Characterizing Turbulence in the Convective Boundary Layer with a Raman Lidar (Invited)
Abstract
The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program's Raman lidar at the ARM Southern Great Plains (SGP) site in north-central Oklahoma has collected water vapor profile data more than 90% of the time since October 2004. Three hundred (300) afternoon cases were identified where the convective boundary layer was quasi-stationary and well-mixed for a 2-hour period, and variance and skewness profiles were derived from the 10-s, 75-m resolution water vapor mixing ratio data. These cases span the entire calendar year, and demonstrate that the water vapor variance at the mixed layer (ML) top changes seasonally, but is more related to the gradient of the water vapor across the entrainment zone. The water vapor variance at the top of the ML shows only weak correlations (r < 0.3) with sensible heat flux, Deardorff convective velocity scale, and turbulence kinetic energy measured at the surface. The mean water vapor skewness is most negative at 0.85 zi, zero at approximately 0.95 zi, and positive above zi, where zi is the depth of the convective ML. The spread in the water vapor skewness is smallest between 0.95 zi and zi. The water vapor skewness at altitudes between 0.6 zi and 1.2 zi is correlated with the magnitude of the water vapor variance at zi, with increasingly negative values of skewness observed deeper in the boundary layer as the variance at zi increases, suggesting that in cases with larger variance at zi there is deeper penetration of the warm, dry free tropospheric air into the boundary layer.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.A34D..01T
- Keywords:
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- 3307 ATMOSPHERIC PROCESSES Boundary layer processes;
- 3379 ATMOSPHERIC PROCESSES Turbulence