Occurrence and properties of substorms associated with pseudobreakups Anita Kullen
Space & Plasma Physics, EES
Occurrence and properties of substorms associated with pseudobreakups Anita Kullen
Space & Plasma Physics, EES
Publications about pseudobreakups
Kullen, A., and T. Karlsson, On the relation between solar wind, pseudobreakups and substorms, J. Geophys. Res., 2004.
Kullen, A., S. Ohtani, and T. Karlsson, Geomagnetic signatures of auroral substorms preceeded by pseudobreakups, J. Geophys. Res., 2009.
Kullen, A., T. Karlsson, J. A. Cumnock, and T. Sundberg, Occurrence and properties of substorms associated with pseudobreakups, J. Geophys. Res., in press, 2010.
During the recent years I have been working on several pseudobreakup studies:
In this seminar I want to summarize the results of these papers.
1. paper: is about solar wind conditions during pseudobreakups and substorms.
2. paper: is about near-Earth tail dipolarization and auroral evolution.
3. paper: is about solar wind energy transfer and response of ionospheric parameters.
Pseudobreakup types
Isolated pseudobreakups Growth-Phase Pseudobreakups Recovery Pseudobreakups
The study is based on global auroral images from Polar:
Here, all local auroral intensifications outside the substorm main phases expansion+recovery are counted as pseudobreakups.
Auroral intensifications without global expansion occur during
quiet times (isolated pbs), before substorm onset (growth-phase pb’s) and at the end of substorm recovery (recovery pb’s).
PS: The definition of pseudobreakups is unclear, most researchers would not define recovery pb’s as pseudobreakups but as PBI’s.
Some expect that pseudobreakups are a near-earth phenomenon, others that they are shortlived or small etc.
To get non-biased results, we include all brightenings seen on Polar UVI.
Key Issue
solar wind
conditions energy transfer
to magnetosphere response of the
polar cap response of the
auroral zone response of the
near-earth tail How do substorms that are preceded by growth-phase pseudobreakups differ from substorms without pseudobreakups ?
We look at the entire chain between solar wind, magnetosphere, near-Earth tail and ionosphere.
We investigate solar wind, ionospheric and magnetospheric conditions for the different pseudobreakup types.
The main focus is on growth-phase pseudobreakups:
We compare solar wind, ionospheric and magnetospheric conditions between substorms with and without pseudobreakups,
to find out why sometimes a pseudbreakup appears just before a substorms and sometimes not.
Near-Earth tail signatures
We first look at the tail signatures during substorms and preceding pseudobreakups
Magnetotail 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
The geosynchronous GOES satellites orbit at about 6 Re around the Earth.
This is close to the substorm onset region.
Substorm onset is connected to a strong dipolarization of B-field, which is
seen as a strong increase of the z-component in the B-field (H-component).
To enhance the dipolarization signature, a standard (quiet time) magnetosphere
model B-field is substracted from the data.
In this example it can be nicely seen: the pseudobreakup is connected to a small hick-up of Bh,
Between pseudobreakup and substorm onset, the tail B-field stretching continues locally,
Substorm onset is connected to a sharp increase of Bh. These signatures are expected from
previous studies.
Substorm signatures in the near-Earth tail
Subtraction of the magnetosphere model T89 B-field for quiet times from GOES data Pseudobreakup Substorm GOES magnetic field data
The geosynchronous GOES satellites orbit at about 6 Re around the Earth.
This is close to the substorm onset region.
Substorm onset is connected to a strong dipolarization of B-field, which is
seen as a strong increase of the z-component in the B-field (H-component).
To enhance the dipolarization signature, a standard (quiet time) magnetosphere
model B-field is substracted from the data.
In this example it can be nicely seen: the pseudobreakup is connected to a small hick-up of Bh,
Between pseudobreakup and substorm onset, the tail B-field stretching continues locally,
Substorm onset is connected to a sharp increase of Bh. These signatures are expected from
previous studies.
Signatures of 10 substorms preceded by pseudobreakups
IMF Bz AE index Tail Bh – Model Bh
Here are the plots for all 10 substorm cases with pseudobreakups.
Row shows IMF Bz, 2. row shows AE index, 3. row shows Bh (corresponds to Bz) – Bh (model), i.e. substracting the background field.
AE index: in most cases AE rises minutes after the auroral onset.
Bh-Bh(T98): in most cases Bh rises many minutes after the auroral onset.
Mapping of GOES tail position to the auroral oval
To study the reason for the dipolarization delay we map GOES tail position along the B-field lines
back to the northern ionosphere (using the T96 model with solar wind and IMF input data).
No delay of dipolarization: GOES maps to onset position
Upper left is the Bh-Bh(T89) curve
The white cross on the UV images shows the mapped position of GOES
In this case, the mapped cross appear right inside the pseudobreakup and the onset region.
No dipolarization seen: GOES is always equatorward of oval
In the case where no dipolarixation is seen,
the mapped GOES position is always outside the auroral oval (earthward from the dipolarization region).
Reason for delayed dipolarization: Dawn- or duskward substorm expansion
In this case, GOES is inside the oval, but dawnward from the onset region.
When the bright region (substorm expansion) reaches GOES, a dipolarization is seen.
Reason for delayed dipolarization: Equatorward oval expansion after onset
In case the dipolarization appears with a strong delay,
GOES position is outside the oval = earthward of the dipolarization region.
The oval expands equatorward during the substorm.
At the point of time when GOES is inside the oval, a dipolarization is seen.
Dipolarization delay versus GOES mapped position in the oval
Duskward of onset Dawnward of onset Dawnward of onset GOES always equatorward Nearly at onset Equatorward of onset Poleward of onset Equatorward of onset Equatorward of onset Equatorward of onset GOES mapped position at substorm onset 0.24 MLT/min duskward 0.10 MLT/min dawnward 0.33 MLT/min dawnward
No dipolarization 0.55 MLT/min duskward 0.08 deg/min equatorward unclear (bad UVI image) 0.08 deg/min equatorward 0.10 deg/min equatorward 0.11 deg/min equatorward Propagation speed of dipolarization region 2 mn 0.82 MLT Feb 25, 99 2.7 MLT -2.38 MLT -2.23 MLT 1.78 MLT -0.82 MLT -0.80 MLT 0.61 MLT -0.19 MLT -0.04 MLT GOES - main onset
Distance 11 mn 17 mn 8 mn - 31 mn 26 mn 25 mn 22 mn 29 mn Dipolarization
Delay Jan 7a, 99 Dec 23, 98 Dec 28, 98 Jan 7b, 99 Jan 15, 99 Feb 24, 99 Dec 3, 98 Dec 14, 98 Dec 6, 98 Date
The table lists the results for all 10 events:
When GOES is at the same longitude, the dipolarization delay is large
When GOES is dawn or duskwardly displaced, the dipolarization delay is short.
In the last column the propagation speed of the dipolarization is calculated.
Expansion of the tail dipolarization region
onset tail onset Propagation speed of tail dipolarization region:
Azimuthal propagation speed: 0.22 MLT/min (Liou et al. [2002] found
0.37 MLT/min)
Earthward propagation speed: 0.09 deg/min
(Liou et al. [2002] found
0.84 deg/min)
Previous work shows, the magnetic field dipolarisation starts locally [Ohtani et al., 1991] and spreads azimuthally [Nagai, 1982; Liou et al., 2002], and radially outward [Jacquey et al. 1991; Ohtani et al., 1992] as well as inward [Ohtani, 1998].
Results
The dipolarization at GOES starts when bright auroral region reaches GOES mapped position. This indicates, the expansion of auroral intensification region and the expansion of the tail dipolarization region are coupled. Thus, the small azimuthal expansion of the smallest substorms indicates an only limited spread of the tail dipolarization region.
For substorms preceded by pseudobreakups, the expansion of the tail dipolarization region in azimuthal direction is as fast as expected from regular substorms. The expansion of the dipolarization region in Earthward direction is 10 times smaller than expected from regular substorms. This is probably connected to a slow Earthward motion of the inner plasma sheet boundary after onset (equatorward motion of the oval boundary).
AE index
One month AE index data with pseudobreakups overlaid
AE index
Substorms with pseudobreakups Substorms without
pseudobreakups Superposed epoch plots for substorms of different strengths, centered around substorm onset.
(Red, yellow, green and blue correspond to strong, medium, small and very small substorms)
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