| 51. |
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| 52. |
- Reinhardt, Manuel, et al.
(författare)
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Aspects of the biological carbon cycle in a ca. 3.42-billion-year-old marine ecosystem
- 2024
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Ingår i: Precambrian Research. - : Elsevier. - 0301-9268 .- 1872-7433. ; 402, s. 107289-107289
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Tidskriftsartikel (refereegranskat)abstract
- Microbial life on Earth was well established in the Paleoarchean, but insight into early ecosystem diversity and thus, the complexity of the early biological carbon cycle is limited. Here we investigated four carbonaceous chert samples from the lower platform facies of the ca. 3.42-billion-year-old Buck Reef Chert, Barberton greenstone belt. The analysis on multiple scales revealed exceptionally well-preserved carbonaceous matter, even on molecular level (aliphatic and aromatic hydrocarbons), resulting from rapid silicification. Geochemical evidence from stable carbon and multiple sulfur isotopes supports the presence of different microbial metabolisms in the Paleoarchean ecosystem. The local biological carbon cycle was dominated by photoautotrophs, but autotrophic sulfate reducers and methane- or acetate-producing microbes were also present. In areas of microbial methane or acetate release, methanotrophs or acetotrophs contributed to the overall biomass. These results highlight the metabolic diversity in the lower platform environment of the Buck Reef Chert, and underline that an advanced biological carbon cycle already existed in the early Archean.
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| 53. |
- Roquet, Fabien, et al.
(författare)
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Estimates of the Southern Ocean general circulation improved by animal-borne instruments
- 2013
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 40:23, s. 6176-6180
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Tidskriftsartikel (refereegranskat)abstract
- Over the last decade, several hundred seals have been equipped with conductivity-temperature-depth sensors in the Southern Ocean for both biological and physical oceanographic studies. A calibrated collection of seal-derived hydrographic data is now available, consisting of more than 165,000 profiles. The value of these hydrographic data within the existing Southern Ocean observing system is demonstrated herein by conducting two state estimation experiments, differing only in the use or not of seal data to constrain the system. Including seal-derived data substantially modifies the estimated surface mixed-layer properties and circulation patterns within and south of the Antarctic Circumpolar Current. Agreement with independent satellite observations of sea ice concentration is improved, especially along the East Antarctic shelf. Instrumented animals efficiently reduce a critical observational gap, and their contribution to monitoring polar climate variability will continue to grow as data accuracy and spatial coverage increase.
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| 54. |
- Telloni, Daniele, et al.
(författare)
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Evolution of Solar Wind Turbulence from 0.1 to 1 au during the First Parker Solar Probe-Solar Orbiter Radial Alignment
- 2021
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 912:2
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Tidskriftsartikel (refereegranskat)abstract
- The first radial alignment between Parker Solar Probe and Solar Orbiter spacecraft is used to investigate the evolution of solar wind turbulence in the inner heliosphere. Assuming ballistic propagation, two 1.5 hr intervals are tentatively identified as providing measurements of the same plasma parcels traveling from 0.1 to 1 au. Using magnetic field measurements from both spacecraft, the properties of turbulence in the two intervals are assessed. Magnetic spectral density, flatness, and high-order moment scaling laws are calculated. The Hilbert-Huang transform is additionally used to mitigate short sample and poor stationarity effects. Results show that the plasma evolves from a highly Alfvenic, less-developed turbulence state near the Sun, to fully developed and intermittent turbulence at 1 au. These observations provide strong evidence for the radial evolution of solar wind turbulence.
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| 55. |
- Telloni, Daniele, et al.
(författare)
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Exploring the Solar Wind from Its Source on the Corona into the Inner Heliosphere during the First Solar Orbiter-Parker Solar Probe Quadrature
- 2021
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Ingår i: Astrophysical Journal Letters. - : Institute of Physics Publishing (IOPP). - 2041-8205 .- 2041-8213. ; 920:1
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Tidskriftsartikel (refereegranskat)abstract
- This Letter addresses the first Solar Orbiter (SO)-Parker Solar Probe (PSP) quadrature, occurring on 2021 January 18 to investigate the evolution of solar wind from the extended corona to the inner heliosphere. Assuming ballistic propagation, the same plasma volume observed remotely in the corona at altitudes between 3.5 and 6.3 solar radii above the solar limb with the Metis coronagraph on SO can be tracked to PSP, orbiting at 0.1 au, thus allowing the local properties of the solar wind to be linked to the coronal source region from where it originated. Thanks to the close approach of PSP to the Sun and the simultaneous Metis observation of the solar corona, the flow-aligned magnetic field and the bulk kinetic energy flux density can be empirically inferred along the coronal current sheet with an unprecedented accuracy, allowing in particular estimation of the Alfven radius at 8.7 solar radii during the time of this event. This is thus the very first study of the same solar wind plasma as it expands from the sub-Alfvenic solar corona to just above the Alfven surface.
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| 56. |
- Telloni, Daniele, et al.
(författare)
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Linking Small-scale Solar Wind Properties with Large-scale Coronal Source Regions through Joint Parker Solar Probe-Metis/Solar Orbiter Observations
- 2022
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Ingår i: Astrophysical Journal. - : IOP Publishing Ltd. - 0004-637X .- 1538-4357. ; 935:2
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Tidskriftsartikel (refereegranskat)abstract
- The solar wind measured in situ by Parker Solar Probe in the very inner heliosphere is studied in combination with the remote-sensing observation of the coronal source region provided by the METIS coronagraph aboard Solar Orbiter. The coronal outflows observed near the ecliptic by Metis on 2021 January 17 at 16:30 UT, between 3.5 and 6.3 R (circle dot) above the eastern solar limb, can be associated with the streams sampled by PSP at 0.11 and 0.26 au from the Sun, in two time intervals almost 5 days apart. The two plasma flows come from two distinct source regions, characterized by different magnetic field polarity and intensity at the coronal base. It follows that both the global and local properties of the two streams are different. Specifically, the solar wind emanating from the stronger magnetic field region has a lower bulk flux density, as expected, and is in a state of well-developed Alfvenic turbulence, with low intermittency. This is interpreted in terms of slab turbulence in the context of nearly incompressible magnetohydrodynamics. Conversely, the highly intermittent and poorly developed turbulent behavior of the solar wind from the weaker magnetic field region is presumably due to large magnetic deflections most likely attributed to the presence of switchbacks of interchange reconnection origin.
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| 57. |
- Telloni, Daniele, et al.
(författare)
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Observation and Modeling of the Solar Wind Turbulence Evolution in the Sub-Mercury Inner Heliosphere
- 2022
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Ingår i: Astrophysical Journal Letters. - : Institute of Physics Publishing (IOPP). - 2041-8205 .- 2041-8213. ; 938:2
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Tidskriftsartikel (refereegranskat)abstract
- This letter exploits the radial alignment between the Parker Solar Probe and BepiColombo in late 2022 February, when both spacecraft were within Mercury's orbit. This allows the study of the turbulent evolution, namely, the change in spectral and intermittency properties, of the same plasma parcel during its expansion from 0.11 to 0.33 au, a still unexplored region. The observational analysis of the solar wind turbulent features at the two different evolution stages is complemented by a theoretical description based on the turbulence transport model equations for nearly incompressible magnetohydrodynamics. The results provide strong evidence that the solar wind turbulence already undergoes significant evolution at distances less than 0.3 au from the Sun, which can be satisfactorily explained as due to evolving slab fluctuations. This work represents a step forward in understanding the processes that control the transition from weak to strong turbulence in the solar wind and in properly modeling the heliosphere.
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| 58. |
- Volwerk, Martin, et al.
(författare)
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Statistical study of linear magnetic hole structures near Earth
- 2021
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Ingår i: Annales Geophysicae. - : COPERNICUS GESELLSCHAFT MBH. - 0992-7689 .- 1432-0576. ; 39:1, s. 239-253
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Tidskriftsartikel (refereegranskat)abstract
- The Magnetospheric Multiscale mission (MMS1) data for 8 months in the winter periods of 2017-2018 and 2018-2019, when MMS had its apogee in the upstream solar wind of the Earth's bow shock, are used to study linear magnetic holes (LMHs). These LMHs are characterized by a magnetic depression of more than 50 % and a rotation of the background magnetic field of less then 10 degrees. A total of 406 LMHs are found and, based on their magnetoplasma characteristics, are split into three categories: cold (increase in density, little change in ion temperature), hot (increase in ion temperature, decrease in density) and sign change (at least one magnetic field component changes sign). The occurrence rate of LMHs is 2.3 per day. All LMHs are basically in pressure balance with the ambient plasma. Most of the linear magnetic holes are found in ambient plasmas that are stable against the mirror-mode generation, but only half of the holes are mirror-mode-stable inside.
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| 59. |
- Watts, Jennifer D., et al.
(författare)
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Carbon uptake in Eurasian boreal forests dominates the high-latitude net ecosystem carbon budget
- 2023
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 29:7, s. 1870-1889
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Tidskriftsartikel (refereegranskat)abstract
- Arctic-boreal landscapes are experiencing profound warming, along with changes in ecosystem moisture status and disturbance from fire. This region is of global importance in terms of carbon feedbacks to climate, yet the sign (sink or source) and magnitude of the Arctic-boreal carbon budget within recent years remains highly uncertain. Here, we provide new estimates of recent (2003–2015) vegetation gross primary productivity (GPP), ecosystem respiration (Reco), net ecosystem CO2 exchange (NEE; Reco − GPP), and terrestrial methane (CH4) emissions for the Arctic-boreal zone using a satellite data-driven process-model for northern ecosystems (TCFM-Arctic), calibrated and evaluated using measurements from >60 tower eddy covariance (EC) sites. We used TCFM-Arctic to obtain daily 1-km2 flux estimates and annual carbon budgets for the pan-Arctic-boreal region. Across the domain, the model indicated an overall average NEE sink of −850 Tg CO2-C year−1. Eurasian boreal zones, especially those in Siberia, contributed to a majority of the net sink. In contrast, the tundra biome was relatively carbon neutral (ranging from small sink to source). Regional CH4 emissions from tundra and boreal wetlands (not accounting for aquatic CH4) were estimated at 35 Tg CH4-C year−1. Accounting for additional emissions from open water aquatic bodies and from fire, using available estimates from the literature, reduced the total regional NEE sink by 21% and shifted many far northern tundra landscapes, and some boreal forests, to a net carbon source. This assessment, based on in situ observations and models, improves our understanding of the high-latitude carbon status and also indicates a continued need for integrated site-to-regional assessments to monitor the vulnerability of these ecosystems to climate change.
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| 60. |
- Witasse, O., et al.
(författare)
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Interplanetary coronal mass ejection observed at STEREO-A, Mars, comet 67P/Churyumov-Gerasimenko, Saturn, and New Horizons en route to Pluto : Comparison of its Forbush decreases at 1.4, 3.1, and 9.9 AU
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 122:8, s. 7865-7890
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Tidskriftsartikel (refereegranskat)abstract
- We discuss observations of the journey throughout the Solar System of a large interplanetary coronal mass ejection (ICME) that was ejected at the Sun on 14 October 2014. The ICME hit Mars on 17 October, as observed by the Mars Express, Mars Atmosphere and Volatile EvolutioN Mission (MAVEN), Mars Odyssey, and Mars Science Laboratory (MSL) missions, 44h before the encounter of the planet with the Siding-Spring comet, for which the space weather context is provided. It reached comet 67P/Churyumov-Gerasimenko, which was perfectly aligned with the Sun and Mars at 3.1 AU, as observed by Rosetta on 22 October. The ICME was also detected by STEREO-A on 16 October at 1 AU, and by Cassini in the solar wind around Saturn on the 12 November at 9.9AU. Fortuitously, the New Horizons spacecraft was also aligned with the direction of the ICME at 31.6 AU. We investigate whether this ICME has a nonambiguous signature at New Horizons. A potential detection of this ICME by Voyager 2 at 110-111 AU is also discussed. The multispacecraft observations allow the derivation of certain properties of the ICME, such as its large angular extension of at least 116 degrees, its speed as a function of distance, and its magnetic field structure at four locations from 1 to 10 AU. Observations of the speed data allow two different solar wind propagation models to be validated. Finally, we compare the Forbush decreases (transient decreases followed by gradual recoveries in the galactic cosmic ray intensity) due to the passage of this ICME at Mars, comet 67P, and Saturn.
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