  We study the occurrence of magnetic storms in space age (1957-2021) using Dst
and Dxt indices. We find 2526/2743 magnetic storms in the Dxt/Dst index, out of
which 45% are weak, 40% moderate, 12% intense and 3% major storms. Occurrence
of storms in space age follows the slow decrease of sunspot activity and the
related change in solar magnetic structure. We quantify the sunspot - CME storm
relation in the five cycles of space age. We explain how the varying solar
activity changes the structure of the heliospheric current sheet (HCS), and how
this affects the HSS/CIR storms. Space age started with a record number of
storms in 1957-1960, with roughly one storm per week. Solar polar fields
attained their maximum in cycle 22, which led to an exceptionally thin HCS, and
a space age record of large HSS/CIR storms in 1990s. In the minimum of cycle
23, for the only time in space age, CME storm occurrence reduced below that
predicted by sunspots. Weak sunspot activity since cycle 23 has weakened solar
polar fields and widened the HCS, which has decreased the occurrence of large
and moderate HSS/CIR storms. Because of a wide HCS, the Earth has spent 50% of
its time in slow solar wind since cycle 23. The wide HCS has also made large
and moderate HSS/CIR storms occur in the early declining phase in recent
cycles, while in the more active cycles 20-22 they occurred in the late
declining phase.
