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【期刊论文】Resonant interactions between propagating gravity wave packets
易帆, Fan Yi*
Journal of Atmospheric and Solar-Terrestrat Physics 61 (1999) 675-691,-0001,():
-1年11月30日
Tbe spatial and temporal evohltion of gravity wave packet interactions is studied numerically. It is shown that Igrougb tile resonant parametric excitation an upgoing gravity wave packet can cause the growth of two secondary waves from noise level up to a significanl inlensity in several bours The prbnary wave packet is apparently debrmed as it decays. Tile energy transfer among tile intenlcling waves is no longer reversible since their amplitudes are Iocalised Therefore the characteristic time for the interactions is of a parlicular significance: it represents a time during whicb the principal energy transfer arises. Beyond the cbaracteristic time the net energy transfer among the interacting waves becomes rather weak, but the local change in the wave energy densities can be Conlsiderable Only a part of the initial energy of the primary wave packet is transferred to the secondary waves during the parametric excilation. The amounts of energy, which each of the two secondary waves extract from the primary wave, are ditthrent, exhibiting a parameter preference in the energy transfer. 1he parametric excitation process can be completed in The propagation lime, For the resonant interaction with two gravity wave packets initially baying large amplitudes, the evolution tale is faster than that in the parametric excitation The primary wave packet can lose most of its energy and finally be reduced to a small fluetuation. The viscous dissipation not only decreases the wave energies but also strongly affects the local energy transfer among the interacting gravity wave packets.
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易帆, Fan Yi, and Zuo Xiao
Joural of Atmaspheric and Solar-Terrestrtal Physics, Vol. 59, No.3, pp. 305-317, 1997.,-0001,():
-1年11月30日
We examine the evolution of three-gravdy-wave interactions, with one initaly much stronger Ihun the other two, in a dissipative atmosphere, The characteristic time is used as an essential lime ca e for depicting the interactions. In the absense of viscosity, the solutions of the lineatized interaction equations, viz., the paramettic instability, give a good description for the evolution of secondary waves up to one-hail ol the characteristic time Beyond this time, the linear solutions are invalid; the evolution must be obtained by solving the complete interaction equations For given initial wave amplitudes, the characteristic time increases with the increasing wavelength of the primary wave; thus the criterion for the validity of resonant interaction approximation may be better satisfied The viscous dissipation makes the characteristoc time larger, and when severe enough a porlion oftbe seuondary waves, particularly at high wavenumbers, may fail to interacl with the primary wave effectively Additionally. the maxima of the energy densities for the secondary wavve are smaller than those in the absence of viscosity. In the ease of a significalt frequeney mismatch, only a fraction of the primary wave energy lakes part in the hlterchange Copyright.
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易帆, Fan Yi, Jfirgen Klostermeyer, and Rudiger Ruster
GEOPHYSICAL RESEARCH LETTERS, VOL. 18, NO.4, PAGES 697-700, APRIL 1991,-0001,():
-1年11月30日
Observations with the SOUSV VHF Radar in the mesolpause region during summer 1989 show lay- ers of strong echo ictensity and wind speeds increasing with height. Occasionally, quasi-manochromatic internal gravity waves occur in the bottom side of the echo layer and vanish in the height intervaI around the echo intensity maximum which tends to increase withh increasing wave amplitude The data anaiysis can be performed using a Boussieesq and a WKB approximation, It shows that the horizontal phase trace velocity of the observed gravity waves is equal to the background wind velocity at the height of the echo intensity maximum. The observations thus reprsent nonlinear gravity wave-critical level encounters pruducing strong turbulence in the neutral gas. But the, estimated euergy disspation rates are too small to produce neutral gas turbulence at scales equal to haft the radar wave!ength yieiding an additional indication for yet unidentified mechanism generating small-scale structure in the electron gas.
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