Swarm Studies of Fieldaligned Currents Scientific and Technical

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Swarm Studies of Field-aligned Currents: Scientific and Technical Challenges Shin(ichi) Ohtani & Jesper W.

Swarm Studies of Field-aligned Currents: Scientific and Technical Challenges Shin(ichi) Ohtani & Jesper W. Gjerloev The Johns Hopkins University Applied Physics Laboratory http: //www. esa. int/spaceinimages/Images/2011/10/Swarm_constellation

Curl-B and Single-satellite Techniques 1 September 2014 SWARM-C SWARM-A 3 May 2014 SWARM-C SWARM-A

Curl-B and Single-satellite Techniques 1 September 2014 SWARM-C SWARM-A 3 May 2014 SWARM-C SWARM-A Curl-B SWARM-A SWARM-C

Large-scale FAC Structures: 1 Hughes [1991] Axford [1964]]

Large-scale FAC Structures: 1 Hughes [1991] Axford [1964]]

Large-scale FAC Structures: 2 Iijima and Potemra [1976] • The entire cycle convection takes

Large-scale FAC Structures: 2 Iijima and Potemra [1976] • The entire cycle convection takes a few hours.

Meso-scale FAC Structures (Upward) FAC Aurora 2 min Henderson et al. [2009]

Meso-scale FAC Structures (Upward) FAC Aurora 2 min Henderson et al. [2009]

Small-scale FAC Structures ~100 km Measured by Reimei (no FAC measurement) Hirahara et al.

Small-scale FAC Structures ~100 km Measured by Reimei (no FAC measurement) Hirahara et al. [2007] http: //darts. jaxa. jp/outreach/month/200711/index. html. en

Two Methods to Calcualte FAC Density: 1 l t Large-scale 100 km~ 10’s min

Two Methods to Calcualte FAC Density: 1 l t Large-scale 100 km~ 10’s min Global FACs Meso-scale 10~100 a few km FACs minutes Small-scale FACs 1~10 km Seconds

Two Methods to Calcualte FAC Density: 2 Single-satellite Method Curl-B Method T 2 T

Two Methods to Calcualte FAC Density: 2 Single-satellite Method Curl-B Method T 2 T 4 DB T 1 T 3 T 2 = T 1 + 5 s T 3 ~ T 1 + (5 to 10) s T 4 ~ T 1 + (10 to 15) s Assumptions: 1. Stationary 2. Infinite Current sheet Assumptions: 1. Stationary 2. Uniform FAC

Two Methods to Calcualte FAC Density: 3 l t Single. Satellite Curl-B Conditional Applicable

Two Methods to Calcualte FAC Density: 3 l t Single. Satellite Curl-B Conditional Applicable Large-scale 100 km~ 10’s min - Inf. sheet? - Stationary Global FACs - Stationary - Uniform Conditional Meso-scale 10~100 a few - Inf. sheet? Marginal km FACs minutes - Stationary Conditional Small-scale 1~10 km Seconds - Inf. sheet? Nonapplicable FACs - Stationary

Two Methods to Calcualte FAC Density: 4 Single-satellite Method Curl-B Method T 2 T

Two Methods to Calcualte FAC Density: 4 Single-satellite Method Curl-B Method T 2 T 4 DB T 1 T 3 T 2 = T 1 + 5 s T 3 ~ T 1 + (5 to 10) s T 4 ~ T 1 + (10 to 15) s Assumptions: 1. Stationary 2. Infinite Current sheet Assumptions: 1. Stationary 2. Uniform FAC

Two Methods to Calcualte FAC Density: 5 l t Single. Satellite Curl-B Conditional Applicable

Two Methods to Calcualte FAC Density: 5 l t Single. Satellite Curl-B Conditional Applicable Large-scale 100 km~ 10’s min - Inf. sheet? - Stationary Global FACs - Stationary - Uniform Conditional Meso-scale 10~100 a few - Inf. sheet? Challenging km FACs minutes - Stationary Conditional Small-scale 1~10 km Seconds - Inf. sheet? Not applicable FACs - Stationary

SWARM Example on 1 September 2014: 1 MLT ~ 00 SML ~ -150 n.

SWARM Example on 1 September 2014: 1 MLT ~ 00 SML ~ -150 n. T followed by an onset Special thanks to Tetsuo Motoba(STEL, Nagoya U) and Natl. Inst. Polar Res. (Japan)

SWARM Example on 1 September 2014: 2 23: 15: 14 UT 23: 15: 24

SWARM Example on 1 September 2014: 2 23: 15: 14 UT 23: 15: 24 UT SWARM-A(MLT: 00: 04)/-C(MLT: 00: 10) 23: 15: 34 UT 23: 15: 44 UT

SWARM Example on 1 September 2014: 3 N-S E-W Curlometer SWARM-A SWARM-C

SWARM Example on 1 September 2014: 3 N-S E-W Curlometer SWARM-A SWARM-C

SWARM Example on 3 May 2014: 1 MLT ~ 00 SML ~ -200~-300 n.

SWARM Example on 3 May 2014: 1 MLT ~ 00 SML ~ -200~-300 n. T Special thanks to Tetsuo Motoba(STEL, Nagoya U) and Natl. Inst. Polar Res. (Japan)

SWARM Example on 3 May 2014: 2 21: 25: 44 UT SWARM-C(MLT: 22: 20)

SWARM Example on 3 May 2014: 2 21: 25: 44 UT SWARM-C(MLT: 22: 20) 21: 25: 54 UT 21: 26: 04 UT 21: 26: 14 UT

SWARM Example on 3 May 2014: 3 N-S Curlometer SWARM-A SWARM-C E-W

SWARM Example on 3 May 2014: 3 N-S Curlometer SWARM-A SWARM-C E-W

Our to-do’s Single-satellite methods: 1. Determine the FAC orientation (minimum variance). 2. Examine the

Our to-do’s Single-satellite methods: 1. Determine the FAC orientation (minimum variance). 2. Examine the max-to-min eigenvalue ratio. 3. Optimize the segmentation of orbits (based on d. B). 4. Validate via comparison with auroral images. 5. Explore 50 Hz data. 23: 15: 14 UT 23: 15: 24 UT 23: 15: 34 UT 23: 15: 44 UT

Our to-do’s Single-satellite methods: 1. Determine the FAC orientation (minimum variance). 2. Examine the

Our to-do’s Single-satellite methods: 1. Determine the FAC orientation (minimum variance). 2. Examine the max-to-min eigenvalue ratio. 3. Optimize the segmentation of orbits (based on d. B). 4. Validate via comparison with auroral images. 5. Explore 50 Hz data. Curl-B methods: 1. Evaluate div. B and compare with any anomaly. 2. Explore the possible use of single-SC results for validating assumptions. (3. Optimize Dt based on the orientation of FACs. )

Physical Distinction of “Static vs. Temporal Structures” l t Single. Satellite Curl-B Conditional Applicable

Physical Distinction of “Static vs. Temporal Structures” l t Single. Satellite Curl-B Conditional Applicable Large-scale 100 km~ 10’s min - Planar? B - Stationary Global E FACs Bostrom [1964] - Stationary - Uniform Conditional~30 km Meso-scale 10~100 a few - Planar? Marginal km FACs minutes - Stationary Conditional Small-scale 1~10 km Seconds - Planar? FACs - Stationary Wygant et al. [2000] Nonapplicable

Swarm Studies of Field-aligned Currents: Scientific and Technical Challenges Shin(ichi) Ohtani & Jesper W.

Swarm Studies of Field-aligned Currents: Scientific and Technical Challenges Shin(ichi) Ohtani & Jesper W. Gjerloev Meso-scale M-I coupling! The Johns Hopkins University Applied Physics Laboratory It is challenging because: - Its time and spatial scales are comparable to those of the satellite separation. - It is in the transition of two physical domains, i. e. , static and Alfvénic current closures. - It’s internal structures are often very dynamic. But its understanding is compelling because: - it is critical to the transition of the global M-I system.