Extreme Space Weather Events during the First Cycles of Epochs with Decreased Solar Activity

The problem of the distribution of extreme and very strong magnetic storms with intensities (G5, G4) in the first cycles (12 and 24) of epochs of lowered solar activity was considered based on homogeneous series of the geomagnetic index Aa with allowance for the modern scale of the intensity of disturbances in the near-Earth space and the scenario of solar cyclicity. The significant decrease in the number of such events and active solar phenomena in the last cycle may indicate that the sunspot and flare activity in solar cycle 12 was significantly higher than that in cycle 24, but it was significantly lower than in solar cycles of the epoch of increased solar activity.

Annual 14C Tree-Ring Data Around 400 AD: Mid- and High-Latitude Records

ABSTRACTTwo tree-ring series, one from a high-latitude pine tree (located in northern Scandinavia) and one from a mid-latitude oak tree (located in eastern Germany) were analyzed for radiocarbon (14C) at annual resolution. The new records cover the calendar date ranges 290–460 AD and 382–486 AD, respectively, overlapping by 79 yr. The series show similar trends as IntCal13. However, some significant deviations around 400 AD are present with lower Δ14C (higher 14C ages). An average offset between the two new series and IntCal13 of about 20 years in conventional 14C age is observed. A latitudinal 14C offset between the tree sites in central and northern Europe, as would be expected due to the relatively large spatial distance, is not recorded, however. Periodic changes in the 14C records are resolved that can be attributed to the “11-year” solar cycle (Schwabe cycle) with cycle length from 9 to 11 years. The magnitude of changes in Δ14C due to the solar cycle is between 1.5 and 3‰. Since solar cyclicity is only partially synchronous between the two new series, reasons for asynchronicity are explored.