arXiv subjects

Timo Qvick

Publications and source records attributed to Timo Qvick.

2 recordsLinked to original sources

arXiv2026

Photospheric index of geomagnetic activity

Geomagnetic indices quantify the disturbances of the Earth's magnetic field. They form an important space weather and space climate record that tracks solar-terrestrial effects on the Earth. Although geomagnetic activity has its origins in the photospheric magnetic fields, the two have so far not been directly related. We develop a photospheric index of geomagnetic activity (PIGA) that measures the geoeffectiveness of the Sun based on photospheric magnetic field as presented in synoptic magnetograms. We construct the PIGA from synoptic magnetograms of Wilcox Solar Observatory by relating the equatorial and axial dipole components of the photospheric magnetic field to the geomagnetic Kp index by means of linear regression. PIGA captures well the evolution of the geomagnetic activity over the past 50 years at the resolution of solar rotation, having linear correlation of 0.71 with the geomagnetic Kp index. PIGA makes it straightforward to measure the geoeffectiveness of the Sun using the dominant structure of the global solar magnetic field. PIGA can for example be used to study the geoeffectiveness of the Sun using historical simulations or the predicted solar magnetic field. PIGA also allows to use observed geomagnetic activity as an additional constraint for the early magnetic field reconstructions of the solar magnetic field.

astro-ph.SR↗

arXiv2022

Magnetic storms during the space age: Occurrence and relation to varying solar activity

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.

astro-ph.SR↗