[1] The aa index, designed to describe the geomagnetic activity at global scale, has been shown to have increased in the twentieth century by about 65%. The increase in the case of a corrected aa is about 38%, similar to the ones of the recently introduced interhour variability (IHV) and interdiurnal variability (IDV) indices of geomagnetic activity. In terms of 11-year running averages, there is a long-term similarity between aa, R (the sunspot number), x, y, z, and r (geomagnetic indices designed to characterize the solar quiet daily variation, controlled by the solar UV radiation), and S (the solar irradiance). We show that the variation depicted by 11-year running averages of aa and R (and by consequence also of the other parameters mentioned) results from the superposition of Hale and Gleissberg cycle signatures in the corresponding time series. The IHV and IDV indices are included in the analysis. The two signals have a substantial contribution in R (10-30% and 20-34%, respectively, of the amplitude of the solar cycle 22) and aa (<12-27% and $30%, respectively, of the corresponding cycle 22 in aa). Characteristics of the two signals in the solar and geomagnetic activity and several implications of the geomagnetic activity and the solar quiet daily variation relationship with various solar outputs at the Hale and Gleissberg timescales are discussed.Citation: Demetrescu, C., and V. Dobrica (2008), Signature of Hale and Gleissberg solar cycles in the geomagnetic activity,
The present study aims to investigate the possible influence of solar/geomagnetic forcing on climate variables, such as the drought index, Danube discharge and large-scale atmospheric indices. Our analysis was performed separately for each season for two time periods, 1901–2000 and 1948–2000. The relationship between terrestrial variables and external indices was established based on the application of (1) information theory elements, namely, synergy, redundancy, total correlation, transfer entropy and (2) wavelet coherence analysis. Bandpass filtering has also been applied. The most significant signature of the solar/geomagnetic forcing in the climate variables was obtained for the data smoothed by the bandpass filter. According to our results, significant solar/geomagnetic forcing appears in the terrestrial variables with a delay of 2–3 years.
Abstract. Of the internal factors, we tested the predictors from the fields of 12 precipitation, temperature, pressure and geopotential at 500hPa. From the external factors, we 13 considered the indices of solar/geomagnetic activity. Our analysis was achieved separately for 14 each season, for two time periods 1901-2000 and 1948-2000. 15 We applied developments in empirical orthogonal functions (EOFs), cross 16 correlations, power spectra, filters, composite maps. In analysis of the correlative results, we 17 took into account, the serial correlation of time series. 18For the atmospheric variables simultaneously, the most significant results (confidence 19 levels of 95%) are related to the predictors, considering the difference between standardized 20 temperatures and precipitation (TPP), except for winter season, when the best predictors are 21 the first principal component (PC1) of the precipitation field and the Greenland-Balkan-22Oscillation index (GBOI). The GBOI is better predictor for precipitation, in comparison with 23North Atlantic Oscillation index (NAOI) for the middle and lower Danube basin. 24The significant results, with the confidence level more than 95%, were obtained for 25 the PC1-precipitation and TPP during winter/spring, which can be considered good predictors 26 for spring/summer discharge in the Danube lower basin. 27
This study addresses the causal links between external factors and the main hydro-climatic variables by using a chain of methods to unravel the complexity of the direct sun–climate link. There is a gap in the literature on the description of a complete chain in addressing the structures of direct causal links of solar activity on terrestrial variables. This is why the present study uses the extensive facilities of the application of information theory in view of recent advances in different fields. Additionally, by other methods (e.g., neural networks) we first tested the existent non-linear links of solar–terrestrial influences on the hydro-climate system. The results related to the solar impact on terrestrial phenomena are promising, which is discriminant in the space-time domain. The implications prove robust for determining the causal measure of climate variables under direct solar impact, which makes it easier to consider solar activity in climate models by appropriate parametrizations. This study found that hydro-climatic variables are sensitive to solar impact only for certain frequencies (periods) and have a coherence with the Solar Flux only for some lags of the Solar Flux (in advance).
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