1. Evidence for Dayside Interhemispheric Field-Aligned Currents During Strong IMF By Conditions Seen by SuperDARN Radars
Joseph B.H. Baker, Bharat Kunduri and J. Michael Ruohoniemi
Center for Space Science and Engineering Research
Virginia Tech

2. The SuperDARN Radars
The Super Dual Auroral Radar Network (SuperDARN) is an international network of high-frequency (HF) radars for researching the Earth’s upper atmosphere, ionosphere, and connection into geospace.

3. Interhemispheric FACs
A strong IMF By component will penetrate the dayside magnetosphere and produce interhemispheric field-aligned currents (FACs) [Kozlovsky et al., 2003].
For a strong negative IMF By component:
NORTHERN HEMISPHERE:
Downward FAC in polar cap
Outward FAC in closed field-line region
Eastward auroral zone convection
SOUTHERN HEMISPHERE:
Upward FAC in polar cap
Downward FAC in closed field line region
Westward auroral zone convection
From Kozlovsky et al. [2003]

4. UT
Southern Hemisphere (Winter)
Northern Hemisphere (Summer)
Afternoon convection is stronger in the southern (winter) hemisphere (left panel)
Interplanetary Magnetic Field (IMF) is southward with negative By component

5. UT
Southern Hemisphere (Winter)
Northern Hemisphere (Summer)
Southern Hemisphere: Field-aligned currents reinforce afternoon convection
Northern Hemisphere: Field-aligned currents counteract afternoon convection

6. UT
Southern Hemisphere (Summer)
Northern Hemisphere (Winter)
Afternoon convection is stronger in the southern (summer) hemisphere (left panel)
Interplanetary Magnetic Field (IMF) is southward with negative By component

7. UT
Southern Hemisphere (Summer)
Northern Hemisphere (Winter)
Southern Hemisphere: Field-aligned currents reinforce afternoon convection
Northern Hemisphere: Field-aligned currents counteract afternoon convection

8. Velocity Differences
Southern hemisphere velocities (left) are mapped into the northern hemisphere (middle) and compared with northern hemisphere velocities (right).
The velocities are clearly higher at the southern footpoints of the closed flux tubes.

9. Estimated FAC Magnitudes
Current Density (nA/m2)
The interhemispheric velocity differences are used to estimate the FAC magnitude.

10. Width of the FAC Channel
Blue = southern velocities
Black = northern velocities
Feb 16th 2005
May 29th, 2005
The FAC channels are 3-6° wide and the velocity difference is strongest at high latitudes.
The velocity difference also decreases moving from noon toward dusk.

11. Summary
During two event periods with strong negative IMF By component, SuperDARN radars observed strong interhemispheric asymmetries in the afternoon sunward convection on closed magnetic field lines.
The observations are consistent with interhemispheric field-aligned currents (FACs) flowing out of the northern hemisphere and into the southern hemisphere on closed magnetic field lines [Kozlovsky et al., 2003].
Estimates for the strength of the FACs have been calculated and the latitudinal width of the FAC channel was found to be 3-6 degrees wide.
The intensity of the FACs decreased moving equatorward from the open-closed field line boundary and moving from noon toward later local times.