Abstract
The vertical flux of horizontal momentum by three-dimensional mountain waves is examined using a linear theory. Analytic solutions for two different wind directions are obtained using numerical Fourier analysis. Although the mountain examined in this note is a fairly two-dimensional one, the results show that, at the tropopause level, the momentum flux greatly decreases to 1/4-1/3 of its near-surface value even over the center area of the mountain when the mean wind crosses the mountain at 45 degrees. It is also suggested that the decrease of the momentum flux observed in IOP-3 of PYREX is caused by both the finite length of the Pyrenees mountains and the slant attack angle of the mean wind.
