gem 2008 summer workshop, zermatt, utah, june 25, 2008 1 institute of geophysics and planetary...

GEM 2008 Summer Workshop, Zermatt, Utah, June 25, 2008 1

Institute of Geophysics and Planetary PhysicsUniversity of California, Los Angeles

THEMIS observations at a substorm onset on March 1, 2008

A. Runov1, V. Angelopoulos1, X.-Z. Zhou1, V.A. Sergeev2, M. V. Kubyshkina2, S. Apatenkov2, I. Voronkov3, J. McFadden4, D. Larson4,

K.-H. Glassmeier5, U. Auster5, W. Magnes6, R. Nakamura6, C. T. Russell1, I. Mann7, S. Mende2, H. Frey2, L. Kepko8, and H.J. Singer9

1. IGPP/ESS, UCLA, Los Angeles, CA, USA2. St. Petersburg State University, St. Petersburg, Russia3. Athabasca University, Edmonton, Alberta, Canada4. SSL, University of California at Berkeley, CA, USA5. TUBS, Braunschweig, Germany6. IWF OEAW, Graz, Austria7. University of Alberta, Edmonton, Alberta, Canada8. SSC, University of New Hampshire, Durham, NH, USA9. NOAA Space Weather Prediction Center, Boulder, CO, USA

Correspondence to: [email protected]


P1

P2P3

P4G12

01:48:50 UT

GBAYG10

THEMIS GBO: Auroral onsets

P1

P3P4

G12

01:54:30 UT

G10

P2

1st (minor) intensification0148:42 UT GBAY

2nd (major) intensification0152:27 UT SNKQ

SNKQ


WIND (time shifted)

GBAY

DRBY

LOYS

KUUJ

CHGB


THEMIS and GOES observations 08-03-01/0100 – 0210 UT

01:48:50 UT

0148:42


Observations in the mid-tail PS

P2: X=-17.4 RE

Tailward fast flows Bz and By variations Ion & electron

energization


Observations in the mid-tail PS

P1: X=-22.7 RE

Same as at P2, but ~30 s later on


Timing of ion fluxes (SST and ESA) variations during the first

tailward flow P2

P1

SST: 50 – 200 keVESA: 5 – 21 keV

P2/THC: Tailward flux • 60 keV-Ion flux increases

at 0148:25 UT; • 190 keV flux increases at

0148:55 UT. Inversed Velocity

Dispersion (IVD, Sarafopoulos and Sarris, 1988)

SC are in the PS: IVD due to the acceleration by the inductive electric field (Taktakishvili et al., 1993)

SC are close to the acceleration region (1-3 RE)


Electron PA distributions at P1 and P2First tailward flow

0148:25


Observations in the near-Earth PS

P4: X=-8.0 RE ~6 min later than the

first activity in the mid-tail PS;

Magnetic field (and cross-tail current) reduction;

Dipolarization; Bursty Ion and

electron energization A step-like increase

of plasma density and pressure.


Observations in the near-Earth PS

P3: X=-9.3 RE The same as at P4,

but ~40 s later on Tailward propagation

of the step-like plasma pressure front at a velocity of 150 km/s.


P3 and P4 FGM measurements(field-aligned coordinates):

Main field (Bz) at P3 and P4 continuously increases (growth phase) until ~0955 UT

Perpendicular components, • δBy and δBx started at 0148:20

– 0148:40 UT, indicating outward FAC underneath the SC.

GOES 10 (PEN coordinates): Positive δBn (eastward!) at

0148- 0155 UT G10 was underneath of the FAC

GOES10, 12: Dipolarization at ~0154:20 UT

Magnetic field variations at P3, P4,GOES 10, GOES 12


2008-03-01/0140 – 0205 UTEvent Timing

0148:25 high-energy electron flux increase at P2 (transient reconnection?) 0148:25 ~60 keV ion flux increase at P2 (acceleration by the inductive E-field) 0148:40 dBy at P3, P4, G10 (FAC) 0148:42 minor auroral onset at GBAY (pseudo-breakup) 0148:45 Pi2 onset at GBAY 0148:45 Tailward fast ion flow, dBy & dBz at P2 0149:30 Tailward fast ion flow, dBy and dBz at P1 0152:21 Auroral onset at SNKQ (substorm) 0153:30 Dipolarization at G12 0154:20 Dipolarization at P4 0154:30 Tailward flow, dBy & dBz at P1 0154:40 Drop of Bt at P4 (cross-tail current reduction/disruption)

0155:00 Tailward flow at P2 0155:21 Auroral onset at KUUJ 0155:50 Dipolarization at P3 0155:50 dVy and dVz at P3 0155:50 Drop of Bt at P3


A Possible Scenario

The observations suggest a two-step development of the activity:

First step: An initial disturbance (probably reconnection) in the mid magnetotail (X~-15 - -17 RE) led to the particle acceleration, the Bz and By perturbations, the plasma bulk flow, and the FAC formation, associated with the first (minor) auroral activation (precursor). The FAC was, likely, generated by the Earthward reconnection outflow. The cross tail current in the near-Earth magnetotail (X~-9 RE) continued building up.

Second step: The rapid reduction (disruption) of the cross-tail current due to hot plasma pile-up, associated with the major onset, developed in the near-Earth plasma sheet. The second tailward flow, observed by P1 and P2, was, likely, generated by a process in the mid tail (probably reconnection), acting simultaneously with (and independent from) the current disruption, observed by P3 and P4 in the near-Earth plasma sheet.


Back up slides


March 1, 2008 THEMIS major conjunction event

0148:50 UT0155:00 UT

01:54:30 UT

gem 2008 summer workshop, zermatt, utah, june 25, 2008 1 institute of geophysics and planetary...

Documents