Tilted atmospheric layer and gravity wave studies by simultaneous DBS/SDI observations with the MU radar during the passage of a trough

In the present paper, simultaneous radar observations in Doppler beam swing ing (DBS) and spatial domain interferometry (SDI) modes with the middle and upper atmosphere (MU) radar are shown for the first time. High aspect sens itive echo layers were found at a 6.0 to 8.6 km altitude range owing to obs ervations in DBS mode. From SDI analysis, the angle of arrival of the backs cattered signals was also deduced. It was found that the layers were tilted from the horizontal plane along the zonal axis with a tilt angle of approx imately 0.7 degrees. Because it is known that tilted aspect sensitive layer s introduce a bias in the radial velocity measurements, we corrected the ve rtical velocities directly measured by the vertical beam in DBS mode, by ta king account of the tilt angle of the layers estimated by the SDI technique . On the other hand, from the analysis of horizontal wind profiles, we obse rved a quasi-monochromatic gravity wave related to the tilted layers. It wa s found that the tilt angle of the phase of wave front is well associated w ith the inclination of the echo layers if the corrected vertical velocity i s used. Finally, the Richardson number estimated at an altitude range where the aspect sensitive echo layers occur presents large positive peaks at th e position of the aspect sensitive echo layers and then seems to be too hig h for turbulent instabilities. Consequently, the observed echo layers may b e stable layers at the most stable phase of the gravity wave.