1,331 research outputs found
Reconstruction of solar activity for the last millennium using Be data
In a recent paper (Usoskin et al., 2002a), we have reconstructed the
concentration of the cosmogenic Be isotope in ice cores from the
measured sunspot numbers by using physical models for Be production in
the Earth's atmosphere, cosmic ray transport in the heliosphere, and evolution
of the Sun's open magnetic flux. Here we take the opposite route: starting from
the Be concentration measured in ice cores from Antarctica and
Greenland, we invert the models in order to reconstruct the 11-year averaged
sunspot numbers since 850 AD. The inversion method is validated by comparing
the reconstructed sunspot numbers with the directly observed sunspot record
since 1610. The reconstructed sunspot record exhibits a prominent period of
about 600 years, in agreement with earlier observations based on cosmogenic
isotopes. Also, there is evidence for the century scale Gleissberg cycle and a
number of shorter quasi-periodicities whose periods seem to fluctuate in the
millennium time scale. This invalidates the earlier extrapolation of
multi-harmonic representation of sunspot activity over extended time intervals.Comment: Submitted to A&
Male homosexual behavior among different age groups in captive stump-tailed macaque (Macaca arctoides): socio-sexual or sexually motivated?
The present study aims to determine whether homosexual behavior in stump-tailed macaque males of different age groups were socio-sexual or sexually motivated. Male homosexual encounters were divided into two categories for analysis; manual genital stimulation and actual mounting. Manual genital stimulation in adult males occurred bidirectional, in the context of social affiliations. There was no significant difference between dominant and subordinate partners in terms of genital stimulation performed or received. Mounting was in double foot-clasp position similar to heterosexual encounter. We identified three types of mounts. All types of mounts occurred unidirectional among adult males and mostly occurred in aggressive context. Unique homosexual encounters was observed between α-male and β-male where mounting involved anal intromission terminated by ejaculation and occurred only during the mating season after the heterosexual copulation between β-male and estrous female, which was known to be sexually motivated. We examined several socio-sexual explanations for male homosexual mounting, including (1) dominance-assertion (2) tension-regulation (3) reconciliation and (4) practice for heterosexual copulation. Homosexual encounters between adult males interpreted: a strict relationship between dominant individuals mounting subordinate individuals, reconciliation attempted by the subordinate; and the mechanism employed to regulated aggression and reestablished social bond among adult males. Mounting among immature males occurred bidirectional. Five evidences indicated the homosexual mounting between immature males as socio-sexual behavior. The evidences based on: (a) the mating season (b) the same day heterosexual encounter (c) assistance provided by adult male to immature males (d) occurrence in the context of play (e) immature males in homosexual mounting and learning heterosexual mounting with adult females. The male-male homosexuality adds a new dimension in sexual behavior of stump-tailed macaque.Â
Solar total and spectral irradiance reconstruction over the last 9000 years
Changes in solar irradiance and in its spectral distribution are among the
main natural drivers of the climate on Earth. However, irradiance measurements
are only available for less than four decades, while assessment of solar
influence on Earth requires much longer records. The aim of this work is to
provide the most up-to-date physics-based reconstruction of the solar total and
spectral irradiance (TSI/SSI) over the last nine millennia. The concentrations
of the cosmogenic isotopes 14C and 10Be in natural archives have been converted
to decadally averaged sunspot numbers through a chain of physics-based models.
TSI and SSI are reconstructed with an updated SATIRE model. Reconstructions are
carried out for each isotope record separately, as well as for their composite.
We present the first ever SSI reconstruction over the last 9000 years from the
individual 14C and 10Be records as well as from their newest composite. The
reconstruction employs physics-based models to describe the involved processes
at each step of the procedure. Irradiance reconstructions based on two
different cosmogenic isotope records, those of 14C and 10Be, agree well with
each other in their long-term trends despite their different geochemical paths
in the atmosphere of Earth. Over the last 9000 years, the reconstructed secular
variability in TSI is of the order of 0.11%, or 1.5 W/m2. After the Maunder
minimum, the reconstruction from the cosmogenic isotopes is consistent with
that from the direct sunspot number observation. Furthermore, over the
nineteenth century, the agreement of irradiance reconstructions using isotope
records with the reconstruction from the sunspot number by Chatzistergos et al.
(2017) is better than that with the reconstruction from the WDC-SILSO series
(Clette et al. 2014), with a lower chi-square-value
Spectroscopic Observations of Propagating Disturbances in a Polar Coronal Hole: Evidence of Slow Magneto-acoustic Waves
We focus on detecting and studying quasi-periodic propagating features that
have been interpreted both in terms of slow magneto-acoustic waves and of high
speed upflows. We analyze long duration spectroscopic observations of the
on-disk part of the south polar coronal hole taken on 1997 February 25 by the
SUMER spectrometer aboard SOHO. We calibrated the velocity with respect to the
off-limb region and obtain time--distance maps in intensity, Doppler velocity
and line width. We also perform a cross correlation analysis on different time
series curves at different latitudes. We study average spectral line profiles
at the roots of propagating disturbances and along the propagating ridges, and
perform a red-blue asymmetry analysis. We find the clear presence of
propagating disturbances in intensity and Doppler velocity with a projected
propagation speed of about km s and a periodicity of
14.5 min. To our knowledge, this is the first simultaneous detection
of propagating disturbances in intensity as well as in Doppler velocity in a
coronal hole. During the propagation, an intensity enhancement is associated
with a blue-shifted Doppler velocity. These disturbances are clearly seen in
intensity also at higher latitudes (i.e. closer to the limb), while
disturbances in Doppler velocity becomes faint there. The spectral line
profiles averaged along the propagating ridges are found to be symmetric, to be
well fitted by a single Gaussian, and have no noticeable red-blue asymmetry.
Based on our analysis, we interpret these disturbances in terms of propagating
slow magneto-acoustic waves.Comment: accepted for publication by A&
Discovery of kilogauss magnetic fields in three DA white dwarfs
We have detected longitudinal magnetic fields between 2 and 4 kG in three (WD
0446790, WD 1105048, WD 2359434) out of a sample of 12 normal DA white
dwarfs by using optical spectropolarimetry done with the VLT Antu 8 m telescope
equipped with FORS1. With the exception of 40 Eri B (4 kG) these are the first
positive detections of magnetic fields in white dwarfs below 30 kG. Although
suspected, it was not clear whether a significant fraction of white dwarfs
contain magnetic fields at this level. These fields may be explained as fossil
relics from magnetic fields in the main-sequence progenitors considerably
enhanced by magnetic flux conservation during the shrinkage of the core. A
detection rate of 25 % (3/12) may indicate now for the first time that a
substantial fraction of white dwarfs have a weak magnetic field. This result,
if confirmed by future observations, would form a cornerstone for our
understanding on the evolution of stellar magnetic fields.
Keywords: stars: white dwarfs - stars: magnetic fields - stars: individual:
WD0446-790, WD1105-048, WD2359-434Comment: 15 pages, 7 figures, Astronomy and Astrophysics, in pres
Evidence for polar jets as precursors of polar plume formation
Observations from the Hinode/XRT telescope and STEREO/SECCHI/EUVI are
utilized to study polar coronal jets and plumes. The study focuses on the
temporal evolution of both structures and their relationship. The data sample,
spanning April 7-8 2007, shows that over 90% of the 28 observed jet events are
associated with polar plumes. EUV images (STEREO/SECCHI) show plume haze rising
from the location of approximately 70% of the polar X-ray (Hinode/XRT) and EUV
jets, with the plume haze appearing minutes to hours after the jet was
observed. The remaining jets occurred in areas where plume material previously
existed causing a brightness enhancement of the latter after the jet event.
Short-lived, jet-like events and small transient bright points are seen (one at
a time) at different locations within the base of pre-existing long-lived
plumes. X-ray images also show instances (at least two events) of
collimated-thin jets rapidly evolving into significantly wider plume-like
structures that are followed by the delayed appearance of plume haze in the
EUV. These observations provide evidence that X-ray jets are precursors of
polar plumes, and in some cases cause brightenings of plumes. Possible
mechanisms to explain the observed jet and plume relationship are discussed.Comment: 10 pages, 4 figures, accepted as APJ Lette
Grand minima and maxima of solar activity: New observational constraints
Using a reconstruction of sunspot numbers stretching over multiple millennia,
we analyze the statistics of the occurrence of grand minima and maxima and set
new observational constraints on long-term solar and stellar dynamo models.
We present an updated reconstruction of sunspot number over multiple
millennia, from C data by means of a physics-based model, using an
updated model of the evolution of the solar open magnetic flux. A list of grand
minima and maxima of solar activity is presented for the Holocene (since 9500
BC) and the statistics of both the length of individual events as well as the
waiting time between them are analyzed.
The occurrence of grand minima/maxima is driven not by long-term cyclic
variability, but by a stochastic/chaotic process. The waiting time distribution
of the occurrence of grand minima/maxima deviates from an exponential
distribution, implying that these events tend to cluster together with long
event-free periods between the clusters. Two different types of grand minima
are observed: short (30--90 years) minima of Maunder type and long (110
years) minima of Sp\"orer type, implying that a deterministic behaviour of the
dynamo during a grand minimum defines its length. The duration of grand maxima
follows an exponential distribution, suggesting that the duration of a grand
maximum is determined by a random process.
These results set new observational constraints upon the long-term behaviour
of the solar dynamo.Comment: 10 Figure
Diversity of butterflies with respect to altitudinal rise at various pockets of the Langtang National Park, central Nepal
The Langtang National Park which covers an area of 1760 sq.km was studied extensively for the occurrence and status of butterflies within the altitudinal ranges of 1500 m at Syaprubensi to 4300 m around Langtang glacier area. Addition to altitudes, the decline in floral diversity with temperature reduction in higher elevation basically controlled the species richness of butterflies specifically above 3000 m elevations. Habitat preference for diverse species of these colorful and agile insects is poorly represented above that elevation. This study conducted at different periods in 2010 and 2011 covering both the spring and summer seasons came up with a list of different status categories of 126 species. A rich diversity was noted at 1500 m (Syaprubensi) to 2900 m at Deurali on the way to the glacier (4300 m). Parnassius hardwickei and Parnassius epaphus epaphus which were seen with good population in previous studies at Dhimsa (3200 m) are at declining stage as a consequence of habitat loss and human interferences
Vegetation types and wildlife occurrence in Baghmara Buffer zone community forest
Baghmara Buffer Zone Community Forest (BBZCF) is located in the central lowland of Nepal by covering 215 ha area. A year round study was conducted on 2010 in the area to find out the vegetation types and associated large wild mammals in that vegetation. To collect the primary data on vegetation 34 parallel transects traversing east to west were established. The transect pass through the all habitat types of BBZCF. Total length of transects were 68 kilometers. Nested quadrates (n = 131) were laid in each transects to collect information about vegetation type and wildlife occurrence. Vegetation types of the area were classified on the basis of Importance Value (IV) of tree species for forest area and Prominance Value (PV) of herbs and grass species in grassland area. Six vegetation types namely Acacia catechu forest, Albizia julibrissin forest, Savana, Dalbergia sissoo forest, Trewia nudiflora forest, and Grassland were reported from the study area. Wildlife signs were found only from naturally regenerated forests areas of BBZCF. On the basis of the availability of indirect signs it was found that wildlife were distributed in Albizia julibrissin forest, Trewia nudiflora forest, and grasslands of the study area. From those vegetation types, Spotted deer, Sambhar, Wild boar, Barking deer, and Rhinos were recorded. Among the studied wildlife, Spotted deer and Sambhar preferred Trewia nudiflora forest and rest of the wildlife preferred Albizia julibrissin forest as their habitats
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