Turbulent and boundary layer characteristics during VOCALS-REx

• Published in: Atmospheric chemistry and physics 2021-02, Vol.21 (3), p.1937-1961
• Main Authors: Dodson, Dillon S, Small Griswold, Jennifer D
• Format: Article
• Language: English
• Subjects: Aerodynamics; Aircraft; Analysis; Atmosphere; Atmospheric boundary layer; Atmospheric pressure; Boundary layer; Boundary layer height; Boundary layers; Buoyancy flux; Cloud height; Cloud precipitation; Cloud thickness; Clouds; Coefficients; Cooling; Correlation analysis; Correlation coefficient; Correlation coefficients; Decoupling; Energy dissipation; Energy exchange; Enthalpy; Entrainment; Evaporation; Evaporative cooling; Fluctuations; Force and energy; Heat; Heat flux; Heat transfer; Kinetic energy; Kinetic energy dissipation; Latent heat; Latent heat flux; Monsoon clouds; Precipitation; Precipitation (Meteorology); Radiational cooling; Sensible heat; Sensible heat flux; Sensible heat transfer; Superhigh frequencies; Surface fluxes; Turbulence; Turbulent boundary layer; Turbulent kinetic energy; Velocity; Vertical profiles; Vertical velocities
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-21-1937-2021

Boundary layer and turbulent characteristics (surface fluxes, turbulent kinetic energy - TKE, turbulent kinetic energy dissipation rate - ϵ), along with synoptic-scale changes in these properties over time, are examined using data collected from 18 research flights made with the CIRPAS Twin Otter Aircraft. Data were collected during the Variability of the American Monsoon Systems (VAMOS) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) at Point Alpha (20.sup." S, 72.sup." W) in October and November 2008 off the coast of South America. The average boundary layer depth is found to be 1148 m, with 28 % of the boundary layer profiles analyzed displaying decoupling. Analysis of correlation coefficients indicates that as atmospheric pressure decreases, the boundary layer height (z.sub.i) increases. As has been shown previously, the increase in z.sub.i is accompanied by a decrease in turbulence within the boundary layer. As z.sub.i increases, cooling near cloud top cannot sustain mixing over the entire depth of the boundary layer, resulting in less turbulence and boundary layer decoupling. As the latent heat flux (LHF) and sensible heat flux (SHF) increase, z.sub.i increases, along with the cloud thickness decreasing with increasing LHF. This suggests that an enhanced LHF results in enhanced entrainment, which acts to thin the cloud layer while deepening the boundary layer.