On the Time Scale of Nocturnal Boundary Layer Cooling in Valleys and Basins and over Plains

Sequences of vertical temperature soundings over flat plains and in a variety of valleys and basins of different sizes and shapes were used to determine cooling-time-scale characteristics in the nocturnal stable boundary layer under clear, undisturbed weather conditions. An exponential function pred...

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Bibliographic Details
Published in:Journal of applied meteorology (1988) 2006-06, Vol.45 (6), p.813-820
Main Authors: De Wekker, Stephan F. J., Whiteman, C. David
Format: Article
Language:English
Subjects:
Air temperature
Atmospheric temperature
Atmospherics
Basins
Boundary layer
Boundary layers
Climatology
Constants
Convection, turbulence, diffusion. Boundary layer structure and dynamics
Cooling
Earth, ocean, space
Exact sciences and technology
Exponential functions
External geophysics
Heat
Heat loss
Mathematical analysis
Meteorology
Nocturnal boundary layer
Radiation
Ranches
Soundings
Stable boundary layer
Surface temperature
Temperature
Temperature measurement
Time constant
Time constants
Topography
Valleys
Weather
Weather conditions
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Summary:Sequences of vertical temperature soundings over flat plains and in a variety of valleys and basins of different sizes and shapes were used to determine cooling-time-scale characteristics in the nocturnal stable boundary layer under clear, undisturbed weather conditions. An exponential function predicts the cumulative boundary layer cooling well. The fitting parameter or time constant in the exponential function characterizes the cooling of the valley atmosphere and is equal to the time required for the cumulative cooling to attain 63.2% of its total nighttime value. The exponential fit finds time constants varying between 3 and 8 h. Calculated time constants are smallest in basins, are largest over plains, and are intermediate in valleys. Time constants were also calculated from air temperature measurements made at various heights on the sidewalls of a small basin. The variation with height of the time constant exhibited a characteristic parabolic shape in which the smallest time constants occurred near the basin floor and on the upper sidewalls of the basin where cooling was governed by cold-air drainage and radiative heat loss, respectively.
ISSN:1558-8424
0894-8763
1558-8432
1520-0450
DOI:10.1175/JAM2378.1