Vertical propagation of submeso and coherent structure in a tall and dense Amazon Forest in different stability conditions PART I: Flow structure within and above the roughness sublayer

Coherent Structures Detection within a Dense Alpine Forest

“…In stable conditions, CS are damped by buoyancy as stability increases; observational studies showed that they tend to become highly intermittent and unable to penetrate in the deeper layers of the vegetation (Launiainen et al, 2007;Dupont and Patton, 2012a,b), similar results were found from DNS analyses Mellado, 2014, 2016;Allouche et al, 2022). In very stable conditions, CS remain confined close to the canopy top (Cava et al, 2022) or may resemble waves ('canopy waves') with similar time scale, transporting energy but not mass (Lee and Baar, 1998;Cava et al, 2004). Further, the flow characteristics may be strongly influenced by the presence of large-scale submeso motions (Mortarini et al, 2019), such as horizontal meandering or gravity waves, in particular in very stable and low wind regimes.…”

“…Further, the flow characteristics may be strongly influenced by the presence of large-scale submeso motions (Mortarini et al, 2019), such as horizontal meandering or gravity waves, in particular in very stable and low wind regimes. Cava et al (2022) analysed data collected above and within a dense Amazonian forest, and showed that the increasing atmospheric stratification produced a gradual lowering of the RSL and the consequent propagation of submeso motions up to the canopy top and within the forest, where submeso motions were able to modulate the forest exchange, particularly the scalar fluxes, as already observed by Santos et al (2016) and Oliveira et al (2018).…”

“…In recent years, experimental (Gao et al, 1989;Paw U et al, 1992;Chen et al, 1997;Dupont and Patton, 2012b,a;Cava et al, 2022;Mortarini et al, 2022), theoretical (Raupach et al, 1996;Finnigan et al, 2009) and numerical studies (Su et al, 1998;Foster et al, 2006;Drobinski et al, 2007;Dias-Júnior et al, 2015) highlighted the important role of coherent structures (CS) on the flow dynamics within and above plant canopies. The literature refers to 'coherent structures' as three-dimensional, well-organized flow patterns with characteristic forms and timescale in which fundamental flow variables (such as wind velocity or temperature) exhibit significant correlation with themselves and with each other in a range of space and time that are significantly larger than the high-frequency turbulent scales (Robinson, 1991;Serafimovich et al, 2011).…”

“…According to the mixing-layer analogy, CS evolve from Kelvin-Helmholtz instabilities triggered by the wind shear at the top of the vegetation; their vertical scale (𝐿 𝑠 , the 'canopy-shear length scale') is proportional to the vorticity thickness related to the inflection point of the wind velocity profile (Raupach et al, 1996). The applicability of the mixing-layer analogy has been assessed for neutral conditions or, anyway, for thermal conditions close to neutrality (Shaw et al, 1995;Brunet and Irvine, 2000;Dupont and Patton, 2012a;Patton et al, 2016), whereas it has been shown that other mechanisms may influence the flow dynamics in convective conditions and strong stable stratification (Cava et al, 2022). In unstable conditions, the organization of turbulence in the RSL is a combination of CS generated by shear processes and larger convective eddies.…”

Inferring the diurnal variability of OH radical concentrations over the Amazon from BVOC measurements

“…Further, the measurements taken at around 80 m are likely to be inside the roughness-sublayer that spans within the ABL from the ground to 2–3 times the canopy height (37 m) 28 , 29 . Turbulence there differs from the layers aloft with strongly inhomogeneous flows of sweeping and ejection motions induced by deceleration of wind at the rough canopy surface 30 , 31 . The timescale of w* represents that of individual large eddies in reaching the top of the ABL.…”