Statistical study on small‐scale ( ≤ 1,000 km) density irregularities in the inner magnetosphere

A statistical survey of small-scale density irregularities near the magnetic equatorial region of the inner magnetosphere was performed using 7-year Van Allen Probes data. The cross-field sizes of these density irregularities are within the order of 1,000 km, corresponding to typical whistler-mode wave ducts. Spatial distributions on L-shells and magnetic local times as well as temporal distributions on geomagnetic indices were analyzed using density data in the plasmasphere, the plasmasphere boundary layer (PBL), and the plasma trough. Inside the plasmasphere, the density fluctuations occur predominantly in the night and dawn sectors at L = 2.5-5. They occur far from PBL and show no significant relation with geomagnetic indices. In the PBL at L > 4.5 and the plasma trough, density irregularities are concentrated in post-midnight during quiet times and extend to all night sectors during active times. Density fluctuation values in the PBL are much higher than those in the other two regions. We discuss connections of irregularities deep inside the plasmasphere to ionospheric electric field disturbances and those in and near the PBL to interchange instabilities.