86 research outputs found
Is Cycle 24 the Beginning of a Dalton-Like Minimum?
The unexpected development of cycle 24 emphasizes the need for a better way
to model future solar activity. In this article, we analyze the accumulation of
spotless days during individual cycles from 1798-2010. The analysis shows that
spotless days do not disappear abruptly in the transition towards an active
sun. A comparison with past cycles indicates that the ongoing accumulation of
spotless days is comparable to that of cycle 5 near the Dalton minimum and to
that of cycles 12, 14 and 15. It also suggests that the ongoing cycle has as
much as 20 \pm 8 spotless days left, from July 2010, before it reaches the next
solar maximum. The last spotless day is predicted to be in December 2012, with
an uncertainty of 11 months. This trend may serve as input to the solar dynamo
theories.Comment: 10 pages, 5 figures. The final publication is available at
http://www.springerlink.co
A new calibrated sunspot group series since 1749: statistics of active day fractions
Although the sunspot-number series have existed since the mid-19th century, they are still the subject of intense debate, with the largest uncertainty being related to the "calibration" of the visual acuity of individual observers in the past. Daisy-chain regression methods are applied to inter-calibrate the observers which may lead to significant bias and error accumulation. Here we present a novel method to calibrate the visual acuity of the key observers to the reference data set of Royal Greenwich Observatory sunspot groups for the period 1900-1976, using the statistics of the active-day fraction. For each observer we independently evaluate their observational thresholds [S_S] defined such that the observer is assumed to miss all of the groups with an area smaller than S_S and report all the groups larger than S_S. Next, using a Monte-Carlo method we construct, from the reference data set, a correction matrix for each observer. The correction matrices are significantly non-linear and cannot be approximated by a linear regression or proportionality. We emphasize that corrections based on a linear proportionality between annually averaged data lead to serious biases and distortions of the data. The correction matrices are applied to the original sunspot group records for each day, and finally the composite corrected series is produced for the period since 1748. The corrected series displays secular minima around 1800 (Dalton minimum) and 1900 (Gleissberg minimum), as well as the Modern grand maximum of activity in the second half of the 20th century. The uniqueness of the grand maximum is confirmed for the last 250 years. It is shown that the adoption of a linear relationship between the data of Wolf and Wolfer results in grossly inflated group numbers in the 18th and 19th centuries in some reconstructions
On the Relation between Solar Activity and Clear-Sky Terrestrial Irradiance
The Mauna Loa Observatory record of direct-beam solar irradiance measurements
for the years 1958-2010 is analysed to investigate the variation of clear-sky
terrestrial insolation with solar activity over more than four solar cycles.
The raw irradiance data exhibit a marked seasonal cycle, extended periods of
lower irradiance due to emissions of volcanic aerosols, and a long-term
decrease in atmospheric transmission independent of solar activity. After
correcting for these effects, it is found that clear-sky terrestrial irradiance
typically varies by about 0.2 +/- 0.1% over the course of the solar cycle, a
change of the same order of magnitude as the variations of the total solar
irradiance above the atmosphere. An investigation of changes in the clear-sky
atmospheric transmission fails to find a significant trend with sunspot number.
Hence there is no evidence for a yet unknown effect amplifying variations of
clear-sky irradiance with solar activity.Comment: 16 pages, 7 figures, in press at Solar Physics; minor changes to the
text to match final published versio
The G-O Rule and Waldmeier Effect in the Variations of the Numbers of Large and Small Sunspot Groups
We have analysed the combined Greenwich and Solar Optical Observing Network
(SOON) sunspot group data during the period of 1874-2011 and determined
variations in the annual numbers (counts) of the small, large and big sunspot
groups (these classifications are made on the basis of the maximum areas of the
sunspot groups). We found that the amplitude of an even-numbered cycle of the
number of large groups is smaller than that of its immediately following
odd-numbered cycle. This is consistent with the well known Gnevyshev and Ohl
rule or G-O rule of solar cycles, generally described by using the Zurich
sunspot number (Rz). During cycles 12-21 the G-O rule holds good for the
variation in the number of small groups also, but it is violated by cycle pair
(22, 23) as in the case of Rz. This behaviour of the variations in the small
groups is largely responsible for the anomalous behaviour of Rz in cycle pair
(22, 23). It is also found that the amplitude of an odd-numbered cycle of the
number of small groups is larger than that of its immediately following
even-numbered cycle. This can be called as `reverse G-O rule'. In the case of
the number of the big groups, both cycle pairs (12, 13) and (22, 23) violated
the G-O rule. In many cycles the positions of the peaks of the small, large,
and big groups are different and considerably differ with respect to the
corresponding positions of the Rz peaks. In the case of cycle 23, the
corresponding cycles of the small and large groups are largely symmetric/less
asymmetric (Waldmeier effect is weak/absent) with their maxima taking place two
years later than that of Rz. The corresponding cycle of the big groups is more
asymmetric (strong Waldmeier effect) with its maximum epoch taking place at the
same time as that of Rz.Comment: 13 pages, 5 figures, 1 table, accepted by Solar Physic
A Simple Method to Check the Reliability of Annual Sunspot Number in the Historical Period 1610-1847
A simple method to detect inconsistencies in low annual sunspot numbers based
on the relationship between these values and the annual number of active days
is described. The analysis allowed for the detection of problems in the annual
sunspot number series clustered in a few specific periods and unambiguous,
namely: i) before Maunder minimum, ii) the year 1652 during the Maunder
minimum, iii) the year 1741 in Solar Cycle -1, and iv) the so-called "lost"
solar cycle in 1790s and subsequent onset of the Dalton Minimum.Comment: 15 pages, 3 figures, to be published in Solar Physic
Width of Sunspot Generating Zone and Reconstruction of Butterfly Diagram
Based on the extended Greenwich-NOAA/USAF catalogue of sunspot groups it is
demonstrated that the parameters describing the latitudinal width of the
sunspot generating zone (SGZ) are closely related to the current level of solar
activity, and the growth of the activity leads to the expansion of SGZ. The
ratio of the sunspot number to the width of SGZ shows saturation at a certain
level of the sunspot number, and above this level the increase of the activity
takes place mostly due to the expansion of SGZ. It is shown that the mean
latitudes of sunspots can be reconstructed from the amplitudes of solar
activity. Using the obtained relations and the group sunspot numbers by Hoyt
and Schatten (1998), the latitude distribution of sunspot groups ("the Maunder
butterfly diagram") for the 18th and the first half of the 19th centuries is
reconstructed and compared with historical sunspot observations.Comment: 16 pages, 11 figures; accepted by Solar Physics; the final
publication will be available at www.springerlink.co
Tests of sunspot number sequences: 2. Using geomagnetic and auroral data
We compare four sunspot-number data sequences against geomagnetic and terrestrial auroral observations. The comparisons are made for the original SIDC (Solar Influences Data Center) composite of Wolf/Zürich/International sunspot number [RISNv1], the group sunspot number [RG] by Hoyt and Schatten (Solar Phys., 181, 491, 1998), the new “backbone” group sunspot number [RBB] by Svalgaard and Schatten (Solar Phys., doi: 10.1007/s11207-015-0815-8, 2016), and the “corrected” sunspot number [RC] by Lockwood, Owens, and Barnard (J. Geophys. Res., 119, 5172, 2014). Each sunspot number is fitted with terrestrial observations, or parameters derived from terrestrial observations to be linearly proportional to sunspot number, over a 30-year calibration interval of 1982 - 2012. The fits are then used to compute test sequences, which extend further back in time and which are compared to RISNv1, RG, RBB, and RC. To study the long-term trends, comparisons are made using averages over whole solar cycles (minimum-to-minimum). The test variations are generated in four ways: i) using the IDV(1d) and IDV geomagnetic indices (for 1845 - 2013) fitted over the calibration interval using the various sunspot numbers and the phase of the solar cycle; ii) from the open solar flux (OSF) generated for 1845 - 2013 from four pairings of geomagnetic indices by Lockwood et al. (Ann. Geophys., 32, 383, 2014) and analysed using the OSF continuity model of Solanki, Schüssler, and Fligge (Nature, 408, 445, 2000) which employs a constant fractional OSF loss rate; iii) the same OSF data analysed using the OSF continuity model of Owens and Lockwood (J. Geophys. Res., 117, A04102, 2012) in which the fractional loss rate varies with the tilt of the heliospheric current sheet and hence with the phase of the solar cycle; iv) the occurrence frequency of low-latitude aurora for 1780 - 1980 from the survey of Legrand and Simon (Ann. Geophys., 5, 161, 1987). For all cases, RBB exceeds the test terrestrial series by an amount that increases as one goes back in time
Tests of sunspot number sequences: 1. Using ionosonde data
More than 70 years ago it was recognised that ionospheric F2-layer critical frequencies [foF2] had a strong relationship to sunspot number. Using historic datasets from the Slough and Washington ionosondes, we evaluate the best statistical fits of foF2 to sunspot numbers (at each Universal Time [UT] separately) in order to search for drifts and abrupt changes in the fit residuals over Solar Cycles 17-21. This test is carried out for the original composite of the Wolf/Zürich/International sunspot number [R], the new “backbone” group sunspot number [RBB] and the proposed “corrected sunspot number” [RC]. Polynomial fits are made both with and without allowance for the white-light facular area, which has been reported as being associated with cycle-to-cycle changes in the sunspot number - foF2 relationship. Over the interval studied here, R, RBB, and RC largely differ in their allowance for the “Waldmeier discontinuity” around 1945 (the correction factor for which for R, RBB and RC is, respectively, zero, effectively over 20 %, and explicitly 11.6 %). It is shown that for Solar Cycles 18-21, all three sunspot data sequences perform well, but that the fit residuals are lowest and most uniform for RBB. We here use foF2 for those UTs for which R, RBB, and RC all give correlations exceeding 0.99 for intervals both before and after the Waldmeier discontinuity. The error introduced by the Waldmeier discontinuity causes R to underestimate the fitted values based on the foF2 data for 1932-1945 but RBB overestimates them by almost the same factor, implying that the correction for the Waldmeier discontinuity inherent in RBB is too large by a factor of two. Fit residuals are smallest and most uniform for RC and the ionospheric data support the optimum discontinuity multiplicative correction factor derived from the independent Royal Greenwich Observatory (RGO) sunspot group data for the same interval
Tests of Sunspot Number Sequences: 4. Discontinuities Around 1946 in Various Sunspot Number and Sunspot-Group-Number Reconstructions
Coronary stent healing in cancer patients: an optical coherence tomography perspective
Objective: This study assessed stent healing patterns and cardiovascular outcomes by optical coherence tomography (OCT) in cancer patients after drug-eluting stent (DES) placement.Background: Cancer treatment, owing to its cytotoxic and antiproliferative effects, could delay stent healing and increase stent thrombosis risk, especially when dual antiplatelet therapy (DAPT) is discontinued early for oncological treatment. OCT can assess stent endothelialization and other healing parameters, which may provide clinical guidance in these challenging scenarios.Methods: This single-center retrospective study enrolled all cancer patients who underwent OCT for assessment of vascular healing patterns after prior DES placement from November 2009 to November 2018. Primary study endpoints were stent healing parameters, including stent coverage, apposition, degree of expansion, neointimal hyperplasia heterogeneity, in-stent restenosis, stent thrombosis, and overall survival (OS).Results: A total of 67 patients were included in this study. Mean time between DES placement and OCT evaluation was 154 +/- 82 days. Stent healing matched published values for DES in non-cancer patients (P >= 0.063). At 1 year, the OS was 86% (95% confidence interval [CI]: 78-96%) with 0% incidence of acute coronary syndrome. Advanced cancers and active chemotherapies were associated with inferior OS (P = 0.024, hazard ratio [HR]: 3.50, 95% CI: 1.18-10.42 and P = 0.026, HR: 2.65, 95% CI: 1.13-6.22, respectively), while stent healing parameters were unassociated with OS. Forty-one patients (61%) had DAPT duration <= 6 months.Conclusions: Stent healing of contemporary DES appears similar in cancer and non-cancer patients. Cardiovascular risk of cancer patients after DES placement can be managed to facilitate timely cancer therapies, as the underlying malignancy and active chemotherapy ultimately determine survival.Cardiovascular Aspects of Radiolog
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