279 research outputs found
Estimates of fire emissions from an active deforestation region in the southern Amazon based on satellite data and biogeochemical modelling
Tropical deforestation contributes to the build-up of atmospheric carbon dioxide in the atmosphere. Within the deforestation process, fire is frequently used to eliminate biomass in preparation for agricultural use. Quantifying these deforestation-induced fire emissions represents a challenge, and current estimates are only available at coarse spatial resolution with large uncertainty. Here we developed a biogeochemical model using remote sensing observations of plant productivity, fire activity, and deforestation rates to estimate emissions for the Brazilian state of Mato Grosso during 2001–2005. Our model of DEforestation CArbon Fluxes (DECAF) runs at 250-m spatial resolution with a monthly time step to capture spatial and temporal heterogeneity in fire dynamics in our study area within the ''arc of deforestation'', the southern and eastern fringe of the Amazon tropical forest where agricultural expansion is most concentrated. Fire emissions estimates from our modelling framework were on average 90 Tg C year<sup>&minus;1</sup>, mostly stemming from fires associated with deforestation (74%) with smaller contributions from fires from conversions of Cerrado or pastures to cropland (19%) and pasture fires (7%). In terms of carbon dynamics, about 80% of the aboveground living biomass and litter was combusted when forests were converted to pasture, and 89% when converted to cropland because of the highly mechanized nature of the deforestation process in Mato Grosso. The trajectory of land use change from forest to other land uses often takes more than one year, and part of the biomass that was not burned in the dry season following deforestation burned in consecutive years. This led to a partial decoupling of annual deforestation rates and fire emissions, and lowered interannual variability in fire emissions. Interannual variability in the region was somewhat dampened as well because annual emissions from fires following deforestation and from maintenance fires did not covary, although the effect was small due to the minor contribution of maintenance fires. Our results demonstrate how the DECAF model can be used to model deforestation fire emissions at relatively high spatial and temporal resolutions. Detailed model output is suitable for policy applications concerned with annual emissions estimates distributed among post-clearing land uses and science applications in combination with atmospheric emissions modelling to provide constrained global deforestation fire emissions estimates. DECAF currently estimates emissions from fire; future efforts can incorporate other aspects of net carbon emissions from deforestation including soil respiration and regrowth
Global fire emissions and the contribution of deforestation, savanna, forest, agricultural, and peat fires (1997-2009)
New burned area datasets and top-down constraints from atmospheric
concentration measurements of pyrogenic gases have decreased the large
uncertainty in fire emissions estimates. However, significant gaps remain in
our understanding of the contribution of deforestation, savanna, forest,
agricultural waste, and peat fires to total global fire emissions. Here we
used a revised version of the Carnegie-Ames-Stanford-Approach (CASA)
biogeochemical model and improved satellite-derived estimates of area
burned, fire activity, and plant productivity to calculate fire emissions
for the 1997–2009 period on a 0.5° spatial resolution with a monthly
time step. For November 2000 onwards, estimates were based on burned area,
active fire detections, and plant productivity from the MODerate resolution
Imaging Spectroradiometer (MODIS) sensor. For the partitioning we focused on
the MODIS era. We used maps of burned area derived from the Tropical Rainfall
Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS) and Along-Track
Scanning Radiometer (ATSR) active fire data prior to MODIS (1997–2000) and
estimates of plant productivity derived from Advanced Very High Resolution
Radiometer (AVHRR) observations during the same period. Average global fire
carbon emissions according to this version 3 of the Global Fire Emissions
Database (GFED3) were 2.0 Pg C year<sup>−1</sup> with significant interannual
variability during 1997–2001 (2.8 Pg C year<sup>−1</sup> in 1998 and
1.6 Pg C year<sup>−1</sup> in 2001). Globally, emissions during 2002–2007 were relatively
constant (around 2.1 Pg C year<sup>−1</sup>) before declining in 2008
(1.7 Pg C year<sup>−1</sup>) and 2009 (1.5 Pg C year<sup>−1</sup>) partly due to lower deforestation
fire emissions in South America and tropical Asia. On a regional basis,
emissions were highly variable during 2002–2007 (e.g., boreal Asia, South
America, and Indonesia), but these regional differences canceled out at a
global level. During the MODIS era (2001–2009), most carbon emissions were
from fires in grasslands and savannas (44%) with smaller contributions
from tropical deforestation and degradation fires (20%), woodland fires
(mostly confined to the tropics, 16%), forest fires (mostly in the
extratropics, 15%), agricultural waste burning (3%), and tropical peat
fires (3%). The contribution from agricultural waste fires was likely a
lower bound because our approach for measuring burned area could not detect
all of these relatively small fires. Total carbon emissions were on average
13% lower than in our previous (GFED2) work. For reduced trace gases such
as CO and CH<sub>4</sub>, deforestation, degradation, and peat fires were more
important contributors because of higher emissions of reduced trace gases
per unit carbon combusted compared to savanna fires. Carbon emissions from
tropical deforestation, degradation, and peatland fires were on average 0.5 Pg C year<sup>−1</sup>.
The carbon emissions from these fires may not be balanced
by regrowth following fire. Our results provide the first global assessment
of the contribution of different sources to total global fire emissions for
the past decade, and supply the community with an improved 13-year fire
emissions time series
Near-Threshold eta Meson Production in Proton-Proton Collisions
The production of eta mesons has been measured in the proton-proton
interaction close to the reaction threshold using the COSY-11 internal facility
at the cooler synchrotron COSY. Total cross sections were determined for eight
different excess energies in the range from 0.5 MeV to 5.4 MeV. The energy
dependence of the total cross section is well described by the available
phase-space volume weighted by FSI factors for the proton-proton and proton-eta
pairs.Comment: 9 pages, 1 table, 5 figure
S-wave eta'-proton FSI; phenomenological analysis of near-threshold production of pi0, eta, and eta' mesons in proton-proton collisions
We describe a novel technique for comparing total cross sections for the
reactions pp --> pp pi(0), pp --> pp eta, and pp --> pp eta' close to
threshold. The initial and final state proton-proton interactions are factored
out of the total cross section, and the dependence of this reduced cross
section on the volume of phase space is discussed. Different models of the
proton-proton interaction are compared. We argue that the scattering length of
the S-wave eta'-proton interaction is of the order of 0.1 fm.Comment: 10 pages, 5 figure
Near Threshold K+K- Meson-Pair Production in Proton-Proton Collisions
The near threshold total cross section and angular distributions of K+K- pair
production via the reaction pp --> ppK+K- have been studied at an excess energy
of Q = 17 MeV using the COSY-11 facility at the cooler synchrotron COSY. The
obtained cross section as well as an upper limit at an excess energy of Q = 3
MeV represent the first measurements on the K+K- production in the region of
small excess energies where production via the channel pp --> pp Phi --> ppK+K-
is energetically forbidden. The possible influence of a resonant production via
intermediate scalar states f0(980) and a0(980) is discussed.Comment: 8 pages, 6 figures, replaced with revised version, accepted for
publication in Phys. Lett.
Nonlinear effects in resonant layers in solar and space plasmas
The present paper reviews recent advances in the theory of nonlinear driven
magnetohydrodynamic (MHD) waves in slow and Alfven resonant layers. Simple
estimations show that in the vicinity of resonant positions the amplitude of
variables can grow over the threshold where linear descriptions are valid.
Using the method of matched asymptotic expansions, governing equations of
dynamics inside the dissipative layer and jump conditions across the
dissipative layers are derived. These relations are essential when studying the
efficiency of resonant absorption. Nonlinearity in dissipative layers can
generate new effects, such as mean flows, which can have serious implications
on the stability and efficiency of the resonance
Energy Dependence of the Near-Threshold Total Cross-Section for the pp --> pp eta' Reaction
Total cross sections for the pp --> pp eta' reaction have been measured in
the excess energy range from Q = 1.53 MeV to Q = 23.64 MeV. The experiment has
been performed at the internal installation COSY-11 using a stochastically
cooled proton beam of the COoler SYnchrotron COSY and a hydrogen cluster
target. The determined energy dependence of the total cross section weakens the
hypothesis of the S-wave repulsive interaction between the eta' meson and the
proton. New data agree well with predictions based on the phase-space
distribution modified by the proton-proton final-state-interaction (FSI) only.Comment: 12 pages, 1 table, 4 figure
Living on the Edge: Increasing Patch Size Enhances the Resilience and Community Development of a Restored Salt Marsh
Foundation species regulate communities by reducing environmental stress and providing habitat for other species. Successful restoration of biogenic habitats often depends on restoring foundation species at appropriate spatial scales within a suitable range of environmental conditions. An improved understanding of the relationship between restoration scale and environmental conditions has the potential to improve restoration outcomes for many biogenic habitats. Here, we identified and tested whether inundation/exposure stress and spatial scale (patch size) can interactively determine (1) survival and growth of a foundation species, Spartina alterniflora and (2) recruitment of supported fauna. We planted S. alterniflora and artificial mimics in large and small patches at elevations above and below local mean sea level (LMSL) and monitored plant survivorship and production, as well as faunal recruitment. In the first growing season, S. alterniflora plant survivorship and stem densities were greater above LMSL than below LMSL regardless of patch size, while stem height was greatest in small patches below LMSL. By the third growing season, S. alterniflora patch expansion was greater above LMSL than below LMSL, while stem densities were higher in large patches than small patches, regardless of location relative to LMSL. Unlike S. alterniflora, which was more productive above LMSL, sessile marine biota recruitment to mimic plants was higher in patches below LMSL than above LMSL. Our results highlight an ecological tradeoff at ~LMSL between foundation species restoration and faunal recruitment. Increasing patch size as inundation increases may offset this tradeoff and enhance resilience of restored marshes to sea-level rise
Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling
This review paper outlines background information and covers recent advances
made via the analysis of spectra and images of prominence plasma and the
increased sophistication of non-LTE (ie when there is a departure from Local
Thermodynamic Equilibrium) radiative transfer models. We first describe the
spectral inversion techniques that have been used to infer the plasma
parameters important for the general properties of the prominence plasma in
both its cool core and the hotter prominence-corona transition region. We also
review studies devoted to the observation of bulk motions of the prominence
plasma and to the determination of prominence mass. However, a simple inversion
of spectroscopic data usually fails when the lines become optically thick at
certain wavelengths. Therefore, complex non-LTE models become necessary. We
thus present the basics of non-LTE radiative transfer theory and the associated
multi-level radiative transfer problems. The main results of one- and
two-dimensional models of the prominences and their fine-structures are
presented. We then discuss the energy balance in various prominence models.
Finally, we outline the outstanding observational and theoretical questions,
and the directions for future progress in our understanding of solar
prominences.Comment: 96 pages, 37 figures, Space Science Reviews. Some figures may have a
better resolution in the published version. New version reflects minor
changes brought after proof editin
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