Ground and Space-based Magnetic Fields during a THEMIS Double-onset Substorm. M. Connors 1 , C. T. Russell 2 , I. Voronkov 1 , E. Donovan 3 , V. Angelopoulos 2 , S. B. Mende 4 , K.-H. Glassmeier 5 , K. Hayashi 6 , E. Spanswick 3 , B. Jackel 3 , H. Frey 4 , J. McFadden 4
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
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.
A comprehensive observatory ideally located for THEMIS conjunctions
54.72 N, 246.7 E
(UCLA mag 1998)
Will be moved in 2008 due to light encroachment
Guest instruments from STELAB:
2. Ground MagnetometryIn 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!
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
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.
April 10 1997
Array Interpretation from a distributed region is even more difficult, complicated by problems of nonuniqueness. An inversion procedure is needed.
AFM Apr 3 1997 red vectors are model, black observed
Note: different event and stations
March 13, 2007 ~0500 UT
Generally positive BY
Moderately disturbed solar wind near ~5 UT onset time
THEMIS in early orbit configuration as “string of pearls” less than one month after launch
66 seconds of imaging: every second image shown
Excellent conjugacy: T89 Kp 3to 5+ shown for E,A,B,D
Hbeta Proton aurora
630 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
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
Brightness in Ewogram Bin
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.
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.
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.
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.