GEOSYNCHRONOUS SIGNATURES OF AURORAL SUBSTORMS PRECEDED BY

PSEUDOBREAKUPS

GEOSYNCHRONOUS SIGNATURES OF AURORAL SUBSTORMS PRECEDED BY

PSEUDOBREAKUPS

A. Kullen (1), S. Ohtani (2), and H. Singer (3)A. Kullen (1), S. Ohtani (2), and H. Singer (3)

(1) Swedish Institute of Space Physics Uppsala(1) Swedish Institute of Space Physics Uppsala(2) The John Hopkins University Applied Physics (2) The John Hopkins University Applied Physics

LaboratoryLaboratory(3) NOAA Space Environment Center (3) NOAA Space Environment Center

IAGA conference, Toulouse, France 2005IAGA conference, Toulouse, France 2005IAGA conference, Toulouse, France 2005IAGA conference, Toulouse, France 2005

IntroductionIntroduction

• MotivationMotivation Whether/how is the near-Earth condition different between

pseudobreakups and main onset ?• MethodMethod

Comparison between global auroral images (Polar UVI) and magnetic signatures at geosynchronous orbit (GOES 8,10).

• Event selectionEvent selection Of 57 growth phase pseudobreakups detected during a 3

month period (Kullen and Karlsson, 2004), all clear events are selected, where a GOES satellite is located between 21 MLT and 3 MLT (10 events).

GOES position mapped on Polar UVI images (using T96 model with 1h averaged sw data

from ACE)

GOES position mapped on Polar UVI images (using T96 model with 1h averaged sw data

from ACE)

GOES magnetic field dataGOES magnetic field data

Subtraction of the T89 B-Subtraction of the T89 B-field for quiet times from field for quiet times from GOES dataGOES data

Pseudobreakup

Substorm

IMF Bz, AE index and GOES data IMF Bz, AE index and GOES data

Reason for delayed tail dipolarization

Reason for delayed tail dipolarization

• Previous results: Previous results: Tail current disruption and

dipolarization are initiallized locally and expand from there

-azimuthally (e.g. Nagai, 1982) -tailward (e.g. Ohtani et al. 1992) -earthward (Ohtani, 1998).

• This study:This study: Pseudobreakup and main

onset appear during relative quiescence on high latitudes. Hence, they map probably tailward of GOES position (Frank and Sigwarth, 2000) i.e., an earthward delay can be expected.

DateDate Pseudo-Pseudo-breakupbreakup

(CGlat)(CGlat)

Main Main onset onset

(CGlat)(CGlat)

Large Large dipolarizdipolariz

ation ation (Cglat)(Cglat)

Jan 7a, Jan 7a, 9999

6363 6363 6363

Jan 7b, Jan 7b, 9999

6565 6565 6565

Dec 28, Dec 28, 9898

66.566.5 6666 6464

Dec 6, 98Dec 6, 98 6767 6767 64.564.5

Dec 14, Dec 14, 9898

6666 6565 6363

Dec 23, Dec 23, 9898

66.566.5 6565 6363

Dec 3, 98Dec 3, 98 66.566.5 6666 6363

Feb 24, Feb 24, 9999

?? 5858 5757

Feb 25, Feb 25, 9999

?? ovaloval widenswidens

Jan 15, Jan 15, 9999

6161 6161 6060

Equatorward oval boundary at 0 MLTEquatorward oval boundary at 0 MLT

No delay of dipolarization: GOES maps to onset position

No delay of dipolarization: GOES maps to onset position

No dipolarization seen:III. GOES always equatorward of oval

No dipolarization seen:III. GOES always equatorward of oval

Reason for delayed dipolarization:I. Oval expansion after onset

Reason for delayed dipolarization:I. Oval expansion after onset

Reason for delayed dipolarization:II. Dawn- or duskward substorm

expansion

Reason for delayed dipolarization:II. Dawn- or duskward substorm

expansion

Results: 1. DipolarizationResults: 1. Dipolarization

• A clear A clear dipolarization is dipolarization is observed at GOES observed at GOES when the region when the region of enhanced of enhanced auroral activity auroral activity reaches the reaches the mapped position mapped position of GOES. This of GOES. This suggests a suggests a connection connection between between expansion of expansion of bright aurora and bright aurora and expansion of tail expansion of tail current disruption current disruption region.region.

DateDate GOES - GOES - main main onsetonset

DistanceDistance

DipolariDipolarization zation

DelayDelay

Reason for delayed Reason for delayed dipolarizationdipolarization

Dec 6, 98Dec 6, 98 -0.04 -0.04 MLTMLT

29 mn29 mn Equatorward Equatorward expansionexpansion

Dec 14, Dec 14, 9898

-0.19 -0.19 MLTMLT

22 mn22 mn Equatorward Equatorward expansionexpansion

Dec 3, 98Dec 3, 98 0.61 MLT0.61 MLT 25 mn25 mn Equatorward Equatorward expansionexpansion

Feb 24, Feb 24, 9999

-0.80 -0.80 MLTMLT

26 mn26 mn Unclear (bad UVI)Unclear (bad UVI)

Jan 15, Jan 15, 9999

-0.82 -0.82 MLTMLT

31 mn31 mn Equatorward Equatorward expansionexpansion

Feb 25, Feb 25, 9999

0.82 MLT0.82 MLT 2 mn2 mn GOES at onsetGOES at onset

Jan 7b, Jan 7b, 9999

1.78 MLT1.78 MLT -- GOES always GOES always equatorwardequatorward

Dec 28, Dec 28, 9898

-2.23 -2.23 MLTMLT

8 mn8 mn Dawnward motionDawnward motion

Dec 23, Dec 23, 9898

-2.38 -2.38 MLTMLT

17 mn17 mn Dawnward motionDawnward motion

Jan 7a, Jan 7a, 9999

2.7 MLT2.7 MLT 11 mn11 mn Duskward motionDuskward motion

H(GOES)-H(T98) at geosynchrounous orbit

H(GOES)-H(T98) at geosynchrounous orbit GOES at same

longitude as pseudobreakup

Summary tail observationsSummary tail observations

• Pseudobreakups are connected to a small hickup Pseudobreakups are connected to a small hickup of Bh (in 7 of 10 cases).of Bh (in 7 of 10 cases).

• Tail B-field stretching continues between Tail B-field stretching continues between pseudobreakups and substorms (in 8 of 10 pseudobreakups and substorms (in 8 of 10 cases).cases).

• A clear dipolarization appears 10-30 minutes A clear dipolarization appears 10-30 minutes after onset of the auroral substorm (in 9 of 10 after onset of the auroral substorm (in 9 of 10 cases).cases).

• Tail B-field stretching continues between auroral Tail B-field stretching continues between auroral substorm onset and large dipolarization.substorm onset and large dipolarization.

Results: 2. PseudobreakupsResults: 2. Pseudobreakups

•Previous results (Kullen and Karlsson, 2004):

Pseudobreakups appear during quiet times with low solar wind velocity, density and IMF.Tyically IMF Bz was weakly southward 0.5-2 hours before a growth phase pseudobreakup.An IMF northturn appears during the following substorm.

•This study: Continued tail B-field stretching between pseudobreakup and main onset.

•Conclusions:These results indicate that growth phase pseudobreakups occur while there is not yet enough free energy in the tail available for a substorm to appear.

growth phase pseudobreakup