Substorm Parameters: A Progress Report
Christine [email protected]
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 [email protected]
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