Publication Date:
2013-10-05
Description:
[1] An aircraft field study [POST; Physics Of Stratocumulus Top] was conducted off the central California Coast in July and August of 2008 to deal with the known difficulty of measuring entrainment rates in the radiatively important stratocumulus [Sc] prevalent in that area. The CIRPAS Twin Otter research aircraft flew 15 quasi-Lagrangian flights in unbroken Sc and carried a full complement of probes including three high data-rate probes UFT-M [Ultra-Fast Temperature probe], PVM [Particulate Volume Monitor] probe, and gust probe. The probes’ co-location near the nose of the Twin Otter permitted estimation of entrainment fluxes and rates with an incloud resolution of 1 m. [2] Results include the following: Application of the conditional-sampling variation of classical mixed layer theory for calculating the entrainment rate into cloud top for POST flights is shown to be inadequate for most of the Sc. Estimated rates resemble previous results after theory is modified to take into account both entrainment and evaporation at cloud top given the strong wind shear and mixing at cloud top. Entrainment rates show a tendency to decrease for large shear values, and the largest rates are for the smallest temperature jumps across the inversion. Measurements indirectly suggest that entrained parcels are primarily cooled by infrared flux divergence rather than cooling from droplet evaporation, while detrainment at cloud top causes droplet evaporation and cooling in the EIL [Entrainment Interface Layer] above cloud top.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
Permalink