Discovery of the pearl waves by Eyvind Sucksdorff

Eyvind Sucksdorff (1899–1955) was an enthusiastic scientist who was the director of Sodankylä Geophysical Observatory (SGO) from 1927 to 1945. He continued magnetic measurements, which were started in 1913 when SGO was established. Sucksdorff observed events with periodically modulated amplitude in the registration of the new La Cour quick-run magnetometers in 1932–35. He interpreted these events to be due to short-period oscillations and called them “rapid micropulsations” or “pearl necklace” due to the shape of the signal in the registration. From the “pearl necklaces” he estimated the upper bound of the oscillation to be 2–3 s. Sucksdorff did not know the accurate values of the eigenperiods of the systems (H, D and Z components of the magnetometer). Later measurements have shown that they were 2–3 s. Nowadays, the pearl pulsations discovered by Sucksdorff 70 years ago are known as a subgroup of Pc1 magnetic pulsations. Sucksdorff published his observations in 1936. He studied both the annual and diurnal distributions of the new pulsations. Comparisons of the records made in Stockholm, Copenhagen and Sodankylä revealed for the first time the global features of Pc1 pulsations. Sucksdorff did not present any explanation for the pearl pulsations he had observed. Leiv Harang from the Auroral Observatory at Tromsø, Norway, published his analysis of rapid registrations made in Tromsø in 1932–36 in the same issue of the Terrestrial Magnetism and Atmospheric Electricity. He used the name “vibrations” for his short-period oscillations.