North Atlantic Oscillation Modulation on Mid-Latitude Cloud Cover and Surface Radiation Balance

Abstract

The North Atlantic Oscillation (NAO) modulates mid-latitude circulation and cloudiness and thereby alters the surface radiation balance across the North Atlantic–European sector. Focusing on northern winter (DJF) 1979–2023 over 45°–55°N, 10°W–15°E, the paper combines ERA5 monthly single-level reanalysis fields with the NOAA monthly NAO index. The paper applies (i) composite differences between positive and negative NAO phases (NAO⁺–NAO⁻) with Welch’s t-test, (ii) grid-point regression on standardized NAO, and (iii) point-cloud diagnostics linking low cloud changes to radiation terms. Results show that NAO⁺ winters feature reduced low-cloud cover, enhanced net shortwave, weakened net longwave, and overall positive net-radiation anomalies; the shortwave contribution dominates the net-radiation response. These results underscore the influence of the NAO on the surface energy balance, with implications for understanding regional climate variability and improving predictive models. These findings highlight a robust wintertime NAO–cloud–radiation coupling over mid-latitude land that shapes the surface energy balance and offers observational constraints for regional climate assessment and model development.