Internal gravity waves generated by a local thermal source in an irrotational zonal-vertical plane: Numerical analysis

Abstract

The vertical and horizontal propagation of internal gravity waves forced by a local thermal source at the lower boundary is examined using the irrotational two-dimensional model developed by Zhang et al. (1995). The source generates waves with the same absolute frequency 1/15 d−1 but different wavenumber. Internal gravity waves with wide spreading frequencies and wavenumbers appear due to wave-wave interactions. The foreced waves 1W (westward-propagating with wavenumber 1) and 1E (eastward-propagating with wavenumber 1), whose absolute phase speeds are 31 m s−1, are predominant. Other forced waves with smaller phase speeds are relatively weaker. These waves interact with the zonal mean flow, causing the flow to alternate with easterly and westerly with a 32-month period. The absolute maximum wind speeds of easterly and westerly are 35 m s−1 which is larger than the largest phase speed of forced waves. The forced waves 1E and 1W may accelerate easterly and westerly up to ±31 m s−1, respectively. The excessive accelerations are due to the self-acceleration of waves 1E and 1W or newly generated high frequency waves 1E and 1W.