ENHANCED RESPONSE OF A STABLY STRATIFIED 2-LAYER ATMOSPHERE TO LOW-LEVEL HEATING

Response of a stably stratified two-layer atmosphere to low-level heat ing is investigated by obtaining and analyzing analytic solution for t he two-dimensional, steady-state, linear perturbation. The ambient win d is assumed to be constant and the Brunt-Vaisala frequency to be piec ewise constant in each layer. The diabatic heating is specified from t he surface to a certain height in the lower layer. In this study, disc ussion is made on only the case that the stability in the lower layer is larger than that in the upper layer. A steady-state solution is pos sible only when the upper layer is not neutrally stratified. If the up per layer is neutrally stratified, the incident wave is totally reflec ted from the layer interface and the wave resonance in the lower layer can result in a wave breaking eventually in the absence of dissipatio n. The lower layer depth to produce the maximum magnitude of the verti cal velocity in the lower layer is presented in terms of the vertical wavelength of dominant gravity wave and the stability ratio between tw o layers. The magnitude of the maximum vertical velocity for this lowe r layer depth is larger than that for the uniform stability case and i t increases as the stability ratio between two layer decreases. The ve rtical velocity in the upper layer is also amplified by the stability ratio between two layers. The reflection coefficient of waves at the l ayer interface and the transmission coefficient through it are obtaine d in terms of the stability ratio. It is shown that the transmission c oefficient is larger than the reflection coefficient. The lower layer depth to produce the maximum magnitude of the horizontal velocity pert urbation is the same as that for the ducting condition by Lindzen and Tung. In the upper layer, the magnitude of the horizontal velocity per turbation is the same as that for the uniform stability case regardles s of the stability ratio. Position of the maximum positive horizontal velocity perturbation at the surface is shifted toward the heating cen ter from the downstream side as the stability ratio decreases. The mom entum flux for the two-layer case is much larger than that for the uni form stability case because both the horizontal and vertical velocity perturbations in the lower layer are amplified by the wave reflection from the layer interface.