Modulation of Atmospheric Nonisothermality and Wind Shears on the Propagation of Seismic Tsunami-Excited Gravity Waves

Resumen

We study the modulation of atmospheric nonisothermality and wind shears on the propagation of seismic tsunami-excited gravity waves by virtue of the vertical wavenumber, m (with its imaginary and real parts, ???? m i and ???? m r , respectively), within a correlated characteristic range of tsunami wave periods in tens of minutes. A generalized dispersion relation of inertio-acoustic-gravity (IAG) waves is obtained by relaxing constraints on Hines? idealized locally-isothermal, shear-free and rotation-free model to accommodate a realistic atmosphere featured by altitude-dependent nonisothermality (up to 100 K/km) and wind shears (up to 100 m/s per km). The obtained solutions recover all of the known wave modes below the 200-km altitude where dissipative terms are assumed negligible. Results include: (1) nonisothermality and wind shears divide the atmosphere into a sandwich-like structure of five layers within the 200-km altitude in view of the wave growth in amplitudes: Layer I (0?18) km, Layer II (18?87) km, Layer III (87?125) km, Layer IV (125?175) km and Layer V (175?200) km; (2) in Layers I, III and V, the magnitude of ???? m i is smaller than Hines? imaginary vertical wavenumber (?????? m i H ), referring to an attenuated growth in the amplitudes of upward propagating waves; on the contrary, in Layers II and IV, the magnitude of ???? m i is larger than that of ?????? m i H , providing a pumped growth from Hines? model; (3) nonisothermality and wind shears enhance ???? m r substantially at an ~100-km altitude for a tsunami wave period ?????? T t s longer than 30 min. While Hines? model provides that the maximal value of ??2?? m r 2 is ~0.05 (1/km2 2 ), this magnitude is doubled by the nonisothermal effect and quadrupled by the joint nonisothermal and wind shear effect. The modulations are weaker at altitudes outside 80?140-km heights; (4) nonisothermality and wind shears expand the definition of the observation-defined ?damping factor?, ß: relative to Hines? classical wave growth with ??=0 ß = 0 , waves are ?damped? from Hines? result if ??>0 ß > 0 and ?pumped? if ??<0 ß < 0 . The polarization of ß is determined by the angle ? between the wind velocity and wave vector.