Physics of Stratocumulus Top (POST): Turbulent mixing across capping inversion

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Abstract

High spatial resolution measurements of temperature and liquid water content, accompanied by moderateresolution 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. © 2013 Author(s).

Figures

  • Fig. 1. Radome of CIRPAS Twin Otter research aircraft with fastresponse instruments used in POST.
  • Fig. 4. Temperature T , liquid water content LWC, and velocity fluctuations (mean values subtracted) in the course of a descent into the stratocumulus cloud deck, illustrated by the altitude (black line), during flight TO10.
  • Fig. 5. As in Fig. 4 but for flight TO13.
  • Fig. 6. Typical high-resolution (∼ 5.5 cm) records of temperature and LWC fluctuations in TISL (upper panel), CTMSL (middle panel) and CTL (bottom panel) from flight TO10.
  • Fig. 7. As in Fig. 6 but for flight TO13.
  • Fig. 8. Typical profiles of LWC collected on porpoises in flight TO10. Each point corresponds to a 1.4 m average (40 Hz data). Four consecutive profiles are shown in each row. Successive rows are from different flight legs in order to illustrate variability of LWC for the whole flight.
  • Fig. 8. Typical profiles of LWC collected on porpoises in flight TO10. Each point corresponds to a 1.4m average (40Hz data). Four consecutive profiles are shown in each row. Successive rows are from
  • Fig. 10. Vertical profiles of droplet number concentration (triangles, blue, upper axis) and percentiles of droplet size distribution (circles) as a function of altitude relative to cloud top (binned to 10 intervals). Measurements from the phase-Doppler interferometer during TO10.

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CITATION STYLE

APA

Malinowski, S. P., Gerber, H., Jen-La Plante, I., Kopec, M. K., Kumala, W., Nurowska, K., … Haman, K. E. (2013). Physics of Stratocumulus Top (POST): Turbulent mixing across capping inversion. Atmospheric Chemistry and Physics, 13(24), 12171–12186. https://doi.org/10.5194/acp-13-12171-2013

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