22 research outputs found
Geoeffectiveness of Coronal Mass Ejections in the SOHO era
The main objective of the study is to determine the probability distributions
of the geomagnetic Dst index as a function of the coronal mass ejection (CME)
and solar flare parameters for the purpose of establishing a probabilistic
forecast tool for the geomagnetic storm intensity. Several CME and flare
parameters as well as the effect of successive-CME occurrence in changing the
probability for a certain range of Dst index values, were examined. The results
confirm some of already known relationships between remotely-observed
properties of solar eruptive events and geomagnetic storms, namely the
importance of initial CME speed, apparent width, source position, and the
associated solar flare class. In this paper we quantify these relationships in
a form to be used for space weather forecasting in future. The results of the
statistical study are employed to construct an empirical statistical model for
predicting the probability of the geomagnetic storm intensity based on remote
solar observations of CMEs and flares
The chaotic solar cycle II. Analysis of cosmogenic 10Be data
Context. The variations of solar activity over long time intervals using a
solar activity reconstruction based on the cosmogenic radionuclide 10Be
measured in polar ice cores are studied. Methods. By applying methods of
nonlinear dynamics, the solar activity cycle is studied using solar activity
proxies that have been reaching into the past for over 9300 years. The
complexity of the system is expressed by several parameters of nonlinear
dynamics, such as embedding dimension or false nearest neighbors, and the
method of delay coordinates is applied to the time series. We also fit a damped
random walk model, which accurately describes the variability of quasars, to
the solar 10Be data and investigate the corresponding power spectral
distribution. The periods in the data series were searched by the Fourier and
wavelet analyses. The solar activity on the long-term scale is found to be on
the edge of chaotic behavior. This can explain the observed intermittent period
of longer lasting solar activity minima. Filtering the data by eliminating
variations below a certain period (the periods of 380 yr and 57 yr were used)
yields a far more regular behavior of solar activity. A comparison between the
results for the 10Be data with the 14C data shows many similarities. Both
cosmogenic isotopes are strongly correlated mutually and with solar activity.
Finally, we find that a series of damped random walk models provides a good fit
to the 10Be data with a fixed characteristic time scale of 1000 years, which is
roughly consistent with the quasi-periods found by the Fourier and wavelet
analyses.Comment: 8 pages, 11 figure
Large-scale horizontal flows in the solar photosphere V: Possible evidence for the disconnection of bi-polar sunspot groups from their magnetic roots
In a recent paper (Svanda et al., 2008, A&A 477, 285) we pointed out that,
based on the tracking of Doppler features in the full-disc MDI Dopplergrams,
the active regions display two dynamically different regimes. We speculated
that this could be a manifestation of the sudden change in the active regions
dynamics, caused by the dynamic disconnection of sunspots from their magnetic
roots as proposed by Schuessler & Rempel (2005, A&A 441, 337). Here we
investigate the dynamic behaviour of the active regions recorded in the
high-cadence MDI data over the last solar cycle in order to confirm the
predictions in the Schuessler's & Rempel's paper. We find that, after drastic
reduction of the sample, which is done to avoid disturbing effects, a large
fraction of active regions displays a sudden decrease in the rotation speed,
which is compatible with the mechanism of the dynamic disconnection of sunspots
from their parental magnetic structures.Comment: 11 pages, 9 figures, 1 table; accepted in Astronomy & Astrophysic
Comparison of the sidereal angular velocity of subphotospheric layers and small bright coronal structures during the declining phase of solar cycle 23
Context. We compare solar differential rotation of subphotospheric layers
derived from local helioseismology analysis of GONG++ dopplergrams and the one
derived from tracing small bright coronal structures (SBCS) using EIT/SOHO
images for the period August 2001 - December 2006, which correspond to the
declining phase of solar cycle 23. Aims. The study aims to find a relationship
between the rotation of the SBCS and the subphotospheric angular velocity. The
northsouth asymmetries of both rotation velocity measurements are also
investigated. Methods. Subphotospheric differential rotation was derived using
ring-diagram analysis of GONG++ full-disk dopplergrams of 1 min cadence. The
coronal rotation was derived by using an automatic method to identify and track
the small bright coronal structures in EIT full-disk images of 6 hours cadence.
Results. We find that the SBCS rotate faster than the considered upper
subphotospheric layer (3Mm) by about 0.5 deg/day at the equator. This result
joins the results of several other magnetic features (sunspots, plages,
faculae, etc.) with a higher rotation than the solar plasma. The rotation rate
latitudinal gradients of the SBCS and the subphotospheric layers are very
similar. The SBCS motion shows an acceleration of about 0.005 deg/day/month
during the declining phase of solar cycle 23, whereas the angular velocity of
subsurface layers does not display any evident variation with time, except for
the well known torsional oscillation pattern. Finally, both subphotospheric and
coronal rotations of the southern hemisphere are predominantly larger than
those of the northern hemisphere. At latitudes where the north-south asymmetry
of the angular velocity increases (decreases) with activity for the SBCS, it
decreases (increases) for subphotospheric layers.Comment: 6pages, 8 figures, Accepted for publication in Astronomy and
Astrophysic
Large-scale horizontal flows in the solar photosphere II: Long-term behaviour and magnetic activity response
Recently, we have developed a method useful for mapping large-scale
horizontal velocity fields in the solar photosphere. The method was developed,
tuned and calibrated using the synthetic data. Now, we applied the method to
the series of Michelson Doppler Imager (MDI) dopplergrams covering almost one
solar cycle in order to get the information about the long-term behaviour of
surface flows. We have found that our method clearly reproduces the widely
accepted properties of mean flow field components, such as torsional
oscillations and a pattern of meridional circulation. We also performed a
periodic analysis, however due to the data series length and large gaps we did
not detect any significant periods. The relation between the magnetic activity
influencing the mean zonal motion is studied. We found an evidence that the
emergence of compact magnetic regions locally accelerates the rotation of
supergranular pattern in their vicinity and that the presence of magnetic
fields generally decelerates the rotation in the equatorial region. Our results
show that active regions in the equatorial region emerge exhibiting a constant
velocity (faster by 60 +/- 9 m/s than Carrington rate) suggesting that they
emerge from the base of the surface radial shear at 0.95 R_sun, disconnect from
their magnetic roots, and slow down during their evolution.Comment: 9 pages, 8 figures, accepted for publication in Astronomy &
Astrophysic
Driving major solar flares and eruptions: a review
This review focuses on the processes that energize and trigger major solar
flares and flux-rope destabilizations. Numerical modeling of specific solar
regions is hampered by uncertain coronal-field reconstructions and by poorly
understood magnetic re- connection; these limitations result in uncertain
estimates of field topology, energy, and helicity. The primary advances in
understanding field destabilizations therefore come from the combination of
generic numerical experiments with interpretation of sets of observations.
These suggest a critical role for the emergence of twisted flux ropes into
pre-existing strong field for many, if not all, of the active regions that pro-
duce M- or X-class flares. The flux and internal twist of the emerging ropes
appear to play as important a role in determining whether an eruption will
develop predom- inantly as flare, confined eruption, or CME, as do the
properties of the embedding field. Based on reviewed literature, I outline a
scenario for major flares and erup- tions that combines flux-rope emergence,
mass draining, near-surface reconnection, and the interaction with the
surrounding field. Whether deterministic forecasting is in principle possible
remains to be seen: to date no reliable such forecasts can be made.
Large-sample studies based on long-duration, comprehensive observations of
active regions from their emergence through their flaring phase are needed to
help us better understand these complex phenomena.Comment: in press for Advances in Space Researc
Real-Time PCR Method as Diagnostic Tool for Detection of Periodontal Pathogens in Patients with Periodontitis
The most common type of periodontal disease is chronic periodontitis, an inflammatory condition caused by pathogenic bacteria in subgingival plaque. The aim of our study was the development of a real-time PCR test as a diagnostic tool for the detection and differentiation of five periodontopathogenic bacteria, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Tannerella forsythia, Prevotella intermedia, and Treponema denticola, in patients with periodontitis. We compared the results of our in-house method with the micro-IDent® semiquantitative commercially available test based on the PCR hybridization method. DNA was isolated from subgingival plaque samples taken from 50 patients and then analyzed by both methods. Comparing the results of the two methods, they show a specificity of 100% for all bacteria. The sensitivity for A. actinomycetemcomitans was 97.5%, for P. gingivalis 96.88%, and for P. intermedia 95.24%. The sensitivity for Tannerella forsythia and T. denticola was 100%. The Spearman correlation factor of two different measurements was 0.976 for A. actinomycetemcomitans, 0.967 for P. gingivalis, 0.949 for P. intermedia, 0.966 for Tannerella forsythia, and 0.917 for T. denticola. In conclusion, the in-house real-time PCR method developed in our laboratory can provide information about relative amount of five bacterial species present in subgingival plaque in patients with periodontitis. It is likely that such a test could be used in dental diagnostics in assessing the efficacy of any treatment to reduce the bacterial burden
New findings supporting the presence of a thick disc and bipolar jets in the beta Lyrae system
Context. Understanding large-scale mass exchange in binaries also requires studies of complicated objects in the rapid phases of the process. beta Lyr is one such object