Oxygen ion response to proton bursty bulk flows. Issue 8 (9th August 2016)

• Record Type: Journal Article
• Authors: Nilsson, Hans; Hamrin, Maria; Pitkänen, Timo; Karlsson, Tomas; Slapak, Rikard; Andersson, Laila; Gunell, Herbert; Schillings, Audrey; Vaivads, Andris
• Is Part Of: Journal of geophysical research. Volume 121:Issue 8(2016:Aug.)
• Page Start: 7535
• Page End: 7546
• Publication Date: 2016-08-09
• Subjects: bursty bulk flow -- plasma sheet -- oxygen ions; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2016JA022498
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: We have used Cluster spacecraft data from the years 2001 to 2005 to study how oxygen ions respond to bursty bulk flows (BBFs) as identified from proton data. We here define bursty bulk flows as periods of proton perpendicular velocities more than 100 km/s and a peak perpendicular velocity in the structure of more than 200 km/s, observed in a region with plasma beta above 1 in the near‐Earth central tail region. We find that during proton BBFs only a minor increase in the O + velocity is seen. The different behavior of the two ion species is further shown by statistics of H + and O + flow also outside BBFs: For perpendicular earthward velocities of H + above about 100 km/s, the O + perpendicular velocity is consistently lower, most commonly being a few tens of kilometers per second earthward. In summary, O + ions in the plasma sheet experience less acceleration than H + ions and are not fully frozen in to the magnetic field. Therefore, H + and O + motion is decoupled, and O + ions have a slower earthward motion. This is particularly clear during BBFs. This may add further to the increased relative abundance of O + ions in the plasma sheet during magnetic storms. The data indicate that O + is typically less accelerated in association with plasma sheet X lines as compared to H + . Key Points: Oxygen ions do not follow the protons in bursty bulk flows, they move much slower Oxygen ions are less accelerated in the plasma sheet than protons The earthward transport of oxygen is slower than for protons