1,319 research outputs found
How much more can sunspots tell us about the solar dynamo?
Sunspot observations inspired solar dynamo theory and continue to do so. Simply counting them established the sunspot cycle and its period. Latitudinal distributions introduced the tough constraint that the source of sunspots moves equator-ward as the cycle progresses. Observations of Hale's polarity law mandated hemispheric asymmetry. How much more can sunspots tell us about the solar dynamo? We draw attention to a few outstanding questions raised by inherent sunspot properties. Namely, how to explain sunspot rotation rates, the incoherence of follower spots, the longitudinal spacing of sunspot groups, and brightness trends within a given sunspot cycle. After reviewing the first several topics, we then present new results on the brightness of sunspots in Cycle 24 as observed with the Helioseismic Magnetic Imager (HMI). We compare these results to the sunspot brightness observed in Cycle 23 with the Michelson Doppler Imager (MDI). Next, we compare the minimum intensities of five sunspots simultaneously observed by the Hinode Solar Optical Telescope Spectropolarimeter (SOT-SP) and HMI to verify that the minimum brightness of sunspot umbrae correlates well to the maximum field strength. We then examine 90 and 52 sunspots in the north and south hemisphere, respectively, from 2010 - 2012. Finally, we conclude that the average maximum field strengths of umbra 40 Carrington Rotations into Cycle 24 are 2690 Gauss, virtually indistinguishable from the 2660 Gauss value observed at a similar time in Cycle 23 with MDI
The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Optimization of the Spectral Line Inversion Code
The Very Fast Inversion of the Stokes Vector (VFISV) is a Milne-Eddington
spectral line inversion code used to determine the magnetic and thermodynamic
parameters of the solar photosphere from observations of the Stokes vector in
the 6173 A Fe I line by the Helioseismic and Magnetic Imager (HMI) onboard the
Solar Dynamics Observatory (SDO). We report on the modifications made to the
original VFISV inversion code in order to optimize its operation within the HMI
data pipeline and provide the smoothest solution in active regions. The changes
either sped up the computation or reduced the frequency with which the
algorithm failed to converge to a satisfactory solution. Additionally, coding
bugs which were detected and fixed in the original VFISV release, are reported
here.Comment: Accepted for publication in Solar Physic
Does the Sun Shrink with Increasing Magnetic Activity?
We have analyzed the full set of SOHO/MDI f- and p-mode oscillation
frequencies from 1996 to date in a search for evidence of solar radius
evolution during the rising phase of the current activity cycle. Like Antia et
al. (2000), we find that a significant fraction of the f-mode frequency changes
scale with frequency; and that if these are interpreted in terms of a radius
change, it implies a shrinking sun. Our inferred rate of shrinkage is about 1.5
km/y, which is somewhat smaller than found by Antia et al. We argue that this
rate does not refer to the surface, but rather to a layer extending roughly
from 4 to 8 Mm beneath the visible surface. The rate of shrinking may be
accounted for by an increasing radial component of the rms random magnetic
field at a rate that depends on its radial distribution. If it were uniform,
the required field would be ~7 kG. However, if it were inwardly increasing,
then a 1 kG field at 8 Mm would suffice.
To assess contribution to the solar radius change arising above 4Mm, we
analyzed the p-mode data. The evolution of the p-mode frequencies may be
explained by a magnetic^M field growing with activity. The implications of the
near-surface magnetic field changes depend on the anisotropy of the random
magnetic field. If the field change is predominantly radial, then we infer an
additional shrinking at a rate between 1.1-1.3 km/y at the photosphere. If on
the other hand the increase is isotropic, we find a competing expansion at a
rate of 2.3 km/y. In any case, variations in the sun's radius in the activity
cycle are at the level of 10^{-5} or less, hence have a negligible contribution
to the irradiance variations.Comment: 10 pages (ApJ preprint style), 4 figures; accepted for publication in
Ap
Differential rotation and meridional flow in the solar supergranulation layer: Measuring the eddy viscosity
We measure the eddy viscosity in the outermost layers of the solar convection
zone by comparing the rotation law computed with the Reynolds stress resulting
from f-plane simulations of the angular momentum transport in rotating
convection with the observed differential rotation pattern. The simulations
lead to a negative vertical and a positive horizontal angular momentum
transport. The consequence is a subrotation of the outermost layers, as it is
indeed indicated both by helioseismology and the observed rotation rates of
sunspots. In order to reproduce the observed gradient of the rotation rate a
value of about 1.5 x 10^{13} cm/s for the eddy viscosity is necessary.
Comparison with the magnetic eddy diffusivity derived from the sunspot decay
yields a surprisingly large magnetic Prandtl number of 150 for the
supergranulation layer. The negative gradient of the rotation rate also drives
a surface meridional flow towards the poles, in agreement with the results from
Doppler measurements. The successful reproduction of the abnormally positive
horizontal cross correlation (on the northern hemisphere) observed for bipolar
groups then provides an independent test for the resulting eddy viscosity.Comment: 6 pages, 8 figures, Astronomy and Astrophysics (subm.
Demographical, personality, alcohol use, and mental health characteristics associated with different alcoholic beverage preferences among students
The study investigates correlates (i.e. demographics, personality, alcohol use and alcohol-related harm, alcohol expectancies, and mental health) of different alcoholic beverage preferences (i.e. beer/alcopops/cider, wine, and liquor/spirits). Data were collected by an online survey during fall 2016. Participants were invited to the survey based on participation in a former survey that was sent to students in Bergen, Norway, in fall 2015. The current sample consists of 5,217 participants. A multinomial regression analysis was conducted, where alcoholic beverage preferences comprised the dependent variable. Several correlates were associated with beverage preferences. For instance, being a woman and the personality trait conscientiousness were inversely related to a preference for beer/alcopops/cider while positively associated with a preference for wine. Preferences for wine or liquor/spirits were positively associated with depression and inversely related to anxiety. Conscientiousness as a personality trait might be a common factor in the relationship between wine preference and favourable health outcomes, and this trait should be controlled for in future studies. The current findings seem contrary to the assumed gender equality in Norway, where the strong association between sex and alcoholic beverage preferences suggests that traditional gender divisions prevail even in the current young and urban sample.publishedVersio
The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Overview and Performance
The Helioseismic and Magnetic Imager (HMI) began near-continuous full-disk
solar measurements on 1 May 2010 from the Solar Dynamics Observatory (SDO). An
automated processing pipeline keeps pace with observations to produce
observable quantities, including the photospheric vector magnetic field, from
sequences of filtergrams. The primary 720s observables were released in mid
2010, including Stokes polarization parameters measured at six wavelengths as
well as intensity, Doppler velocity, and the line-of-sight magnetic field. More
advanced products, including the full vector magnetic field, are now available.
Automatically identified HMI Active Region Patches (HARPs) track the location
and shape of magnetic regions throughout their lifetime.
The vector field is computed using the Very Fast Inversion of the Stokes
Vector (VFISV) code optimized for the HMI pipeline; the remaining 180 degree
azimuth ambiguity is resolved with the Minimum Energy (ME0) code. The
Milne-Eddington inversion is performed on all full-disk HMI observations. The
disambiguation, until recently run only on HARP regions, is now implemented for
the full disk. Vector and scalar quantities in the patches are used to derive
active region indices potentially useful for forecasting; the data maps and
indices are collected in the SHARP data series, hmi.sharp_720s. Patches are
provided in both CCD and heliographic coordinates.
HMI provides continuous coverage of the vector field, but has modest spatial,
spectral, and temporal resolution. Coupled with limitations of the analysis and
interpretation techniques, effects of the orbital velocity, and instrument
performance, the resulting measurements have a certain dynamic range and
sensitivity and are subject to systematic errors and uncertainties that are
characterized in this report.Comment: 42 pages, 19 figures, accepted to Solar Physic
General and alcohol-related social media use and mental health: A large-sample longitudinal study
The current study aimed to investigate if general and alcohol-related social media use predicts symptoms of depression and anxiety. Students in Bergen, Norway, participated in a Web-based survey during fall 2015 (T1) and a follow-up survey during fall 2016 (T2). A total of 5217 participated in both surveys. Crude and adjusted linear regression analyses were conducted to investigate if social media use at T1 predicted depression and anxiety at T2. Several social media use variables (e.g., using Instagram) were positively associated with depression and anxiety over time, but these associations became non-significant when covariates were controlled for. Number of online friends was inversely related to depression whereas using Twitter was positively related to anxiety at T2, when covariates were controlled for. The effect sizes of the observed associations were all very small. The current study found little support for a relationship between social media use and mental health.publishedVersio
Physical routes for the synthesis of kesterite
This paper provides an overview of the physical vapor technologies used to synthesize Cu2ZnSn(S,Se)4
thin films as absorber layers for photovoltaic applications. Through the years, CZT(S,Se) thin films
have been fabricated using sequential stacking or co-sputtering of precursors as well as using
sequential or co-evaporation of elemental sources, leading to high-efficient solar cells. In addition,
pulsed laser deposition of composite targets and monograin growth by the molten salt method were
developed as alternative methods for kesterite layers deposition. This review presents the growing
increase of the kesterite-based solar cell efficiencies achieved over the recent years. A historical
description of the main issues limiting this efficiency and of the experimental pathways designed to
prevent or limit these issues is provided and discussed as well. Afinal section is dedicated to the
description of promising process steps aiming at further improvements of solar cell efficiency, such as
alkali doping and bandgap grading1. R Caballero and M León acknowledge financial support via the Spanish Ministry of Science, Innovation and Universities project (WINCOST, ENE2016-80788-C5-2-R) and thank H2020 EU Programme under the project INFINITE-CELL (H2020-MSCA-RISE-2017-777968).
2. S Canulescu and J Schou acknowledge the support from Innovation Fund Denmark.
3. D-H Kim acknowledges financial support via the DGIST R&D Program of the Ministry of Science and ICT, KOREA (18-BD-05).
4.C. Malerba acknowledges the support from the Italian Ministry of Economic development in the framework of the Operating Agreement with ENEA for the Research on the Electric System.
5.A Redinger acknowledges financial support via the FNR Attract program, Project : SUNSPOT, Nr.11244141.
6. E Saucedo thanks H2020 EU Programme under the projects STARCELL (H2020-NMBP-03-2016-720907) and INFINITE-CELL (H2020-MSCA-RISE-2017-777968), the Spanish Ministry of Science, Innovation and Universities for the IGNITE project (ENE2017-87671-C3-1-R), and the European Regional Development Funds (ERDF, FEDER Programa Competitivitat de Catalunya 2007–2013). IREC belong to
the SEMS (Solar Energy Materials and Systems) Consolidated Research Group of the ‘Generalitat de Catalunya’ (Ref. 2017 SGR 862).
7. Taltech acknowledges financial support via the Estonian Ministry of Education and Research funding project IUT19-28 and the European Union Regional Development Fund, Project TK141.
8. B Vermang has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme (Grant Agreement No 715027
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