title: Climatology of nocturnal low-level jets over North Africa and implications for modeling mineral dust emission.
abstract: [1] This study presents the first climatology for the dust emission amount associated with Nocturnal Low-Level Jets (NLLJs) in North Africa. These wind speed maxima near the top of the nocturnal boundary layer can generate near-surface peak winds due to shear-driven turbulence in the course of the night and the NLLJ breakdown during the following morning. The associated increase in the near-surface wind speed is a driver for mineral dust emission. A new detection algorithm for NLLJs is presented and used for a statistical assessment of NLLJs in 32 years of ERA-Interim reanalysis from the European Centre for Medium-Range Weather Forecasts. NLLJs occur in 29% of the nights in the annual and spatial mean. The NLLJ climatology shows a distinct annual cycle with marked regional differences. Maxima of up to 80% NLLJ frequency are found where low-level baroclinicity and orographic channels cause favorable conditions, e.g., over the Bodélé Depression, Chad, for November-February and along the West Saharan and Mauritanian coast for April-September. Downward mixing of NLLJ momentum to the surface causes 15% of mineral dust emission in the annual and spatial mean and can be associated with up to 60% of the total dust amount in specific areas, e.g., the Bodélé Depression and south of the Hoggar-Tibesti Channel. The sharp diurnal cycle underlines the importance of using wind speed information with high temporal resolution as driving fields for dust emission models.Citation:Fiedler, S., K. Schepanski, B. Heinold, P. Knippertz, and I. Tegen (2013), Climatology of nocturnal low-level jets over North Africa and implications for modeling mineral dust emission, J. Geophys. Res. Atmos., 118, 6100-6121, doi:10.1002/jgrd.50394.
authors.affiliation: School of Earth and Environment, University of Leeds Leeds, UK.
authors.forename: S
authors.initials: S
authors.lastname: Fiedler
authors.affiliation: School of Earth and Environment, University of Leeds Leeds, UK ; Now at Leibniz Institute for Tropospheric Research Leipzig, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Schepanski
authors.affiliation: School of Earth and Environment, University of Leeds Leeds, UK ; Now at Leibniz Institute for Tropospheric Research Leipzig, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Heinold
authors.affiliation: School of Earth and Environment, University of Leeds Leeds, UK.
authors.forename: P
authors.initials: P
authors.lastname: Knippertz
authors.affiliation: Leibniz Institute for Tropospheric Research Leipzig, Germany.
authors.forename: I
authors.initials: I
authors.lastname: Tegen
keywords: ERA-Interim reanalysis; Harmattan; Saharan heat low; diurnal cycle; dust emission; nocturnal low-level jet