Abstract
Abstract. High spatial resolution measurements of temperature and liquid water content, accompanied by moderate-resolution measurements of humidity and turbulence, collected during the Physics of Stratocumulus Top experiment are analyzed. Two thermodynamically, meteorologically and even optically different cases are investigated. An algorithmic division of the cloud-top region into layers is proposed. Analysis of dynamic stability across these layers leads to the conclusion that the inversion capping the cloud and the cloud-top region is turbulent due to the wind shear, which is strong enough to overcome the high static stability of the inversion. The thickness of this mixing layer adapts to wind and temperature jumps such that the gradient Richardson number stays close to its critical value. Turbulent mixing governs transport across the inversion, but the consequences of this mixing depend on the thermodynamic properties of cloud top and free troposphere. The effects of buoyancy sorting of the mixed parcels in the cloud-top region are different in conditions that permit or prevent cloud-top entrainment instability. Removal of negatively buoyant air from the cloud top is observed in the first case, while buildup of the diluted cloud-top layer is observed in the second one.
Highlights
Exchange processes between stratocumulus (Sc) clouds and the free troposphere (FT) above them have been intensively investigated in many research campaigns (e.g., Albrecht et al, 1988; Lenschow et al, 1988; Stevens et al, 2003; Bretherton et al, 2004)
All these values fall into the range of uncertainty of the entrainment velocity estimated from the boundary layer growth rate and large-scale subsidence
High-resolution airborne measurements performed in the course of the POST research campaign allow the division of the cloud-top region into layers: non-turbulent free troposphere, turbulent capping inversion sublayer, turbulent cloudtop mixing sublayer and the cloud layer below
Summary
Exchange processes between stratocumulus (Sc) clouds and the free troposphere (FT) above them have been intensively investigated in many research campaigns (e.g., Albrecht et al, 1988; Lenschow et al, 1988; Stevens et al, 2003; Bretherton et al, 2004). We examine in detail two very different pled in the course of porpoise-like flight segments across cases of stratocumulus top, documented by means of high the EIL, as shown in Fig. 3 of Gerber et al (2010) In this spatial resolution (∼ 1 m or less) measurements of veloc- study we focus on fine-scale measurements collected with. WpMinoadsli,itnivaoenwldyskbmiueiotxyaianln.,gt2ar0na1dt1i/)o.rsInristhine2g3fo(Glloewrbienrg et al, 2010, 2013; we analyze details of the EIL structure in two POST cases, TO10 and TO13, which correspond to the classical and non-classical regimes the modernized Ultra Fast Thermometer (UFT-M) (Kumala et al1.0,020 013), Particulat1e00V0olume Monitor1P00V0M-100 (Gerber identified above, in order to understand similarities and differences between the behaviors of the cloud top in these two et al, 1994), and other fast-response instruments collocated in clo80s0e proximity aroun80d0 the radome of th8e00aircraft (Fig. 1). There is a substantial variability of the shear layer among the penetrations
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