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The role of thermal stratification on the co‐spectral properties of momentum transport above an Amazonian forest

Journal Article · · Quarterly Journal of the Royal Meteorological Society
DOI:https://doi.org/10.1002/qj.5024· OSTI ID:3006801
 [1];  [2];  [3];  [4];  [5]
  1. Univ. di Milano (Italy)
  2. Duke Univ., Durham, NC (United States)
  3. National Oceanic and Atmospheric Administration (NOAA), Oak Ridge, TN (United States). Air Resources Laboratory
  4. Federal Inst. of Pará (Brazil)
  5. Univ. of Helsinki (Finland)
The influence of thermal stratification on the turbulent kinetic energy balance has been widely studied; however, its influence on the turbulent stress remains less explored in the presence of tall vegetated canopies and less ideal micrometeorological conditions. Here, the impact of thermal stratification on turbulent momentum flux is considered in the roughness sublayer (RSL) and the atmospheric surface layer (ASL) using the Amazon Tall Tower Observatory (ATTO) in Brazil. A scalewise co‐spectral budget (CSB) model is developed using standard closure schemes for the pressure–velocity decorrelation. The CSB revealed that the co‐spectrum $${F}_{wu}\left({k}_x\right)$$ between longitudinal (u') and vertical (w') velocity fluctuations is impacted by the energy spectrum of the vertical velocity $${E}_{ww}\left({k}_x\right)$$ and the much less studied longitudinal heat‐flux co‐spectrum $${F}_{u{\theta}_{\mathrm{v}}}\left({k}_x\right)$$, where $${\theta}_{\mathrm{v}}^{\prime }$$ are temperature fluctuations and $${k}_x$$ is the longitudinal wavenumber. Under stable, very stable, and dynamic–convective conditions, the scaling exponent $${F}_{wu}\left({k}_x\right)$$ in for the inertial subrange (ISR) scales is dominated by $${F}_{u{\theta}_{\mathrm{v}}}\left({k}_x\right)$$ instead of $${E}_{ww}\left({k}_x\right)$$. A near $${k}_x^{-7/3}$$scaling in $${F}_{u{\theta}_{\mathrm{v}}}\left({k}_x\right)$$ robust to large variations in thermal stratification is found, whereas the Kolmogorov ISR scaling for $${E}_{ww}\left({k}_x\right)\sim {k}_x^{-5/3}$$ is not found. The scale‐dependent decorrelation time between u' and w' is dominated by $${\epsilon}^{-1/3}{k}_x^{-2/3}$$ in the ISR, but is nearly constant for eddies larger than the vertical velocity integral scale, regardless of stability. Implications of these findings for generalized stability correction functions that are based on the turbulent stress budget instead of the turbulent kinetic energy budget are discussed.
Research Organization:
Univ. of California, Los Angeles, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Biological and Environmental Research (BER)
Grant/Contract Number:
SC0022072
OSTI ID:
3006801
Journal Information:
Quarterly Journal of the Royal Meteorological Society, Journal Name: Quarterly Journal of the Royal Meteorological Society Journal Issue: 772 Vol. 151; ISSN 1477-870X; ISSN 0035-9009
Publisher:
Royal Meteorological SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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