The dissipation of transient gravity waves propagating in a shear flow

RODAS C. AND M. PULIDO

Bologna (Italy)

Conferencia; SPARC 4th General Assembly; 2008

SPARC, WCRP

Transience gravity waves that are propagating in a shear flow toward their critical levels are examined using ray tracing technique and a higher degree approximation (quasi-optical approximation). We find three breaking regimes as a function of frequency spectrum width and the wave amplitude. Conservative waves with enough amplitude and narrow frequency spectrum attain the convective instability before they reach the maximum wave amplitude. On the other extreme, small amplitude highly transience conservative waves reach the convective instability for very long times and small amplitudes. Through numerical experiments we show that highly transience gravity waves propagating towards their critical levels in a viscous medium (we use viscocity values representative of the middle atmosphere) are dissipated without reaching the convective instability threshold for their entire life cycle. The consequences of these results in orographic waves propagating in a wind turning with height are also examined.