高等大气动力学：第10讲 平流层重力波.pptx

;What are Waves? Waves are oscillations which propagate in the space. The waves can be differentiated on the basis of the restoring forces.The major restoring forces are 1. Compressibility forces (acoustic waves). 2. Density stratification by gravitational forces. 3. Rotation of the Earth,represented by Coriolis parameter f. ;Concept of Wave;Wave Phase and Wave Speed;Therefore from the above equation we can write;Group Velocity;Contd…;The change of temperature with height is known as atmospheric lapse rate (Γ). This is a simple way of determining atmospheric stability. In troposphere, the temperature decreases with height at the rate of 6.5° C/km. This is known as environmental lapse rate (Γe). When the parcel temperature changes due to an expansion or compression, dry adiabatically the temperature decreases with height at the rate of 9.8° C/km. This is the dry adiabatic lapse rate (Γd).;Introduction of Atmospheric Waves;;Some basic conservation laws and forces to understand the gravity wave theory;Significance: Have dramatic effects on the circulation in planetary atmospheres through the wave drag and diffusion they induced (Holton et. al., 1983). ;Acoustic or Sound Waves Sound waves, or acoustic waves, are longitudinal waves. That is, they are waves in which the particle oscillations are parallel to the direction of propagation. Sound is propagated by the alternating adiabatic compression and expansion of the medium. The resulting oscillating pressure gradient force will be balanced by an oscillating acceleration of the air in the adjoining region. The result of this continual adiabatic increase and decrease of pressure through alternating compression and rarefaction is, a sinusoidal pattern of pressure and velocity perturbations that propagates to the right down the tube. Individual air parcels do not, however, have a net rightward motion; they only oscillate back and forth while the pressure pattern moves rightward at the speed of sound.;Shallow Water Gravity