Researchreanalysisdata assimilationenergy balanceera5
Reanalysis Models Expose Global Energy And Mass Imbalances
8.1
Andy May (May 2025) publishes a paper examining weather reanalysis systems ERA5 and MERRA-2, arguing they are model outputs rather than observations and discussing their assimilation-induced errors. The paper quantifies imbalances—ERA5 TOA mean radiative imbalance 0.68 ± 0.6 Wm-2 (2000–2020) and MERRA-2 TOA flux bias ≈ -4 Wm-2 (2001–2015)—and highlights impacts on precipitation, clouds, and radiation studies.
Key Points
- 1State reanalysis systems (ERA5, MERRA-2) are model assimilations, not direct measurements of atmospheric state.
- 2Quantify energy/mass errors: ERA5 TOA imbalance 0.68±0.6 Wm-2; MERRA-2 shows ≈ -4 Wm-2 bias.
- 3Warn that researchers relying on reanalysis inherit biases affecting precipitation, cloud, radiation, and trend analyses.
Scoring Rationale
Broad, credible analysis with industry-scale implications; limited novelty since it consolidates known reanalysis biases rather than introducing new methods.
Sources
Public references used for this report.
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