In Situ Observation of a Magnetopause Indentation that Is Correspondent to Throat Aurora and Is Caused by Magnetopause Reconnection

• Published in: Geophysical research letters Vol. 49; no. 15
• Main Authors: Qiu, HuiXuan, Han, De‐Sheng, Wang, BoYi, Feng, HuiTing, Li, Bin, Zhou, Su, Shi, Run, Yang, HuiGen, Zhang, Y.‐L.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16-08-2022
• Subjects: Auroral arcs; Auroral oval; Auroras; DMSP satellites; Equatorial regions; Indentation; Magnetopause; magnetopause indentation; Magnetopause reconnection; Magnetosheath; Magnetospheres; Meteorological satellite program; Meteorological satellites; Questions; Satellite observation; Satellites; Sensors; Signatures; Solar wind; solar wind discontinuity; Special Sensor Ultraviolet Spectrographic Imager; Spectroscopy; throat aurora; Throats; Variance analysis
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL099408

Throat auroras have been suggested to correspond to magnetopause indentations, but how such indentations can be generated is an open question. Using coordinated magnetopause in situ and two‐dimensional auroral imaging observations, we showed that a transient magnetopause crossing observed by Time History of Events and Macroscale Interactions during Substorms near the dayside magnetopause corresponds to a throat aurora observed by Defense Meteorological Satellite Program/Special Sensor Ultraviolet Spectrographic Imager. The magnetopause crossing was confirmed to present a localized magnetopause indentation rather than arise from motion of the whole magnetopause. Using the minimum variance analysis and Walén test methods, we captured clear reconnection signatures at either boundary of the indentation. Also, an upstream solar wind discontinuity and a magnetosheath variation were identified to correlate well with the magnetopause indentation occurrence. These observations suggest that the magnetopause indentation was generated by reconnection and lend solid support to an assumption that throat aurora is produced by a particular reconnection that can develop inward the magnetosphere at a much‐localized region.
Plain Language Summary
The equatorward boundary of the discrete auroral oval near magnetic local noon is generally regarded as the open‐close field line boundary, which corresponds to the roughly smooth magnetopause boundary. Throat auroras are some north‐south aligned discrete auroral arcs attached at the equatorward edge of discrete auroral oval near local noon. Therefore, the throat auroras have been suggested to correspond to magnetopause indentations. However, no in situ observations show the existence of such indentations and how the indentations can be generated is also an open question. Taking advantage of coordinated Time History of Events and Macroscale Interactions during Substorms and Defense Meteorological Satellite Program/Special Sensor Ultraviolet Spectrographic Imager observations, we provided multipoint in situ observations, confirming that a transient magnetopause crossing correspondent to a typical throat aurora event was a magnetopause indentation. Also, with these observations, we captured clear reconnection signatures at either boundary of the indentation. Combined with the two‐dimensional morphology of the throat aurora, such magnetopause reconnection signatures may imply that during the generation of the throat aurora there exist an inwardly u‐shaped X line along the magnetopause indentation boundary.
Key Points
A localized magnetopause indentation correspondent to throat aurora is confirmed by multipoint in situ observations for the first time
Reconnection signatures at either boundary of the magnetopause indentation are captured by in situ observations for the first time
An upstream solar wind discontinuity is identified to be correlated with the occurrence of throat aurora for the first time