Does Correction Factor Vary with Solar Cycle?

장헌영,오성진 한국우주과학회 2012 Journal of Astronomy and Space Sciences Vol.29 No.2

Monitoring sunspots consistently is the most basic step required to study various aspects of solar activity. To achieve this goal, the observers must regularly calculate their own correction factor k and keep it stable. Relatively recently, two observing teams in South Korea have presented interesting papers which claim that revisions that take the yearly-basis k into account lead to a better agreement with the international relative sunspot number Ri, and that yearly k apparently varies with the solar cycle. In this paper, using artificial data sets we have modeled the sunspot numbers as a superposition of random noise and a slowly varying background function, and attempted to investigate whether the variation in the correction factor is coupled with the solar cycle. Regardless of the statistical distributions of the random noise, we have found the correction factor increases as sunspot numbers increase, as claimed in the reports mentioned above. The degree of dependence of correction factor k on the sunspot number is subject to the signal-to-noise ratio. Therefore, we conclude that apparent dependence of the value of the correction factor k on the phase of the solar cycle is not due to a physical property, but a statistical property of the data.

Maximum Sunspot Numbers and Active Days

장헌영 한국우주과학회 2013 Journal of Astronomy and Space Sciences Vol.30 No.3

Parameters associated with solar minimum have been studied to relate them to solar activity at solar maximum so that one could possibly predict behaviors of an upcoming solar cycle. The number of active days has been known as a reliable indicator of solar activity around solar minimum. Active days are days with sunspots reported on the solar disk. In this work, we have explored the relationship between the sunspot numbers at solar maximum and the characteristics of the monthly number of active days. Specifically, we have statistically examined how the maximum monthly sunspot number of a given solar cycle is correlated with the slope of the linear relationship between monthly sunspot numbers and the monthly number of active days for the corresponding solar cycle. We have calculated the linear correlation coefficient r and the Spearman rank-order correlation coefficient rs for data sets prepared under various conditions. Even though marginal correlations are found, they turn out to be insufficiently significant (r ~ 0.3). Nonetheless, we have confirmed that the slope of the linear relationship between monthly sunspot numbers and the monthly number of active days is less steep when solar cycles belonging to the "Modern Maximum" are considered compared with rests of solar cycles. We conclude, therefore, that the slope of the linear relationship between monthly sunspot numbers and the monthly number of active days is indeed dependent on the solar activity at its maxima, but that this simple relationship should be insufficient as a valid method to predict the following solar activity amplitude.

On Mode Correlation of Solar Acoustic Oscillations

장헌영 한국우주과학회 2009 Journal of Astronomy and Space Sciences Vol.26 No.3

In helioseismology it is normally assumed that p-mode oscillations are excited in a statistically independent fashion. Unfortunately, however, this issue is not clearly settled down in that two experiments exist, which apparently look in discrepancy. That is, Appourchaux et al.(2000) looked at bin-to-bin correlation and found no evidence that the assumption is invalid. On the other hand, Roth (2001) reported that p-mode pairs with nearby frequencies tend to be anti-correlated, possibly by a mode-coupling effect. This work is motivated by an idea that one may test if there exists an excess of anticorrelated power variations of pairs of solar p-modes. We have analyzed a 72-day MDI spherical-harmonic time series to examine temporal variations of p-mode power and their correlation. The power variation is computed by a running-window method after the previous study by Roth (2001), and then distribution function of power correlation between mode pairs is produced. We have confirmed Roth's result that there is an excess of anti-correlated p-mode pairs with nearby frequencies. On the other hand, the amount of excess was somewhat smaller than the previous study. Moreover, the distribution function does not exhibit significant change when we paired modes with non-nearby frequencies, implying that the excess is not due to mode coupling. We conclude that the origin of this excess of anticorrelations may not be a solar physical process, by pointing out the possibility of statistical bias playing the central role in producing the excess.

A NEW METHOD FOR NORTH-SOUTH ASYMMETRY OF SUN SPOT AREA

장헌영 한국우주과학회 2007 Journal of Astronomy and Space Sciences Vol.24 No.4

We have studied the temporal variation in the North-South asymmetry of the sunspotarea duringthe periodfrom 1874 to 2007. Thoughthe 9-yearperiodicityis commonlyreported, shorter periodicities is till under study. We mploy the cepstrum analy-sis method to analyze the noisy power spectrum of the North-South asymmetry. Wedemonstrate that thecleanedground noise level. Some of short period peaks in the power spectrum disappear afterdeconvolution. Itshouldbe, however,pointedoutthatpowerspectrummightlook lesnoisy because of altering process during deconvolution. We conclude by pointingout that a more sophisticateltering algorithm is required to produce a precise and

TIME/FREQUENCY ANALYSIS OF TERRESTRIAL IMPACT CRATER RECORDS

장헌영 한국우주과학회 2006 Journal of Astronomy and Space Sciences Vol.23 No.3

The terrestrial impact cratering record recently has been examined in the time domainby Chang & Moon (2005). It was found that the. .. Myr periodicity in the impactcratering rate exists over the last. ... Myrs. Such a periodicitycan be foundregard-less of the lower limit of the diameter up to. . .. km. It immediately called prosand cons. The aim of this paper is two-fold: (1) to test if reported periodicities canbe obtained with an independent method, (2) to see, as attempted earlier, if the phaseis modulated. To achieve these goals we employ the time/frequency analysis and forthe rst time apply this method to the terrestrial impact cratering records. We haveconrmed that without exceptions noticeable peaks appear around. .. Myr, corre-spondingto a frequencyof. . . ........ . . We also ndperiodicitiesin the data baseincluding small impact craters, which are longer. Though the time/frequency analysisallows us to observe directly phase variations, we cannot nd any indications of suchchanges. Instead, modes display slow variations of powerin time. The time/frequencyanalysis shows a nonstationary behavior of the modes. The power can grow from justabove the noise level and then decrease back to its initial level in a time of order of 10Myrs.

Correlation Between Collimation-Corrected Peak Luminosity and Spectral Lag of Gamma-ray Bursts in the Source Frame

장헌영 한국우주과학회 2012 Journal of Astronomy and Space Sciences Vol.29 No.3

We revisit the relation between the peak luminosity Liso and the spectral time lag in the source frame. Since gamma-ray bursts (GRBs) are generally thought to be beamed, it is natural to expect that the collimation-corrected peak luminosity may well correlate with the spectral time lag in the source frame if the lag-luminosity relation in the GRB source frame exists. With 12 long GRBs detected by the Swift satellite, whose redshift and spectral lags in the source frame are known, we computed L0,H and L0,W using bulk Lorentz factors Γ0,H and Γ0,W archived in the published literature, where the subscripts H and W represent homogeneous and wind-like circumburst environments, respectively. We have confirmed that the isotropic peak luminosity correlates with the spectral time lag in the source frame. We have also confirmed that there is an anti-correlation between the source-frame spectral lag and the peak energy, Epeak (1 + z) in the source frame. We have found that the collimation-corrected luminosity correlates in a similar way with the spectral lag, except that the correlations are somewhat less tight. The correlation in the wind density profile seems to agree with the isotropic peak luminosity case better than in the homogeneous case. Finally we conclude by briefly discussing its implications.

VARIATION IN NORTH-SOUTH ASYMMETRY OF SUN SPOT AREA

장헌영 한국우주과학회 2007 Journal of Astronomy and Space Sciences Vol.24 No.2

The existence of the North-South asymmetry of the solar activity is widely acceptedeven though the phenomenon is not yet satisfactorily understood. We have studiedthe temporal variations in the North-South asymmetry of the sunspot area during theperiod from May in 1874 to April in 2007. The combined data have been examinedfor periodicity in the solar activity North-South asymmetry. We have found that (i)solar northern and southern hemispheres show an asymmetric behavior, in terms ofa sunspot area, (ii) sunspot areas in northern and southern hemispheres show clearlythe 11 year periodicity when they were analyzed separately, as they do when analyzedtogether, (iii) in addition to the general 11 year periodicity in both northern and south-ern hemisphere solar activities, there are also noticeable shorter periodicities otherthan the 11 year periodicity in the asymmetry in North-South activity. Finally, weconclude by pointing out the importance of studying the North-South asymmetry ofthe solar activity.

TITIUS-BODE’S Relation and 55 Cancri

장헌영 한국우주과학회 2008 Journal of Astronomy and Space Sciences Vol.25 No.3

Two kinds of important issues on Titius-Bode’s relation have been discussed up to now: one is if there is a simple mathematical relation between distances of natural bodies orbiting a central body, and the other is if there is any physical basis for such a relation. These may be tackled by answering a question whether Titius-Bode’s relation is valid universally in exo-planetary systems. We have examined whether Titius- Bode’s relation is also applicable to exo-planetary systems by statistically studying the distribution of the ratio of rotational periods of two planets in an exo-planetary system, 55 Cnc, by comparing it with that derived from Titius-Bode’s relation. We find that the distribution of the ratio of rotational periods of randomly chosen two planets in the 55 Cnc system is apparently inconsistent with that derived from Titius-Bode’s relation. The probability that two data sets are drawn from the same distribution function is 50 %. We also find that the Fourier power spectra show that the distribution of the semi-major axis of planets in the 55 Cnc system seems to be stretched. We conclude by pointing out that large numbers of planets should be examined to more convincingly explain the distribution of the distance of planetary formatio Two kinds of important issues on Titius-Bode’s relation have been discussed up to now: one is if there is a simple mathematical relation between distances of natural bodies orbiting a central body, and the other is if there is any physical basis for such a relation. These may be tackled by answering a question whether Titius-Bode’s relation is valid universally in exo-planetary systems. We have examined whether Titius- Bode’s relation is also applicable to exo-planetary systems by statistically studying the distribution of the ratio of rotational periods of two planets in an exo-planetary system, 55 Cnc, by comparing it with that derived from Titius-Bode’s relation. We find that the distribution of the ratio of rotational periods of randomly chosen two planets in the 55 Cnc system is apparently inconsistent with that derived from Titius-Bode’s relation. The probability that two data sets are drawn from the same distribution function is 50 %. We also find that the Fourier power spectra show that the distribution of the semi-major axis of planets in the 55 Cnc system seems to be stretched. We conclude by pointing out that large numbers of planets should be examined to more convincingly explain the distribution of the distance of planetary formatio

Normalized Cross-Correlations of Solar Cycle and Physical Characteristics of Cloud

장헌영 한국우주과학회 2019 Journal of Astronomy and Space Sciences Vol.36 No.4

We explore the associations between the total sunspot area, solar north-south asymmetry, and Southern Oscillation Index (SOI) and the physical characteristics of clouds by calculating normalized cross-correlations, motivated by the idea that the galactic cosmic ray (GCR) influx modulated by solar activity may cause changes in cloud coverage, and in turn the Earth’s climate. Unlike previous studies based on the relative difference, we have employed cloud data as a whole time-series without detrending. We consider this important because the relative difference only yields a meaningful result when the relative change is similar to the overall trend. As a result, we found that the coverage of high-level and low-level cloud is at a maximum when the solar north-south asymmetry is close to the minimum, and one or two years after the solar north-south asymmetry is at a maximum, respectively. It has been determined that the global surface air temperature is at a maximum five years after the solar north-south asymmetry is at a maximum, and that the optical depth is at a minimum when the solar north-south asymmetry is at a maximum. We also found that during the descending period of solar activity, the coverage of low-level cloud is at a maximum, and global surface air temperature and cloud optical depth are at a minimum, and that the total column water vapor is at a maximum one or two years after the solar maximum.

LATITUDINAL DISTRIBUTION OF SUNSPOTS AND DURATION OF SOLAR CYCLES

장헌영 한국천문학회 2015 Journal of The Korean Astronomical Society Vol.48 No.6

We study an association between the duration of solar activity and characteristics of the latitude distribution of sunspots by means of center-of-latitude (COL) of sunspots observed during the period from 1878 to 2008 spanning solar cycles 12 to 23. We first calculate COL by taking the area- weighted mean latitude of sunspots for each calendar month to determine the latitudinal distribution of COL of sunspots appearing in the long and short cycles separately. The data set for the long solar cycles consists of the solar cycles 12, 13, 14, 20, and 23. The short solar cycles include the solar cycles 15, 16, 17, 18, 19, 21, and 22. We then fit a double Gaussian function to compare properties of the latitudinal distribution resulting from the two data sets. Our main findings are as follows: (1) The main component of the double Gaussian function does not show any significant change in the central position and in the full-width-at-half-maximum (FWHM), except in the amplitude. They are all centered at 11◦ with FWHM of 5◦. (2) The secondary component of the double Gaussian function at higher latitudes seems to differ in that even though their width remains fixed at 4◦, their central position peaks at 22.1◦ for the short cycles and at 20.7◦ for the long cycles with quite small errors. (3) No significant correlation could be established between the duration of an individual cycle and the parameters of the double Gaussian. Finally, we conclude by briefly discussing the implications of these findings on the issue of the cycle 4 concerning a lost cycle.