The chart below tests the hypothesis that elevated geomagnetic activity, measured by the planetary Ap index, tends to precede weaker equity return as geomagnetic disturbances can subtly impair mood and raise risk aversion. This idea draws from decades of space-weather and market research showing direct and inverse relationships between Ap (or related Kp) readings and subsequent market performance.
S&P 500 vs. Ap Index (Apr-Oct 2026). Projected Ap peaks: Sep 4 (Fri), Sep 17–20 (Thu-Sun), Oct 1 (Thu). The chart overlays daily S&P 500 candles with Ap shifted forward by three calendar days—the short lag that currently best balances the classic weekly effect reported in the literature with practical trading-day alignment—then extends the series with the NOAA 45-day Ap outlook. Daily Ap comes from GFZ Potsdam; the dashed forward segment is the latest NOAA SWPC 45-day Ap forecast issued August 22, 2026.
However impressive the historical correlation may appear, its reliability as a guide to future correlations is inherently limited, as NOAA’s 45-day Ap outlook is a low-resolution climatological forecast whose skill declines rapidly beyond the first week. Moreover, the forcasted activity levels shown in the chart are modest (Ap 8–15) and well below classic geomagnetic storm thresholds. Short-term machine-learning Ap forecasts— e.g. the NKUA LSTM 72-hour tool or GFZ's own ap/apo models—may be better suited to assessing correlations with, and projecting, financial-instrument price behavior, although this possibility has yet to be tested.