Substorm Parameters: A Progress Report

Christine Gabrielsecgabrielse@ucla.edu

Sergey Apatenkov, Nathaniel Frissell, Stefan Kiehas, Jiang Liu, Kyle Murphy, Toshi Nishimura,

Jonathan Rae, Geoff Reeves, Andrei Runov, Victor Sergeev, Emma Spanswick, Taku Takada

Wednesday, September 16, 2009THEMIS SWT Meeting, Annapolis

www.igpp.ucla.edu/themis/events

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)

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 ~124 events (2008 added since GEM)– Events: only looked at “substorms” during major & minor

THEMIS conjunctions– Event added to table due to AE rise

Today– Progress Report– Explain criteria

T0: Auroral Intensification

Mean Brightness (Counts) over time

Integrated Intensity

2009 Criteria: When at least one bin sees a sudden, sharp increase in intensity

2008 Criteria: Integrated over entire imager

(Akin to & collaborating with Nishimura)Earlier Question: 90/250 Nishimura events during THM conjunction19/86 of our 2007-08 chosen events

AE Onset Selection– If return to quiet, marked 2nd

AE Onset

– Note 1st onset matches in-

situ observed onsets In-situ Onset example

Flux Transport

Pi2s

Pi2s

AE

Bx

Bz

Vx

Ey: efs

Ey: -vxB

Pt & PbVx

Flux Transport(Int Ey)

Ey(-vxB)

AE Index Automated Initial rise time

– Max AE w/in 5 min– Max AE of that rise

Secondary rise time– Secondary max AE

values

Requirements:– No disturbance 3 min prior– Bz disturbance lasts 3

minutes

Onset selection:– Sharp change in Bz: dBz/dt– Onset of Bz that grows 20%

past the previous 3 minutes & lasts 3 minutes

– Onset where growth starts, not point where passes the background

Bz Variation Onset Selection

Bz Variation Onset Selection Examples

20% criteria

Objectivity is difficult; Analysis of P3 alters perception of P4

Sharp vs. gentle slope

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

Peak velocityVx (total)

Peak velocityVx (perp)

Ts-3min to Ts+3min

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(a) Timings are different, but polarity is the same

(b) Timings are different, and polarity are opposite

Bxyz [nT]GSM

Vxyz [km/s]GSM (mom)

Vpxyz [km/s]GSM

Vxyz [km/s]GSM (reduced)

Observations: midlatitude observatories 20-55° CGLata) <55° to avoid influence of complicated auroral currents

b) >20° to avoid SQ variation influence

Input data: INTERMAGNET + THEMIS GBO best coverage at 04-09 UT

Substorm current wedge parameters using midlatitude magnetometers.

In 2009 tail season SCW parameters can be determined for about 50% substorms during major / minor conjunctions

Using THEMIS footpoints can determine if s/c are within the SCW

Ygsm limit: -7 to 7 Re

AE

Bz

Vx

FluxEy

AE

Bz

Vx

Ey

AE

Bz

VxFlux

Ey

AE

T0 = Auroral Intensification

BzVx

Ey

Preliminary Observations

S/C Location & Distance from NS found using GSFC 4D Viewer Tipsod (Tsyganenko Model)

P1

P2P3P4P5

P1

P2

P3

P4

P5

www.igpp.ucla.edu/themis/events

Substorm Parameters: A Progress Report

Christine Gabrielsecgabrielse@ucla.edu

Sergey Apatenkov, Nathaniel Frissell, Stefan Kiehas, Jiang Liu, Kyle Murphy, Toshi Nishimura,

Jonathan Rae, Geoff Reeves, Andrei Runov, Victor Sergeev, Emma Spanswick, Taku Takada

Wednesday, September 16, 2009THEMIS SWT Meeting, Annapolis

www.igpp.ucla.edu/themis/events

T0 = 1st AE Onset

Bz

Vx

Flux

Ey

Bz

Vx

Flux

Ey

Ygsm limit: -5 to 5 Re

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