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Title: Enhanced Temperature-Humidity Similarity Caused by Entrainment Processes With Increased Wind Shear

Abstract

A number of studies already suggested that entrainment of warm/dry air from aloft degrades the similarity between air temperature (T) and specific humidity (q) in the atmospheric surface layer (ASL). Less is known about entrainment of cool/dry air on the ASL T-q similarity. Using eddy covariance measurements over a large inland water surface, enhanced T-q similarity with increased friction velocity (u*) was measured during daytime unstable conditions. Explaining this enhancement is the main goal of this work. Cool/dry air masses originating and advecting from land set the upper boundary condition on a quasi-equilibrated internal boundary layer embedding the warm/moist ASL over water. With increased u*, the entrainment velocity (dhI/dt ∝ u*) increases, thereby enhancing entrainment of cool/dry air originating from land, where t is time and hI is the internal boundary layer depth. By analyzing the scale-dependent (spectral) correlation coefficients, the enhanced T-q similarity with increased u* was shown to originate from spectral correlation coefficients in the middle- to low-frequency ranges (large eddies » z, the distance from the surface). With further increases in u*, similarity between T and q within large eddies was further enhanced and phase differences between T and q was reduced. Quadrant analysis showed large increasesmore » in flux and time fractions of downward large cool/dry eddies with increasing u*. These results provide evidence that enhanced entrainment of synchronized, large cool/dry eddies was a primary cause for the increased T-q similarity with increasing u*.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [4]
  1. Washington State Univ., Pullman, WA (United States)
  2. Boston Univ., MA (United States)
  3. Duke Univ., Durham, NC (United States)
  4. Univ. of Colorado, Boulder, CO (United States)
Publication Date:
Research Org.:
Duke Univ., Durham, NC (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1539732
Grant/Contract Number:  
SC0011461
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research: Atmospheres
Additional Journal Information:
Journal Volume: 123; Journal Issue: 8; Journal ID: ISSN 2169-897X
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; Meteorology & Atmospheric Sciences

Citation Formats

Gao, Zhongming, Liu, Heping, Li, Dan, Katul, Gabriel G., and Blanken, Peter D. Enhanced Temperature-Humidity Similarity Caused by Entrainment Processes With Increased Wind Shear. United States: N. p., 2018. Web. doi:10.1029/2017jd028195.
Gao, Zhongming, Liu, Heping, Li, Dan, Katul, Gabriel G., & Blanken, Peter D. Enhanced Temperature-Humidity Similarity Caused by Entrainment Processes With Increased Wind Shear. United States. doi:10.1029/2017jd028195.
Gao, Zhongming, Liu, Heping, Li, Dan, Katul, Gabriel G., and Blanken, Peter D. Mon . "Enhanced Temperature-Humidity Similarity Caused by Entrainment Processes With Increased Wind Shear". United States. doi:10.1029/2017jd028195. https://www.osti.gov/servlets/purl/1539732.
@article{osti_1539732,
title = {Enhanced Temperature-Humidity Similarity Caused by Entrainment Processes With Increased Wind Shear},
author = {Gao, Zhongming and Liu, Heping and Li, Dan and Katul, Gabriel G. and Blanken, Peter D.},
abstractNote = {A number of studies already suggested that entrainment of warm/dry air from aloft degrades the similarity between air temperature (T) and specific humidity (q) in the atmospheric surface layer (ASL). Less is known about entrainment of cool/dry air on the ASL T-q similarity. Using eddy covariance measurements over a large inland water surface, enhanced T-q similarity with increased friction velocity (u*) was measured during daytime unstable conditions. Explaining this enhancement is the main goal of this work. Cool/dry air masses originating and advecting from land set the upper boundary condition on a quasi-equilibrated internal boundary layer embedding the warm/moist ASL over water. With increased u*, the entrainment velocity (dhI/dt ∝ u*) increases, thereby enhancing entrainment of cool/dry air originating from land, where t is time and hI is the internal boundary layer depth. By analyzing the scale-dependent (spectral) correlation coefficients, the enhanced T-q similarity with increased u* was shown to originate from spectral correlation coefficients in the middle- to low-frequency ranges (large eddies » z, the distance from the surface). With further increases in u*, similarity between T and q within large eddies was further enhanced and phase differences between T and q was reduced. Quadrant analysis showed large increases in flux and time fractions of downward large cool/dry eddies with increasing u*. These results provide evidence that enhanced entrainment of synchronized, large cool/dry eddies was a primary cause for the increased T-q similarity with increasing u*.},
doi = {10.1029/2017jd028195},
journal = {Journal of Geophysical Research: Atmospheres},
number = 8,
volume = 123,
place = {United States},
year = {2018},
month = {4}
}

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