Dust emission and transport mechanisms in the central Sahara: Fennec ground-based observations from Bordj Badji Mokhtar, June 2011

A detailed analysis of the first ever high-resolution ground-based dust observations in the remote central Sahara is presented from observations at Bordj Badji Mokhtar (BBM), taken during the Fennec project in June 2011. Detailed case studies are presented for three dust-producing mechanisms (cold pool outflows, low-level jets (LLJs), and dry convective plumes). The results confirm the importance of cold pools in dust emission and transport in the region. Forty-five percent of the dust over BBM is generated by local emission in cold pool outflows. Twenty-seven percent of the dust is advected rather than locally emitted dust; on three occasions, it is advected over 500km to BBM by cold pool outflows. Dust that has been in long-range transport to the area within such cold pool outflows is found to carry larger particles and be responsible for higher dust loadings than fresh uplift. LLJs are of tertiary importance in the partitioning, responsible for 14% dust over BBM. Dry convective plumes are identifiable in the data but produce much less significant quantities of dust, approximately 2% of the June total. The cube of wind speed has a stronger correlation with dust emission than wind speed. The correlation is strongest (at 95% confidence) for LLJ-induced emission (0.88), followed by locally emitting cold pools (0.78).