Synoptic-scale controls of fog and low-cloud variability in the Namib Desert

Synoptic-scale atmospheric disturbances significantly influence fog and low-cloud formation in the Namib Desert, enhancing their occurrence through two primary mechanisms: increased longwave cooling of the marine boundary layer due to a drier free troposphere and onshore advection of marine air masses. A 14-year dataset of satellite observations, combined with reanalysis data, revealed that fog/low-cloud days exhibit distinct large-scale pressure patterns compared to clear days, with advected marine air masses dominating over subsiding continental air masses. These findings, supported by air mass back trajectories and wind pattern analysis, challenge the notion that Namib fog is purely locally generated, instead highlighting its advective nature and maintenance through cloud-top radiative cooling. The study also identified seasonal variations in synoptic-scale influences on fog variability, providing a new conceptual model to guide future research on coastal fog regimes.

Andersen, H., Cermak, J., Fuchs, J., Knippertz, P., Gaetani, M., Quinting, J., Sippel, S., & Vogt, R. (2020). Synoptic-scale controls of fog and low-cloud variability in the Namib Desert. Atmospheric Chemistry and Physics, 20(6), 3415–3438. https://doi.org/10.5194/acp-20-3415-2020