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Sharp boundary layer top inversions and stratocumulus boundary layer structure captured in kilometre

Figure: Sounding of potential temperature profile (dashed line) obtained at Brest on Jan 27th, 2003 at 00 UTC obtained during a pronounced high pressure synoptic situation as depicted by the underlying surface pressure maps (Courtesy: German weather service 2003). Profile from simulation performed at 2 km is shown in red.

High pressure systems are associated with strong large-scale descending motions. As the air sinks through the atmosphere it is warmed due to increased compression which leads to the formation of temperature inversions, such as the one shown above. Capturing this particular inversion of 12 K at an altitude of just 500 metres, is challenging for any weather prediction model. It requires an adequate representation and balancing of the large-scale subsidence rate with the boundary layer mixing, which acts to deepen the boundary layer, and in turn depends on the surface fluxes and cloud processes such as cloud top radiative cooling.

In this study, we showed that inversions can indeed be simulated at the kilometre scale (and even coarser scales) using common boundary layer and cloud-radiative parameterisations.

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