6,683 research outputs found
ERBE and AVHRR Cirrus cloud fire study
Understanding the impact of cirrus clouds on the global radiation budget is essential to determining the role of clouds in the process of climate change. The ongoing Earth Radiation Budget Experiment (ERBE) is charged with measuring the global radiation balance at the top of the atmosphere. The International Satellite Cloud Climatology Project (ISCCP) is measuring global cloud amounts and properties over a time frame similar to ERBE. Specific cloud properties are absent from the ERBE program, while ISCCP lacks the broadband radiances necessary to determine the total radiation fields. Together, results from these two global programs have the potential for improving the knowledge of the relationship between cirrus clouds and the Earth radiation balance. The First ISCCP Regional Experiment (FIRE), especially its cirrus Intensive Field Observations (IFO), provides opportunities for studying radiation measurements from the ERBE taken over areas with known cirrus cloud properties. Satellite measurements taken during the IFO are used to determine the broadband radiation fields over cirrus clouds and to examine the relationship between narrowband and broadband radiances over various known scenes. The latter constitutes the link between the ERBE and the ISCCP
Physical Constraints in Grassland Ecosystems
Key points
1. Grassland system management must account adequately for biophysical and biochemical processes.
2. Amenity turf, especially sports turf, provides an excellent case study on how biology and physics interact to impact on the functioning of a grass ecosystem.
3. Microorganisms produce hydrophobic compounds that act to decrease water ingress and alter the function of the soil-grass ecosystem
New attempts to understand nanodiamond stardust
We report on a concerted effort aimed at understanding the origin and history
of the pre-solar nanodiamonds in meteorites including the astrophysical sources
of the observed isotopic abundance signatures. This includes measurement of
light elements by secondary ion mass spectrometry (SIMS), analysis of
additional heavy trace elements by accelerator mass spectrometry (AMS) and
dynamic calculations of r-process nucleosynthesis with updated nuclear
properties. Results obtained indicate: a) there is no evidence for the former
presence of now extinct 26Al and 44Ti in our diamond samples other than what
can be attributed to silicon carbide and other "impurities"; this does not
offer support for a supernova (SN) origin but neither does it negate it; b)
analysis by AMS of platinum in "bulk diamond" yields an overabundance of r-only
198Pt that at face value seems more consistent with the neutron burst than with
the separation model for the origin of heavy trace elements in the diamonds,
although this conclusion is not firm given analytical uncertainties; c) if the
Xe-H pattern was established by an unadulterated r-process, it must have been a
strong variant of the main r-process, which possibly could also account for the
new observations in platinum.Comment: Workshop on Astronomy with Radioactvities VII; Publications of the
Astronomical Society of Australia, accepte
Fermion Quasi-Spherical Harmonics
Spherical Harmonics, , are derived and presented (in a
Table) for half-odd-integer values of and . These functions are
eigenfunctions of and written as differential operators in the
spherical-polar angles, and . The Fermion Spherical Harmonics
are a new, scalar and angular-coordinate-dependent representation of fermion
spin angular momentum. They have symmetry in the angle , and hence
are not single-valued functions on the Euclidean unit sphere; they are
double-valued functions on the sphere, or alternatively are interpreted as
having a double-sphere as their domain.Comment: 16 pages, 2 Tables. Submitted to J.Phys.
Gas Component Transport Across the Soil-Atmosphere Interface for Gases of Different Density: Experiments and Modeling
We investigate the influence of near-surface wind conditions on subsurface gas transport and on soil-atmosphere gas exchange for gases of different density. Results of a sand tank experiment are supported by a numerical investigation with a fully coupled porous medium-free flow model, which accounts for wind turbulence. The experiment consists of a two-dimensional bench-scale soil tank containing homogeneous sand and an overlying wind tunnel. A point source was installed at the bottom of the tank. Gas concentrations were measured at multiple horizontal and vertical locations. Tested conditions include four wind velocities (0.2/1.0/2.0/2.7 m/s), three different gases (helium: light, nitrogen: neutral, and carbon dioxide: heavy), and two transport cases (1: steady-state gas supply from the point source; 2: transport under decreasing concentration gradient, subsequent to termination of gas supply). The model was used to assess flow patterns and gas fluxes across the soil surface. Results demonstrate that flow and transport in the vicinity of the surface are strongly coupled to the overlying wind field. An increase in wind velocity accelerates soil-atmosphere gas exchange. This is due to the effect of the wind profile on soil surface concentrations and due to wind-induced advection, which causes subsurface horizontal transport. The presence of gases with pronounced density difference to air adds additional complexity to the transport through the wind-affected soil layers. Wind impact differs between tested gases. Observed transport is multidimensional and shows that heavy as well as light gases cannot be treated as inert tracers, which applies to many gases in environmental studies. © 2020. The Authors
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