On the Dawn‐Dusk Asymmetry of the Kelvin‐Helmholtz Instability Between 2007 and 2013

Using data from Time History of Events and Macroscale Interactions during Substorms (THEMIS), a statistical study was performed to determine whether a dawn‐dusk asymmetry exists in the occurrence rates of the Kelvin‐Helmholtz instability during Parker‐Spiral (PS) and Ortho‐Parker‐Spiral (OPS) orientations of the interplanetary magnetic field (IMF). It is determined from the data that there is a strong preference toward the dawnside during PS orientation, and although a preference to the duskside during OPS is suggested, this requires further study for an unambiguous confirmation. The uncertainty in the OPS result is due to a low number of events, which satisfied our selection criteria. Because IMF is statistically in PS orientation, the Kelvin‐Helmholtz instability (KHI) preference for the dawn flank during this orientation may help explain the origin of the plasma sheet asymmetry of cold component ions because it has been shown that KHI can drive kinetic‐scale wave activity capable of ion heating. Plain Language Summary Velocity shear at the planetary boundary layers can form large‐scale waves and vortices that can transport and heat plasma of solar wind origin into the magnetosphere. The present paper investigates dawn‐dusk asymmetry of the observations of these Kelvin‐Helmholtz (KH) waves during 6 years of Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft observations. The results clearly show a dawn‐favored asymmetry of the KH occurrence rates. This may help explain the dawn‐favored density and temperature asymmetry of the cold component ions of the Earth's magnetospheric plasma sheet, because KH waves have been linked to particle heating via secondary processes such as magnetic reconnection and kinetic wave activity. Key Points Statistical study of the KHI occurrence rate shows a strong preference toward the dawnside for Parker‐Spiral IMF A preference toward the duskside is observed for northward IMF The KH events are observed during higher SW speeds at the dusk sector