Cluster observations of surface waves in the ion jets from magnetotail reconnection

We present a Cluster spacecraft investigation of plasma sheet-confined waves and the associated Poynting flux in strong ion jets near a reconnection region in the geomagnetic tail at ∼-17 Re. Using phase lag analysis, we determine from multispacecraft measurements the phase front, wavelength, and phase velocity of the waves with spacecraft frame frequencies from 0.03 Hz to 1 Hz. The wave phase velocities were found to be directed nearly perpendicular to the local magnetic field laying in the plasma sheet plane. The strong evidence that the waves were driven by ion velocity shears has been provided. The waves are confined by the plasma sheet and their amplitude diminishes in the tail lobes. The δE/δB ratios are mostly on the order of the Alfven speed. The observed wave characteristics are different from plasma sheet flapping observed at the same time. The field-aligned Poynting flux was found to be directed away from the reconnection region. The values of earthward Poynting flux (100 ergs/cm²s or 0.1 W/m²) and longitudinal scales (10-100 km) mapped to the auroral ionosphere suggest that the observed waves may provide energy needed to accelerate auroral particles and may drive observed motions in auroral curls.