11-year solar activity cycle and the US GDP index (1948 – 2025): R2=1.0 (SA growth phase), R2=0.99 (SA decline phase)

This paper uses a methodological approach developed by W.S. Jevonson and A.L. Chizhevsky. The years of the solar cycle were numbered in the order established in solar astrophysics and compared with the average values of the US GDP indices and Wolf numbers. The determination coefficient R2 on the Wolf number diagram for the US GDP index in the CA growth phase (years 1–4 of cycles, 29 years of observation) was 1.0, while in the decline phase (years 4–11 of cycles, 55 years of observation) it was 0.99. The diagram data shows the minimum values of the US GDP indices in the region of extremes (maximums and minimums) of the Wolf numbers. A three-zone neuroendocrine model of the cyclical dynamics of US GDP has been developed. 1. "Biological depression" zone (Wolf number (W) < 20): A deficiency of ultraviolet radiation leads to a decrease in serotonin levels, creating a mood of pessimism and stagnation of US GDP. 2. "Biological optimum" zone (W = 20–130): Sufficient levels of serotonin and melatonin ensure optimism and peak growth rates of US GDP with a lag of 1 year. 3. "Biological Stress" Zone (W > 130): Extreme solar activity suppresses melatonin production (according to R. Reiter's concept), causing "exhaustion pessimism," a decline in consumer and investment activity, and a sharp decline in US GDP growth. The identified relationships allow us to predict the US GDP index. With a predicted 2026 Wolf number of 93.76, the predicted US GDP for 2026 is 3.33%.