Temperature variations in the dayside magnetosheath and their dependence on ion‐scale magnetic structures: THEMIS statistics and measurements by MMS

• Published in: Journal of geophysical research. Space physics 2017-06, Vol.122 (6), p.6165-6184
• Main Authors: Dimmock, A. P., Osmane, A., Pulkkinen, T. I., Nykyri, K., Kilpua, E.
• Format: Article
• Language: English
• Subjects: Asymmetry; Correlation; dawn‐dusk asymmetry; Geostatistics; ion heating; Ion temperature; Magnetic fields; Magnetic properties; Magnetosheath; Magnetospheres; nonadiabatic heating; Solar wind; Solar wind velocity; Statistical analysis; Temperature changes; Temperature fluctuations; Temperature variations; Wave-particle interactions; wave‐particle interaction; Wind speed
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2016JA023729

The magnetosheath contains an array of waves, instabilities, and nonlinear magnetic structures which modify global plasma properties by means of various wave‐particle interactions. The present work demonstrates that ion‐scale magnetic field structures (∼0.2–0.5 Hz) observed in the dayside magnetosheath are statistically correlated to ion temperature changes on orders 10–20% of the background value. In addition, our statistical analysis implies that larger temperature changes are in equipartition to larger amplitude magnetic structures. This effect was more pronounced behind the quasi‐parallel bow shock and during faster solar wind speeds. The study of two separate intervals suggests that this effect can result from both local and external drivers. This manuscript presents two separate case studies, one from using THEMIS (Time History of Events and Macroscale Interactions during Substorms) data and another from Magnetospheric Multiscale; these measurements are then supported by extensive THEMIS statistical observations. These results could partly explain the 10–20% dawn‐favored asymmetry of the magnetosheath ion temperature seed population and contribute to the dawn‐favored asymmetry of cold component ions in the cold dense plasma sheet. Key Points A positive correlation exists between the amplitude of magnetic fluctuations and temperature variation Temperature fluctuations are strongly associated with larger local in ion‐scale magnetic structures than the fluid input at the shock The amplitude of ion gyroscale fluctuations and in situ temperature variations are favored by the dawn flank