Middle and upper atmosphere radar observations of turbulence and movement of midlatitude sporadic E irregularities

Abstract

Midlatitude field‐aligned irregularities (FAI) associated with sporadic E layers were continuously observed on June 17–19, 1989, with the middle and upper atmosphere radar to investigate spatial and temporal behaviors of the 3.2‐m‐scale FAI. Using Doppler spectrum, mean Doppler velocity, and echo intensity data, we present some features of the plasma turbulence and irregularity movement pertinent to two types of radar echoes: “continuous echoes” appearing at 90‐ to 100‐km altitudes at night and in the morning, and “quasi‐periodic (QP) echoes” appearing at 95‐ to 125‐km altitudes at night. For both types of echoes, echo intensities and Doppler velocities were modulated with periods of 5–20 min due to gravity wave activities. Most of the enhanced echoes were located within the region where Doppler velocities tend to be close to zero. On many occasions there were velocity shears across the enhanced echo region. The Doppler velocities and echoing‐patch movements for the continuous echoes are compared with the existing F region plasma drift and neutral wind models, respectively, to find a partial consistency. General characteristics of the Doppler velocity and spectral width associated with the QP echoes are consistent with previous observational results. Unusual movement of the FAI sheet related to the QP echoes is discussed in the light of recent theory.