Nocturnal surface-layer characteristics at the bottom of a valley

• Published in: Boundary-layer meteorology Vol. 112; no. 1; pp. 159 - 177
• Main Authors: MORAES, O. L. L, ACEVEDO, O. C, DA SILVA, R, MAGNAGO, R, SIQUEIRA, A. C
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer 01-07-2004; Springer Nature B.V
• Subjects: Boundaries; Boundary layer; Convection, turbulence, diffusion. Boundary layer structure and dynamics; Distortion; Earth, ocean, space; Exact sciences and technology; External geophysics; Fluid dynamics; Fluxes; Mathematical analysis; Meteorology; Sensible heat; Stability; Statistics; Topography; Turbulence; Valleys; Wind speed; Brazil; South America; Sensible heat; meteorology; Surface layer; Turbulent transfer; Wind velocity; Random error; troposphere; turbulence; Intermittency; Momentum transfer; winds; Atmospheric boundary layer; heat transfer; stability
• ISSN: 0006-8314; 1573-1472
• DOI: 10.1023/B:BOUN.0000020163.36907.f9

Nighttime data collected at the bottom of a valley locatedin southern Brazil are studied. The analyzed quantities includemomentum and sensible heat fluxes, turbulence statistics andintermittency factors, and their relationship to the stability parameter.The proper interval for averaging and flux calculations is foundto be 20 min, based on the comparison of the fluxes and therandom error associated in their determination. Each data seriesis classified as calm or windy, according to the mean windspeed. A much better dependency of the variables in terms of thestability parameter is found under windy conditions. Analysis ofthe wind direction and topographic scales indicates that distortioneffects under calm conditions affect the flow, while the flow is inlocal equilibrium for windy conditions. In this case, the sensible heatflux shows a minimum for a value of z/L=0.08, while the momentumflux and the normalized scales of the wind components andtemperature decrease monotonically as the stability increases. Anintermittency factor is proposed and shown to be larger (moreintermittency) for more stable conditions.