Introduction

In Kunduri et al., [2017]

Mid-latitude SuperDARN based SAPS statistical study.
SAPS are more frequent than we expect (even during quiet times).
Developed SuperDARN based SAPS location model.
Analyzed SAPS speeds using gridded line-of-sight velocity data, assuming SAPS flow direction is perfectly westward.

Current Study

Focussed analysis of SAPS velocities to obtain magnitude and direction with improved resolution.
Discuss typical range of SAPS velocities in SuperDARN observations using two events.
Analyze the average statistical characteristics of SAPS velocities (magnitude and direction) and electrostatic potentials with MLT.
Discuss the spread observed in SAPS velocities.

SuperDARN range gate width - 45 km.
Define a global grid to get best possible latitudinal resolution. Grid size 0.5 MLAT and 1 MLT.

Apply L-shell fitting at each grid cell. The MLT extent used to apply L-shell fitting is variable (1-3 MLT).
Discard bad fits. Assume direction is same as closest good fit.

Figure shows L-shell velocities.
Circles indicate location with good L-shell fits. Asterisks indicate locations whose directions were assumed to be the same as the nearest good fit.
Results are comparable to Clausen et al [2012].

Event on 2011-May-29 at 0400 UT. Dst : -31 nT.
Velocities as low as 75 - 150 m/s are observed.
E-fields < 5 mV/m are observed. Typically between 5-10 mV/m.
Results slightly lower than estimated in Nagano et al [2015] (150-200 m/s).
Lower E-fields are not sufficient for frictinal heating ( > 50 mV/m) [Schunk et al., 1975]

Mean SAPS potentials at different Asy-H bins (derived by poleward integration of velocities).
At highest disturbance levels potentials can be as high as 45-50 kV. During quiet times we can see potential drops up to 15 kV.
Results are in agreement with Foster and Vo [2002].
Goldstein et al [2005] used Foster and Vo [2002] average characteristics to develop a SAPS magnetospheric model (when Kp >= 4).
Combining results from Kunduri et al [2017] and this study better SAPS model can be developed.
New results on quiet time SAPS would be useful in understanding inner magnetospheric conditions.

Cumulative Distribution Fucntions of SAPS velocities at different Asy-H bins for same location.
For the lowest bin there is more than 80% chance that vel < 500 m/s is observed while for hte highest bin there is more than 80% chance that vel > 1000m/s is observed.
Even for highest bin, there is 40 % chance that vel < 750 m/s is observed.

Conclusions

Focussed analysis on SAPS velocities and potentials on a statistical scale at higher latitudinal resolution.
SuperDARN observes SAPS under quiet geomagnetic conditions too. Some events with electric fields less than 5 mV/m and others where electric fields go beyond 100 mV/m are observed. Traditional SAPS mechanisms can't explain the low velocity events.
SAPS velocities increase with geomagnetic activity and during disturbed times increase linearly towards dusk. Consistent with previous studies.
Quiet time SAPS don't exhibit a linear relation with MLT.
SAPS flows turn increasingly poleward towards dusk. They need eventually merge with high-latitude convection.
SAPS potentials are similar to previous studies. Can be used along with the Kunduri et al [2017] SAPS location model to improve magnetospheric models [Goldstein et al 2005].
Disturbed time SAPS velocities exhibit high degree of spread. Suggesting many factors such as ionospheric conductivity and high latitude convection influence SAPS velocities.

By Bharat Kunduri