Namib Fog Life Cycle Analysis - Satellite Remote Sensing (NaFoLiCA-S)

• Applicant: Professor Dr. Jan Cermak
• Subject Area: Physical Geography
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 282001949

• Final Report Year: 2021

Final Report Abstract

In NaFoLiCA-S, we studied the fog and low cloud system of the Namib Desert from a satellite perspective. The main technical advances and scientific findings of the project are listed below: • Using of geostationary satellite data in the infrared, the first fully-diurnal (24h) satellite-based FLC detection was developed. In validation against station measurements, the detection technique was shown to perform well. The developed FLC detection technique was applied to develop a climatological FLC product for the entire observation period of MSG SEVIRI (2004–ongoing). • On the basis of the novel FLC product, and complementary data from active-sensors and ground-based in situ measurements, a coherent picture of the climatological seasonal, diurnal, and vertical-distribution patterns could be accomplished, leading to a new conceptual model of the spatiotemporal dynamics of FLCs along the southern West African coastline. The findings of NaFoLiCA-S also increase the value of existing historical literature of station observations, as they help their interpretation. • For the first time, synoptic-scale influences on FLC occurrence in the Namib were found. We were able to show that FLC situations differ significantly from clear-sky conditions at local to synoptic scales. Namib-region fog was shown to be associated almost exclusively with the advection of moist marine air masses under a anomalously dry free troposphere. The latter facilitates longwave cooling of the cloud top, which maintains and increases FLC cover. We could demonstrate that seasonal differences exist at the drive synoptic-scale that influence FLC occurrence. For example, during April–June, a large-scale free-tropospheric moisture transport was observed into continental southern Africa on FLC days, which leads to a surface heating over the continent due to its greenhouse effect which in turn facilitates onshore advection of cloudy marine air masses. With this project we were able to extract new information on the Namib-region fog system, and future studies will profit from the data and insights generated within NaFoLiCA-S.

Publications

• (2018). First fully diurnal fog and low cloud satellite detection reveals life cycle in the Namib. Atmospheric Measurement Techniques, 11(July):5461–5470
  Andersen, H. and Cermak, J.
  
• (2019). Probing the fog life-cycles in the Namib desert. Bulletin of the American Meteorological Society
  Spirig, R., Vogt, R., Larsen, J. A., Feigenwinter, C., Wicki, A., Parlow, E., Adler, B., Kalthoff, N., Cermak, J., Andersen, H., Fuchs, J., Bott, A., Hacker, M., Wagner, N., Maggs-Kölling, G., Wassenaar, T., and Seely, M.
  
• (2019). Spatiotemporal dynamics of fog and low clouds in the Namib unveiled with ground- and space-based observations. Atmospheric Chemistry and Physics, 19:4383–4392
  Andersen, H., Cermak, J., Solodovnik, I., Lelli, L., and Vogt, R.
  
• (2020). Synoptic-scale controls of fog and low-cloud variability in the Namib Desert. Atmospheric Chemistry and Physics, 20(6):3415–3438
  Andersen, H., Cermak, J., Fuchs, J., Knippertz, P., Gaetani, M., Quinting, J., Sippel, S., and Vogt, R.