Transient Upstream Mesoscale Structures: Drivers of Solar-Quiet Space Weather

TL;DR

This paper reviews how transient upstream mesoscale structures (TUMS) can trigger localized space weather disturbances independently of large solar wind events, especially during solar minima.

Contribution

It identifies and describes the role of four major TUMS types in driving quiet-time space weather phenomena, expanding understanding beyond large-scale solar wind impacts.

Findings

TUMS are linked to localized geomagnetic and auroral disturbances.

Quiet space weather events are more frequent during solar minima.

TUMS can cause significant space weather effects without large solar wind disturbances.

Abstract

In recent years, it has become increasingly clear that space weather disturbances can be triggered by transient upstream mesoscale structures (TUMS), independently of the occurrence of large-scale solar wind (SW) structures, such as interplanetary coronal mass ejections and stream interaction regions. Different types of magnetospheric pulsations, transient perturbations of the geomagnetic field and auroral structures are often observed during times when SW monitors indicate quiet conditions, and have been found to be associated to TUMS. In this mini-review we describe the space weather phenomena that have been associated with four of the largest-scale and the most energetic TUMS, namely hot flow anomalies, foreshock bubbles, travelling foreshocks and foreshock compressional boundaries. The space weather phenomena associated with TUMS tend to be more localized and less intense compared to geomagnetic storms. However, the quiet time space weather may occur more often since, especially during solar minima, quiet SW periods prevail over the perturbed times.