28,584 research outputs found
Surface flux transport modeling for solar cycles 15--21: effects of cycle-dependent tilt angles of sunspot groups
We model the surface magnetic field and open flux of the Sun from 1913 to
1986 using a surface flux transport model, which includes the observed
cycle-to-cycle variation of sunspot group tilts. The model reproduces the
empirically derived time evolution of the solar open magnetic flux, and the
reversal times of the polar fields. We find that both the polar field and the
axial dipole moment resulting from this model around cycle minimum correlate
with the strength of the following cycle.Comment: Accepted for publication by Ap
An investigation of pulsar searching techniques with the Fast Folding Algorithm
Here we present an in-depth study of the behaviour of the Fast Folding
Algorithm, an alternative pulsar searching technique to the Fast Fourier
Transform. Weaknesses in the Fast Fourier Transform, including a susceptibility
to red noise, leave it insensitive to pulsars with long rotational periods (P >
1 s). This sensitivity gap has the potential to bias our understanding of the
period distribution of the pulsar population. The Fast Folding Algorithm, a
time-domain based pulsar searching technique, has the potential to overcome
some of these biases. Modern distributed-computing frameworks now allow for the
application of this algorithm to all-sky blind pulsar surveys for the first
time. However, many aspects of the behaviour of this search technique remain
poorly understood, including its responsiveness to variations in pulse shape
and the presence of red noise. Using a custom CPU-based implementation of the
Fast Folding Algorithm, ffancy, we have conducted an in-depth study into the
behaviour of the Fast Folding Algorithm in both an ideal, white noise regime as
well as a trial on observational data from the HTRU-S Low Latitude pulsar
survey, including a comparison to the behaviour of the Fast Fourier Transform.
We are able to both confirm and expand upon earlier studies that demonstrate
the ability of the Fast Folding Algorithm to outperform the Fast Fourier
Transform under ideal white noise conditions, and demonstrate a significant
improvement in sensitivity to long-period pulsars in real observational data
through the use of the Fast Folding Algorithm.Comment: 19 pages, 15 figures, 3 table
Mesogranular structure in a hydrodynamical simulation
We analyse mesogranular flow patterns in a three-dimensional hydrodynamical
simulation of solar surface convection in order to determine its
characteristics. We calculate divergence maps from horizontal velocities
obtained with the Local Correlation Tracking (LCT) method. Mesogranules are
identified as patches of positive velocity divergence. We track the
mesogranules to obtain their size and lifetime distributions. We vary the
analysis parameters to verify if the pattern has characteristic scales. The
characteristics of the resulting flow patterns depend on the averaging time and
length used in the analysis. We conclude that the mesogranular patterns do not
exhibit intrinsic length and time scales
On the Snow Line in Dusty Protoplanetary Disks
The snow line, in Hayashi's (1981) model, is where the temperature of a black
body that absorbed direct sunlight and re-radiated as much as it absorbed,
would be 170~K. It is usually assumed that the cores of the giant planets,
e.g., Jupiter, form beyond the snow line. Since Hayashi, there have been a
series of more detailed models of the absorption by dust of the stellar
radiation, and of accretional heating, which alter the location of the snow
line. We have attempted a "self-consistent" model of a T Tauri disk in the
sense that we used dust properties and calculated surface temperatures that
matched observed disks. We then calculated the midplane temperature for those
disks, with no accretional heating or with small (<10^-8) accretion rates. Our
models bring the snow line in to the neighbourhood of 1 AU; not far enough to
explain the close planetary companions to other stars, but much closer than in
recent starting lines for orbit migration scenarios.Comment: 9 pages, 1 figure, to appear in ApJ,528,200
Limits to solar cycle predictability: Cross-equatorial flux plumes
Within the Babcock-Leighton framework for the solar dynamo, the strength of a
cycle is expected to depend on the strength of the dipole moment or net
hemispheric flux during the preceding minimum, which depends on how much flux
was present in each hemisphere at the start of the previous cycle and how much
net magnetic flux was transported across the equator during the cycle. Some of
this transport is associated with the random walk of magnetic flux tubes
subject to granular and supergranular buffeting, some of it is due to the
advection caused by systematic cross-equatorial flows such as those associated
with the inflows into active regions, and some crosses the equator during the
emergence process.
We aim to determine how much of the cross-equatorial transport is due to
small-scale disorganized motions (treated as diffusion) compared with other
processes such as emergence flux across the equator. We measure the
cross-equatorial flux transport using Kitt Peak synoptic magnetograms,
estimating both the total and diffusive fluxes. Occasionally a large sunspot
group, with a large tilt angle emerges crossing the equator, with flux from the
two polarities in opposite hemispheres. The largest of these events carry a
substantial amount of flux across the equator (compared to the magnetic flux
near the poles). We call such events cross-equatorial flux plumes. There are
very few such large events during a cycle, which introduces an uncertainty into
the determination of the amount of magnetic flux transported across the equator
in any particular cycle. As the amount of flux which crosses the equator
determines the amount of net flux in each hemisphere, it follows that the
cross-equatorial plumes introduce an uncertainty in the prediction of the net
flux in each hemisphere. This leads to an uncertainty in predictions of the
strength of the following cycle.Comment: A&A, accepte
Are there spurious temperature trends in the United States Climate Division database
The United States (U.S.) Climate Division data set is commonly used in applied climatic studies in the United States. The divisional averages are calculated by including all available stations within a division at any given time. The averages are therefore vulnerable to shifts in average station location or elevation over time, which may introduce spurious trends within these data. This paper examines temperature trends within the 15 climate divisions of New England, comparing the NCDC\u27s U.S. Divisional Data to the U.S. Historical Climate Network (USHCN) data. Correlation and multiple regression revealed that shifts in latitude, longitude, and elevation have affected the quality of the NCDC divisional data with respect to the USHCN. As a result, there may be issues with regard to their use in decadal- to century-scale climate change studies
Perceiving and expressing feelings through actions in relation to individual differences in empathic traits : the Action and Feelings Questionnaire (AFQ)
Peer reviewedPublisher PD
The Waldmeier Effect in Sunspot Cycles
We discuss two aspects of the Waldmeier Effect, namely (1) the rise times of
sunspot cycles are anti-correlated to their strengths (WE1) and (2) the rates
of rise of the cycles are correlated to their strengths (WE2). From analysis of
four different data sets we conclude that both WE1 and WE2 exist in all the
data sets. We study these effects theoretically by introducing suitable
stochastic fluctuations in our regular solar dynamo model.Comment: Magnetic Coupling between the Interior and Atmosphere of the Sun;
Astrophysics and Space Science Proceeding
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