1. Gravity wave breaking over the central Alps: Role of complex topography Qingfang Jiang, UCAR/NRL, Monterey James D. Doyle, NRL, Monterey, CA Acknowledgements: MAP scientists and staff.

2. COAMPS Grid 1 1200 UTC (6 h) October 21, 1999 Terrain (gray scale) Wind vectors (500mb) Geopotential Height Contours (500mb) Large Scale Conditions

3. Terrain Electra flight track Turbulence Upstream Sounding

4. SABL + Vertical Displacement

5. GPS Dropsonde Trajectories 1 2 3 4 5 7 6 100km 20km

6. 309 311 307 1 2 3 4 5 7 6 Manual Isentropic Analysis of GPS Dropsonde Data

7. 309 311 307 1 2 3 4 5 7 6 Manual Isentropic Analysis of GPS Dropsonde Data

8. Along Flight Track Wind Component 21 5 -2 5 20

9. Vipiteno Soundings (0600, 0900 UTC)

10. V (m/s) W (m/s) Potential temp. (K) Terrain (m) Flight Level Data Examples

11. TKE, Leg1 TKE, Leg2 Buoyancy Production Rates Terrain Turbulent Kinetic Energy

12. COAMPS, 4 th mesh (~1 km) Potential temperature (solid contours) Along flight wind component (in grayscale) Turbulent kinetic energy (dashed lines)

13. COAMPS 2D Idealized Simulations Smooth terrain Smaller-scale terrain superposed on the lee-slope h=hw + hm*[1-cos(2πkx/a)]

14. Drag vs. Wave Number of Small Scale Terrain h=h w +hm*[1-cos(2πkx/a)] Where, h w : is the large-scale terrain height, a: is the large-scale terrain width, k: is the small scale terrain wave number

15. Conclusions The observed wave-breaking event was associated with the presence of a critical level, backward wind shear, and small Richardson number. GPS dropsondes observed strong flow descent associated with severe down-slope winds, and local convective instability in breaking regions. The structure of the wave- breaking section resembles a hydraulic jump. The underlying terrain and observed waves show multiscale features. Idealized simulations indicate that small-scale terrain superposed on larger scale terrain promotes wave breaking and enhances downslope winds, turbulence, and drag.