Spatiotemporal dynamics of fog and low clouds in the Namib unveiled with ground- and space-based observations
2018
Abstract. Fog is an essential component of Namib-region ecosystems. Current knowledge
on Namib-region fog patterns and processes is limited by a lack of coherent
observations in space and time. In this study, data from multiple satellite
platforms and station measurements paint a coherent picture of the
spatiotemporal dynamics of fog and low cloud (FLC) distribution. It is found
that observed seasonal FLC patterns derived from satellite observations
differ from fog measurements at coastal station locations, whereas they agree
further inland. This is linked to an observed seasonal cycle in the vertical
structure of FLCs that determines the probability of low-level clouds touching
the ground. For the first time, these observations are complemented by
spatially coherent statistics concerning the diurnal cycle of FLCs using
geostationary satellite data. The average timing of the start of the diurnal
FLC cycle is found to strongly depend on the distance to the coastline
(correlation ≈0.85 north of 25 ∘ S), a clear indication of
dominant advective processes. In the central Namib, FLCs typically occur 2–4 h
later than in other coastal regions, possibly due to local advection
patterns. The findings lead to a new conceptual model of the spatiotemporal
dynamics of fog and low clouds in the Namib.
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