Modulation of precipitation by a mesoscale gravity wave in northern Italy: Detection and analysis

A 6 h event of increased and gravity-wave modulated stratiform rain with a period of approximately 1 h is described and two wave generation mechanisms (geostrophic adjustment and shear instability) are investigated. The predictions of a linear stability analysis of the flow (an unstable mode of about 100 km wavelength originating from the shear instability of the tropospheric jet and propagating in a duct encompassing almost the entire troposphere) are shown to agree very well with the measurements from a microbarometer network and wind-profiler soundings.