| 1. |
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| 2. |
- de Jong, R. S., et al.
(författare)
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4MOST : Project overview and information for the First Call for Proposals
- 2019
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Ingår i: The Messenger. - : European Southern Observatory. - 0722-6691. ; 175, s. 3-11
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We introduce the 4-metre Multi-Object Spectroscopic Telescope (4MOST), a new high-multiplex, wide-field spectroscopic survey facility under development for the four-metre-class Visible and Infrared Survey Telescope for Astronomy (VISTA) at Paranal. Its key specifications are: a large field of view (FoV) of 4.2 square degrees and a high multiplex capability, with 1624 fibres feeding two low-resolution spectrographs (R = λ/Δλ ~ 6500), and 812 fibres transferring light to the high-resolution spectrograph (R ~ 20 000). After a description of the instrument and its expected performance, a short overview is given of its operational scheme and planned 4MOST Consortium science; these aspects are covered in more detail in other articles in this edition of The Messenger. Finally, the processes, schedules, and policies concerning the selection of ESO Community Surveys are presented, commencing with a singular opportunity to submit Letters of Intent for Public Surveys during the first five years of 4MOST operations.
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| 3. |
- Abdalla, E., et al.
(författare)
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Cosmology intertwined : A review of the particle physics, astrophysics, and cosmology associated with the cosmological tensions and anomalies
- 2022
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Ingår i: Journal of High Energy Astrophysics. - : Elsevier BV. - 2214-4048 .- 2214-4056. ; 34, s. 49-211
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Tidskriftsartikel (refereegranskat)abstract
- The standard Λ Cold Dark Matter (ΛCDM) cosmological model provides a good description of a wide range of astrophysical and cosmological data. However, there are a few big open questions that make the standard model look like an approximation to a more realistic scenario yet to be found. In this paper, we list a few important goals that need to be addressed in the next decade, taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant H0, the σ8–S8 tension, and other less statistically significant anomalies. While these discordances can still be in part the result of systematic errors, their persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the necessity for new physics or generalisations beyond the standard model. In this paper, we focus on the 5.0σ tension between the Planck CMB estimate of the Hubble constant H0 and the SH0ES collaboration measurements. After showing the H0 evaluations made from different teams using different methods and geometric calibrations, we list a few interesting new physics models that could alleviate this tension and discuss how the next decade's experiments will be crucial. Moreover, we focus on the tension of the Planck CMB data with weak lensing measurements and redshift surveys, about the value of the matter energy density Ωm, and the amplitude or rate of the growth of structure (σ8,fσ8). We list a few interesting models proposed for alleviating this tension, and we discuss the importance of trying to fit a full array of data with a single model and not just one parameter at a time. Additionally, we present a wide range of other less discussed anomalies at a statistical significance level lower than the H0–S8 tensions which may also constitute hints towards new physics, and we discuss possible generic theoretical approaches that can collectively explain the non-standard nature of these signals. Finally, we give an overview of upgraded experiments and next-generation space missions and facilities on Earth that will be of crucial importance to address all these open questions.
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| 4. |
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| 6. |
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| 7. |
- Goodwin, L. V., et al.
(författare)
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Swarm in situ observations of F region polar cap patches created by cusp precipitation
- 2015
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 42:4, s. 996-1003
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution in situ measurements from the three Swarm spacecraft, in a string-of-pearls configuration, provide new insights about the combined role of flow channel events and particle impact ionization in creating F region electron density structures in the northern Scandinavian dayside cusp. We present a case of polar cap patch formation where a reconnection-driven low-density relative westward flow channel is eroding the dayside solar-ionized plasma but where particle impact ionization in the cusp dominates the initial plasma structuring. In the cusp, density features are observed which are twice as dense as the solar-ionized background. These features then follow the polar cap convection and become less structured and lower in amplitude. These are the first in situ observations tracking polar cap patch evolution from creation by plasma transport and enhancement by cusp precipitation, through entrainment in the polar cap flow and relaxation into smooth patches as they approach the nightside auroral oval.
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| 8. |
- Nagatsuma, T., Nozawa, S., Buchert, S.C. and Fujii, R.
(författare)
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High latitude Pi3 pulsations observed by the EISCAT VHF radar.
- 2001
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Ingår i: Advances in Space Research. ; 28:7, s. 1093-1096
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Tidskriftsartikel (refereegranskat)abstract
- Long period irregular magnetic pulsations, Pi3, are found from EISCAT/VHF radar observations at the high latitude in the dawn sector on Sept. 29, 1996. From the comparison between the radar and ground magnetometer data, it is suggested that the meandering
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| 9. |
- Ozden, C., et al.
(författare)
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FDG Uptake in the Basal Forebrain as Measured by Digital High-Resolution PET Is a Promising Marker of Basal Forebrain Degeneration in the Lewy Body Disease Spectrum A Pilot Study
- 2020
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Ingår i: Clinical Nuclear Medicine. - : Ovid Technologies (Wolters Kluwer Health). - 0363-9762 .- 1536-0229. ; 45:4, s. 261-266
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Tidskriftsartikel (refereegranskat)abstract
- Purpose Cognitive decline in diseases of the Lewy body spectrum (LBS) is linked to dysfunction/degeneration of the basal forebrain (BF). Assessment of glucose metabolism in the BF by FDG PET is hampered by the small size of the BF and limited spatial resolution of conventional PET. This pilot study tested the feasibility of assessing BF glucose metabolism by high-resolution digital PET (dPET). Patients and Methods The retrospective study included 12 LBS patients (61-86 years, 5 demented). Whole-brain stereotactic normalization to anatomical standard space was followed by local stereotactic normalization of a 7 x 7 x 7-cm(3) box around the BF to a custom-made 1 x 1 x 1-mm(3) FDG dPET template. FDG uptake was scaled voxelwise to mean FDG uptake in the pons. Scaled FDG uptake in the BF was compared between demented and nondemented LBS patients and tested for correlation with cortical FDG uptake. Results Scaled FDG uptake in the BF was significantly lower in demented compared with nondemented patients (1.14 +/- 0.09 vs 1.25 +/- 0.06, P = 0.031). Brain-wide voxel-based testing for correlations with scaled FDG uptake in the BF revealed a large cluster comprising medial and ventrolateral frontal cortex, anterior cingulate cortex, insular cortex, and striatum as well as smaller clusters in motor cortex and occipital cortex (P < 0.001, uncorrected). Conclusions These results suggest that dementia-associated BF degeneration in LBS can be sensitively measured as reduced BF FDG uptake on dPET. More accurate delineation of the BF based on individual high-resolution MRI might be useful to make optimal use of improved spatial resolution of dPET and to correct for possible disease- and age-dependent partial volume effects.
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| 10. |
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| 11. |
- Lunde, J., et al.
(författare)
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Ion-dispersion and rapid electron fluctuations in the cusp : a case study
- 2008
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Ingår i: Annales Geophysicae. - 0992-7689 .- 1432-0576. ; 26:8, s. 2485-2502
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Tidskriftsartikel (refereegranskat)abstract
- We present results from co-ordinated measurements with the low altitude REIMEI satellite and the ESR (EISCAT Svalbard Radar), together with other ground-based instruments carried out in February 2006. The results mainly relate to the dayside cusp where clear signatures of so-called ion-dispersion are seen in the satellite data. The cusp ion-dispersion is important for helping to understand the temporal and spatial structure of magnetopause reconnection. Whenever a satellite crosses boundaries of flux tubes or convection cells, cusp structures such as ion-dispersion will always be encountered. In our case we observed 3 distinct steps in the ion energy, but it includes at least 2 more steps as well, which we interpret as temporal features in relation to pulsed reconnection at the magnetopause. In addition, fast variations of the electron flux and energy occurring during these events have been studied in detail. The variations of the electron population, if interpreted as structures crossed by the REIMEI satellite, would map near the magnetopause to similar features as observed previously with the Cluster satellites. These were explained as Alfven waves originating from an X-line of magnetic reconnection.
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| 12. |
- Marklund, G.T., Ivchenko, N., Karlsson, T., Fazakerley, A., Dunlop, M., Lindqvist, P.A., Buchert, S., Owen, C., Taylor, M., Vaivalds, A., Carter, P., Andre, M. and Balogh, A.
(författare)
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Temporal evolution of the electric field accelerating electrons away from the auroral ionosphere.
- 2001
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Ingår i: Nature. ; 414:6865, s. 724-727
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Tidskriftsartikel (refereegranskat)abstract
- The bright night-time aurorae that are visible to the unaided eye are caused by electrons accelerated towards Earth by an upward-pointing electric field(1-3). On adjacent geomagnetic field lines the reverse process occurs: a downward-pointing electric fie
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| 13. |
- Marklund, Göran T., et al.
(författare)
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Temporal evolution of the electric field accelerating electrons away from the auroral ionosphere
- 2001
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 414:6865, s. 724-727
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Tidskriftsartikel (refereegranskat)abstract
- The bright night-time aurorae that are visible to the unaided eye are caused by electrons accelerated towards Earth by an upward-pointing electric field(1-3). On adjacent geomagnetic field lines the reverse process occurs: a downward-pointing electric field accelerates electrons away from Earth(4-11). Such magnetic-field-aligned electric fields in the collisionless plasma above the auroral ionosphere have been predicted(12), but how they could be maintained is still a matter for debate(13). The spatial and temporal behaviour of the electric fields-a knowledge of which is crucial to an understanding of their nature-cannot be resolved uniquely by single satellite measurements. Here we report on the first observations by a formation of identically instrumented satellites crossing a beam of upward-accelerated electrons. The structure of the electric potential accelerating the beam grew in magnitude and width for about 200 s, accompanied by a widening of the downward-current sheet, with the total current remaining constant. The 200-s timescale suggests that the evacuation of the electrons from the ionosphere contributes to the formation of the downward-pointing magnetic-field-aligned electric fields. This evolution implies a growing load in the downward leg of the current circuit, which may affect the visible discrete aurorae.
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| 14. |
- Ogawa, Y., et al.
(författare)
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Characteristics of ion upflow and downflow observed with the European Incoherent Scatter Svalbard radar
- 2009
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 114:5, s. A05305-
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated how geomagnetic activity, the solar wind (SW), and the interplanetary magnetic field (IMF) influence the occurrence of the F-region/topside ionospheric ion upflow and downflow. Occurrence of dayside ion upflow observed with the European Incoherent Scatter Svalbard radar (ESR) at 75.2 degrees magnetic latitude is highly correlated with the SW density, as well as with the strength of the IMF By component. We suggest that this correlation exists because the region where ion upflow occurs is enlarged owing to SW density and IMF By magnitude, but it does not move significantly in geomagnetic latitude. The occurrence frequency of dayside ion upflow displays peaks versus the geomagnetic activity index (Kp), SW velocity, and negative IMF Bz component; that is, ion upflow is less frequently seen at the highest values of these parameters. Dayside ion downflow in the F-region/topside ionosphere occurs only when the Kp index and/or SW velocity are high or when IMF Bz is largely negative. The ion downflow is likely due to ballistic return of the ion upflow. We suggest that the region of ion upflow not only becomes larger but also moves equatorward with increasing Kp, SW velocity, and negative IMF Bz. The ESR can so be poleward of the upflow region and observe ions convecting poleward and returning ballistically downward.
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| 15. |
- Ogawa, Y., et al.
(författare)
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On the source of the polar wind in the polar topside ionosphere : First results from the EISCAT Svalbard radar
- 2009
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 36:24, s. L24103-
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Tidskriftsartikel (refereegranskat)abstract
- We present quantitative radar observations of both hydrogen ion (H+) and oxygen ion (O+) upflow in the topside polar ionosphere using measurements that were recently carried out with the EISCAT Svalbard Radar and the Reimei satellite. H+ upflow was clearly observed equatorward of the cusp above 500 km altitude. Within the cusp the H+ density was very low, and the upflow was dominated by O+ ions, but on closed field lines the H+ became the larger contributor to the upward flux above about 550 km. The total flux seemed to be conserved, and so below 550 km altitude O+ (with a small upward velocity of similar to 50 m s(-1)) appeared to determine the upward flux which was then maintained by H+! in the topside ionosphere. We also found that the H+ density in the topside polar ionosphere was several times higher than current predictions of ionospheric models like IRI2001.
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| 16. |
- Ogawa, Y., et al.
(författare)
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On the statistical relation between ion upflow and naturally enhanced ion-acoustic lines observed with the EISCAT Svalbard radar
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. A03313-
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated characteristics of ion upflow and naturally enhanced ion-acoustic lines (NEIALs) based on the European Incoherent Scatter (EISCAT) Svalbard radar (ESR) data continuously obtained between March 2007 and February 2008. For the ion upflow study we have used approximately 78,000 field-aligned profiles obtained with the ESR. For the NEIAL study we have identified approximately 1500 NEIALs in the ESR data at altitudes between 100 and 500 km. The occurrence frequency of ion upflow shows two peaks, at about 0800 and 1300 magnetic local time (MLT), while only one strong peak is seen around 0900 MLT for NEIALs. The upward ion flux also has only one peak around 1100-1300 MLT. The occurrence frequency of ion upflow varies strongly over season. It is higher in winter than in summer, whereas NEIALs are more frequent in summer than in winter. NEIALs frequently occur under high geomagnetic activity and also high solar activity conditions. Approximately 10% of NEIALs in the F region ionosphere were accompanied by NEIALs in the E region (occurred at altitudes below 200 km). About half of the E region enhanced echoes did not have an F region counterpart. Upshifted NEIALs dominate in the E region whereas downshifted NEIALs are usually stronger above an altitude of 300 km. The high occurrence frequency of NEIALs in the prenoon region (0800-1000 MLT) might be associated with acceleration of thermal ions to suprathermal ones. At the same MLT and geomagnetic latitude suprathermal ions and broadband extremely low frequency (BBELF) wave activity have been observed, according to previous studies.
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| 17. |
- Ogawa, Y., et al.
(författare)
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Solar activity dependence of ion upflow in the polar ionosphere observed with the European Incoherent Scatter (EISCAT) Tromso UHF radar
- 2010
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115, s. A07310-
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Tidskriftsartikel (refereegranskat)abstract
- The influence of solar activity upon ion upflow in the polar ionosphere was investigated using data obtained by the European Incoherent Scatter (EISCAT) Tromso UHF radar between 1984 and 2008. In agreement with other work we find that the upward ion flux is generally higher when solar activity is high than when it is low. Ion upflow events and also the upward velocity behave the opposite: they are more frequently seen and higher, respectively, at times of low solar activity. In any year about 30-40% ion upflow is accompanied by similar to 500 K higher electron temperature than the background temperature at 400 km altitude. Electron and ion heating in connection with upflow is nearly twice as prevalent during high solar activity as it is at low activity. The acceleration of ions by pressure gradients and ambipolar electric field becomes larger when solar activity is low than when it is high. This variation of the average acceleration is caused by the different shapes of electron density profiles for low and high solar activities. Ions start to flow up at above 450 km altitude when solar activity was high, and lower, at 300-500 km altitude, at low solar activity. It is suggested that the solar activity influences long-term variations of the ion upflow occurrence because it modulates the density of neutral particles, the formation of the F2 density peak, and ion-neutral collision frequencies in the thermosphere and ionosphere.
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| 18. |
- Ogawa, Y., et al.
(författare)
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Upper atmosphere cooling over the past 33 years
- 2014
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 41:15, s. 5629-5635
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical models and observations have suggested that the increasing greenhouse gas concentration in the troposphere causes the upper atmosphere to cool and contract. However, our understanding of the long-term trends in the upper atmosphere is still quite incomplete, due to a limited amount of available and well-calibrated data. The European Incoherent Scatter radar has gathered data in the polar ionosphere above TromsO for over 33years. Using this long-term data set, we have estimated the first significant trends of ion temperature at altitudes between 200 and 450km. The estimated trends indicate a cooling of 10-15K/decade near the F region peak (220-380km altitude), whereas above 400km the trend is nearly zero or even warming. The height profiles of the observed trends are close to those predicted by recent atmospheric general circulation models. Our results are the first quantitative confirmation of the simulations and of the qualitative expectations.
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| 19. |
- Vaivads, A., et al.
(författare)
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What high altitude observations tell us about the auroral acceleration : A cluster/DMSP conjunction
- 2003
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 30:3
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Tidskriftsartikel (refereegranskat)abstract
- [1] Magnetic conjugate observations by Cluster and DMSP F14 satellites are used to study the field lines of auroral arc. Cluster is well above the acceleration region and observes upward keV ion beams and bipolar electric structures. The integrated potential at Cluster altitudes shows a dip that is consistent with the keV electron acceleration energy at low altitude. The earthward Poynting flux at Cluster altitudes is comparable to the electron energy flux at low altitudes. Thus, for this event the auroral acceleration can be described as a quasi-stationary potential structure with equipotential lines reaching the Cluster altitudes. The arc forms at the outer edge of the plasma sheet at a density gradient. Multiple Cluster satellite measurements allow us to study the density increase associated with the development of the arc, and to estimate the velocity of the structure. The quasi-potential structure itself may be part of an Alfven wave.
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