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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.

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. [ABSTRACT FROM AUTHOR]

To analyze the influence of high‐speed jets (HSJs) on the position of the magnetopause during long‐term radial interplanetary magnetic fields (IMFs), we report three events of magnetopause expansions and indentions by HSJs observed by Time History of Events and Macroscale Interactions during Substorms. In these events, the upstream solar wind condition is stable and the IMF direction is quasi‐radial, characterized by the cone angle less than 30°. Actually, such upstream conditions are rare, especially when the HSJ is observed near the magnetopause crossing time. The actual positions of the magnetopause in these three cases are further away from Earth than that shown by the empirical models. A local indention in the magnetopause caused by HSJ is inferred by the inward movement of the magnetopause from the compression of HSJ. It is the first time to report the simultaneous magnetopause expansion under radial IMF and magnetopause indention caused by HSJ. Plain Language Summary: High‐speed jets (HSJs) are localized high dynamic pressure pulses observed in the magnetosheath. It is generated downstream of the bow shock and moves toward the magnetopause. Typically, strong HSJs will reach the magnetopause, compress the surrounding plasma, and produce local indentions. Meanwhile, the radial interplanetary magnetic fields (IMFs) are more favorable for the generation and propagation of the HSJ. However, radial IMF conditions also lead to an outward movement of the magnetopause compared to the empirical model. Therefore, based on these two opposing physical processes of the magnetopause, we selected three cases of HSJ under long‐term radial IMFs to analyze their influence on the position of the magnetopause. The result shows that under the long‐term quasi‐radial IMF conditions, the dayside magnetopause expands, compared to its shown by the empirical model. Then, the subsequent HSJ compress the plasma and locally move the expanded magnetopause inward. It is the first time to report the simultaneous magnetopause expansion under radial IMF and indention caused by HSJ. Key Points: Magnetopause crossings from Time History of Events and Macroscale Interactions during Substorms under prolonged radial interplanetary magnetic field (IMF) are investigatedSimultaneous magnetopause expansion under prolonged radial IMF and magnetopause indention caused by high‐speed jet are reported [ABSTRACT FROM AUTHOR]