Abstract. This paper presents the Meso-NH model version 5.4. Meso-NH is an atmospheric non hydrostatic research model that is applied to a broad range of resolutions, from synoptic to turbulent scales, and is designed for studies of physics and chemistry. It is a limited-area model employing advanced numerical techniques, including monotonic advection schemes for scalar transport and fourth-order centered or odd-order WENO advection schemes for momentum. The model includes state-of-the-art physics parameterization schemes that are important to represent convective-scale phenomena and turbulent eddies, as well as flows at larger scales. In addition, Meso-NH has been expanded to provide capabilities for a range of Earth system prediction applications such as chemistry and aerosols, electricity and lightning, hydrology, wildland fires, volcanic eruptions, and cyclones with ocean coupling. Here, we present the main innovations to the dynamics and physics of the code since the pioneer paper of Lafore et al. (1998) and provide an overview of recent applications and couplings.

No abstract

A bulk microphysical scheme which predicts the concentrations and mixing ratios of cloud droplets and raindrops is presented. The scheme draws its originality from the use of generalized gamma law as basis functions for the drop size distributions and also from the attention paid to performing analytical integrations of most of the microphysical transfer rates. The numerical representation of each process has been reviewed throughout and specific tests have been made to evaluate separately the accuracy of the scheme compared with a bin-size model. The scheme, which depends on the specification of a few input parameters shaping the activation spectrum, is incorporated in a three-dimensional non-hydrostatic model with some applications given in a companion paper (Part m.

No abstract

No abstract

The West African monsoon interacts strongly with the land surface, yet knowledge of these interactions is severely limited by the lack of observations of surface energy fluxes. Within the framework of the AMMA project, three eddy covariance flux stations were installed to sample the three main surface types near Hombori (Mali) in the central Sahel at 15.3°N, and a fourth station was installed near Bamba in the northern Sahel at 17.1°N to sample semi-desert conditions. Observed land types near Hombori comprised a grassland growing on sandy soil (near the village of Agoufou), a flooded forest in a clay-soil depression (Kelma), and a bare rocky soil (Eguerit). The energy balance closure at the grassland site was satisfactory, but less so at the flooded forest site. Surface water heat storage during the flood and advection probably were responsible for most of the imbalance. The daily sensible heat flux (H) was fairly constant throughout the year at Bamba and Eguerit, with only a slight increase during the monsoon season corresponding to increased net radiation. By contrast, the seasonal cycle of the grassland site was marked, with H decreasing during the monsoon season from 70 Wm-2 in May to 20 Wm-2 in August. The flooded woodland exhibited the strongest contrast between the dry and wet seasons, with daily sensible heat flux close to zero during the flood. During the peak monsoon season, the two vegetated sites had the highest net radiation and the lowest sensible heat flux, as a consequence of the strong evapotranspiration rates caused by both high soil moisture availability and high Leaf Area Index. Lateral fluxes of water were found to be strong drivers of inter-site sensible and latent heat fluxes variability, with water leaving bare rocky soils as surface runoff and ending in the clay depressions (e.g., Kelma), whereas the sandy soils were locally endorheic, with most of the rainfall being rapidly returned to the atmosphere.An attempt was made to scale the sensible heat flux up to the scale of the AMMA northern supersite (60 km by 60 km), following a simple scaling scheme, which accounted for the contrasting surface types and water regimes. The super-site average sensible heat flux proved to be close to the grassland sensible heat flux, in part because grassland occupies 55% of the area. A strong spatial variability was caused by the difference in water regime and vegetation type, at a scale large enough to potentially influence the atmospheric properties such as the boundary layer

Abstract. A simple parametric relationship is established between factors describing the shape of cloud condensation nuclei (CCN) activation spectra and observable properties of the aerosol population they grow on (size distribution and solubility). This is done independently for maritime and continental aerosol types because of their very different characteristics. The data used for the multiple statistical adjustments in the procedure described in this paper are generated by running a numerical model of aerosol growth coupled to a simple cloud droplet activation scheme. Each aerosol population (maritime and continental) is assumed to be of homogeneous chemical composition, lognormally distributed and with variable solubility. The parameterization is then evaluated using a large set of aerosol populations with randomized properties. Finally, the study presents a preliminary analysis of the most important aerosol properties that influence the shape of the CCN spectra. An idealized scenario of a clean maritime boundary layer cloud perturbed by anthropogenic emissions (such as the ship track problem) illustrates the capability of the parameterization to selectively increfise the cloud droplet concentration in a partially polluted cloud. The calibration results presented in this paper are not meant to be the definitive activation spectra produced by any lognormally distributed aerosols. These results are indeed a step toward an objective initialization of CCN spectra and hence toward the computation of cloud droplet concentrations based on measurable multimodal aerosol features, as required by three-dimensional numerical models with a coupled interactive aerosol module.

No abstract