Ground and Space-based Magnetic Fields during a THEMIS

Double-onset Substorm

M. Connors1, C. T. Russell2, I. Voronkov1, E. Donovan3, V. Angelopoulos2, S. B. Mende4, K.-H. Glassmeier5, K. Hayashi6, E. Spanswick3, B.

Jackel3, H. Frey4, J. McFadden4

(1Athabasca U, 2UCLA, 3U. Calgary, 4UC Berkeley, 5TU Braunschweig, 6U. Tokyo)

Cluster 15 Workshop, Tenerife March 2008 Image: Mikko Syrjäsuo

Abstract (Main Points)In support of THEMIS, ground-based auroral optical and magnetic detection in North America has recently been greatly improved.

Magnetic data is now available from enough locations to support quantitative studies, including techniques based on forward modeling.

We use Automated Regional Modeling (ARM) to specify the locations and strength of electrojets and field-aligned currents (FAC).

On March 13, 2007, THEMIS was conjugate to central North America, clear weather prevailed, and a double onset (5:08 and 5:36 UT) substorm took place.

Spacecraft data support the use of the Tsyganenko 89 tail model during periods near the onsets.

The ground perturbations are well represented by a 3-D substorm current wedge system.

Mapping changes can be studied with a combination of ground and spacecraft data.

A surge-like current system permits very accurate verification of the mapping of the second onset, and its current is detected at the spacecraft.

1. Athabasca University Geophysical Observatory (AUGO)

54.72 N, 246.7 ECGM (2005) 62.0, 306.5L=4.55

Founded 2002(UCLA mag 1998)Will be moved in 2008 due to light encroachment

A comprehensive observatory ideally located for THEMIS conjunctions

AUGO’s Instrumentation

Guest instruments from STELAB:

1. Multispectal ASC including Hβ

2. 64 Hz induction coil3. proton spectrometer

1. UCLA Fluxgate2. THEMIS GBO Camera3. KEO NORSTAR Camera

2. Ground Magnetometry In a Sun-to-Mud approach, we are in the mud…

EDMO UCLA magnetometer installed by Martin Connors (Tom Sawyer-like technique applied to astronomer Brian Martin) in December 2004

Often the locales are less agreeable than Tenerife (Kanji Hayashi in LaRonge, Canada, mid-October 2004). This magnetometer

was critical to this study: wide and dense placement is essential!

Red Deer

Lethbridge

Paddle Prairie

Edmonton

Athabasca

Calgary

Slave Lake

Sites installed fully and data available (2 Hz) since Oct 4, 2005Inuvik 2006

Inuv

ik

Athabasca University has assisted or runs 16 sites in Canada (white triangles and purple dots in Western Canada). Most data available through UCLA, STEP website, or on request. PEA and SFV hoped for soon. New Polaris sites on E. Coast of Hudson Bay were installed in 2007.Some THEMIS GBOs not shown.

3. Optical FacilitiesRed circles show the fields of view (FOVs) of THEMIS Ground-

Based Observatories (GBOs). Most have imager + mag. Small blue circles show positions of U.S. subauroral magnetometers (GEONS) whose data is available at themis.ssl.berkeley.edu

4. Data Interpretation for Ground-based Magnetometers: Automated Forward Modelling (AFM)

can help.

For meridian data, AFM adjusts current and borders

The method is however, much more general and includes field-aligned currents in realistic 3-d configurations. Midlatitude perturbations can be included as can a Dst-like parameter.

Inversion tells us more by giving simple parameters extracted from several ground stations

April 10 1997

Array Interpretation from a distributed region is even more difficult, complicated by problems of

nonuniqueness. An inversion procedure is needed.

• On the ground, one detects primarily the magnetic effects of the Hall currents associated with the auroral oval electric field

• FAC effects CAN be observed from the ground

AFM Apr 3 1997 red vectors are model, black observed

Ability to match input data is best near the middle of the chain (although often not in Z due to electrojet structure)

Note: different event and stations

Event Study March 13 2007

• A pseudo-breakup at 05:08 was followed by a full onset at 05:36 on March 13, 2007

• THEMIS was in its initial string-of-pearls orbit with all FGM turned on but only some plasma sensing on THEMIS-A

• Four THEMIS spacecraft were very well placed with respect to the activity

• Ground-based networks were also well placed

Cluster

THEMIS

March 13, 2007 ~0500 UT

Cluster FGM

Moderately disturbed solar wind near ~5 UT onset time

Generally positive BY

T89 Kp>6 GSM XZ

GSM XY

05:08 UT

E

AB

D

C

THEMIS in early orbit configuration as “string of pearls” less than one month after launch

Very stretched!

66 seconds of imaging: every second image shown

Excellent conjugacy: T89 Kp 3to 5+ shown for E,A,B,D

Hbeta Proton aurora630 nm Redline

Proton precipitation was intense in this event as shown by MSP, also imaged by STELAB OMTI Imager at Athabasca (not shown). Onset arc was poleward of the proton aurora.

Arc that brightens

Inner Edge of Plasma Sheet

Quantitative study of the onset arc

m~120

Bri

ghtn

ess

in E

wog

ram

Bin

Brightness on Arc at Fixed MLONs

At ALL longitudes, the pre-onset arc faded measurably before onset and then a brightening took place in the same region

Bx

Bz

THEMIS D

THEMIS B

THEMIS A

THEMIS E

ESA Ions

ESA Electrons1e7,8

1e3,4

0508 0536

THEMIS superposed magnetic Bx and TH A low energy ions

Dipolarization seems to be plasma sheet recovery

THEMIS superposed magnetic Bx and TH A electrons

First onset at 05:08 was marked by plasma sheet recovery

Second onset at 05:36 showed a plasma dropout and a strong Y component (often a field-aligned current signature)

The optical data for onset #2 is not as good, what does magnetic data tell us?

At 05:33, the pseudo-breakup is fully developed. Its perturbations are well matched by a substorm current wedge. Black = observation. Red = model.

Pseudobreakup/Onset Comparison at Maximum extent

Pseudobreakup Onset

Observed

Model

Mapping to Space

One can in principle map precipitation regions to space and hope to hit a spacecraft showing related particle fluxes.

One can in principle map field-aligned currents derived from regional modelling to space and see broader effects.

However we have seen that diamagnetic effects can be large and near the plasma sheet, dominant.

Need to examine discreet, recognizable features.

• To what degree can we do mapping?

• Lines in panels a,b,e,f show T89 B levels for different stretching

• Also note in panels g and h the large Y signature at 05:36 onset

FAC

The Y signature at Fort Churchill can originate from a northward ionospheric current joining FAC sheets to north and south.The eastward perturbation at the THEMIS spacecraft can arise from a FAC sheet in space passing over the spacecraft.

T89 Model Study

The Y perturbation could arise from a current sheet moving inward with its foot moving equatorward at the time of dipolarization. This would ‘move’ the spacecraft in between two current sheets.

There is some evidence of the equatorward motion of auroras at onset;

in addition the sequence of Y perturbation at the E and A spacecraft suggests inward motion of the field line. This suggests that the modelling of this distinctive feature on ground and at the

spacecraft is basically correct, and that T89 with an adjusted activity factor maps correctly.

Conclusions

• Ground enhancements for THEMIS have greatly improved auroral monitoring, both optical and magnetic, in North America

• For Cluster, optical does not benefit as much as for THEMIS due to “NH summer” orbit

• We can quantitatively deal with magnetic data• We can map into the tail with some confidence

based on studies of distinctive features

Acknowledgements

• Mark Moldwin, Andrei Runov (UCLA)• Canadian Space Agency and University of Alberta

for CARISMA data, accessed through cssdp.ca; NRCan for CANMOS data.

• This work funded by Canada Research Chairs, Canada Foundation for Innovation, AU, and NSERC

• FMI IMAGE data used in making Slide 10• A. Balogh, ICSTM, for Cluster FGM via CDAWeb• N. Tsyganenko for availability of model software