Article Type:
Research Article

Where is the Interface of the Stratocumulus-Topped PBL?

C-H. Moeng National Center for Atmospheric Research,* Boulder, Colorado

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B. Stevens Department of Atmospheric Sciences, University of California, Los Angeles, Los Angeles, California

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P. P. Sullivan National Center for Atmospheric Research,* Boulder, Colorado

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Print Publication:
01 Jul 2005
DOI:
https://doi.org/10.1175/JAS3470.1
Page(s):
2626–2631
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Abstract

Various locally defined (not horizontal mean) interfaces between the stratocumulus-topped PBL and the free atmosphere are investigated using a fine-resolution large-eddy simulation with a vertical grid spacing of about 4 m. The local cloud-top height is found to be always below the height where the maximum gradient of the local sounding occurs, and the maximum-gradient height is always below the interface where PBL air can reach via turbulent motions. The distances between these local interfaces are of significant amount, a few tens of meters on average. Air between the cloud-top and maximum-gradient interfaces is fully turbulent, unsaturated, but rather moist. Air between the maximum-gradient and turbulent-mixing interfaces consists of turbulent motions that are intermittent in space and time. The simulated flow shows no clearly defined interface that separates cloudy, turbulent air mass from clear, nonturbulent air above, even locally.

* The National Center for Atmospheric Research is sponsored by the National Science Foundation

Corresponding author address: Dr. Chin-Hoh Moeng, MMM Division, NCAR, P.O. Box 3000, Boulder, CO 80307-3000. Email: moeng@ucar.edu

Abstract

Various locally defined (not horizontal mean) interfaces between the stratocumulus-topped PBL and the free atmosphere are investigated using a fine-resolution large-eddy simulation with a vertical grid spacing of about 4 m. The local cloud-top height is found to be always below the height where the maximum gradient of the local sounding occurs, and the maximum-gradient height is always below the interface where PBL air can reach via turbulent motions. The distances between these local interfaces are of significant amount, a few tens of meters on average. Air between the cloud-top and maximum-gradient interfaces is fully turbulent, unsaturated, but rather moist. Air between the maximum-gradient and turbulent-mixing interfaces consists of turbulent motions that are intermittent in space and time. The simulated flow shows no clearly defined interface that separates cloudy, turbulent air mass from clear, nonturbulent air above, even locally.

* The National Center for Atmospheric Research is sponsored by the National Science Foundation

Corresponding author address: Dr. Chin-Hoh Moeng, MMM Division, NCAR, P.O. Box 3000, Boulder, CO 80307-3000. Email: moeng@ucar.edu

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