FG: Testing Proposed Links between Mesoscale Auroral and Polar Cap Dynamics and Substorms

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2017 Workshop Tentative Agenda


Focus Group Leaders

  • Kyle Murphy (NASA GSFC)
  • Toshi Nishimura (UCLA)
  • Emma Spanswick (University of Calgary)
  • Jian Yang (Rice University)


  • 2015-2019 (5 years)

Research Area

  • Magnetotail and Plasma Sheet (MPS)


For decades the debate on substorms had centered on the ‘outside-in’ (reconnection) and ‘inside-out’ (current disruption) scenarios. However, recent ground-based observations have suggested a hybrid model, wherein the substorm is initiated by flows that may originate from the dayside, cross the polar cap, move through the open/closed boundary where they trigger localized reconnection, and then trigger substorm expansion after reaching the near-Earth transition region. This is radically different from the previous and intensely debated proposals. However, there are important disagreements in the community regarding both the interpretation of the ground-based (ASI, redline, and radar) observations and the proposed picture. Furthermore, the complete idea now includes the new proposal that flow structures from within the polar cap trigger localized tail reconnection, an idea which is of major importance for full understanding of tail reconnection, but which has not received much attention in the past. It is the purpose of this proposed focus group to bring together key players in this area to work together on the new questions of the auroral and magnetotail sequence leading to substorm onset, in a CDAW/GEM style format. Though our central focus is on substorms, we will also compare to non-substorm time phenomena because some key features are common in different levels of magnetic activity. Due to the structure of GEM as a working group style meeting, and the potential impact of this new paradigm on understanding the Geospace environment, GEM is the ideal venue through which to rigorously evaluate the newly proposed paradigms. Due to the importance of ground-based observations for the proposed topics, this focus group will encourage collaboration between GEM and CEDAR.


  • Can we rigorously evaluate substorm precursor occurrence and association?
  • What are similarities and differences of PBIs/streamers/plasma sheet flows during isolated substorms, active‐time substorms and non‐substorm times?
  • What can auroral observation tell us about the sources, timing and properties of magnetospheric flows?
  • How does the asymmetric and bursty nature of plasma sheet transport and plasma sheet wave instability influence substorm onset and other types of auroral brightening?
  • How do plasma sheet fast flows/streamers couple to lobe/polar cap phenomena?


It has now been five years since the initial work of Nishimura et al. [2010] and Lyons et al. [2010], and the group has now expanded their work with numerous follow-on studies. There is therefore sufficient evidence that something of interest is occurring; yet a significant number of studies that questions their finding exist, and there is yet to be a consensus on interpretation of the data. There is intense scientific interest in the community on this topic, and the discussions have reached a critical stage. In addition to a large amount of existing satellite and ground-based data, this focus group will provide a stage to discuss initial results from new data, including those from a new campaign of THEMIS-MMS-ground coordination in year 2015-2017, and new redline (6300 Å) data from highly sensitive cameras. A focus group on this topic couldn't be more timely or appropriate for GEM.

Relation to existing focus groups

Currently there exists no FG where the type of activity described here could occur. This FG will work with the “Scientific Magnetic Mapping & Techniques” FG, as well as the “Tail-inner magnetosphere interactions” FG, from the standpoint of ‘bubbles’, and "Magnetic Reconnection in the Magnetosphere" FG. Additionally, once the observable features are better quantified, the results could be fed into the “Geospace Systems Science" FG for better integration with the global models and systems-science methodologies that are the focus of that group.

Goals and deliverables

The primary goal of the focus group is to determine if, when, and under what conditions, localized flux tubes convecting across the polar cap lead to depleted entropy flow bursts within the plasmasheet that can trigger the reconfiguration of the nightside magnetosphere that is known as a substorm. The result of the FG will be a rigorous community assessment of the role of pre-onset polar cap flows and auroral zone streamers (as proxies for magnetospheric flows) on magnetospheric reconfiguration, as well as on localized tail reconnection. In addition to a series of published research papers, the results will be communicated directly to the GGCM modelers, as these new observations provide new constraints and metrics that the models will have to match.

  • Community-wide consensus of substorm precursors
  • Consensus on connection between the lobe (polar cap) and plasma sheet (oval) and its influence on reconnection and substorm
  • Developing tools to quantify key auroral features (such as streamers)
  • Model validations by characterizing location, size, motion and timing of precursors
  • A series of publications on these outcomes

Expected Activities

This will primarily be an intensive data analysis focus group, with immersive discussions and very few presentations. We will invite a small number of speakers (both from GEM and CEDAR) to present their results on selected events, and ask several experienced community members to join as panelists for facilitating discussions with audience. We will also encourage modelers to present simulation results for assisting interpretation of observations and for obtaining physical pictures. One goal is to return to the original GEM model of active data analysis, and we may try a ‘two-screen’ approach to improve interactions and discussions.

A primary objective of the proposed focus group is to reach consensus on the significance of and how to interpret auroral streamers and polar patches, and their associated flow structures, in the context of substorm development. For the first two years we anticipate a few short presentations to provide the framework, then the team will work on identifying a subset of events to analyze in detail (this will also occur well before each summer workshop) – starting first with isolated substorms, then moving onto intensifications embedded in strong activity. In later years, similarities and differences of substorm-time and nonsubstorm-time sequences will be discussed.

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