Internal Gravity Waves Generated by a Local Thermal Source in an Irrotational Zonal-Vertical Plane: Numerical Analysis

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 (west-ward-propagating with wavenumber 1) and IE (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 pe-riod. 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 IE 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 IE and 1W or newly generated high frequency waves IE and 1W The horizontal propagation of the waves are mainly affected by the forcing and wave-low interactions which lead to fast-slow variations of wave phase speed and amplitude.