A Baseline for Global Weather and Climate Simulations at 1 km Resolution

Abstract

In an attempt to advance the understanding of the Earth's weather and climate by representing deep convection explicitly, we present a global, four-month simulation (November 2018 to February 2019) with ECMWF's hydrostatic Integrated Forecasting System (IFS) at an average grid spacing of 1.4 km. The impact of explicitly simulating deep convection on the atmospheric circulation and its variability is assessed by comparing the 1.4 km simulation to the equivalent well-tested and calibrated global simulations at 9 km grid spacing with and without parametrized deep convection. The explicit simulation of deep convection at 1.4 km results in a realistic large-scale circulation, better representation of convective storm activity, and stronger convective gravity wave activity when compared to the 9 km simulation with parametrized deep convection. Comparison of the 1.4 km simulation to the 9 km simulation without parametrized deep convection shows that switching off deep convection parametrization at a too coarse resolution (i.e., 9 km) generates too strong convective gravity waves. Based on the limited statistics available, improvements to the Madden-Julian Oscillation or tropical precipitation are not observed at 1.4 km, suggesting that other Earth system model components and/or their interaction are important for an accurate representation of these processes and may well need adjusting at deep convection resolving resolutions. Overall, the good agreement of the 1.4 km simulation with the 9 km simulation with parametrized deep convection is remarkable, despite one of the most fundamental parametrizations being turned off at 1.4 km resolution and despite no adjustments being made to the remaining parametrizations. Plain Language Summary We present the world's first global simulation of an entire season of the Earth's atmosphere with 1.4 km average grid spacing and the top of the modeled atmosphere as high as 80 km. Albeit only a single realization due to its considerable computational cost, the resulting model output provides a reference and guidance for future simulations. For illustration we compare to simulations at 9 km grid spacing that represent the state of the art in numerical weather prediction and are still considerably finer when compared to models that are used for climate projections today. Thanks to its unprecedented detail, the simulation output will support future model development and satellite mission planning and may be seen as a prototype contribution to a future digital twin of our Earth.

Model intercomparison of COSMO 5.0 and IFS 45r1 at kilometer-scale grid spacing

“…However, this paper focuses on the hydrostatic spectral model version of IFS which is still very competitive in terms of timeto-solution even at kilometer-scale (e.g. Kuhnlein et al, 2019;Schulthess et al, 2019;Dueben et al, 2020;Wedi et al, 2021).…”

“…Manabe et al, 1965) when using a hydrostatic model with around 10 km grid spacing and the use of a nonhydrostatic model for a grid spacing of 5 km. Recent global real-world simulations with the hydrostatic IFS at a grid spacing of 1.45 km by Dueben et al (2020) and Wedi et al (2021) produced realistic results and did not show deficiencies that could be directly attributed to the invalidity of the hydrostatic assumption at this resolution.…”

Technical note: Lowermost-stratosphere moist bias in ECMWF IFS model diagnosed from airborne GLORIA observations during winter–spring 2016

“…The flights on 26 February and 13 March 2016 allow us to investigate how the moist bias develops in the late winter and early spring. The choice of the shown data was constrained by the dates of the flights, availability of the GLORIA chemistry mode data, observations under sufficiently cloud-free conditions, and availability of observations within the LMS in the polar sub-vortex region (for explanation of the "sub-vortex" region, see e.g., Werner et al, 2010). In the following, we show two-dimensional vertical cross sections of GLORIA water vapor observations along the HALO flight tracks and compare the observations to the ECMWF system.…”

ECLand: The ECMWF Land Surface Modelling System

“…The new implementation allows to significantly accelerate the computational performance of ECLand in offline mode at all resolutions and enables efficient simulation at very high resolutions such as 1km (with a throughput of one year of global simulation per day). This throughput is important for a range of new developments including accounting for urban areas (see section 3.6, Figure 26) and their carbon emissions within the future Copernicus CO 2 service as well as the foreseen developments under the Destination Earth initiative (DestinE), which aims at creating a high-precision digital twins of the Earth [74].…”