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

Journal of Marine Science and Engineering

John Z. G. Ma¹ 

[1] Department of Physical Sciences, Embry-Riddle Aeronautical University, Daytona Beach, FL 32114, USA;

关键词: seismic tsunami;    gravity wave;    nonisothermality;    wind shears;   

DOI  :  10.3390/jmse4010004

来源: DOAJ

【 摘 要 】

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 iandm 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 ofm iis smaller than Hines’ imaginary vertical wavenumber ( mi H), referring to an attenuated growth in the amplitudes of upward propagating waves; on the contrary, in Layers II and IV, the magnitude ofm iis larger than that ofmi H, providing a pumped growth from Hines’ model; (3) nonisothermality and wind shears enhancem rsubstantially at an ∼100-km altitude for a tsunami wave periodTt s longer than 30 min. While Hines’ model provides that the maximal value ofmr2is ∼0.05 (1/km2 ), 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”, β: relative to Hines’ classical wave growth withβ = 0 , waves are “damped” from Hines’ result ifβ > 0and “pumped” ifβ < 0 . The polarization of β is determined by the angle θ between the wind velocity and wave vector.

【 授权许可】

Unknown