Occurrence and properties of substorms associated with pseudobreakups

Occurrence and properties Occurrence and properties of substorms associated of substorms associated

with pseudobreakupswith pseudobreakups

Anita KullenAnita Kullen

Space & Plasma Physics, EESSpace & Plasma Physics, EES

2Sept 8, 2010 Alfven Lab Seminar, EES, KTH

Publications about pseudobreakupsPublications about pseudobreakups

1.1. Kullen, A., and T. Karlsson, Kullen, A., and T. Karlsson, On the relation between On the relation between solar wind, pseudobreakups and substormssolar wind, pseudobreakups and substorms, , J. J. Geophys. Res.Geophys. Res., 2004. , 2004.

2.2. Kullen, A., S. Ohtani, and T. Karlsson, Kullen, A., S. Ohtani, and T. Karlsson, Geomagnetic Geomagnetic signatures of auroral substorms preceeded by signatures of auroral substorms preceeded by pseudobreakupspseudobreakups, , J. Geophys. Res.J. Geophys. Res., 2009. , 2009.

3.3. Kullen, A., T. Karlsson, J. A. Cumnock, and T. Kullen, A., T. Karlsson, J. A. Cumnock, and T. Sundberg, Sundberg, Occurrence and properties of substorms Occurrence and properties of substorms associated with pseudobreakupsassociated with pseudobreakups, , J. Geophys. Res., J. Geophys. Res., in press, in press, 2010. 2010.


Pseudobreakup typesPseudobreakup types

Isolated pseudobreakups

Growth-Phase Pseudobreakups

Recovery Pseudobreakups


Key IssueKey Issue

How do substorms that are preceded How do substorms that are preceded by growth-phase pseudobreakups by growth-phase pseudobreakups differ from substorms without differ from substorms without pseudobreakups ?pseudobreakups ?

solar wind conditions

energy transfer to magnetosphere

response of thepolar cap

response of theauroral zone

response of the near-earth tail


Near-Earth tail signaturesNear-Earth tail signatures


Magnetotail dipolarization during substormsMagnetotail dipolarization during substorms

[W. Baumjohan and R.A. Treumann, Basic Space Plasma Physics, 1996]

Stretched tail B-field

Dipolarized tail B-field

Bh

Bh

NENL versus TCD model

What develops first, Near-Earth Neutral Line or tail current disruption ? Tail current disruption

Near-Earth Neutral Line


Substorm signatures in the near-Earth tailSubstorm signatures in the near-Earth tail

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

Pseudobreakup Substorm

GOES magnetic field data


Signatures of 10 substorms preceded by Signatures of 10 substorms preceded by pseudobreakupspseudobreakups

Signatures of 10 substorms preceded by Signatures of 10 substorms preceded by pseudobreakupspseudobreakups

IMF Bz

AE index

Tail Bh – Model Bh


Mapping of GOES tail position Mapping of GOES tail position to the auroral ovalto the auroral oval


No delay of dipolarization: No delay of dipolarization:

GOES maps to onset positionGOES maps to onset position


No dipolarization seen:No dipolarization seen:GOES is always equatorward of ovalGOES is always equatorward of oval


Reason for delayed dipolarization:Reason for delayed dipolarization:Dawn- or duskward substorm expansionDawn- or duskward substorm expansion


Reason for delayed dipolarization: Reason for delayed dipolarization: Equatorward oval expansion after onsetEquatorward oval expansion after onset


Dipolarization delay versus GOES Dipolarization delay versus GOES mapped position in the ovalmapped position in the oval

DateDate GOES - main GOES - main onsetonset

DistanceDistance

Dipolarization Dipolarization

DelayDelayGOES mapped position at GOES mapped position at substorm onsetsubstorm onset

Propagation speed of Propagation speed of dipolarization regiondipolarization region

Dec 6, 98Dec 6, 98 -0.04 MLT-0.04 MLT 29 mn29 mn Equatorward of onsetEquatorward of onset 0.11 deg/min equatorward0.11 deg/min equatorward

Dec 14, 98Dec 14, 98 -0.19 MLT-0.19 MLT 22 mn22 mn Equatorward of onsetEquatorward of onset 0.10 deg/min equatorward0.10 deg/min equatorward

Dec 3, 98Dec 3, 98 0.61 MLT0.61 MLT 25 mn25 mn Equatorward of onsetEquatorward of onset 0.08 deg/min equatorward0.08 deg/min equatorward

Feb 24, 99Feb 24, 99 -0.80 MLT-0.80 MLT 26 mn26 mn Poleward of onsetPoleward of onset unclear (bad UVI image)unclear (bad UVI image)

Jan 15, 99Jan 15, 99 -0.82 MLT-0.82 MLT 31 mn31 mn Equatorward of onsetEquatorward of onset 0.08 deg/min equatorward0.08 deg/min equatorward

Feb 25, 99Feb 25, 99 0.82 MLT0.82 MLT 2 mn2 mn Nearly at onsetNearly at onset 0.55 MLT/min duskward0.55 MLT/min duskward

Jan 7b, 99Jan 7b, 99 1.78 MLT1.78 MLT -- GOES always equatorwardGOES always equatorward No dipolarizationNo dipolarization

Dec 28, 98Dec 28, 98 -2.23 MLT-2.23 MLT 8 mn8 mn Dawnward of onsetDawnward of onset 0.33 MLT/min dawnward0.33 MLT/min dawnward

Dec 23, 98Dec 23, 98 -2.38 MLT-2.38 MLT 17 mn17 mn Dawnward of onsetDawnward of onset 0.10 MLT/min dawnward0.10 MLT/min dawnward

Jan 7a, 99Jan 7a, 99 2.7 MLT2.7 MLT 11 mn11 mn Duskward of onsetDuskward of onset 0.24 MLT/min duskward0.24 MLT/min duskward


Expansion of the tail dipolarization regionExpansion of the tail dipolarization regionPrevious work shows, the magnetic field dipolarisation Previous work shows, the magnetic field dipolarisation starts locally [starts locally [Ohtani et al.,Ohtani et al., 1991] and spreads azimuthally 1991] and spreads azimuthally [[Nagai,Nagai, 1982; 1982; Liou et al.,Liou et al., 2002], and radially outward 2002], and radially outward [[Jacquey et al.Jacquey et al. 1991; 1991; Ohtani et al.,Ohtani et al., 1992] as well as inward 1992] as well as inward [[Ohtani,Ohtani, 1998]. 1998].

onsettail onset

Propagation speed of tail Propagation speed of tail dipolarization region:dipolarization region:

Azimuthal propagation Azimuthal propagation speed:speed: 0.22 MLT/min0.22 MLT/min (Liou (Liou et al. [2002] found et al. [2002] found 0.37 MLT/min0.37 MLT/min))

Earthward propagation Earthward propagation speed:speed: 0.09 deg/min0.09 deg/min (Liou et al. [2002] found (Liou et al. [2002] found 0.84 deg/min0.84 deg/min))


ResultsResults The dipolarization at GOES starts when bright The dipolarization at GOES starts when bright

auroral region reaches GOES mapped position.auroral region reaches GOES mapped position. This indicates, the expansion of auroral This indicates, the expansion of auroral intensification region and the expansion of the intensification region and the expansion of the tail dipolarization region are coupled. tail dipolarization region are coupled. Thus, the Thus, the small azimuthal expansion of the smallest small azimuthal expansion of the smallest substorms indicates an only limited spread of the substorms indicates an only limited spread of the tail dipolarization region.tail dipolarization region.

For substorms preceded by pseudobreakups, the For substorms preceded by pseudobreakups, the expansion of the tail dipolarization region in expansion of the tail dipolarization region in azimuthal direction is as fast as expected from azimuthal direction is as fast as expected from regular substorms.regular substorms. The expansion of the The expansion of the dipolarization region in Earthward direction is 10 dipolarization region in Earthward direction is 10 times smaller than expected from regular times smaller than expected from regular substorms. substorms. This is probably connected to a slow This is probably connected to a slow Earthward motion of the inner plasma sheet Earthward motion of the inner plasma sheet boundary after onset (equatorward motion of the boundary after onset (equatorward motion of the oval boundary). oval boundary).


AE indexAE index


One month AE index data One month AE index data with pseudobreakups overlaidwith pseudobreakups overlaid


AE indexAE indexSuperposed epoch plots for Superposed epoch plots for substorms of different substorms of different strengths, centered around strengths, centered around substorm onset.substorm onset.(Red, yellow, green and blue (Red, yellow, green and blue correspond to strong, medium, correspond to strong, medium, small and very small small and very small substorms)substorms)

Substorms with pseudobreakups

Substorms without pseudobreakups


Solar wind conditionsSolar wind conditions


IMF magnitude, solar wind velocity IMF magnitude, solar wind velocity and densityand density

IMF magnitude sw velocity sw density


Solar wind conditions: IMF BzSolar wind conditions: IMF Bz



Superposed epoch Superposed epoch plots for substorms plots for substorms of different of different strengths, centered strengths, centered around substorm around substorm onset.onset.


Solar wind energy transfer Solar wind energy transfer into the magnetosphereinto the magnetosphere


Loading-unloading substorm modelLoading-unloading substorm model

1. IMF Bz turns southward 1 hour before onset.

2. During the southward IMF period open magnetic field-lines are added via dayside reconnection.

3. When ”enough” energy has been stored in the magnetosphere via addition of open magnetic flux, this energy is released via a substorm.

Growing region of open magnetic flux

IMF Bz

t

substorm

Dayside reconnection Nightside reconnection

Substorm onset


Solar wind merging E-fieldSolar wind merging E-fieldOval size

Max AE

Average AE



growth-phase pseudobreakups

Em integrated over the Em integrated over the last three hours before last three hours before onset versus a) oval size, onset versus a) oval size, b) maximal AE during b) maximal AE during substorm c) average AE substorm c) average AE during substorm.during substorm.

Em integrated over Em integrated over the last southward the last southward IMF period before IMF period before onset versus time.onset versus time.

Em = vBtsin2(Θ/2)


Polar cap signaturesPolar cap signatures


PC potential dropPC potential drop

Substorms with pseudobreakupsSubstorms without pseudobreakups

Dayside

nightside

highlatitude

PC potential drop at nightisde proportional to AL[Lockwood et al., 2009]

PC potential drop at dayside proportional to Em[Lockwood et al., 2009]

12

00


AE index, PC index and Em in comparisonAE index, PC index and Em in comparison

Superposed epoch plots Superposed epoch plots for AE index, solar wind for AE index, solar wind merging field Em, merging field Em, northern and southern PC northern and southern PC index, centered around index, centered around substorm onset.substorm onset.

PC north

AE index PC south

Em field



Winter PC index (here PC north) proportional to AE Winter PC index (here PC north) proportional to AE [[Janzhura etJanzhura et al., 2007] al., 2007]

Summer PC index (here PC south) Summer PC index (here PC south) proportional to Em proportional to Em [[Janzhura etJanzhura et al., 2007] al., 2007]


SummarySummary Solar wind conditions:Solar wind conditions: Typical solar wind conditions during growth- Typical solar wind conditions during growth-

phase pseudobreakups and subsequent substorms include low IMF phase pseudobreakups and subsequent substorms include low IMF magnitude and solar wind velocity, and weakly southward IMF Bz.magnitude and solar wind velocity, and weakly southward IMF Bz.

Energy transfer into the magnetosphere:Energy transfer into the magnetosphere: A necessary condition for A necessary condition for growth phase pseudobreakups to occur is that the amount of energy growth phase pseudobreakups to occur is that the amount of energy transferred into the magnetosphere the hours before onset has not transferred into the magnetosphere the hours before onset has not exceeded a certain limit. exceeded a certain limit.

Ionospheric parameters:Ionospheric parameters: AE index, PC indices, and PC potential drop AE index, PC indices, and PC potential drop values are low as compared to regular substorms.values are low as compared to regular substorms.

Substorm characteristics:Substorm characteristics: Substorms preceded by pseudobreakups Substorms preceded by pseudobreakups are typically weak, and appear as isolated events after hours of low are typically weak, and appear as isolated events after hours of low geomangetic activity.geomangetic activity.

growth phase pseudobreakup

Occurrence and properties of substorms associated with pseudobreakups

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