capability. A set of OpenIFS experiments is compared against CAMS operational analyses, which provide a useful reference representation of the evolving dust plume. The objective is to evaluate how well OpenIFS reproduces the timing, transport and magnitude of the trans-Atlantic dust outbreak before moving on to more detailed analysis of its vertical structure and meteorological impacts.

Literature

Experiments

Available Data and Simulations

Worked Solution

Python scripts are provided to visualise both CAMS analysis data and OpenIFS model output. These scripts use the Earthkit software package to extract aerosol optical depth fields, compute regional averages, and generate diagnostic figures.
The first stage of the analysis focuses on dust aerosol optical depth (DAOD) and total aerosol optical depth (AOD) at 550 nm.

Barbados Box Time Series

The first diagnostic averages AOD over the Barbados region (12–15°N, 60–57°W), following the regional box used by Rushley et al. (2026). The figure compares CAMS analyses with the nudged OpenIFS simulation and the four lagged-start hindcasts.
!barbados_aod_timeseries.png|width=900!
Figure 1. Barbados-box average dust AOD (top) and total AOD (bottom) at 550 nm during August 2023. The principal Saharan dust outbreak occurred during 14–16 August, when CAMS analyses show dust AOD exceeding 0.4 and total AOD approaching 0.7. All OpenIFS experiments reproduce the major event, although differences in peak magnitude and timing become apparent as forecast lead time increases.

Atlantic Dust Transport Hovmöller Diagram

The second diagnostic illustrates the westward propagation of Saharan dust across the tropical Atlantic. Dust AOD is averaged between 12°N and 15°N and plotted as a function of longitude and time.
!barbados_aod_hovmoeller.png|width=1200!
Figure 2. Longitude–time (Hovmöller) diagram of dust AOD at 550 nm averaged between 12°N and 15°N. The left panel shows the CAMS analysis, the centre panel the ERA5-nudged OpenIFS simulation, and the right panel the free-running OpenIFS simulation initialised on 12 August 2023. The diagonal bands indicate westward transport of Saharan dust across the Atlantic towards Barbados (vertical dashed line). The OpenIFS simulations reproduce the large-scale propagation and timing of the main dust plume observed in the CAMS analyses.

Summary

The initial comparison demonstrates that OpenIFS 48r1 successfully captures the large-scale evolution of the August 2023 Saharan dust outbreak. The Barbados time series show that all simulations reproduce the principal dust event during 14–16 August, while the Hovmöller diagrams confirm realistic westward transport across the tropical Atlantic. These diagnostics provide a useful first validation of the case study and establish a foundation for future analyses involving vertical dust structure, Saharan Air Layer dynamics, and comparison with observational datasets from the MAGPIE campaign.

OpenIFS Experiments

• We provide experiment data packs that allow the simulation of a time period within the described event by conducting an OpenIFS forecast experiment with interactive atmospheric composition.

• The pack includes the global initial experiment data and boundary conditions, including time-varying wildfire emissions, for a forecast from 12 August 2024 with a duration of 15 days.

• The data is provided on the N80 horizontal model grid (T159) which has approximately 125km / 1.125 degree grid spacing, and on 137 vertical model levels.

• The experiment can be run as a free-running forecast experiment, or alternatively with synoptic meteorology constrained by nudging towards six-hourly ECMWF ERA5 reanalyses.

• We provide plotting scripts using the ECMWF earthkit Python package to generate plots from the OpenIFS model outputs.