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Do we (need to) care about canopy radiation schemes in DGVMs? Caveats and potential impacts
Dynamic global vegetation models (DGVMs) are an essential part of current state-of-the-art Earth system models. In recent years, the complexity of DGVMs has increased by incorporating new important processes like, e.g., nutrient cycling and land cover dynamics, while biogeophysical processes like surface radiation have not been developed much further. Canopy radiation models are however very important for the estimation of absorption and reflected fluxes and are essential for a proper estimation of surface carbon, energy and water fluxes.
The present study provides an overview of current implementations of canopy radiation schemes in a couple of state-of-the-art DGVMs and assesses their accuracy in simulating canopy absorption and reflection for a variety of different surface conditions. Systematic deviations in surface albedo and fractions of absorbed photosynthetic active radiation (faPAR) are identified and potential impacts are assessed.
The results show clear deviations for both, absorbed and reflected, surface solar radiation fluxes. FaPAR is typically underestimated, which results in an underestimation of gross primary productivity (GPP) for the investigated cases. The deviation can be as large as 25% in extreme cases. Deviations in surface albedo range between −0.15 ≤ Δα ≤ 0.36, with a slight positive bias on the order of Δα ≈ 0.04. Potential radiative forcing caused by albedo deviations is estimated at −1.25 ≤ RF ≤ −0.8 (W m−2), caused by neglect of the diurnal cycle of surface albedo.
The present study is the first one that provides an assessment of canopy RT schemes in different currently used DGVMs together with an assessment of the potential impact of the identified deviations. The paper illustrates that there is a general need to improve the canopy radiation schemes in DGVMs and provides different perspectives for their improvement
Recombination dramatically speeds up evolution of finite populations
We study the role of recombination, as practiced by genetically-competent
bacteria, in speeding up Darwinian evolution. This is done by adding a new
process to a previously-studied Markov model of evolution on a smooth fitness
landscape; this new process allows alleles to be exchanged with those in the
surrounding medium. Our results, both numerical and analytic, indicate that for
a wide range of intermediate population sizes, recombination dramatically
speeds up the evolutionary advance
New insights in the scope of heterogeneously catalyzed epoxidation of 1,3-butadiene to 3,4-epoxy-1-butene
Microscopic dynamics of thin hard rods
Based on the collision rules for hard needles we derive a hydrodynamic
equation that determines the coupled translational and rotational dynamics of a
tagged thin rod in an ensemble of identical rods. Specifically, based on a
Pseudo-Liouville operator for binary collisions between rods, the Mori-Zwanzig
projection formalism is used to derive a continued fraction representation for
the correlation function of the tagged particle's density, specifying its
position and orientation. Truncation of the continued fraction gives rise to a
generalised Enskog equation, which can be compared to the phenomenological
Perrin equation for anisotropic diffusion. Only for sufficiently large density
do we observe anisotropic diffusion, as indicated by an anisotropic mean square
displacement, growing linearly with time. For lower densities, the Perrin
equation is shown to be an insufficient hydrodynamic description for hard
needles interacting via binary collisions. We compare our results to
simulations and find excellent quantitative agreement for low densities and
qualtitative agreement for higher densities.Comment: 21 pages, 6 figures, v2: clarifications and improved readabilit
Further notes on the capture of a Carcharhinus leucas, in a northeastern Atlantic oceanic insular shelf, the Azores archipelago, Portugal
Copyright © 2006 Société Française d’Ichtyologie.In March 1993, a specimen of Carcharhinus leucas was captured by fishermen on the south coast of Te rceira Island, the Azores Archipelago. Its head was recovered and its jaws were preserved. This is the first capture of this species on an oceanic insular shelf in the Atlantic. The distribution of C. leucas in this ocean is commented.RÉSUMÉ: Note complémentaire sur la capture de Carcharhinus leucas (Carcharhinidae) dans une île océanique de l’Atlantique nord-est, l’archipel des Açores, Portugal. En mars 1993, un spécimen de Carcharhinus leucas a été capturé par des pêcheurs sur la côte sud de l’île Terceira dans l’archipel desAçores. Sa tête a été récupérée et ses mâchoires préservées. Il s’agit de la première capture de cette espèce sur une plateforme océanique de l’Atlantique. La distribution de C. leucas dans cet océan est commentée
Cosmological stretching of perturbations on a cosmic string
We investigate the effects of cosmological expansion on the spectrum of
small-scale structure on a cosmic string. We simulate the evolution of a string
with two modes that differ in wavelength by one order of magnitude. Once the
short mode is inside the horizon, we find that its physical amplitude remains
unchanged, in spite of the fact that its comoving wavelength decreases as the
longer mode enters the horizon. Thus the ratio of amplitude to wavelength for
the short mode becomes larger than it would be in the absence of the long mode.Comment: 11 pages, 5 postscript figure
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