GEOMAGNETIC-ACTIVITY AND THE SOLAR-WIND DURING THE MAUNDER MINIMUM

We used a strong (r = 0.96) correlation between Ii-year averages of su nspot number (SSN) and the geomagnetic aa index to infer that the mean level of geomagnetic activity during the Maunder Minimum (1645-1715) was approximately a third of that observed for recent solar cycles (si milar to 7 nT VS. similar to 24 nT). We determined the variation of Ii -year averages of solar wind speed (v) and the southward component of the interplanetary magnetic field (B-s) with cycle-averaged SSN for th e two most recent cycles and also compared cycle-averaged variations o f v(2)B(s) and aa for the same interval. We then extrapolated these ob served solar wind variations to Maunder Minimum conditions (mean SSN o f similar to 2 and mean aa value of similar to 7 nT) to deduce that, o n average, the solar wind during that period was somewhat slower (v = 340 +/- 50 km s(-1)), and the interplanetary magnetic field much smoot her (B-s = 0.3+/-0.1 nT), than at present (similar to 440 km s(-1) and similar to 1.2 nT). Various lines of evidence (including Be-10 data) suggest that, despite the virtual absence of sunspots that characteriz ed the Maunder Minimum, the 11-year geomagnetic (solar wind) cycle per sisted throughout this period.