Mixed-Layer Budget Analysis of the Diurnal Cycle of Entrainment in Southeast Pacific Stratocumulus
- 1 October 2005
- journal article
- Published by American Meteorological Society in Journal of the Atmospheric Sciences
- Vol. 62 (10), 3775-3791
- https://doi.org/10.1175/jas3561.1
Abstract
Mixed-layer budgets of boundary layer mass, moisture, and liquid water static energy are estimated from 6 days of data collected at 20°S, 85°W (a region of persistent stratocumulus) during the East Pacific Investigation of Climate (EPIC) stratocumulus cruise in 2001. These budgets are used to estimate a mean diurnal cycle of entrainment and, by diagnosing the fluxes of humidity and liquid water static energy necessary to maintain a mixed-layer structure, of buoyancy flux. Although the entrainment rates suggested by each of the budgets have significant uncertainty, the various methods are consistent in predicting a 6-day mean entrainment rate of 4 ± 1 mm s−1, with higher values at night and very little entrainment around local noon. The diurnal cycle of buoyancy flux suggests that drizzle, while only a small term in the boundary layer moisture budget, significantly reduces subcloud buoyancy flux and may induce weak decoupling of surface and cloud-layer turbulence during the early morning hours, a structure that is maintained throughout the day by shortwave warming. Finally, the diurnal cycle of entrainment diagnosed from three recently proposed entrainment closures is found to be consistent with the observationally derived values.Keywords
This publication has 50 references indexed in Scilit:
- Diurnal cycle of liquid water path over the subtropical and tropical oceansGeophysical Research Letters, 2002
- Cloud transitions and decoupling in shear‐free stratocumulus‐topped boundary layersGeophysical Research Letters, 2000
- Thermodynamic structure and entrainment of stratocumulus over the Southern OceanJournal of Geophysical Research: Solid Earth, 1998
- Evaluation of the Vertical Structure of Zonally Averaged Cloudiness and Its Variability in the Atmospheric Model Intercomparison ProjectJournal of Climate, 1996
- Bulk parameterization of air‐sea fluxes for Tropical Ocean‐Global Atmosphere Coupled‐Ocean Atmosphere Response ExperimentJournal of Geophysical Research: Oceans, 1996
- Marine boundary layer structure and fractional cloudinessJournal of Geophysical Research: Solid Earth, 1995
- Observations of Diurnal Variation in a Cloud-capped Marine Boundary LayerJournal of the Atmospheric Sciences, 1991
- Surface‐based remote sensing of the observed and the Adiabatic liquid water content of stratocumulus cloudsGeophysical Research Letters, 1990
- An observational study of the structure of stratiform cloud sheets: Part II. EntrainmentQuarterly Journal of the Royal Meteorological Society, 1986
- Marine Stratocumulus Convection. Part I: Governing Equations and Horizontally Homogeneous SolutionsJournal of the Atmospheric Sciences, 1979