321 research outputs found
Mapping of water-related ecosystem services in the uMngeni catchment using a daily time-step hydrological model for prioritisation of ecological infrastructure investment – Part 1: Context and modelling approach
South Africa is a semi-arid country which frequently faces water shortages, and experienced a severe drought in the 2016 and 2017 rainfall seasons. Government is under pressure to continue to deliver clean water to the growing population at a high assurance of supply. Studies now show that the delivery of water may be sustained not only through built infrastructure such as dams and pipelines, but also through investment in ecological infrastructure (EI). A daily time-step hydrological model was used to map areas which should be prioritised for protection or rehabilitation to sustain the delivery of water-related ecosystem services within the uMngeni catchment. We focused on three water-related ecosystem services, i.e.: water supply, sustained baseflow, erosion control/avoidance of excessive sediment losses. The two key types of degradation were modelled, namely, overgrazing and the invasion of upland areas by Black Wattle (Acacia mearnsii). This, Part 1 of a paper in 2 parts, provides a discussion on the role of EI in delivering water-related ecosystem services, describes the motivation for the study, and the methods used in modelling and mapping the catchment. The results of this modelling exercise are presented in Part 2, which also explores and illustrates the potential hydrological benefits of rehabilitation and protection of EI in the uMngeni Catchment.Keywords: water, ecosystem services, hydrological modelling, ecological infrastructure, water securit
An Outer Planet Beyond Pluto and Origin of the Trans-Neptunian Belt Architecture
Trans-Neptunian objects (TNOs) are remnants of a collisionally and
dynamically evolved planetesimal disk in the outer solar system. This complex
structure, known as the trans-Neptunian belt (or Edgeworth-Kuiper belt), can
reveal important clues about disk properties, planet formation, and other
evolutionary processes. In contrast to the predictions of accretion theory,
TNOs exhibit surprisingly large eccentricities, e, and inclinations, i, which
can be grouped into distinct dynamical classes. Several models have addressed
the origin and orbital evolution of TNOs, but none have reproduced detailed
observations, e.g., all dynamical classes and peculiar objects, or provided
insightful predictions. Based on extensive simulations of planetesimal disks
with the presence of the four giant planets and massive planetesimals, we
propose that the orbital history of an outer planet with tenths of Earth's mass
can explain the trans-Neptunian belt orbital structure. This massive body was
likely scattered by one of the giant planets, which then stirred the primordial
planetesimal disk to the levels observed at 40-50 AU and truncated it at about
48 AU before planet migration. The outer planet later acquired an inclined
stable orbit (>100 AU; 20-40 deg) because of a resonant interaction with
Neptune (an r:1 or r:2 resonance possibly coupled with the Kozai mechanism),
guaranteeing the stability of the trans-Neptunian belt. Our model consistently
reproduces the main features of each dynamical class with unprecedented detail;
it also satisfies other constraints such as the current small total mass of the
trans-Neptunian belt and Neptune's current orbit at 30.1 AU. We also provide
observationally testable predictions.Comment: 80 pages, 24 figures, 7 tables. Accepted for publication in The
Astronomical Journa
Dynamical determination of the Kuiper Belt's mass from motions of the inner planets of the Solar System
In this paper we dynamically determine the mass of the Kuiper Belt Objects by
exploiting the latest observational determinations of the orbital motions of
the inner planets of the Solar System. Our result, in units of terrestrial
masses, is 0.033 +/- 0.115 by modelling the Classical Kuiper Belt Objects as an
ecliptic ring of finite thickness. A two-rings model yields for the Resonant
Kuiper Belt Objects a value of 0.018 +/- 0.063. Such figures are consistent
with recent determinations obtained with ground and space-based optical
techniques. Some implications for precise tests of Einsteinian and
post-Einsteinian gravity are briefly discussed.Comment: LaTex, 12 pages, no figures, 4 tables, 27 references. One reference
added. To appear in Monthly Notices of the Royal Astronomical Societ
Comet 17P/Holmes in Outburst: The Near Infrared Spectrum
Jupiter family comet 17P/Holmes underwent a remarkable outburst on UT 2007
Oct. 24, in which the integrated brightness abruptly increased by about a
factor of a million.We obtained near infrared (0.8 - 4.2 micron) spectra of
17P/Holmes on UT 2007 Oct. 27, 28 and 31, using the 3.0-m NASA Infrared
Telescope Facility (IRTF) atop Mauna Kea. Two broad absorption bands were found
in the reflectance spectra with centers (at 2 micron and 3 micron,
respectively) and overall shapes consistent with the presence of water ice
grains in the coma. Synthetic mixing models of these bands suggest an origin in
cold ice grains of micron size. Curiously, though, the expected 1.5 micron band
of water ice was not detected in our data, an observation for which we have no
explanation. Simultaneously, excess thermal emission in the spectra at
wavelengths beyond 3.2 micron has a color temperature of 360 +/- 40 K
(corresponding to a superheat factor of ~ 2.0 +/- 0.2 at 2.45 AU). This is too
hot for these grains to be icy. The detection of both water ice spectral
features and short-wavelength thermal emission suggests that the coma of
17P/Holmes has two components (hot, refractory dust and cold ice grains) which
are not in thermal contact. A similarity to grains ejected into the coma of
9P/Tempel 1 by the Deep Impact spacecraft is noted.Comment: 27 pages, 11 figures, accepted for publication in A
An upper limit for the water outgassing rate of the main-belt comet 176P/LINEAR observed with Herschel/HIFI
176P/LINEAR is a member of the new cometary class known as main-belt comets
(MBCs). It displayed cometary activity shortly during its 2005 perihelion
passage that may be driven by the sublimation of sub-surface ices. We have
therefore searched for emission of the H2O 110-101 ground state rotational line
at 557 GHz toward 176P/LINEAR with the Heterodyne Instrument for the Far
Infrared (HIFI) on board the Herschel Space Observatory on UT 8.78 August 2011,
about 40 days after its most recent perihelion passage, when the object was at
a heliocentric distance of 2.58 AU. No H2O line emission was detected in our
observations, from which we derive sensitive 3-sigma upper limits for the water
production rate and column density of < 4e25 molec/s and of < 3e10 cm^{-2},
respectively. From the peak brightness measured during the object's active
period in 2005, this upper limit is lower than predicted by the relation
between production rates and visual magnitudes observed for a sample of comets
by Jorda et al. (2008) at this heliocentric distance. Thus, 176P/LINEAR was
likely less active at the time of our observation than during its previous
perihelion passage. The retrieved upper limit is lower than most values derived
for the H2O production rate from the spectroscopic search for CN emission in
MBCs.Comment: 5 pages, 2 figures. Minor changes to match published versio
Observational detection of eclipses of J5 Amalthea by the Galilean satellites
We carried out observations of the small jovian satellite Amalthea (J5) as it
was being eclipsed by the Galilean satellites near the 2009 equinox of Jupiter
in order to apply the technique of mutual event photometry to the astrometric
determination of this satellite's position. The observations were carried out
during the period 06/2009-09/2009 from the island of Maui, Hawaii and Siding
Spring, Australia with the 2m Faulkes Telescopes North and South respectively.
We observed in the near-infrared part of the spectrum using a PanStarrs-Z
filter with Jupiter near the edge of the field in order to mitigate against the
glare from the planet. Frames were acquired at rates >1/min during eclipse
times predicted using recent JPL ephemerides for the satellites. Following
subtraction of the sky background from these frames, differential aperture
photometry was carried out on Amalthea and a nearby field star. We have
obtained three lightcurves which show a clear drop in the flux from Amalthea,
indicating that an eclipse took place as predicted. These were model-fitted to
yield best estimates of the time of maximum flux drop and the impact parameter.
These are consistent with Amalthea's ephemeris but indicate that Amalthea is
slightly ahead of, and closer to Jupiter than, its predicted position by
approximately half the ephemeris uncertainty in these directions. We argue that
a ground-based campaign of higher-cadence photometry accurate at the 5% level
or better during the next season of eclipses in 2014-15 should yield positions
to within 0".5 and affect a corresponding improvement in Amalthea's ephemeris.Comment: Published in A&A in 2010; 6 pages, 2 figures, 3 table
Methane, ammonia, and their irradiation products at the surface of an intermediate-size KBO? A portrait of Plutino (90482) Orcus
Orcus is an intermediate-size 1000km-scale Kuiper Belt Object in 3:2
mean-motion resonance with Neptune, in an orbit very similar to that of Pluto.
We present visible and near-infrared photometry and spectroscopy obtained with
the Keck 10m-telescope and the Gemini 8m-telescope . We confirm the unambiguous
detection of crystalline water ice as well as absorption in the 2.2\mu m
region. Both in the visible and near-infrared Orcus' spectral properties appear
to be homogeneous over time (and probably rotation) at the resolution
available. From Hapke radiative transfer models involving intimate mixtures of
various ices we find for the first time that ammonium (NH+4) and traces of
ethane (C2 H6), which are most probably solar irradiation products of ammonia
and methane, and a mixture of methane and ammonia (diluted or not) are the best
candidates to improve the description of the data with respect to a simple
water ice mixture (Haumea type surface). The possible more subtle structure of
the 2.2\mu m band(s) should be investigated thoroughly in the future for Orcus
and other intermediate size Plutinos to better understand the methane and
ammonia chemistry at work, if any. We investigated the thermal history of Orcus
with a new 3D thermal evolution model. Simulations over 4.5 x109 yrs with an
input 10% porosity, bulk composition of 23% amorphous water ice and 77% dust,
and cold accretion show that even with the action of long-lived radiogenic
elements only, Orcus should have a melted core and most probably suffered a
cryovolcanic event in its history which brought large amounts of crystalline
ice to the surface. The presence of ammonia in the interior would strengthen
the melting process. The crystalline water ice possibly brought to the surface
by a past cryovolcanic event sbe detectable after several billion years despite
the irradiation eects, as demonstrated by recent laboratory experiments.Comment: 15 pages, 9 figure
P/2010A2 LINEAR - I: An impact in the Asteroid Main Belt
Comet P/2010A2 LINEAR is a good candidate for membership with the Main Belt
Comet family. It was observed with several telescopes (ESO NTT, La Silla;
Gemini North, Mauna Kea; UH 2.2m, Mauna Kea) from 14 Jan. until 19 Feb. 2010 in
order to characterize and monitor it and its very unusual dust tail, which
appears almost fully detached from the nucleus; the head of the tail includes
two narrow arcs forming a cross. The immediate surroundings of the nucleus were
found dust-free, which allowed an estimate of the nucleus radius of 80-90m. A
model of the thermal evolution indicates that such a small nucleus could not
maintain any ice content for more than a few million years on its current
orbit, ruling out ice sublimation dust ejection mechanism. Rotational spin-up
and electrostatic dust levitations were also rejected, leaving an impact with a
smaller body as the favoured hypothesis, and ruling out the cometary nature of
the object.
The impact is further supported by the analysis of the tail structure.
Finston-Probstein dynamical dust modelling indicates the tail was produced by a
single burst of dust emission. More advanced models, independently indicate
that this burst populated a hollow cone with a half-opening angle alpha~40degr
and with an ejection velocity v_max ~ 0.2m/s, where the small dust grains fill
the observed tail, while the arcs are foreshortened sections of the burst cone.
The dust grains in the tail are measured to have radii between a=1-20mm, with a
differential size distribution proportional to a^(-3.44 +/- 0.08). The dust
contained in the tail is estimated to at least 8x10^8kg, which would form a
sphere of 40m radius. Analysing these results in the framework of crater
physics, we conclude that a gravity-controlled crater would have grown up to
~100m radius, i.e. comparable to the size of the body. The non-disruption of
the body suggest this was an oblique impact.Comment: 15 pages, 11 figures, in pres
TNOs are Cool: A survey of the trans-Neptunian region V. Physical characterization of 18 Plutinos using Herschel PACS observations
We present Herschel PACS photometry of 18 Plutinos and determine sizes and
albedos for these objects using thermal modeling. We analyze our results for
correlations, draw conclusions on the Plutino size distribution, and compare to
earlier results. Flux densities are derived from PACS mini scan-maps using
specialized data reduction and photometry methods. In order to improve the
quality of our results, we combine our PACS data with existing Spitzer MIPS
data where possible, and refine existing absolute magnitudes for the targets.
The physical characterization of our sample is done using a thermal model.
Uncertainties of the physical parameters are derived using customized Monte
Carlo methods. The correlation analysis is performed using a bootstrap Spearman
rank analysis. We find the sizes of our Plutinos to range from 150 to 730 km
and geometric albedos to vary between 0.04 and 0.28. The average albedo of the
sample is 0.08 \pm 0.03, which is comparable to the mean albedo of Centaurs,
Jupiter Family comets and other Trans-Neptunian Objects. We were able to
calibrate the Plutino size scale for the first time and find the cumulative
Plutino size distribution to be best fit using a cumulative power law with q =
2 at sizes ranging from 120-400 km and q = 3 at larger sizes. We revise the
bulk density of 1999 TC36 and find a density of 0.64 (+0.15/-0.11) g cm-3. On
the basis of a modified Spearman rank analysis technique our Plutino sample
appears to be biased with respect to object size but unbiased with respect to
albedo. Furthermore, we find biases based on geometrical aspects and color in
our sample. There is qualitative evidence that icy Plutinos have higher albedos
than the average of the sample.Comment: 18 pages, 8 figures, 8 tables, accepted for publication in A&
Experiences with improved cookstoves in Southern Africa
This study explores user experiences with improved cookstoves, drawing on findings from household surveys conducted in South Africa, Mozambique, Malawi and Zambia. Investigations were conducted on fuel and stove preferences; experiences with improved biomass cookstoves; the rationale for fuel and stovestacking subsequent to the initial uptake of improved biomass cookstoves; and aspirations for energy and fuel use among improved biomass cookstove users. Significant differences were identified in the perceived benefits of improved biomass cookstoves in the four countries and their priorities, with the most important benefits being fuel and cost savings. These would affect the reference frames within which end-users adopt improved biomass cookstoves. Local circumstances and diverse sets of priorities that affect household decisions need to be considered when promoting or rolling out improved cookstove initiatives
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