loading page

Persistent pressure gradient as a driver of the substorm current wedge: A statistical study
  • +6
  • Xiangning Chu,
  • Robert L. McPherron,
  • Jacob Bortnik,
  • Vassilis Angelopoulos,
  • Tung-Shin Hsu,
  • James M. Weygand,
  • Jinxing Li,
  • Xin Cao,
  • Homayon Aryan
Xiangning Chu
Laboratory for Atmospheric and Space Physics

Corresponding Author:[email protected]

Author Profile
Robert L. McPherron
University of California Los Angeles
Author Profile
Jacob Bortnik
University of California Los Angeles
Author Profile
Vassilis Angelopoulos
University of California Los Angeles
Author Profile
Tung-Shin Hsu
IGPP/UCLA
Author Profile
James M. Weygand
Department of Earth, Planetary, and Space Sciences
Author Profile
Jinxing Li
Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles
Author Profile
Xin Cao
Laboratory for Atmospheric and Space Physics
Author Profile
Homayon Aryan
University of California Los Angeles
Author Profile

Abstract

The substorm current wedge (SCW) is believed to be driven by pressure gradients and vortices associated with fast flows. Therefore, it is expected that relevant observations are organized by the SCW’s central meridian, which cannot be determined using in-situ observations. This study takes advantage of the SCW inversion technique, which provides essential information about an SCW (e.g., location and strengths of field-aligned currents (FACs) and investigates the generation mechanisms of the SCW. First, we have found good temporal and spatial correlations between earthward flows and substorm onsets identified using the midlatitude positive bay (MPB) index. Over half of the flows are observed within 10 minutes of substorm onsets. Most flows (85%) were located inside the SCW between its upward and downward FACs. Second, superposed epoch analysis (SPEA) shows that the onset-associated flow velocity has a flow-scale (3-min) peak, while the equatorial thermal pressure has a substorm-scale (>30 min) enhancement and a trend similar to the westward electrojet and FACs in the SCW. Third, the pressure gradient calculated using in-situ observations is well organized in the SCW frame and points toward the SCW’s central meridian. These facts suggest that the SCW is likely sustained by substorm-scale pressure gradient rather than flow-scale flow vortices. The nonalignment between the pressure gradient and flux tube volume could generate an SCW with a quadrupole FAC pattern, similar to that seen in global MHD and RCM-E simulations. Their magnetic effects on the ground and geosynchronous orbit resemble a classic one-loop SCW.