Substorm Parameters: A Progress Report

Christine Gabrielsecgabrielse@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, 2009GEM

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 ~40 events – Events: only looked at substorms during major & minor THEMIS

conjunctions

Today– Progress Report– Explain criteria

T0: Auroral Intensification Criteria: When at least one bin sees a sudden, sharp

increase in intensity

Mean Brightness (Counts) over time

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)

Bz Variation Onset Selection Examples

THD: 20 % criteriaTHA: start of variation that goes above background

No disturbance 3 min priorBz disturbance lasts 3 minutes

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

Preliminary Observations

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

P1

P2P3P4P5

Ygsm limit: -7 to 7 Re

AE

Bz

Vx

Flux

Ey

AE

Bz

Vx

Ey

AE

Bz

VxFlux

Ey

AE

T0 = Auroral Intensification

Bz

T0 = 1st AE Onset

Bz

Vx

Flux

Ey

Bz

Vx

Flux

Ey

Ygsm limit: -5 to 5 Re

Substorm Parameters: A Progress Report

Christine Gabrielsecgabrielse@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, 2009GEM

www.igpp.ucla.edu/themis/events

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