GPS TEC observations of dynamics of the mid-latitude trough during substorms



[1] In this study, we combine GPS vertical total electron content (VTEC) and other complementary instruments, such as the Poker Flat incoherent scatter radar and all-sky imagers, to investigate the dynamics of the mid-latitude trough during non-storm time substorms for solar minimum condition and focus on Alaska region. We find that the poleward wall of the mid-latitude trough shifts equatorward rapidly after substorm onset with a maximum speed reaching 4°–5° of geomagnetic latitude per hour. This equatorward motion results in narrowing and even disappearance of the mid-latitude trough and is due to enhanced energetic electron precipitation. The mid-latitude trough can reappear during the substorm recovery phase as auroral activity retreats poleward. This phenomenon has not been reported before probably because of limited field-of-view of previous instruments used in trough studies. Comparisons of the trough minimum location predicted by models that are based on global Kp and AE indices show good agreement before substorm activity reaches the peak and relatively poor agreement during the recovery phase. The observations suggest that a local index, such as the local AL index, may be a better index to use to parameterize the trough location at a given meridian than a global index.