Description of the project

The WG “Atmospheric Dynamics” coordinates the DACCIWA consortium (Peter Knippertz) and leads two (out of seven) work packages (WPs).

In WP6 (“Precipitation Processes”, Andreas Fink) satellite and re-analysis data as well as additional measurements during the field campaign in 2016 are investigated with respect to the dynamics of precipitation types in the moist coastal zone of West Africa. Simulations with the “Weather Research and Forecasting (WRF)” model driven by re-analysis data deliver additional insights in relevant rainfall processes. A new precipitation meso-network in southern Ghana and the coordination of the DACCIWA radiosonde campaign are also part of WP6.

WP7 (“Monsoon Processes”, Peter Knippertz) investigates whether the extensive low and mid-level clouds in southern West Africa can influence the continental-scale West African monsoon circulation through impacts on the radiation and water budget.

Our group “Land Surfaces and Boundary Layer” leads work package WP1 “Boundary Layer Dynamics”.

Together with our English, French and African partners we aim to identify the meteorological controls on the whole process chain from the formation of nocturnal stratus clouds, via the daytime transition to convective cloud, and the formation of deep precipitating clouds. This will be achieved performing detailed intensive in-situ and remote sensing observations in addition to highly resolved model simulations (LES simulations). The intensive operation period will include measurements of the energy-balance components at the Earth’s surface, the mean and turbulent conditions in the nocturnal and daytime ABL as well as measurements of the de- and entrainment processes between the ABL and the free troposphere. The meteorological measurements will be supplemented by air chemical observations.

In the framework of DACCIWA we are contributing to work packages "Atmospheric Chemistry" (WP3) and "Cloud-Aerosol Interactions" (WP4).

By using the regional scale atmospheric model COSMO-ART we quantify the influence of the atmospheric composition on radiative forcing, the two-way coupling between aerosols and cloud droplets as well as precipitation and shed light on the characteristics of cloud microphysics and dynamics in southern West Africa (SWA). Within the research domain several emission sources are relevant. This includes natural emissions (e.g. sea salt, dimethyl sulfide (DMS), mineral dust and biogenic volatile organic compounds) but especially also anthropogenic emissions (e.g. from cities, transportation, industry, vegetation fires and gas flaring in the petroleum production areas). We already updated the parameterization of the biogenic emissions and developed a parameterization for gas flaring emissions.  

Figure 1 shows the currently used simulation domains. Based on the blue domain with a grid mesh size of 0.25° (28km) and a relatively large extension, even the Saharan mineral dust emissions and the biomass burning emissions in Central Africa can be considered. The green box shows the second nesting with a grid mesh size of 0.0446° (5km) for SWA. The second nesting (red box) has a grid mesh size of 0.02679° (3km). We have a special interest in the influence of the aerosols on the nocturnal low-level stratus.

Fig. 1. Currently used COSMO-ART simulation domains for DACCIWA; blue (grid mesh size: 28km), green: first nesting (grid mesh size: 5km) and red: second nesting (grid mesh size: 3km).

In addition to the research work, numerical forecasts with COSMO-ART for the aircraft campaign in June/July will be performed. The German Weather Service (DWD) provides ICON forecasts for the meteorological boundary conditions. The simulated distributions of aerosols and trace gas concentrations will support the decision-making of the flight routes for the DACCIWA research aircrafts. In Figure 2 the black carbon concentration in 850 hPa in microgram per square meter is presented for a pre-operational forecast valid for the 1st of August 2015, 12 UTC.

Fig. 2. Forecast of the black carbon concentration in 850 hPa (microgram per square meter); initialization on Friday 31st of July 12 UTC, valid for Saturday 1st of August 2015 12 UTC (t+24h).