Vorticity Within Bursty Bulk Flows: Convective Versus Kinetic

Based on four‐point Magnetospheric Multiscale observation, we carefully analyze the vorticity field in the course of a reconnection jet on 27 June 2017. In this event, the convective electric field (Ec) is overwhelmed by the kinetic electric field (Ek). Accordingly, the ω‐field in the course of the BBF is dominated by kinetic vorticity (ωk). The ω‐field in the Ek‐dominated bursty bulk flow (BBF) is characterized by perpendicular anisotropy. Comparison of velocity‐curl vorticity (ω=∇×V $\mathbf{\omega }=\nabla \times \mathbf{V}$) with E/B induced vorticity confirms a greater contribution to the BBF vorticity by E (ωE=(B⋅∇)E/B2 ${\mathbf{\omega }}_{\mathbf{E}}=(\mathbf{B}\cdot \nabla )\boldsymbol{E}/{\boldsymbol{B}}^{2}$) than by B (ωB=(E⋅∇)B/B2 ${\mathbf{\omega }}_{\mathbf{B}}=(\mathbf{E}\cdot \nabla )\mathbf{B}/{\boldsymbol{B}}^{2}$). Power spectrum density reveals that in the Ek‐dominated BBF, the Ec and Ek spectra have different power laws. Ec dominates the B‐spectrum while Ek dominates the E‐spectrum. The Ec(B) spectrum has a −5/3‐like slope below 0.25 Hz but a −3‐like above 0.25 Hz. The Ek(E) spectrum is −5/3‐like at the low‐frequency end (below 0.1 Hz) but −2‐like at the high‐frequency end (above 2 Hz). Within its medium frequency range, the spectrum is flat. Particularly, the Ek(E) spectrum exhibits the bump at 1–2 Hz in the frequency domain. The solitary/bipolar E‐spikes, with typical temporal scale of 0.3–1 s, are likely responsible for the E‐bump. Finally, we statistically analyze and compare the vorticity field in Ek‐dominated and Ec ‐dominated BBFs. The result demonstrates that the Ek‐dominated BBF tends to have stronger vorticity than the Ec ‐dominated BBF. Key Points Within the reconnection jet, the kinetic‐E (Ek) could overwhelm convective‐E (Ec) and the flow is kinetic‐vorticity (ωk) dominated Spectra of Ec and Ek have different power laws. The Ek‐spectrum exhibits the “abnormal bump” at 1–3‐Hz in the frequency domain About a third of bursty bulk flows (BBFs) are Ek‐dominated. This highlights the potential significance of the dissipation on BBF evolution