Foreshock Transient Generated ULF Waves in the Magnetosphere

Abstract:

Foreshock transients are frequently observed upstream from the bow shock (such as Hot Flow Anomalies, foreshock cavities, and foreshock bubbles). They play a significant role in the mass, energy and momentum transport from the solar wind into the magnetosphere and impact the whole magnetosphere-ionosphere system. Hot flow anomalies (HFAs) are events observed near planetary bow shocks that are characterized by greatly heated solar wind plasmas and substantial flow deflection. Several studies have demonstrated that transient phenomena near the bow shock can generate ULF waves in the Earth’s magnetosphere. (This is different from the low-latitude Pc3 waves that are driven by upstream waves in the ion foreshock.) The ULF waves generated by transient phenomena near the bow shock in both Pc3 and Pc5 ranges have been reported. In addition, there may be considerable variation between ULF waves resulting from different transient features. E.g., Hartinger et al. (2013) showed mostly compressional waves, Eastwood et al. (2011) and Zhao et al. (2017) showed standing Alfvén waves, and Shen et al. (2018) showed both compressional and Alfvén waves. The magnetospheric response could be global or localized. The different effects might be caused by the different pressure variation profiles associated with the transients, size of the transients, and the location where the waves were observed in the magnetosphere.