The North-South Asymmetry in the Green Corona

The north-south asymmetry of the Fe XIV 530.3 nm coronal emission line (the green corona) over cycle 22 was investigated. The green corona line brightness was dominant in the southern hemisphere during cycle 22 (A = –0.07), except for short periods of the ascending phase of the activity cycle. The asymmetry of the semi-annual mean over the period 1940 – 1996 was also studied. The asymmetry, during these years, reached its maximum in 1962 – 1966, and then decreased. Important periodicities of the asymmetry in cycle 22, e.g., 158 and 350 days, 2.39 years were found. Similar periodicities were also detected in the years 1940 – 1996. An FFT analysis was used to detect these periodicities.     

Interannual variability of United States cloudiness

United States cloudiness data for 1950–1992 show quasi-biennial (QBO) and quasi-triennial (QTO) oscillations which match partly with the QBO and QTO of the Southern Oscillation (SO) index (the Tahiti minus Darwin pressure), but not with the QBO of the 50-mb equatorial zonal wind. Cloudiness also shows significant periodicities near 4.2 and 7.5 years, and probably a sunspot cycle effect (periodicities 11–14 years), with minimum cloudiness at or soon after sunspot minima, though this could also be due to periodicities of 10 and 17 years observed in the SO index. During 1955-1970, cloudiness increased by about 1%. Thereafter, it remained almost steady for the eastern and central parts of the USA, but continued to rise until about 1980 for the western USA.     

Signature of ENSO Signals in the Coral Growth Rate Record of Arabian Sea and Indian Monsoons

We examine here three sets of recently published data: (1) Updated Indian Rainfall (IRF) time series of the entire country covering the time span of 1826–1994, (2) coral growth rate time series for a period of 42 years spanning 1948–1990 from the Arabian Sea, and (iii) NINO3 temperature records to investigate the signature of ENSO response of the Indian monsoon. Multiple spectral techniques (e.g., multi-taper method (MTM), maximum entropy method (MEM), wavelet and cross spectra) are used to identify the coherent cyclic and nonstationary modes in these records. MTM analysis of IRF time series resolves statistically significant variability (>90% C.I) (i) at multi-decadal (66–70 years) scales related to the well-known global temperature variability of internal atmospheric-ocean origin, (ii) relatively weak signals at 13 and 22 years (solar cycles) and (iii) the 2.5 to 7.5-year cycles associated with the ENSO frequency band. The MTM spectra of the coral growth rate record also reveal statistically significant periodicities (>90% C.I.) within 1.8–4.2 ENSO frequency band, and a relatively weak signal at 12.8 years. MEM analysis confirms the stability of above spectral peaks. Wavelet spectral analyses of the above time series reveal nonstationary localized modes of ENSO evolution corresponding to 2–7 years and higher order terms. Although matching periodicities are present in these records, cross-spectral analysis of IRF and NINO3 temperature records exhibits significant coherency (>80% CI) only at periods 5.4 years and 2.7 years, suggesting the significant role of ENSO dynamics in organizing the subtle Indian monsoon at these frequencies. These results may provide significant implication for the modeling of Indian monsoon.     

Solar Activity Effects on Gravity Wave Activity Inferred from Radio Wave Absorption in the Lower Ionosphere

The low frequency (LF) nighttime radio-wave absorption in the lower ionosphere has been measured at Prhonice (50°N, 15°E) in central Europe for over 35 years. Digital measurements, performed since summer 1988, allow absorption oscillations in the period range 10 – 180 mins, which are believed to reflect gravity wave activity, to be derived. Unfortunately, problems with the transmitter in recent years terminated the evaluation of gravity wave activity. The analysis of the available information (6 years of data) allows two conclusions to be drawn as to the effects of the solar activity on gravity wave activity: (1) there is no detectable effect of the solar 27-day variation on gravity wave activity; (2) there is an indication that the positive effect of the 11-year solar cycle on gravity wave activity in the winter half of the year is remarkable (lack of data in summer). The result concerning the solar cycle effect is, to a certain extent, preliminary, because the available data do not cover a complete solar cycle. A comparison with results from other stations and an interpretation of results are presented.     

Sunspot numbers and area-weighted united states monthly temperature and precipitation

Spectral analyses were made of derived area-index series of areas subject to extreme temperatures and precipitation as well as cross-spectral analyses of the area-index series with double sunspot cycle (Zurich) numbers. Superposed epoch analyses also were made of area-index series versus various double-sunspot cycle phases. Area series for wet and dry Junes, warm Junes, defined June drought, and warm Januaries all show statistically significant double sunspot cycle (21 year) periodicities. The 21-year cycle of above-normal June precipitation is most striking and has not received previous recognition.Journal Paper No. J-10007 of the Iowa Agric. and Home Econ. Exp. Stn., Iowa State University, Ames, IA, 50011, Project 2397.     

Prediction possibilities of Arosa total ozone

Using the periodicities obtained by a Maximum Entropy Spectral Analysis (MESA) of the Arosa total ozone data (CC) series for 1932–1971, the values predicted for 1972 onwards were compared with the observed values of the (AD) series. A change of level was noticed, with the observed (AD) values lower by about 7 D.U. Also, the matching was poor in 1980, 1981, 1982. In the monthly values, the most prominent periodicity was the annual wave, comprising some 80% variance. In the 12 month running averages, the annual wave was eliminated and the most prominent periodicity wasT=3.7 years, encompassing roundly 20% variance. This and other periodicities atT=4.7, 5.4, 6.2, 10 and 16 years were all statistically significant at a 3.5a priori i.e., 2a posteriori level. However, the predictions from these were unsatisfactory, probably because some of these periodicities may betransient i.e., changing amplitudes and/or phases with time. Thus, no meaningful prediction seem possible for Arosa total ozone.     

The sunspot areas and the relative sunspot numbers

Summary Within each sunspot cycle the yearly means (A) of the daily sunspot areas increase faster than the corresponding sunspot numbers (R) from the minimum to the maximum of solar activity and then decrease also faster than these numbers till the next minimum. Relation (A)=16.7 (R), frequently used so far, is approximately valid only for the years in the vicinity of the sunspot maximum. Instead of that, author gives the relations: for the years preceding the sunspot maximum, for the years following the sunspot maximum, wherea andb are constants,T _R is the time of rise of the corresponding sunspot cycle expressed in years, andk takes the valuek=0 for the year of maximum solar activity andk=1, 2, 3, ... for the first, second, third ... year preceding or following that of maximum solar activity. The monthly means of the daily sunspot areas show a similar variation, but in this case the ratioq=AR varies with a greater amplitude both within each sunspot cycle and from cycle to cycle. The values ofq corresponding to all months of a given year in the sunspot cycle are contained between two limits depending on the time of rise.

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Résumé Les valeurs moyennes (A) des aires diurnes des taches solaires à chaque année depuis 1878 augmentent plus rapidement du minimum vers le maximum de l'activité solaire que les nombres de Wolf correspondants (R). Elles diminuent aussi plus rapidement que les nombres de Wolf du maximum vers le minimum de l'activité solaire. La relation adoptée (A)=16.7 (R) ne s'applique pas avec une approximation satisfaisante que seulement pour les années voisines celle du maximum de l'activité solaire. L'auteur propose les relations: pour les années qui précédent le maximum, pour les années qui suivent le maximum, oùa, b sont des constantes,T _R le temps d'ascension du cycle correspondant exprimé en années et la parametrek prend la valeurk=0 à l'année du maximum de l'activité solaire etk=1, 2, 3 ... pour les années qui précédent et qui suivent celle du maximum. Les valeurs moyennes des aires diurnes des taches à chaque mois, suivent la même marche mais dans ce cas le rapportq=AR present des larges variations. Il oscille pourtant extre deux limites qui dependent du temps d'ascension.

     

On the periodic variations of geomagnetic activity indices Ap and ap

Yearly averages of geomagnetic activity indices Ap for the years 1967–1984 are compared to the respective averages of v² · B_s, where v is the solar wind velocity and B_s is the southward interplanetary magnetic field (IMF) component. The correlation of both quantities is known to be rather good. Comparing the averages of Ap with v² and B_s separately we find that, during the declining phase of the solar cycle, v² and during the ascending phase B_s have more influence on Ap. According to this observation (using Fourier spectral analysis) the semiannual and 27 days, Ap variations for the years 1932–1993 were analysed separately for years before and after sunspot minima. Only those time-intervals before sunspot minima with a significant 27-day recurrent period of the IMF sector structure and those intervals after sunspot minima with a significant 28–28.5-day recurrent period of the sector structure were used. The averaged spectra of the two Ap data sets clearly show a period of 27 days before and a period of 28–29 days after sunspot minimum. Moreover, the phase of the average semiannual wave of Ap is significantly different for the two groups of data: the Ap variation maximizes near the equinoxes during the declining phase of the sunspot cycle and near the beginning of April and October during the ascending phase of the sunspot cycle, as predicted by the Russell-McPherron (R-M) mechanism. Analysing the daily variation of ap in an analogue manner, the same equinoctial and R-M mechanisms are seen, suggesting that during phases of the solar cycle, when ap depends more on the IMF-B_s component, the R-M mechanism is predominant, whereas during phases when ap increases as v increases the equinoctial mechanism is more likely to be effective.     

Time variations of geomagnetic activity indices Kp and Ap: an update

Kp and Ap indices covering the period 1932 to 1995 are analysed in a fashion similar to that attempted by Bartels for the 1932–1961 epoch to examine the time variations in their characteristics. Modern analysis techniques on the extended data base are used for further insight. The relative frequencies of occurrence of Kp with different magnitudes and the seasonal and solar cycle dependences are seen to be remarkably consistent despite the addition of 35 years of observations. Many of the earlier features seen in the indices and special intervals are shown to be replicated in the present analysis. Time variations in the occurrence of prolonged periods of geomagnetic calm or of enhanced activity are presented and their relation to solar activity highlighted. It is shown that in the declining phase the occurrence frequencies of Kp = 4–5 (consecutively over 4 intervals) can be used as a precursor for the maximum sunspot number to be expected in the next cycle. The semiannual variation in geomagnetic activity is reexamined utilising not only the Ap index but also the occurrence frequencies of Kp index with different magnitudes. Lack of dependence of the amplitude of semiannual variation on sunspot number is emphasised. Singular spectrum analysis of the mean monthly Ap index shows some distinct periodic components. The temporal evolution of 44 month, 21 month and 16 month oscillations are examined and it is postulated that while QBO and the 16 month oscillations could be attributed to solar wind and IMF oscillations with analogous periodicity, the 44 month variation is associated with a similar periodicity in recurrent high speed stream caused by sector boundary passage. It is reconfirmed that there could have been only one epoch around 1940 when solar wind speed could have exhibited a 1.3-year periodicity comparable to that seen during the post-1986 period.     

Quasi-Biennial and Quasi-Triennial Oscillations in some atmospheric parameters

A spectral analysis of the 12-month running averages of several atmospheric parameters for 40 years (1951–1990) indicated prominent QBO (Quasi-Biennial Oscillations) and QTO (Quasi-Triennial Oscillations). The 50 mb tropical wind has a very prominent QBO peak atT=2.33 years, which was well reflected in N. Pole 30 mb temperature but not in average surface air temperatures of Northern and Southern Hemispheres. The 50 mb wind had no prominent QTO; but sea-surface temperatures showed prominent QTO at 3.6 years as well as peaks at 4.8 years (also shown by N. Pole 30 mb temperature) which matched very well with similar peaks in the Pacific SST and SO (Southern Oscillation) index. Specific humidity in the lower troposphere (1000 and 700 mb) and temperature at 300 mb obtained by radiosondes in the western Pacific for 15 years (1974–1988) showed mainly a biennial oscillation.     

Prediction of sunspot number amplitude and solar cycle length for cycles 24 and 25

The prediction of solar activity strength for solar cycles 24 and 25 is made on the basis of extrapolation of sunspot number spectral components. Monthly sunspot number data during the 1850–2007 interval (solar cycles 9–23) are decomposed into several levels and searched for periodicities by iterative regression in each level. For solar cycle 24, the peak is predicted in November 2013 with a sunspot number of 113.3. The cycle is expected to be weak, with a length of 133 mo (months) or 11.1 yr. The sunspot number maximum in cycle 25 is predicted to occur in April 2023 with a sunspot number 132.1 and a solar cycle length of 118 mo or 9.8 yr. Thus, solar cycle 24 is predicted to have an intensity 23% lower than cycle 23, and cycle 25 will be 5% lower than cycle 23.     

Quasi-biennial oscillation in foF2 at the south crest of the equatorial anomaly

The aim of this paper is to report some periodicities observed in the ionospheric parameter foF2 measured at Tucuman (26.9°S; 65.4°W), station placed near the southern crest of the equatorial anomaly. For that, monthly medians of foF2 at several hours of LT for the period 1958–1987 are used. The data are run with Fast Fourier Transform (FFT). Data gaps (4–5 months) are filled by means of linear interpolation. Several periodicities are present. Besides the solar cycle dominant dependence (11 years), semi-annual, annual, five years and quasi-biennial periodicities are also observed. A marked quasi-biennial periodicity is observed at daytime and nighttime hours being their greater amplitude at local noon and midnight. Different mechanisms or combined effects possibly cause them. It is suggested that the solar activity by means of extreme ultraviolet radiation (EUV), which present a quasi-biennial oscillation (QBO) and it is responsible for the ionization, could be the dominant mechanism for the diurnal quasi-biennial periodicity of foF2. At night, since the photoionization by extreme ultraviolet radiation is not significant and the F2 layer is lower than during daytime (100 km) other mechanism may be operative for the quasi-biennial periodicity observed. Possibly the stratospheric QBO contributes to the modulation of the observed behaviour in foF2 at night. This result is preliminary because it needs to be extended to other stations so as to extract definite conclusions. Moreover, we cannot dismiss the possibility of a combined effect of both these mechanisms mainly at daytime and/or QBO influence of geomagnetic parameters.     

Transition of solar cycle length in association with the occurrence of grand solar minima indicated by radiocarbon content in tree-rings

In this paper, we review the variation of the 11-year solar cycle since the 15th century revealed by the measurement of radiocarbon content in single-year tree-rings of Japanese cedar trees. Measurements of radiocarbon content in absolutely dated tree-rings provide a calibration curve for accurate dating of archaeological matters, but at the same time, enable us to examine the variations of solar magnetic activity in the pre-historical period. The Sun holds several long-term quasi-cyclic variations in addition to the fundamental 11-year sunspot activity cycle and the 22-year polarity reversal cycle, and it is speculated that the property of the 11-year and the 22-year solar cycle varies in association with such long-term quasi-cycles. It is essential to reveal the details of solar variations around the transition time of solar dynamo for illuminating the mechanisms of the long-term solar variations. We therefore have investigated the property of the 11-year and 22-year cycles around the two grand solar minima; the Maunder Minimum (1645–1715 AD) and the Spoerer Minimum (1415–1534 AD), the periods of prolonged sunspot minima. As a result, slight stretching of the “11-year” and the “22-year” solar cycles was found during these two grand solar activity minima; continuously during the Maunder Minimum and only intermittently during the Spoerer Minimum. On the contrary, normal or slightly shortened 11-year cycles were detected during the interval period of these two minima. It suggests the inverse correlation between the solar cycle length and solar magnetic activity level, and also the change of meridional flow during the grand solar activity minima. Further measurements for the beginning of the grand solar minima will provide a clue to the occurrence of such prolonged sunspot disappearance. We also discuss the effect of solar variations to radiocarbon dating.     

Fractal approach of the temporal earthquake distribution in the Hellenic arc-trench system

The time clustering of earthquakes occurring in the Hellenic arc-trench system is quantitatively analyzed by means of the fractal dimension,D, of their time distribution in the time intervals of 1950–1985 (M _s >-4.5) and 1964–1985 (M _s 4.0). The results obtained imply that scale-invariant clustering holds over very large scale lengths of time,T, with 2²–2⁸T (in min) 2²⁰–2²², depending on the seismotectonic segment considered. In all segments a common feature is the relation between theD ₁,D ₂ andD ₃-values found for shallow, intermediate-depth and all-depth shocks, respectively:D ₃>D₁>D₂. TheD-values found for shallow shocks range between 0.137 and 0.191 with the exception of the Ionian Islands and Cretan segments where anomalously high values (D=0.221–0.251) have been determined. We discuss possible seismotectonic interpretations of the results.     

The sunspot cycle, the QBO, and the total ozone over Northeastern Europe: a connection through the dynamics of stratospheric circulation

The interaction between the factors of the quasi-biennial oscillation (QBO) and the 11-year solar cycle is considered as an separate factor influencing the interannual January–March variations of total ozone over Northeastern Europe. Linear correlation analysis and the running correlation method are used to examine possible connections between ozone and solar activity at simultaneous moment the QBO phase. Statistically significant correlations between the variations of total ozone in February and, partially, in March, and the sunspot numbers during the different phases of QBO are found. The running correlation method between the ozone and the equatorial zonal wind demonstrates a clear modulation of 11-y solar signal for February and March. Modulation is clearer if the QBO phases are defined at the level of 50 hPa rather than at 30 hPa. The same statistical analyses are conducted also for possible connections between the index of stratospheric circulation C₁ and sunspot numbers considering the QBO phase. Statistically significant connections are found for February. The running correlations between the index C₁ and the equatorial zonal wind show the clear modulation of 11-y solar signal for February and March. Based on the obtained correlations between the interannual variations of ozone and index C₁, it may be concluded that a connection between solar cycle – QBO – ozone occurs through the dynamics of stratospheric circulation.     

Temperature variability in central Mexico and its possible association to solar activity

Minimum extreme temperature variability from five meteorological stations in the central part of Mexico covering a period from 1920 to 1990 is examined. We found a correlation coefficient (r=0.65) between these temperature records and geomagnetic activity. Furthermore, by performing spectral analysis peaks were obtained with similar periodicities to those found in the sunspot number, the magnetic solar cycle, cosmic ray fluxes and geomagnetic activity; all of these phenomena are modulated by solar activity. Signals with periodicities comparable to those observed in El Niño and the Quasi-Biennial Oscillation were also identified. We conclude that the solar signal is probably present in the minimum extreme temperature record of the central part of Mexico.     

Differences between Mean Sea Levels for the Pacific,Atlantic and Indian Oceans From Topex/Poseidon Altimetry

Geopotential values W of the mean equipotential surfaces representing the mean ocean topography were computed on the basis of four years (1993 - 1996) TOPEX/POSEIDON altimeter data: W = 62 636 854.10m ² s ^–2 for the Pacific (P), W = 62 636 858.20m ² s ^–2 for the Atlantic (A), W = 62 636 856.28m ²s^–2 for the Indian (I) Oceans. The corresponding mean separations between the ocean levels were obtained as follows: A – P = – 42 cm, I– P = – 22 cm, I – A = 20 cm, the rms errors came out at about 0.3 cm. No sea surface topography model was used in the solution.     

Decade fluctuations in the rotation rate of the earth in the last 200 years

Maximum Entropy Spectral Analysis and Multiple Regression Analysis of the 200 year series (1781–1980) of the change in L.O.D. (Length of Day) revealed significant peaks atT=21, 32, 50, 63 and possibly 120 years. The periodsT=22 and 44 years seem to be stable over 200 years.     

Spectrum of geomagnetic activity in the period range 5–60 days: possible lunar influences

The series of daily Ap-indices has been subdivided into pentades (1932–1936 etc.) and spectra with fine-frequency resolution have been calculated for the indices in each of these intervals. Daily sunspot numbers have been processed in the same way. The average spectrum from all spectra in the pentades, as well as the spectrum from the whole interval have been calculated, and significant peaks have been determined. There is a significant difference between the spectra in the pentades containing the solar activity minimum (1932–1936, 1942–1946 etc.) and those containing the solar activity maximum (1937–1941, 1947–1951 etc.). Most peaks can be interpreted as a response to solar rotation and to the structure of solar wind speed (two high-speed streams per solar rotation), both modulated by the 11-year, annual and semi-annual waves. No significant peak corresponding to the period of the synodic month, or its half has been found. This result suggests that the influence of lunar cycles on some natural phenomena (if any) is not mediated by geomagnetic activity.