We present a one-dimensional model of the formation and viscous evolution of protoplanetary disks. The formation of the early disk is modeled as the result of the gravitational collapse of an ...isothermal molecular cloud. The disk's viscous evolution is integrated according to two parameterizations of turbulence: the classical α representation and a β parameterization, representative of non-linear turbulence driven by the keplerian shear. We apply the model to DM Tau and GM Aur, two classical T-Tauri stars with relatively well-characterized disks, retrieving the evolution of their surface density with time. We perform a systematic Monte-Carlo exploration of the parameter space (i.e. values of the α-β parameters, and of the temperature and rotation rate in the molecular cloud) to find the values that are compatible with the observed disk surface density distribution, star and disk mass, age and present accretion rate. We find that the observations for DM Tau require $0.001<\alpha<0.1$ or $2\times 10^{-5}<\beta<5\times 10^{-4}$. For GM Aur, we find that the turbulent viscosity is such that $4\times 10^{-4}<\alpha<0.01$ or $2\times 10^{-6}<\beta<8\times 10^{-5}$. These relatively large values show that an efficient turbulent diffusion mechanism is present at distances larger than ~$10\,$AU. This is to be compared to studies of the variations of accretion rates of T-Tauri stars versus age that mostly probe the inner disks, but also yield values of $\alpha\sim 0.01$. We show that the mechanism responsible for turbulent diffusion at large orbital distances most probably cannot be convection because of its suppression at low optical depths.
Venus's atmosphere presents an enigmatic global circulation with winds that rotate around the planet 60 times faster than the slow rotation of the surface. For decades the connection between the ...atmospheric super rotation and atmospheric waves has been suspected. However, the characterization of how these atmospheric waves originate, interact with the global circulation, and dissipate has been difficult. Recent results from the Akatsuki mission (Imai et al., 2019, https://doi.org/10.1029/2019JE006065) show explicitly the emergence of planetary‐scale Kelvin and Rossby waves at the upper cloud tops and how they transform from one type of wave to other giving new insights in the atmospheric super rotation.
Plain Language Summary
Venus is a mysterious planet in many aspects. One of them is its global atmospheric circulation. In a planet that rotates so slowly that its year (224.7 Earth days) is only 1.9 times longer than its solar day (116.7 Earth days), the visible clouds rotate around the planet with velocities of ∼360 km/hr, touring the planet in ∼4 Earth days. A crucial element to power these winds is atmospheric waves that transport energy and momentum through the atmosphere. However, a good characterization of the waves and the changes they impose on the winds has been missing from results of Venus exploration collected by a variety of space missions. In a recent analysis of images of the upper clouds of Venus obtained by the Akatsuki mission, Imai et al. (2019, https://doi.org/10.1029/2019JE006065) characterize changes in the winds and albedo of the planet as planetary‐scale waves develop, transform from one type into another, and vanish. Their study opens the door to an improved understanding of the role of the planetary‐scale waves in shaping Venus superrotating winds.
Key Points
Venus atmospheric variability is partially linked to large‐scale waves affecting winds and albedo
Observations from Akatsuki characterized these waves as nonpermanent Kelvin and Rossby waves
Small‐amplitude Kelvin waves form larger Rossby waves that survive tens of days and vanish
Environmental impacts of utility-scale solar energy Hernandez, R.R.; Easter, S.B.; Murphy-Mariscal, M.L. ...
Renewable & sustainable energy reviews,
January 2014, 2014, 2014-1-00, 20140101, Letnik:
29
Journal Article
Recenzirano
Odprti dostop
Renewable energy is a promising alternative to fossil fuel-based energy, but its development can require a complex set of environmental tradeoffs. A recent increase in solar energy systems, ...especially large, centralized installations, underscores the urgency of understanding their environmental interactions. Synthesizing literature across numerous disciplines, we review direct and indirect environmental impacts – both beneficial and adverse – of utility-scale solar energy (USSE) development, including impacts on biodiversity, land-use and land-cover change, soils, water resources, and human health. Additionally, we review feedbacks between USSE infrastructure and land-atmosphere interactions and the potential for USSE systems to mitigate climate change. Several characteristics and development strategies of USSE systems have low environmental impacts relative to other energy systems, including other renewables. We show opportunities to increase USSE environmental co-benefits, the permitting and regulatory constraints and opportunities of USSE, and highlight future research directions to better understand the nexus between USSE and the environment. Increasing the environmental compatibility of USSE systems will maximize the efficacy of this key renewable energy source in mitigating climatic and global environmental change.
We quantify the effect of dust accumulation at Jezero crater by means of a Dust Correction Factor (DCF) for the solar radiation measured by the photodiodes of the Radiation and Dust Sensor of the ...Mars 2020 mission. After one Mars Year, dust on the photodiode surface attenuated 25%–30% of the incoming solar radiation. The DCF did not decrease monotonically; we use a model to reproduce its evolution and to derive dust deposition and lifting rates, showing that dust removal is 9 times larger at Jezero crater than at InSight's location in western Elysium Planitia. The model fit obtained using observed opacities is further improved when fed with dust sedimentation rates simulated by a GCM that considers a particle size distrtibution. Projections show seasonal net dust removal, being encouraging for the long‐term survival of solar‐powered missions to Jezero or similarly active dust lifting regions.
Plain Language Summary
Dust is ubiquitous in the Martian atmosphere, accumulating on both natural and artificial surfaces. Dust particularly affects the performance and lifetime of missions: the termination of InSight and MER‐B operations are recent examples. Dust accumulation shows a seasonal behavior, and attenuated 25%–30% of the incoming solar radiation on Perseverance after the first Mars Year of the mission. Dust removal is almost 10 times larger than at InSight's location: projections indicate that surfaces at Jezero will be periodically partially cleaned. The estimations of the effect of the accumulated dust as a function of time are encouraging for solar‐powered missions to regions with similar amounts of dust lifting, which might be determined from orbital data on where dust storms originate, dust devils or their tracks are found, or seasonal albedo changes are noted. In addition, the quantification of the effect of accumulated enables future studies requiring more accurate knowledge of incoming solar radiation at the surface.
Key Points
We present the evolution of dust accumulation at Jezero crater for more than one Mars Year
We derive dust deposition and removal rates: removal is 9 times more efficient than at the InSight location in western Elysium Planitia
Projections show that surfaces at Jezero will experience seasonal net dust removal, encouraging solar‐powered missions
Objective
To evaluate and compare the symptomatology and clinical findings in hyposecretory dry eye of the treatment with platelet‐rich plasma (PRP) and artificial tears of sodium hyaluronate (SH).
...Methods
Blind single‐centre prospective comparative randomized study including 83 patients with hyposecretory dry eye and mean age of 64.0 years. Two groups were differentiated depending on the treatment applied: 44 patients treated with PRP (PRP group), and 39 patients treated with artificial tears of SH (SH group). Changes in Schimer test, tear osmolarity, corneal and conjunctival staining, tear film break‐up time (TF‐BUT), conjunctival hyperaemia, dry eye‐related symptoms with the Ocular Surface Disease Index questionnaire, and caliciform cell density were evaluated during 30 days of treatment.
Results
Significantly larger reduction in symptomatology (p < 0.001), visual improvement (p < 0.001), reduction in hyperaemia (p < 0.001), and corneal and conjunctival staining (p < 0.001), increment of Schirmer test outcome (p ≤ 0.005), and reduction of osmolarity were found in the PRP group in both eyes compared to SH group at 15 and 30 days of treatment. Likewise, a significantly higher increment of caliciform cell density (p < 0.001) was found in the PRP group. Strong and statistically significant correlations were found in the PRP group of the change achieved in visual acuity, hyperaemia, osmolarity, and conjunctival and corneal staining with the baseline values of these variables (p < 0.001).
Conclusion
PRP treatment in hyposecretory dry eye induces a more significant positive effect over symptomatology and different dry eye signs than SH, especially in moderate and severe cases.
A trend of increasing woody plant density, or woody thickening, has been observed across grassland and woodland ecosystems globally. It has been proposed that increasing atmospheric CO
2
is a major ...driver of broad scale woody thickening, though few field-based experiments have tested this hypothesis. Our study utilises a Free Air CO
2
Enrichment experiment to examine the effect of elevated CO
2
(eCO
2
) on three mechanisms that can cause woody thickening, namely (i) woody plant recruitment, (ii) seedling growth, and (iii) post-disturbance resprouting. The study took place in a eucalypt-dominated temperate grassy woodland. Annual assessments show that juvenile woody plant recruitment occurred over the first 3 years of CO
2
fumigation, though eCO
2
did not affect rates of recruitment. Manipulative experiments were established to examine the effect of eCO
2
on above-ground seedling growth using transplanted
Eucalyptus tereticornis
(Myrtaceae) and
Hakea sericea
(Proteaceae) seedlings. There was no positive effect of eCO
2
on biomass of either species following 12 months of exposure to treatments. Lignotubers (i.e., resprouting organs) of harvested
E. tereticornis
seedlings that were retained in situ for an additional year were used to examine resprouting response. The likelihood of resprouting and biomass of resprouts increased with lignotuber volume, which was not itself affected by eCO
2
. The presence of herbaceous competitors and defoliation by invertebrates and pathogens were found to greatly reduce growth and/or resprouting response of seedlings. Our findings do not support the hypothesis that future increases in atmospheric CO
2
will, by itself, promote woody plant recruitment in eucalypt-dominated temperate grassy woodlands.
► Long-term analysis of Venus atmospheric dynamics at cloud levels. ► Stability of atmospheric superrotation at low latitudes and subsolar wind variability. ► Meridional circulation at the upper ...cloud and null meridional circulation at the lower cloud. ► Detailed comparison with previous missions data.
The Venus Express (VEX) mission has been in orbit to Venus for more than 4 years now. The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument onboard VEX observes Venus in two channels (visible and infrared) obtaining spectra and multi-wavelength images of the planet that can be used to sample the atmosphere at different altitudes. Day-side images in the ultraviolet range (380
nm) are used to study the dynamics of the upper cloud at 66–72
km while night-side images in the near infrared (1.74
μm) map the opacity of the lower cloud deck at 44–48
km. Here we present a long-term analysis of the global atmospheric dynamics at these levels using a large selection of orbits from the VIRTIS-M dataset covering 860 Earth days that extends our previous work (Sánchez-Lavega, A. et al. 2008. Geophys. Res. Lett. 35, L13204) and allows studying the variability of the global circulation at the two altitude levels. The atmospheric superrotation is evident with equatorial to mid-latitudes westward velocities of 100 and 60
m
s
−1 in the upper and lower cloud layers. These zonal velocities are almost constant in latitude from the equator to 50°S. From 50°S to 90°S the zonal winds at both cloud layers decrease steadily to zero at the pole. Individual cloud tracked winds have errors of 3–10
m
s
−1 with a mean of 5
m
s
−1 and the standard deviations for a given latitude of our zonal and meridional winds are 9
m
s
−1. The zonal winds in the upper cloud change with the local time in a way that can be interpreted in terms of a solar tide. The zonal winds in the lower cloud are stable at mid-latitudes to the tropics and present variability at subpolar latitudes apparently linked to the activity of the South polar vortex. While the upper cloud presents a net meridional motion consistent with the upper branch of a Hadley cell with peak velocity
v
=
10
m
s
−1 at 50°S, the lower cloud meridional motions are less organized with some cloud features moving with intense northwards and southwards motions up to
v
=
±15
m
s
−1 but, on average, with almost null global meridional motions at all latitudes. We also examine the long-term behavior of the winds at these two vertical layers by comparing our extended wind tracked data with results from previous missions.
The sound of a Martian dust devil Murdoch, N; Stott, A E; Gillier, M ...
Nature communications,
12/2022, Letnik:
13, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Dust devils (convective vortices loaded with dust) are common at the surface of Mars, particularly at Jezero crater, the landing site of the Perseverance rover. They are indicators of atmospheric ...turbulence and are an important lifting mechanism for the Martian dust cycle. Improving our understanding of dust lifting and atmospheric transport is key for accurate simulation of the dust cycle and for the prediction of dust storms, in addition to being important for future space exploration as grain impacts are implicated in the degradation of hardware on the surface of Mars. Here we describe the sound of a Martian dust devil as recorded by the SuperCam instrument on the Perseverance rover. The dust devil encounter was also simultaneously imaged by the Perseverance rover's Navigation Camera and observed by several sensors in the Mars Environmental Dynamics Analyzer instrument. Combining these unique multi-sensorial data with modelling, we show that the dust devil was around 25 m large, at least 118 m tall, and passed directly over the rover travelling at approximately 5 m s
. Acoustic signals of grain impacts recorded during the vortex encounter provide quantitative information about the number density of particles in the vortex. The sound of a Martian dust devil was inaccessible until SuperCam microphone recordings. This chance dust devil encounter demonstrates the potential of acoustic data for resolving the rapid wind structure of the Martian atmosphere and for directly quantifying wind-blown grain fluxes on Mars.
Increasing evidence suggests that community-level responses to human-induced biodiversity loss start with a decrease of interactions among communities and between them and their abiotic environment. ...The structural and functional consequences of such interaction losses are poorly understood and have rarely been tested in real-world systems. Here, we analysed how 5 years of progressive, size-selective exclusion of large, medium, and small vertebrates and invertebrates-a realistic scenario of human-induced defaunation-impacts the strength of relationships between above- and belowground communities and their abiotic environment (hereafter ecosystem coupling) and how this relates to ecosystem functionality in grasslands. Exclusion of all vertebrates results in the greatest level of ecosystem coupling, while the additional loss of invertebrates leads to poorly coupled ecosystems. Consumer-driven changes in ecosystem functionality are positively related to changes in ecosystem coupling. Our results highlight the importance of invertebrate communities for maintaining ecological coupling and functioning in an increasingly defaunated world.
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