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Oscillatory Flows in the Magnetotail Plasma Sheet: Cluster Observations of the Distribution Function
Author(s) -
De Spiegeleer A.,
Hamrin M.,
Gunell H.,
Volwerk M.,
Andersson L.,
Karlsson T.,
Pitkänen T.,
Mouikis C. G.,
Nilsson H.,
Kistler L. M.
Publication year - 2019
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2018ja026116
Subject(s) - northern hemisphere , flux (metallurgy) , plasma sheet , southern hemisphere , physics , event (particle physics) , ion , spacecraft , plasma , atmospheric sciences , kinetic energy , cluster (spacecraft) , distribution function , astrophysics , magnetosphere , chemistry , astronomy , classical mechanics , organic chemistry , computer science , programming language , quantum mechanics
Plasma dynamics in Earth's magnetotail is often studied using moments of the distribution function, which results in losing information on the kinetic properties of the plasma. To better understand oscillatory flows observed in the midtail plasma sheet, we investigate two events, one in each hemisphere, in the transition region between the central plasma sheet and the lobes using the 2‐D ion distribution function from the Cluster 4 spacecraft. In this case study, the oscillatory flows are a manifestation of repeated ion flux enhancements with pitch angle changing from 0° to 180° in the Northern Hemisphere and from 180° to 0° in the Southern Hemisphere. Similar pitch angle signatures are observed seven times in about 80 min for the Southern Hemisphere event and three times in about 80 min for the Northern Hemisphere event. The ion flux enhancements observed for both events are slightly shifted in time between different energy channels, indicating a possible time‐of‐flight effect from which we estimate that the source of particle is located ∼5–25 R E and ∼40–107 R E tailward of the spacecraft for the Southern and Northern Hemisphere event, respectively. Using a test particle simulation, we obtain ∼21–46 R E for the Southern Hemisphere event and tailward of X ∼ − 65 R E (outside the validity region of the model) for the Northern Hemisphere event. We discuss possible sources that could cause the enhancements of ion flux.