An Analytical Model for the Distribution of CO2 Sources and Sinks, Fluxes, and Mean Concentration Within the Roughness Sub-Layer     

Mario B. Siqueira  Gabriel G. Katul 《Boundary-Layer Meteorology》2010,135(1):31-50

A one-dimensional analytical model that predicts foliage CO₂ uptake rates, turbulent fluxes, and mean concentration throughout the roughness sub-layer (RSL), a layer that extends from the ground surface up to 5h, where h is canopy height, is proposed. The model combines the mean continuity equation for CO₂ with first-order closure principles for turbulent fluxes and simplified physiological and radiative transfer schemes for foliage uptake. This combination results in a second-order ordinary differential equation in which soil respiration (R) and CO₂ concentration well above the RSL are imposed as lower and upper boundary conditions, respectively. An inverse version of the model was tested against datasets from two contrasting ecosystems: a tropical forest (h = 40m) and a managed irrigated rice canopy (h = 0.7m), with good agreement noted between modelled and measured mean CO₂ concentration profiles within the entire RSL. Sensitivity analysis on the model parameters revealed a plausible scaling regime between them and a dimensionless parameter defined by the ratio between external (R) and internal (stomatal conductance) characteristics controlling the CO₂ exchange process. The model can be used to infer the thickness of the RSL for CO₂ exchange, the inequality in zero-plane displacement between CO₂ and momentum, and its consequences on modelled CO₂ fluxes. A simplified version of the solution is well suited for being incorporated into large-scale climate models. Furthermore, the model framework here can be used to a priori estimate relative contributions from the soil surface and the atmosphere to canopy-air CO₂ concentration, thereby making it synergetic to stable isotopes studies.  相似文献   

Discussion of simple stability criteria for stars with central helium burning     

M. Gabriel  S. Refsdal  H. Ritter 《Astrophysics and Space Science》1975,36(2):439-450

The validity of simple stability criteria for stars with central He-burning used in earlier papers is investigated. The determinant of secular stability for σ=0 is related to quantities defined as far as possible at the surface of the He-core and at the bottom of the envelope. This relation is used to discuss the validity of two intuitive criteria for secular stability.  相似文献   

Opal-associated particulate phosphorus: Implications for the marine P cycle     

Jennifer C. Latimer  Gabriel M. Filippelli  Derrick R. Newkirk 《Geochimica et cosmochimica acta》2006,70(15):3843-3854

Previous attempts to evaluate ocean P mass balance and residence time have utilized sequential extraction techniques to isolate and analyze P associated with Fe and Mn oxides and oxyhydroxides, authigenic minerals, detrital, and organic phases. However, in many oceanographic settings, diatoms are the primary producers, and the traditional sequential extraction protocol does not result in complete dissolution of diatom frustules and may not liberate all of the opal intrinsic P associated with the frustules themselves. By adding an opal dissolution step to the end of the extraction protocol, additional P was liberated from the sediments, suggesting that there is an opal-associated P fraction that likely contributes to total reactive P concentrations. In opal-rich sediments, the opal-associated P fraction averages as much as 50-60% of extractable P, and total reactive P concentrations are often more than double when the opal-associated P fraction is included. The presence of opal-intrinsic P potentially has significant implications for ocean P mass balance and residence time of P in the oceans. For example, P burial has possibly been underestimated in settings dominated by diatoms. Additionally, consideration of a significant sedimentary opal-P component suggests that the residence time of P in the oceans may be even shorter than currently suspected.  相似文献   

Alpine lake sediment records of the impact of glaciation and climate change on the biogeochemical cycling of soil nutrients     

Gabriel M. Filippelli  Brian Menounos  A.J. Timothy Jull 《Quaternary Research》2006,66(1):158-166

Lake sediment cores from the Coast Mountains of British Columbia were analyzed using chemical sequential extractions to partition the dominant geochemical fractions of phosphorus (P). The P fractions include mineral P (the original source of bioavailable P), occluded P (bound to soil oxides), and organic P (remains of organic matter). By comparing P fractions of soil and recent lake sediment samples, these fractions are shown to be a valid proxy for landscape-scale nutrient status. Changes in soil development for an alpine watershed (Lower Joffre Lake) are inferred from the P fractions in the basin's outlet lake sediments. Glacially sourced mineral P dominates at the base of the core, but several rapid shifts in P geochemistry are evident in the first ∼3000 yr of the record. The latter indicates an interval of early and rapid soil nutrient maturation from ∼9600 to 8500 cal yr BP and a significant influx of slope-derived material into Lower Joffre Lake. A substantial increase in mineral P occurs at ca. 8200 cal yr BP, consistent with the cold event in the vicinity of the North Atlantic at that time. The more recent record reveals a continual increase in the proportion of mineral P from glacial sources to the lake, indicating a trend toward cooler conditions in the Coast Mountains.  相似文献   

Evaluation of Gravity Anomalies Directly from Satellite Observations     

Gabriel Obenson 《Geophysical Journal International》1972,30(1):69-83

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Biogenic debris from the pelagic tunicate, Oikopleura dioica, and its role in the vertical transport of a transuranium element     

Gabriel Gorsky  Nicholas S. Fisher  Scott W. Fowler 《Estuarine, Coastal and Shelf Science》1984,18(1):13-23

The accumulation and retention of ²⁴¹Am by the pelagic tunicate Oikopleura dioica were examined using laboratory cultures and radiotracer methodology. Animals (i.e., trunks and tails) and discarded empty houses accumulated Am from seawater, giving volume/volume concentration factors of 59±8 and 10±1, respectively. The half-time for retention of Am in empty labelled houses transferred to non-contaminated seawater was 29 h; the retention half-time of Am in houses discarded by larvaceans feeding on Am-labelled diatoms was 219 h; the half-time of Am in fecal pellets produced by animals feeding on a monospecific diet of diatoms was 134 h, and 247 h for fecal pellets from animals fed a mixed diet. Approximately 30% of filtered cells remained in houses after the houses were discarded. Sinking rates of discarded houses and fecal pellets were found to vary with temperature and size, ranging from 26–157 m day^?1 (house) and from 25–166 m day^?1 (fecal pellets). The ubiquity and abundance of appendicularians, together with their prodigious production of houses (e.g., 10±2 houses day^?1 at 17°C for each experimental animal) point to their potential significance in the vertical transport of Am, and probably other reactive metals, to intermediate depths in the ocean.  相似文献   

Period and phase of the 88-year solar cycle and the Maunder minimum: Evidence for a chaotic sun     

J. Feynman  Stephen B. Gabriel 《Solar physics》1990,127(2):393-403

The problem of whether the solar dynamo is quasi-periodic or chaotic is addressed by examining 1500 years of sunspot, geomagnetic and auroral activity cycles. We find sub-harmonics of the fundamental solar cycle period during the years preceding the Maunder minimum and loss of phase of the subharmonic on emergence from it. These phenomena are indicative of chaos. They indicate that the solar dynamo is chaotic and is operating in a region close to the transition between period doubling and chaos. Since Maunder type minima reoccur irregularly for millennia, it appears that the Sun remains close to this transition to and from chaos. We postulate this as a universal characteristic of solar type stars caused by feedback in the dynamo number.  相似文献   

Measurements on the Lyman alpha corona     

A. H. Gabriel 《Solar physics》1971,21(2):392-400

As a result of a collaborative rocket experiment carried out during the solar eclipse on 7 March, 1970, measurements have been made of the brightness of Lyman from the corona, at heights between 5 × 10⁴ and 5 × 10⁵ km above the limb. The emission is shown to occur primarily through the resonance scattering of chromospheric Lyman from the residual neutral hydrogen in the corona. Both the absolute value and radial fall-off of the brightness agree well with calculations based on solar density models. The Lyman emission has similar variations around the limb to the white light corona, showing in particular an equatorial enhancement.  相似文献   

High resolution stellar spectroscopy with VBT echelle spectrometer     

N. Kameswara Rao  S. Sriram  K. Jayakumar  F. Gabriel 《Journal of Astrophysics and Astronomy》2005,26(2-3):331-338

The optical design and performance of the recently commissioned fiber fed echelle spectrometer of 2.34 meter Vainu Bappu Telescope are described. The use of it for stellar spectroscopic studies is discussed.  相似文献   

A comparison between two simultaneous sets of current measurements in the Straint of Juan de Fuca     

Gabriel Godin 《Estuarine, Coastal and Shelf Science》1984,19(4):451-461

A comparison is made between a set of current measurements in a section across the Strait of Juan de Fuca and those recorded further upstream at Race Rocks at a single depth. No outstanding common qualitative features are noted. Cross spectra reveal a low correlation for the subtidal current and suggest an intensification of the diurnal modulation of the flow at Race Rocks. The high correlation in the tidal bands allows to calculate this portion of the tidal current at Race Rocks which is coherent with the one sensed across the section.  相似文献