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Substorm Parameters: A Progress Report

This progress report discusses the complex parameters surrounding substorm events, particularly focusing on auroral intensification and corresponding onset criteria. The report outlines the diversity in definition among researchers and presents a unified approach to the identification of key substorm parameters based on extensive data from various observations. Significant emphasis is placed on the analysis of Bz variations, auroral breakup characteristics, and timing criteria, critical for understanding substorm dynamics. This document serves as a valuable resource for researchers and practitioners in space science and magnetosphere studies.

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Substorm Parameters: A Progress Report

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  1. Substorm Parameters: A Progress Report Christine Gabrielse cgabrielse@ucla.edu Sergey Apatenkov, Nathaniel Frissell, Stefan Kiehas, Jiang Liu, Kyle Murphy, Jonathan Rae, Geoff Reeves, Andrei Runov, Victor Sergeev, Emma Spanswick, Taku Takada Thursday, June 25, 2009 GEM www.igpp.ucla.edu/themis/events

  2. Introduction • March THEMIS SWT meeting discussion • Much diversity between authors on the definition of terms • Substorm parameter table • General characterization of event/onset and of the geometry of conjunction • Characterization of auroral breakup • Characterization of potential signature of reconnection onset • Characterization of current disruption • Onset times (ie Bz variation, auroral intensification, Ey variation, |Vx| increase) • Values (ie Peak amplitude of Vx flow, s/c footpoint locations, s/c distance from neutralsheet, type of Bz variation, beta, flux transport, LANL injection data)

  3. Introduction • March THEMIS SWT meeting discussion • T0: Want consistency among substorm community • T0 = Auroral intensification. Historical, everyone can agree • Epoch timing analysis • Committee formed • Young researchers having experience with timing • Define onset criteria: Consistent, objective “formula” • Now, ~80 parameters and ~40 events • Events: only looked at substorms during major & minor THEMIS conjunctions • Today • Progress Report • Explain criteria

  4. T0: Auroral Intensification • Criteria: When at least one bin sees a sudden, sharp increase in intensity Mean Brightness (Counts) over time

  5. AE Pi2s • AE Onset Selection • If return to quiet, marked 2nd AE Onset • Note 1st onset matches in-situ observed onsets • In-situ Onset example Pi2s Bx Bz Ey (-vxB) Vx Flux Transport (Int Ey) Ey: efs Ey: -vxB Flux Transport Vx Pt & Pb

  6. Bz Variation Onset Selection Examples No disturbance 3 min prior Bz disturbance lasts 3 minutes THA: start of variation that goes above background THD: 20 % criteria

  7. Bxyz[nT] GSM Ts-3min to Ts+3min Vxyz[km/s] GSM (mom) Peak velocity Vx (total) Vpxyz[km/s] GSM Vxyz[km/s] GSM (reduced) Peak velocity Vx (perp) • C7ab/D7ab parameters • Peak amplitude of outflow Vx (perp/total) w/in 3 min of Ey increase (km/s) • Dataset • Bxyz in GSM: FGL data • Vxyz in GSM: ESA mom/ reduced data (TBD for ESA&SST) • Vpxyz: estimated from Bxyz{3s} & Vxyz

  8. (a) Timings are different, but polarity is the same Bxyz[nT] GSM Vxyz[km/s] GSM (mom) Vpxyz[km/s] GSM Vxyz[km/s] GSM (reduced) • Problem: • Peak times are sometimes different for perp and total velocity (b) Timings are different, and polarity are opposite

  9. Substorm current wedge parameters using midlatitude magnetometers. Observations:midlatitude observatories 20-55° CGLata) <55° to avoid influence of complicated auroral currentsb) >20° to avoid SQ variation influenceInput data: INTERMAGNET + THEMIS GBO best coverage at 04-09 UT In 2009 tail season SCW parameters can be determined for about 50% substorms during major / minor conjunctions

  10. S/C Location & Distance from NS found using GSFC 4D Viewer Tipsod (Tsyganenko Model) P1 Preliminary Observations P2 P3 P4 P5

  11. T0 = Auroral Intensification Ygsm limit: -7 to 7 Re AE AE Bz Bz Vx Vx Flux Flux Ey Ey AE AE Bz Bz Vx Ey

  12. T0 = 1st AE Onset Ygsm limit: -5 to 5 Re Bz Vx Flux Ey Bz Vx Flux Ey

  13. Substorm Parameters: A Progress Report Christine Gabrielse cgabrielse@ucla.edu Sergey Apatenkov, Nathaniel Frissell, Stefan Kiehas, Jiang Liu, Kyle Murphy, Jonathan Rae, Taku Takada, Andrei Runov, Victor Sergeev, Emma Spanswick Thursday, June 25, 2009 GEM www.igpp.ucla.edu/themis/events

  14. Bz Variation Onset • Criteria • The time when Bz significantly changes with respect to the variations within the previous 3 minutes and this change leads to significant disturbances for the next 3 minutes • If there is a “sharp increase", i.e., dBz/dt, this is called the onset. • If not, onset is a change in DBz/B by at least 20% of the previous 3 minutes for more than 3 of the following minutes • 20% was used as the minimum for a first run through, but may be increased after more analysis • Onset defined when the Bz disturbance starts and not when it goes beyond/under the background, i.e., when the disturbance reaches a specific value

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