GPS Tec Observations of Dynamics of the Mid-Latitude Trough During Substorms

Abstract

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 K_p 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.

Key Points:

• Multi-instrument study of mid-latitude trough dynamics during substorms
• Trough narrows/disappears during expansion and reappears during recovery phase
• Observed trough locations are compared with empirical model predictions