A. Kilcik

Time Distributions of Large and Small Sunspot Groups Over Four Solar Cycles

Here we analyze solar activity by focusing on time variations of the number of sunspot groups (SGs) as a function of their modified Zurich class. We analyzed data for solar cycles 20-23 by using Rome (cycles 20 and 21) and Learmonth Solar Observatory (cycles 22 and 23) SG numbers. All SGs recorded during these time intervals were separated into two groups. The first group includes small SGs (A, B, C, H, and J classes by Zurich classification), and the second group consists of large SGs (D, E, F, and G classes). We then calculated small and large SG numbers from their daily mean numbers as observed on the solar disk during a given month. We report that the time variations of small and large SG numbers are asymmetric except for solar cycle 22. In general, large SG numbers appear to reach their maximum in the middle of the solar cycle (phases 0.45-0.5), while the international sunspot numbers and the small SG numbers generally peak much earlier (solar cycle phases 0.29-0.35). Moreover, the 10.7 cm solar radio flux, the facular area, and the maximum coronal mass ejection speed show better agreement with the large SG numbers than they do with the small SG numbers. Our results suggest that the large SG numbers are more likely to shed light on solar activity and its geophysical implications. Our findings may also influence our understanding of long-term variations of the total solar irradiance, which is thought to be an important factor in the Sun-Earth climate relationship.

Nonlinear Prediction of Solar Cycle 24

Sunspot activity is highly variable and challenging to forecast. Yet forecasts are important, since peak activity has profound effects on major geophysical phenomena including space weather (satellite drag, telecommunications outages) and has even been correlated speculatively with changes in global weather patterns. This paper investigates trends in sunspot activity, using new techniques for decadal-scale prediction of the present solar cycle (cycle 24). First, Hurst exponent H analysis is used to investigate the autocorrelation structure of the putative dynamics; then the Sugihara-May algorithm is used to predict the ascension time and the maximum intensity of the current sunspot cycle. Here we report H = 0.86 for the complete sunspot number data set (1700-2007) and H = 0.88 for the reliable sunspot data set (1848-2007). Using the Sugihara-May algorithm analysis, we forecast that cycle 24 will reach its maximum in 2012 December at approximately 87 sunspot units.

MAXIMUM CORONAL MASS EJECTION SPEED AS AN INDICATOR OF SOLAR AND GEOMAGNETIC ACTIVITIES

We investigate the relationship between the monthly averaged maximal speeds of coronal mass ejections (CMEs), international sunspot number (ISSN), and the geomagnetic Dst and Ap indices covering the 1996-2008 time interval (solar cycle 23). Our new findings are as follows. (1) There is a noteworthy relationship between monthly averaged maximum CME speeds and sunspot numbers, Ap and Dst indices. Various peculiarities in the monthly Dst index are correlated better with the fine structures in the CME speed profile than that in the ISSN data. (2) Unlike the sunspot numbers, the CME speed index does not exhibit a double peak maximum. Instead, the CME speed profile peaks during the declining phase of solar cycle 23. Similar to the Ap index, both CME speed and the Dst indices lag behind the sunspot numbers by several months. (3) The CME number shows a double peak similar to that seen in the sunspot numbers. The CME occurrence rate remained very high even near the minimum of the solar cycle 23, when both the sunspot number and the CME average maximum speed were reaching their minimum values. (4) A well-defined peak of the Ap index between 2002 May and 2004 August was co-temporal with the excess of the mid-latitude coronal holes during solar cycle 23. The above findings suggest that the CME speed index may be a useful indicator of both solar and geomagnetic activities. It may have advantages over the sunspot numbers, because it better reflects the intensity of Earth-directed solar eruptions.

Dynamics in Sunspot Umbra as Seen in New Solar Telescope and Interface Region Imaging Spectrograph Data

We analyse sunspot oscillations using Interface Region Imaging Spectrograph (IRIS) slit-jaw and spectral data and narrow-band chromospheric images from the New Solar Telescope (NST) for the main sunspot in NOAA AR 11836. We report that the difference between the shock arrival times as measured the Mg II k 2796.35\AA\ and Si IV 1393.76\AA\ line formation levels changes during the observed period and peak-to-peak delays may range from 40~s to zero. The intensity of chromospheric shocks also displays a long term (about 20~min) variations. NSTs high spatial resolution \ha\ data allowed us to conclude that in this sunspot umbral flashes (UFs) appeared in the form of narrow bright lanes stretched along the light bridges and around clusters of umbral bright points. Time series also suggested that UFs preferred to appear on the sunspot-center side of light bridges, which may indicate the existence of a compact sub-photospheric driver of sunspot oscillations. The sunspots umbra as seen in the IRIS chromospheric and transition region data appears bright above the locations of light bridges and the areas where the dark umbra is dotted with clusters of umbral dots. Co-spatial and co-temporal data from the Atmospheric Imaging Assembly on board Solar Dynamics Observatory showed that the same locations were associated with bright footpoints of coronal loops suggesting that the light bridges may play an important role in heating the coronal sunspot loops. Finally, the power spectra analysis showed that the intensity of chromospheric and transition region oscillations significantly vary across the umbra and with height, suggesting that umbral non-uniformities and the structure of sunspot magnetic fields may play a role in wave propagation and heating of umbral loops.

SOLAR RADIUS VARIATIONS: AN INQUISITIVE WAVELENGTH DEPENDENCE

Recent solar radius determinations from space observations of Mercury and Venus transits have been made by different teams in 2003, 2006, 2012, and 2014. Seemingly the results are not consistent: the authors interpreted the discrepancies as caused by the different methods of analysis. However, looking at the wavelength dependence and adding other available observations from X-EUV up to radio, a typical wavelength dependence can be found, reflecting the different heights at which the lines are formed. Measurements obtained during different periods of time would, in principle, allow us to detect a signature of radius temporal dependence. However, the available data are not sufficiently numerous to detect a significant dependence, at least at the level of the uncertainty at which the observations were made. Lastly, no unique theoretical model is available today to reproduce the strong wavelength dependence of the solar radius, which shows an unexpected minimum at around (6.6 ± 1.9) μm, after a parabolic fit.

Possible traces of solar activity effect on the surface air temperature of mid-latitudes

In this study we investigate the effects of solar activity on the surface air temperature of mid-latitudes. This enables us to understand existence of solar activity effects on the tem- perature. We used surface air temperature and pressure data as climate parameters, and solar flare index data as solar activity indicator, for the 25 - 50 degree longitude and 30 - 70 degree latitude zone, including Turkey and European part of Russia. We considered the parameters temperature, pressure and flare index data for the period ranging from January 1975 to the end of December 2007, which covers almost three solar cycles, namely 21 st ,2 2 nd ,a nd 23 rd . We found some significant correlations between solar activity and surface air temperature for cycles 22 and 23 for some zones. We applied multitaper method to obtain the cyclic behavior of surface air temperature data sets. The most pronounced power peaks were found by this transform around 1.2 and 2.5 years which were reported earlier for some solar activity indicators. We concluded that signature of solar activity effect exists on surface air temperature of mid-latitudes where we studied.

Temporal and Periodic Variations of Sunspot Counts in Flaring and Non-Flaring Active Regions

We analyzed temporal and periodic variations of sunspot counts (SSCs) in flaring (C-, M-, or X-class flares), and non-flaring active regions (ARs) for nearly three solar cycles (1986 through 2016). Our main findings are as follows: i) temporal variations of monthly means of the daily total SSCs in flaring and non-flaring ARs behave differently during a solar cycle and the behavior varies from one cycle to another; during Solar Cycle 23 temporal SSC profiles of non-flaring ARs are wider than those of flaring ARs, while they are almost the same during Solar Cycle 22 and the current Cycle 24. The SSC profiles show a multi-peak structure and the second peak of flaring ARs dominates the current Cycle 24, while the difference between peaks is less pronounced during Solar Cycles 22 and 23. The first and second SSC peaks of non-flaring ARs have comparable magnitude in the current solar cycle, while the first peak is nearly absent in the case of the flaring ARs of the same cycle. ii) Periodic variations observed in the SSCs profiles of flaring and non-flaring ARs derived from the multi-taper method (MTM) spectrum and wavelet scalograms are quite different as well, and they vary from one solar cycle to another. The largest detected period in flaring ARs is 113±1.6days

Critical frequencies of the ionospheric F1 and F2 layers during the last four solar cycles: Sunspot group type dependencies

113\pm 1.6~\mbox{days}

The Ratio Between the Number of Sunspot and the Number of Sunspot Groups

while we detected much longer periodicities (327±13

Temporal Offsets between Maximum CME Speed Index and Solar, Geomagnetic, and Interplanetary Indicators during Solar Cycle 23 and the Ascending Phase of Cycle 24

327\pm 13