13th Conference on Applied Climatology and the 10th Conference on Aviation, Range, and Aerospace Meteorology

Thursday, 16 May 2002: 11:00 AM
Case studies of turbulence and vertical motion experienced by research aircraft during MAP-SOP South Foehn cases
Petra Malcher, Univ. of Innsbruck, Innsbruck, Tirol, Austria; and H. Puempel and I. Vergeiner
Poster PDF (676.8 kB)
During south foehn periods strong mountain induced winds and turbulence cause potential hazards to aircraft operations, especially during take off and landing at Innsbruck Airport as well as during low-level flight operations in the vicinity of Innsbruck Airport. So far, there had been no investigation on the intensity and the occurrence of aircraft related turbulence in the Innsbruck area. Current knowledge is mainly based on pilots' experience and the subjective knowledge of local meteorologists.

In this investigation in situ aircraft measurements, acquired in the Inn and Wipp Valley during four south foehn events of the field phase of the Mesoscale Alpine Programme (MAP) in autumn 1999, have been analysed, with particular emphasis on strong mountain induced winds and turbulence. The information on aircraft related turbulence has been derived from the 1 Hz airborne vertical wind measurements from which vertical accelerations were computed . The intensity and the distribution of turbulence and up- and downdrafts are displayed by means of vertical cross sections and plane views of the Inn and Wipp Valley. The cross sectional analyses are more suggestive in the Wipp Valley than in the Inn Valley, as it is less wide and the aircraft measurements were carried out along vertically stacked flight paths.

The analyses of turbulence and up- and downdrafts reveal some repetitive pattern. The occurrence of significant turbulence (above 2.45 m/s**2) was concentrated in specific areas, namely the exits of the Obernberg, the Gschnitz, the Stubai and the Wipp Valley, as well as the lee of the Patscherkofel and along the Nordkette. In the Inn- and the Wipp Valley turbulence was observed principally below an elevation of 2800 m msl, occuring only sporadically up to 3500 m msl. In several cases the measured turbulence exceeds 0.5g (4.9 m/s**2). Up- and downdrafts are probably induced by topography, most pronounced between the Brenner Pass and the Gschnitz Valley as well as in the lee of the Patscherkofel. The vertical wind speed in these up- and downwind regions reached up to +- 6 m/s. Futhermore, the relation between turbulence and strong wind shear, hydraulic jumps and singular points in the flow regime, is shown.

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