An Overview of Solar Orbiter Observations of Interplanetary Shocks in Solar Cycle 25

TL;DR

This paper presents a comprehensive survey of the first 100 interplanetary shocks observed by Solar Orbiter during solar cycle 25, analyzing their properties, wave environments, and energetic particle responses in the inner heliosphere.

Contribution

It provides the first in situ measurements of interplanetary shocks at various distances, including a new shock identification algorithm and accessible dataset for further research.

Findings

Quasi-parallel shocks and high-speed shocks are more common closer to the Sun.

Approximately 50% of shocks show upstream fluctuations caused by shock interactions.

Complex energetic particle responses are observed, influenced by pre-existing solar wind structures.

Abstract

Interplanetary shocks are fundamental constituents of the heliosphere, where they form as a result of solar activity. We use previously unavailable measurements of interplanetary shocks in the inner heliosphere provided by Solar Orbiter, and present a survey of the first 100 shocks observed in situ at different heliocentric distances during the rising phase of solar cycle 25. The fundamental shock parameters (shock normals, shock normal angles, shock speeds, compression ratios, Mach numbers) have been estimated and studied as a function of heliocentric distance, revealing a rich scenario of configurations. Comparison with large surveys of shocks at 1~au show that shocks in the quasi-parallel regime and with high speed are more commonly observed in the inner heliosphere. The wave environment of the shocks has also been addressed, with about 50\% of the events exhibiting clear shock-induced upstream fluctuations. We characterize energetic particle responses to the passage of IP shocks at different energies, often revealing complex features arising from the interaction between IP shocks and pre-existing fluctuations, including solar wind structures being processed upon shock crossing. Finally, we give details and guidance on the access use of the present survey, available on the EU-project ``solar energetic particle analysis platform for the inner heliosphere'' (SERPENTINE) website. The algorithm used to identify shocks in large datasets, now publicly available, is also described.