PIV Measurements in the Atmospheric Boundary Layer within and above a Mature Corn Canopy. Part II: Quadrant-Hole Analysis

Abstract

Quadrant-hole (Q-H) analysis is applied to PIV data acquired just within and above a mature corn canopy. The Reynolds shear stresses, transverse components of vorticity, as well as turbulence production and cascading part of dissipation rates are conditionally sampled in each quadrant, based on stress and vorticity magnitudes. The stresses are representative of large-scale events, while the vorticity is dominated by small-scale shear. Dissipation rates (cascading energy fluxes) are evaluated by fitting −5/3 slope lines to the conditionally sampled and averaged spatial energy spectra, while the Reynolds stresses, vorticity, and production rates are calculated directly from the spatial distributions of two velocity components. The results demonstrate that sweep (quadrant 4) and ejection (quadrant 2) events are the dominant contributors to the Reynolds shear stress, consistent with previous observations. The analysis also shows a strong correlation between magnitudes of dissipation rate and vorticity. The dissipation rates and vorticity magnitudes are higher in quadrants 1 and 4, that is, when the horizontal component of the fluctuating velocity is positive, peaking in quadrant 1. Both are weakly correlated with the Reynolds stresses except for rare quadrant 1 events. However, the more frequently occurring quadrant 4 events are the largest contributors to the dissipation rate. The production rate inherently increases with increasing stress magnitude, but lacks correlation with vorticity. Quadrants 2 and 4 contribute the most to production. However, the contribution of quadrant 1 events to negative production should not be ignored above canopy. The results show a strong disconnection between small-scale- and large-scale-dominated phenomena.

Analysis of coherent structures and atmosphere-canopy coupling strength during the CABINEX field campaign

“…Rather than tune H to agree with the wavelet analysis, we used a constant H (H = 1) for our analysis as determined by other studies to be a suitable threshold value (Bogard and Tiederman, 1986;Comte-Bellow et al, 1978). Sensitivity of our results to H was evaluated; similar to other studies, we found the number of events decreases quickly with larger hole sizes (see Appendix A) (Baldocchi and Meyers, 1988;Bergstrom and Hogstrom, 1989;Mortiz, 1989;Shaw et al, 1983;Zhu et al, 2007). Multiple detections occurring from the same event are separated from independent events using a time frequency parameter (τ ).…”

“…It has been applied to study canopy turbulence in crop (Finnigan, 1979;Shaw et al, 1983;Zhu et al, 2007) and forest ecosystems (Baldocchi and Meyers, 1988;Bergstrom and Hogstrom, 1989;Gardiner, 1994;Mortiz, 1989;Thomas and Foken, 2007). Q-H analysis provides information about turbulent structures by separating the fluctuating velocity components (u and w ) into four categories based on sign.…”

The influence of local meteorological conditions on the circadian rhythm of corn (Zea mays L.) pollen emission

“…Soldati, 2005) that the ejection-sweep cycles are instrumental in the entrainment, dispersal and deposition of heavy particles. Ejection-sweep cycles in corn canopy flows have been investigated by Shaw et al (1983) and by Zhu et al (2006Zhu et al ( , 2007a using a technique called Quadrant-Hole (Q-H) analysis (Willmarth and Lu, 1972). This analysis was applied to the sonic anemometers' data using increasing threshold values, the lowest being juwj ¼ 0:01 m 2 s À2 which corresponds to s w % 0.12 m s À1 since s w /u * % 1.2 following Monin-Obukhov scaling (Kaimal and Finnigan, 1994) and u à = ffiffiffiffiffiffiffiffiffi ffi juwj p D E % 1.…”

Investigation of turbulence flow and sediment entrainment around a bridge pier

“…Although quadrant analysis is traditionally performed for conditional sampling of the Reynolds shear stress and turbulent heat flux, recent studies (e.g., Poggi et al 2004;Ghisalberti and Nepf 2006;Zhu et al 2007;Afzalimehr et al 2011) extended the technique to include more general properties of turbulence in plant canopy flows, such as turbulent kinetic energy, vorticity, and dissipation rate. Jafari and Keshavarzi (2010) investigated turbulence flow and sediment entrainment over the ripples by using quadrant analysis.…”