Statistics of velocity fluctuations observed by SuperDARN under steady interplanetary magnetic field conditions

A study of velocity fluctuations observed by the Super Dual Auroral Radar Network (SuperDARN) HF radar network is presented. The study was undertaken with the goals of determining the level of fluctuation due to internal magnetospheric processes, and to examine the probability of observing a significant velocity fluctuation within any given time interval. The study included 6 years of observations from periods when the interplanetary magnetic field (IMF) was moderately southward and steady. It was assumed that the IMF that encounters the magnetosphere is the same as that observed at a spacecraft located upstream from the Earth and that all variability of the plasma convection is due either to variability of the IMF driver or to internal magnetospheric processes. IMF variability away from the satellite was examined statistically by comparing the distributions of observations for the ACE and Wind satellites. The distribution of velocity fluctuations and their waiting time distribution were examined over a grid of latitude and local time. It was found that the waiting time is scale free over the range of times that could be examined. From the waiting time distributions, the probability of observing fluctuations within various time intervals was determined over the grid. It was found that the probability of observing a significant velocity fluctuation is high for all local times in the high-latitude region.