Gravity waves over the eastern Alps: A synopsis of the 25 October 1999 event (IOP 10) combining in-situ and remote sensing measurements with a high-resolution simulation

Abstract

In situ and lidar data acquired during six repetitive flight legs across Grossglockner (3797 m, highest summit of the eastern Alps) reveal a coherent structure of the mountain-wave field generated by a south-westerly cross-Alpine flow on 25 October 1999 during Intensive Observing Period (IOP) 10 of the Mesoscale Alpine Programme (MAP). The downward-looking laser system sampling at 100 Hz provides distinct wave-induced signatures in the layered clouds below the cruising altitude of about 11 km. Data obtained from three sondes dropped from the aircraft hint at mid-tropospheric wave breaking in the lee of the main Alpine crest. The measurements are juxtaposed with results from a nested, non-hydrostatic simulation (2 km horizontal resolution for the finest grid). Wave-cloud signatures in satellite images (from Meteosat and the National Oceanic and Atmospheric Administration satellites) are used for comparisons with the simulation in a region away from the aircraft track. Sensitivity experiments reveal the regular wave response to be induced by the background profile and re-enforced by the suitably spaced terrain