Multi-payload measurement of transverse velocity shears in the topside ionosphere

Using a multi‐payload sounding rocket mission, we present the first direct measurement of velocity shear in the topside auroral ionosphere. In regions of large, ∼200 mV/m, transient electric fields we directly measure differences in the plasma drift velocity. From these differences, shear frequencies reaching ±6Hz are measured. These directly measured shears are compared with the shear inferred from single payload measurements. It is shown this traditional measurement of shear overestimates the shear frequency by a factor of two for this event, highlighting the importance of the temporal component of near‐DC electric field structures. Coincident with these strong fields and shears are enhanced emissions of broadband, extremely low frequency (BB‐ELF) plasma waves, and a narrowband wave emission near the H+‐O+bi‐ion resonant frequency. Key Points We present direct observation of velocity shear in the auroral ionosphere These directly measured shears are a factor of two lower than inferred shears Associated with the shears are BB‐ELF and narrow band plasma wave emissions