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Wiley, Quarterly Journal of the Royal Meteorological Society, 689(141), p. 1442-1456, 2014

DOI: 10.1002/qj.2453

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The sensitivity of nocturnal low‐level jets and near‐surface winds over the Sahel to model resolution, initial conditions and boundary‐layer set‐up

Journal article published in 2014 by K. Schepanski, P. Knippertz, S. Fiedler, F. Timouk, J. Demarty ORCID
This paper was not found in any repository, but could be made available legally by the author.
This paper was not found in any repository, but could be made available legally by the author.

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Abstract

This study explores simulations using the numerical Weather Research and Forecasting (WRF) model with respect to the representation of the nocturnal low-level jet (LLJ) over the Sahel. Three sets of experiments are designed to investigate the sensitivity with respect to (1) the boundary-layer and surface-layer schemes including local and non-local closures, (2) the horizontal grid spacing and the number of vertical levels within the lowest kilometre and (3) the role of initial and boundary data. In total 27 simulations are performed on one host domain and two nested domains for a representative LLJ case study on 9 November 2006. The ability of the individual simulations to represent the life-cycle of the nocturnal LLJ is validated against observations carried out in the framework of the African Monsoon Multidisciplinary Analysis special observation periods: Surface wind observations from Agoufou, Bamba and Banizoumbou, atmospheric wind profiles derived from Atmospheric Radiation Measurement Mobile Facility wind radar measurements at Niamey and profiles from radiosondes launched at Niamey. All runs reproduce the general characteristics of the observed LLJs satisfactorily. In contrast to earlier studies, results are more sensitive to the choice of the initial and boundary data (here GFS and ECMWF), than to the used boundary-layer and surface schemes or to model grid resolution. The sensitivity to the model grid resolution is surprisingly minor. Considerable differences between the individual stations suggest that local surface conditions such as roughness length, albedo or soil moisture may play an important role for the observed mismatch between model simulations and observations.