65 research outputs found
ERI Spring-Summer 2014 Newsletter
Ecological Restoration Institute Spring-Summer 2014 Newslette
Solar-Cycle Characteristics Examined in Separate Hemispheres: Phase, Gnevyshev Gap, and Length of Minimum
Research results from solar-dynamo models show the northern and southern
hemispheres may evolve separately throughout the solar cycle. The observed
phase lag between the hemispheres provides information regarding the strength
of hemispheric coupling. Using hemispheric sunspot-area and sunspot-number data
from Cycles 12 - 23, we determine how out of phase the separate hemispheres are
during the rising, maximum, and declining period of each solar cycle.
Hemispheric phase differences range from 0 - 11, 0 - 14, and 2 - 19 months for
the rising, maximum, and declining periods, respectively. The phases appear
randomly distributed between zero months (in phase) and half of the rise (or
decline) time of the solar cycle. An analysis of the Gnevyshev gap is conducted
to determine if the double-peak is caused by the averaging of two hemispheres
that are out of phase. We confirm previous findings that the Gnevyshev gap is a
phenomenon that occurs in the separate hemispheres and is not due to a
superposition of sunspot indices from hemispheres slightly out of phase. Cross
hemispheric coupling could be strongest at solar minimum, when there are large
quantities of magnetic flux at the Equator. We search for a correlation between
the hemispheric phase difference near the end of the solar cycle and the length
of solar-cycle minimum, but found none. Because magnetic flux diffusion across
the Equator is a mechanism by which the hemispheres couple, we measured the
magnetic flux crossing the Equator by examining magnetograms for Solar Cycles
21 - 23. We find, on average, a surplus of northern hemisphere magnetic flux
crossing during the mid-declining phase of each solar cycle. However, we find
no correlation between magnitude of magnetic flux crossing the Equator, length
of solar minima, and phase lag between the hemispheres.Comment: 15 pages, 7 figure
Recovering Joys Law as a Function of Solar Cycle, Hemisphere, and Longitude
Bipolar active regions in both hemispheres tend to be tilted with respect to
the East West equator of the Sun in accordance with Joys law that describes the
average tilt angle as a function of latitude. Mt. Wilson observatory data from
1917 to 1985 are used to analyze the active-region tilt angle as a function of
solar cycle, hemisphere, and longitude, in addition to the more common
dependence on latitude. Our main results are as follows: i) We recommend a
revision of Joys law toward a weaker dependence on latitude (slope of 0.13 to
0.26) and without forcing the tilt to zero at the Equator. ii) We determine
that the hemispheric mean tilt value of active regions varies with each solar
cycle, although the noise from a stochastic process dominates and does not
allow for a determination of the slope of Joys law on an 11-year time scale.
iii) The hemispheric difference in mean tilt angles, 1.1 degrees + 0.27, over
Cycles 16 to 21 was significant to a three-sigma level, with average tilt
angles in the northern and southern hemispheres of 4.7 degrees + 0.26 and 3.6
degrees + 0.27 respectively. iv) Area-weighted mean tilt angles normalized by
latitude for Cycles 15 to 21 anticorrelate with cycle strength for the southern
hemisphere and whole-Sun data, confirming previous results by Dasi-Espuig,
Solanki, Krivova, et al. (2010, Astron. Astrophys. 518, A7). The northern
hemispheric mean tilt angles do not show a dependence on cycle strength. vi)
Mean tilt angles do not show a dependence on longitude for any hemisphere or
cycle. In addition, the standard deviation of the mean tilt is 29 to 31 degrees
for all cycles and hemispheres indicating that the scatter is due to the same
consistent process even if the mean tilt angles vary.Comment: 13 pages, 4 figures, 3 table
A Standard Law for the Equatorward Drift of the Sunspot Zones
The latitudinal location of the sunspot zones in each hemisphere is
determined by calculating the centroid position of sunspot areas for each solar
rotation from May 1874 to June 2011. When these centroid positions are plotted
and analyzed as functions of time from each sunspot cycle maximum there appears
to be systematic differences in the positions and equatorward drift rates as a
function of sunspot cycle amplitude. If, instead, these centroid positions are
plotted and analyzed as functions of time from each sunspot cycle minimum then
most of the differences in the positions and equatorward drift rates disappear.
The differences that remain disappear entirely if curve fitting is used to
determine the starting times (which vary by as much as 8 months from the times
of minima). The sunspot zone latitudes and equatorward drift measured relative
to this starting time follow a standard path for all cycles with no dependence
upon cycle strength or hemispheric dominance. Although Cycle 23 was peculiar in
its length and the strength of the polar fields it produced, it too shows no
significant variation from this standard. This standard law, and the lack of
variation with sunspot cycle characteristics, is consistent with Dynamo Wave
mechanisms but not consistent with current Flux Transport Dynamo models for the
equatorward drift of the sunspot zones.Comment: 12 pages, 7 color figure
Analytical and numerical comparisons of two methods of estimation of additive × additive interaction of QTL effects
Modeling the Subsurface Structure of Sunspots
While sunspots are easily observed at the solar surface, determining their
subsurface structure is not trivial. There are two main hypotheses for the
subsurface structure of sunspots: the monolithic model and the cluster model.
Local helioseismology is the only means by which we can investigate
subphotospheric structure. However, as current linear inversion techniques do
not yet allow helioseismology to probe the internal structure with sufficient
confidence to distinguish between the monolith and cluster models, the
development of physically realistic sunspot models are a priority for
helioseismologists. This is because they are not only important indicators of
the variety of physical effects that may influence helioseismic inferences in
active regions, but they also enable detailed assessments of the validity of
helioseismic interpretations through numerical forward modeling. In this paper,
we provide a critical review of the existing sunspot models and an overview of
numerical methods employed to model wave propagation through model sunspots. We
then carry out an helioseismic analysis of the sunspot in Active Region 9787
and address the serious inconsistencies uncovered by
\citeauthor{gizonetal2009}~(\citeyear{gizonetal2009,gizonetal2009a}). We find
that this sunspot is most probably associated with a shallow, positive
wave-speed perturbation (unlike the traditional two-layer model) and that
travel-time measurements are consistent with a horizontal outflow in the
surrounding moat.Comment: 73 pages, 19 figures, accepted by Solar Physic
Modelagem da Lagoa da Pampulha: uma ferramenta para avaliar o impacto da bacia hidrográfica na dinâmica do fitoplâncton
The beam and detector of the NA62 experiment at CERN
NA62 is a fixed-target experiment at the CERN SPS dedicated to measurements of rare kaon decays. Such measurements, like the branching fraction of the K+ → π+ ν bar nu decay, have the potential to bring significant insights into new physics processes when comparison is made with precise theoretical predictions. For this purpose, innovative techniques have been developed, in particular, in the domain of low-mass tracking devices. Detector construction spanned several years from 2009 to 2014. The collaboration started detector commissioning in 2014 and will collect data until the end of 2018. The beam line and detector components are described together with their early performance obtained from 2014 and 2015 data
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