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

Abstract

Multiple echo centers of a mesosphere-summer-echo layer (MSE) observed by thesix-receiver OSWIN VHF radar (54.1°N, 11.8°E) were examined with the coherent radarimaging (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 receivingconfigurations of meridional and zonal aligned antenna groups reveal that the echocenters clustered in three distinct groups above the range height of ~86 km. The centralgroup of echo centers was around the direction of radar beam; however, the off-zenithangles of the two side groups, ranging between several and 20 degrees, increased withascendant range height. Two potential causes of the echoes in the two side groupswere examined on the basis of simulation calculation, namely, tilted structures in the layerand 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 towave activities, can also produce the features similar to the observations. This isdemonstrated by simulation calculation with wavy reflecting layers, in which the wavesare supposed to modulate the multiple reflecting layers, with increasing amplitudes, tilted shapes, asynchronous phases, and horizontal travel. Copyright 2008 by the American Geophysical Union.