Peter Boakes1, Steve Milan2, Adrian Grocott2, Mervyn Freeman3, Gareth Chisham3, Gary Abel3, Benoit Hubert4, Victor Sergeev5 Rumi Nakamura1, Wolfgang Baumjohann1

A Superposed Epoch Analysis on the Impact of Differing Solar Wind‐

Magnetosphere Driving Conditions on Substorm Particle Injection and

Ionospheric Substorm Convection

ICS11, Lüneburg, Germany - September 2012

(1) Space Research Institute, Austrian Academy of Sciences, Graz, Austria. (2) University of Leicester, UK. (3) British Antarctic Survey, Cambridge, UK. (4) Laboratory of Planetary and Atmospheric Physics, University of Liège, Liège, Belgium. (5) St. Petersburg State University, Earth Physics Department, St.

Petersburg, Russia.

Many substorm signatures, one of the most commonly used to identify substorms is the injection of energetic particles to geosynchronous orbit, as seen by the LANL SC.

Boakes et al., 2009 showed that not all substorms identified from global auroral imagery (Frey et al., 2003) could be associated with particle injection at LANL.

Classified 306 events with good LANL coverage from Dec/Jan 2000-2002 into three categories:

Category 1 (100/306): associated with classical substorm injection signature, dispersionless injection at midnight and/or energy dispersed injection signatures at later/earlier MLTs.

Category 2 (114/306): events showed complicated injection signatures, covering all energetic particle fluctuations not following the classic substorm signature.

Category 3 (92/306): events with no particle fluctuations observed.

Introduction

Using the method of Boakes et al., 2008 to identify the OCB from global auroral images (IMAGE FUV), we determine open flux (Fpc) by integrating the radial component of the Earths magnetic filed through the area of enclosed by the OCB.

Determine open flux distributions for all times (~12000 auroral images from Dec/Jan 2000-2002), substorm onset time (135), and each LANL category.

Category 1 (61 events) occur at higher values of Fpc than either category 2 or 3. 3Boakes et al., 2009

Cat 1

Cat 2

Cat 3

Cat 1+2

All

Fra

ctio

nal O

ccur

renc

e

Fpc (GWb)

Open Magnetic Flux Distribution

A Superposed Epoch Analysis of LANL categories

Category 1 (100 events)

Null

A Superposed Epoch Analysis of LANL categories

Category 1 (100 events)

• Category 1 events- show all the expected signatures of a “classic” substorm occurring due to a large southward turning of the IMF Bz component during otherwise average solar wind conditions..

A Superposed Epoch Analysis of LANL categories

Category 2 (114 events)

Category 1 (100 events)

• Category 2 events-Strongly driven on the dayside throughout substorm expansion. More active IMF conditions/driving.

A Superposed Epoch Analysis of LANL categories

Category 3 (92 events)

Category 2 (114 events)

Category 1 (100 events)

• Category 3- Weak activity and driving.

Superposed Auroral Boundary Motions

• Using method Boakes et al., 2008 to identify location of the OCB from IMAGE WIC, superpose OCB latitude around the time of substorm onset.

Minutes Relative to Onset

Mag

neti

c L

atit

ude

Mag

neti

c L

atit

ude

Superposed Auroral Boundary Motions

• Using method Boakes et al., 2008 to identify location of the OCB from IMAGE WIC, superpose OCB latitude around the time of substorm onset.

• Category 1 events- Show global response (expansion and contraction) to substorm growth and expansion phases.

Minutes Relative to Onset

Mag

neti

c L

atit

ude

Mag

neti

c L

atit

ude

Superposed Auroral Boundary Motions

• Using method Boakes et al., 2008 to identify location of the OCB from IMAGE WIC, superpose OCB latitude around the time of substorm onset.

• Category 1 events- Show global response (expansion and contraction) to substorm growth and expansion phases.

• Category 2 events- Delayed or no recover of boundary latitudes on the dayside auroral oval, consistent with addition of open flux and continued solar wind driving on the dayside.

Minutes Relative to Onset

Mag

neti

c L

atit

ude

Mag

neti

c L

atit

ude

Superposed Auroral Boundary Motions

• Using method Boakes et al., 2008 to identify location of the OCB from IMAGE WIC, superpose OCB latitude around the time of substorm onset.

• Category 1 events- Show global response (expansion and contraction) to substorm growth and expansion phases.

• Category 2 events- Delayed or no recover of boundary latitudes on the dayside auroral oval, consistent with addition of open flux and continued solar wind driving on the dayside.

• Category 3 events- Boundary motions are localised.

Minutes Relative to Onset

Mag

neti

c L

atit

ude

Mag

neti

c L

atit

ude

• Super Dual Auroral Radar Network (SuperDARN) provides almost continuous line-of-sight ionospheric convection velocities in the auroral regions.

• The ‘map potential’ technique (Ruohoniemi and Baker, 1998) is used to map velocities to a polar grid and find the best-fit solution to the electrostatic potential.

Superposed Ionospheric Convection

Superposed Ionospheric Convection

-20 mins

-20 mins

Onset

Onset

Superposed Ionospheric Convection

+20 mins

+20 mins

+40 mins

+40 mins

Superposed Ionospheric Convection

+60 mins

+60 mins

+90 mins

+90 mins

Category 3• Category 3 events show little variation in convection flows prior/following onset.

-20 mins

-20 mins

Onset

Onset

Not all substorms identified from global auroral imagery could be associated with geosynchronous particle injection.

Category 1 events (particle injection events, 100/306) show all the classical signatures of global substorm events (loading-unloading).

Category 2 events (varied activity, 114/306 events) are associated with active periods and continuous solar wind energy input throughout substorm expansion and recovery (directly driven).

Category 3 events (no injection, 92/306) occur on contracted auroral ovals with weak solar wind driving and are more localized/weaker tail reconnection events/substorms.

Superposed Ionospheric convection flows show distinct differences between particle injection categories related to flow driving from coupled dayside reconnection and nightside substorm activity.

More studies are needed of the ionospheric convection response to different types of substorms.

Summary