Coherent radar imaging of mesosphere summer echoes: Influence of radar beam pattern and tilted structures on atmospheric echo center

Multiple echo centers of a mesosphere‐summer‐echo layer (MSE) observed by the six‐receiver OSWIN VHF radar (54.1°N, 11.8°E) were examined with the coherent radar imaging (CRI) technique. The data were collected by different observational modes: vertical and oblique radar beams with the receiving configurations of 3 × 2, 6 × 1 (meridional alignment) and 1 × 6 (zonal alignment) antenna groups. The unique receiving configurations of meridional and zonal aligned antenna groups reveal that the echo centers clustered in three distinct groups above the range height of ∼86 km. The central group of echo centers was around the direction of radar beam; however, the off‐zenith angles of the two side groups, ranging between several and 20 degrees, increased with ascendant range height. Two potential causes of the echoes in the two side groups were examined on the basis of simulation calculation, namely, tilted structures in the layer and additionally, the influence of radar beam pattern. It is indicated that some echoes, originating from the lower part (∼86 km) at larger off‐zenith angles. The tilted structures, which are considered to be related to wave activities, can also produce the features similar to the observations. This is demonstrated by simulation calculation with wavy reflecting layers, in which the waves are supposed to modulate the multiple reflecting layers, with increasing amplitudes, tilted shapes, asynchronous phases, and horizontal travel.