Ozone exchange within and above an irrigated Californian orchard

In this study, the canopy effects on the vertical ozone exchange within and above Californian orchard are investigated. We examined the comprehensive dataset obtained from the Canopy Horizontal Array Turbulence Study (CHATS). CHATS typifies a rural central Californian site, with O3 mixing ratios of less than 60 ppb and moderate NOx mixing ratios. The CHATS campaign covered a complete irrigation cycle, with our analysis including periods before and after irrigation. Lower O3 mixing ratios were found following irrigation, together with increased wind speeds, decreased air temperatures and increased specific humidity. Friction velocity, sensible heat and gas fluxes above the canopy were estimated using variations on the flux-gradient method, including a method which accounts for the roughness sublayer (RSL). These methods were compared to fluxes derived from observed eddy diffusivities of heat and friction velocity. We found that the use of the RSL parameterization, which accounts for the canopy-induced turbulent mixing above the canopy, resulted in a stronger momentum, heat, and ozone exchange fluxes above this orchard, compared to the method which omits the RSL. This was quantified by the increased friction velocity, heat flux and ozone deposition flux of up to 12, 29, and 35% at 2.5 m above the canopy, respectively. Within the canopy, vertical fluxes, as derived from local gradients and eddy diffusivity of heat, were compared to fluxes calculated using the Lagrangian inverse theory. Both methods showed a presence of vertical flux divergence of friction velocity, heat and ozone, suggesting that turbulent mixing was inefficient in homogenizing the effects driven by local sources and sinks on vertical exchange of those quantities. This weak mixing within the canopy was also corroborated in the eddy diffusivities of friction velocity and heat, which were calculated directly from the observations. Finally, the influence of water stress on the O3 budget was examined by comparing the results prior and after the irrigation. Although the analysis is limited to the local conditions, our in situ measurements indicated differences in the O3 mixing ratio prior and after irrigation during CHATS. We attribute these O3 mixing ratio changes to enhanced biological emission of volatile organic compounds (VOCs), driven by water stress

New Techniques for Relating Dynamically Close Galaxy Pairs to Merger and Accretion Rates : Application to the SSRS2 Redshift Survey

We introduce two new pair statistics, which relate close galaxy pairs to the merger and accretion rates. We demonstrate the importance of correcting these (and other) pair statistics for selection effects related to sample depth and completeness. In particular, we highlight the severe bias that can result from the use of a flux-limited survey. The first statistic, denoted N_c, gives the number of companions per galaxy, within a specified range in absolute magnitude. N_c is directly related to the galaxy merger rate. The second statistic, called L_c, gives the total luminosity in companions, per galaxy. This quantity can be used to investigate the mass accretion rate. Both N_c and L_c are related to the galaxy correlation function and luminosity function in a straightforward manner. We outline techniques which account for various selection effects, and demonstrate the success of this approach using Monte Carlo simulations. If one assumes that clustering is independent of luminosity (which is appropriate for reasonable ranges in luminosity), then these statistics may be applied to flux-limited surveys. These techniques are applied to a sample of 5426 galaxies in the SSRS2 redshift survey. Using close dynamical pairs, we find N_c(-21<M_B<-18) = 0.0226+/-0.0052 and L_c(-21<M_B<-18) = 0.0216+/-0.0055 10^{10} h^2 L_sun at z=0.015. These are the first secure estimates of low-z close pair statistics. If N_c remains fixed with redshift, simple assumptions imply that ~ 6.6% of present day galaxies with -21<M_B<-18 have undergone mergers since z=1. When applied to redshift surveys of more distant galaxies, these techniques will yield the first robust estimates of evolution in the galaxy merger and accretion rates. [Abridged]Comment: 26 pages (including 10 postscript figures) plus 3 gif figures. Accepted for publication in ApJ. Paper (including full resolution images) also available at http://www.astro.utoronto.ca/~patton/ssrs2, along with associated pair classification experiment (clickable version of Figure 5

A Hubble Space Telescope Snapshot Survey of Dynamically Close Galaxy Pairs in the CNOC2 Redshift Survey

We compare the structural properties of two classes of galaxies at intermediate redshift: those in dynamically close galaxy pairs, and those which are isolated. Both samples are selected from the CNOC2 Redshift Survey, and have redshifts in the range 0.1 < z <0.6. Hubble Space Telescope WFPC2 images were acquired as part of a snapshot survey, and were used to measure bulge fraction and asymmetry for these galaxies. We find that paired and isolated galaxies have identical distributions of bulge fractions. Conversely, we find that paired galaxies are much more likely to be asymmetric (R_T+R_A >= 0.13) than isolated galaxies. Assuming that half of these pairs are unlikely to be close enough to merge, we estimate that 40% +/- 11% of merging galaxies are asymmetric, compared with 9% +/- 3% of isolated galaxies. The difference is even more striking for strongly asymmetric (R_T+R_A >= 0.16) galaxies: 25% +/- 8% for merging galaxies versus 1% +/- 1% for isolated galaxies. We find that strongly asymmetric paired galaxies are very blue, with rest-frame B-R colors close to 0.80, compared with a mean (B-R)_0 of 1.24 for all paired galaxies. In addition, asymmetric galaxies in pairs have strong [OII]3727 emission lines. We conclude that close to half of the galaxy pairs in our sample are in the process of merging, and that most of these mergers are accompanied by triggered star formation.Comment: Accepted for publication in the Astronomical Journal. 40 pages, including 15 figures. For full resolution version, please see http://www.trentu.ca/physics/dpatton/hstpairs

Self-Referential Noise and the Synthesis of Three-Dimensional Space

Generalising results from Godel and Chaitin in mathematics suggests that self-referential systems contain intrinsic randomness. We argue that this is relevant to modelling the universe and show how three-dimensional space may arise from a non-geometric order-disorder model driven by self-referential noise.Comment: Figure labels correcte

Modeling canopy-induced turbulence in the Earth system: a unified parameterization of turbulent exchange within plant canopies and the roughness sublayer (CLM-ml v0)

Land surface models used in climate models neglect the roughness sublayer and parameterize within-canopy turbulence in an ad hoc manner. We implemented a roughness sublayer turbulence parameterization in a multilayer canopy model (CLM-ml v0) to test if this theory provides a tractable parameterization extending from the ground through the canopy and the roughness sublayer. We compared the canopy model with the Community Land Model (CLM4.5) at seven forest, two grassland, and three cropland AmeriFlux sites over a range of canopy heights, leaf area indexes, and climates. CLM4.5 has pronounced biases during summer months at forest sites in midday latent heat flux, sensible heat flux, gross primary production, nighttime friction velocity, and the radiative temperature diurnal range. The new canopy model reduces these biases by introducing new physics. Advances in modeling stomatal conductance and canopy physiology beyond what is in CLM4.5 substantially improve model performance at the forest sites. The signature of the roughness sublayer is most evident in nighttime friction velocity and the diurnal cycle of radiative temperature, but is also seen in sensible heat flux. Within-canopy temperature profiles are markedly different compared with profiles obtained using Monin–Obukhov similarity theory, and the roughness sublayer produces cooler daytime and warmer nighttime temperatures. The herbaceous sites also show model improvements, but the improvements are related less systematically to the roughness sublayer parameterization in these canopies. The multilayer canopy with the roughness sublayer turbulence improves simulations compared with CLM4.5 while also advancing the theoretical basis for surface flux parameterizations

Swimming is never without risk: opening up on learning through activism and research

This article examines my own becoming as Elisabeth and as a researcher. It is about working as a support worker, coaching teams that are trying to realize inclusive education for a child, and my PhD process, which relies on these practices. My intention here is to unfold several aspects, blockages, possibilities, and tensions that can make sense of my messy struggle. The never-ending learning through working with people, listening to their stories, and taking responsibility are important ingredients of my engagement. It is necessary to provide insights and justify my multiple positions to avoid falling into a narcissistic trap. In doing so, I will seek help from Levinas and in concepts of Deleuze and Guattari to (re-)construct my own understanding

Ordovician Stratigraphy, and the Physiography of Part of Southeastern Indiana

Within recent years field conferences sponsored by the Geological Survey, Indiana Department of Conservation, and the Department of Geology, Indiana University, have reviewed outstanding exposures and of parts of the Silurian, Devonian, Mississippian, and Pennsylvanian systems in southern Indiana. This conference is concerned, in part, with the stratigraphy and paleontology of the Ordovician rocks exposed in southeastern Indiana