ARTEMIS Observations of Foreshock Transients in the Midtail Foreshock

Foreshock transients such as hot flow anomalies (HFAs) are frequently observed in the dayside foreshock. They can disturb the local bow shock, magnetopause, and consequently the magnetosphere-ionosphere system through dynamic pressure perturbations. Recent multipoint observations found that such perturbations can even propagate from the dayside to the midtail. However, whether the drivers of such perturbations, foreshock transients, persist in the midtail foreshock has not been observed. Thus, it is unclear whether the observed nightside magnetosheath/magnetopause perturbations are traveling waves or continuously driven by a propagating foreshock transient. Using two Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) spacecraft, we report direct observational evidence of foreshock transients in the midtail foreshock. We present a case study showing an elongated mature HFA propagating with its driver discontinuity from TH-C (X similar to -43 R-E) to TH-B (X similar to -48 R-E). Our results confirm that foreshock transients disturb not only the dayside bow shock but also the nightside bow shock while propagating tailward.