Quantification of the Direct Solar Impact on Some Components of the Hydro-Climatic System

Abstract

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).

Keywords: causality; climate response; entropy transfer; neural networks; solar impact; time series; wavelet analysis.

Figure 1

Nonlinearities between the Solar Flux (X1) and the climate variables NAOI (X2) and the Danube discharge at the Orsova station (X3) during winter (1948–2000). Plane projection: (a) for (X1, X2), (b) for (X1, X3), (c) for (X2, X3) and (d) space projection for (X1, X2, X3).

Figure 2

Wavelet spectrum in winter (1948–2000) for Solar Flux (top) and NAOI (bottom).

Figure 3

Wavelet coherence (WTC) between Solar Flux and NAOI in winter for: (a) Simultaneously (Lag = 0) time series (1948–2000); (b–d) Solar Flux in advance of NAOI with Lag from 1 to 3 years.

Figure 3

Wavelet coherence (WTC) between Solar Flux and NAOI in winter for: (a) Simultaneously (Lag = 0) time series (1948–2000); (b–d) Solar Flux in advance of NAOI with Lag from 1 to 3 years.

Figure 4

Standardized time series of Solar Flux (red) and NAOI (green) in winter for: (a) Lag = 0 (1948–2000) and (b) Lag = 3 (Solar Flux 1948–1997; NAOI 1951–2000).