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[1] We describe observations from the Fennec supersite at Bordj-Badji Mokhtar made during the June 2011 Fennec Intensive Observation Period. These are the first detailed in-situ observations of meteorology and dust from the central Sahara, close to the centre of the Saharan Heat Low and the summertime dust maximum. Historically, a shortage of such Saharan observations has created problems for evaluating processes, models and remote sensing. [2] There was a monsoon influence at BBM before the 8th and after the 12th June, with dry Harmattan winds in between. A split boundary layer, generated by ventilation from the Atlantic, persisted during the drier phase. Extensive cold-pools (haboobs) and microburst-type events were regularly observed. Moisture reached BBM at night from the monsoon and the embedded haboobs. As well as the regularly occurring nocturnal low-level jet (LLJ), a Saharan upper boundary-layer (650-hPa) jet was observed, where winds feel drag from dry convection in the afternoon. This jet is linked to the diurnal cycles of moisture and cloud. Most dust was observed in the cloudier monsoon-affected periods and co-varying dust and cloud amounts explain most of the variations in shortwave radiation that control the surface sensible flux. Dustiness is related to a standard parameterisation of uplift using 10-m winds (“uplift potential”) and this is used to estimate uplift. Around 50% of uplift is nocturnal. Around 30% is from the LLJ and 50% from haboobs, which are mainly nocturnal. This demonstrates, for the first time from observations, the key role of haboobs, which are problematic for models.

[1] Radiosonde data from Fennec supersite-1 in the remote central Sahara have been used to evaluate the impact of convectively generated cold pool outflows on model errors. Model predictions are too warm and dry, with cold pools contributing significantly to the mean bias. Although dust concentrations are high within cold pools, the sign of the errors is inconsistent with radiative impacts of dust. Cold pools cause 29% of the meridional humidity flux, but this contribution is absent in the forecast and analysis. Assimilating radiosondes reduces the errors, but significant temperature and meridional humidity flux biases remain at night. The model biases are consistent with the larger-scale heat low biases in the operational Met Office Unified Model and can be linked to known issues with convective parameterizations used in all global weather and climate models. This study suggests that the misrepresentation of moist convective processes can affect continental-scale biases, altering the West African monsoon circulation.