1. On Strong Coupling between the Harang Reversal Evolution and Substorm Dynamics: A Synthesis of SuperDARN, DMSP and IMAGE Observations
Shasha Zou1, Larry Lyons1, Chih-Ping Wang1,
Athanasios Boudouridis1, Mike Ruohoniemi2,
Phillip Anderson3
University of California, Los Angeles, USA
Applied Physics Laboratory, John Hopkins University, USA
University of Texas at Dallas, USA

2. Physics of the Harang Reversal
Introduction:
Physics of the Harang Reversal
Less energetic protons
j||
from LLBL
j||
Finite width of tail E
Median energy proton drift pass
More energetic protons from far tail
The Harang reversal results from dawn-dusk pressure asymmetry in the near-earth plasma sheet [Erickson et al., 1991]
A part of the Region-2 field-aligned (shielding) current system

3. Onset FUV Imager/WIC Particle Injection & Positive Bay
18 March :26:30 UT
Particle Injection & Positive Bay
Onset
21 MLT

4. TIGER Radar Pair Observation 18 March 2005 10:26-10:28 UT
18 MLT
Merged vector
Line-of-sight vector
-80°
-70°
-60°
21 MLT
24 MLT
Substorm onset occurs at the center of the Harang reversal.

5. · + 18 March 2005 0952-0954 UT 18 MLT DMSP F13/ F16
Equatorward Boundary
SAPS
24 MLT

6. TIGER Radar Pair Observation
18 March :26-10:28 UT
SAPS
Majority of the westward flows equatorward of the Harang reversal are SAPS.

7. Four More Events 1 Jan. 2005 1236-1238 UT 11 Feb. 2005 1044-1046 UT
6 Nov UT
3 Dec UT

8. SAPS electric field response at onset

9. 18 March 2005
Growth Phase Evolution of the Harang Reversal
Onset ?

10. Summary and Conclusions
1. Relationship between substorm onset and HR?
HR observed during all nine substorm events we analyzed.
Substorm onset occurs at center of Harang flow shear, suggesting that substorm upward FAC comes out of ionosphere from there.
2. Relation of HR to other Region-2 features?
Majority of westward flows equatorward of HR are SAPS.
Onset observed just poleward of SAPS implies that onset occurs near inner edge of electron plasma sheet.
3. Evolution of HR flows after onset?
Depend strongly on their location relative to that of onset.
SAPS suddenly increase at onset.
The observations demonstrate a strong coupling between HR evolution and substorm dynamics, suggesting that nightside R-2 physics is closely associated with substorm dynamics.