In order to determine nonlinear energy exchanges into individual triad interactions in the frequency domain,spectral formulas are derived by use of the cross-spectral technique. First time attempt has been made to und...In order to determine nonlinear energy exchanges into individual triad interactions in the frequency domain,spectral formulas are derived by use of the cross-spectral technique. First time attempt has been made to understandthe problem of maintenance of low frequency waves for tropical weather system by using this technique.The TOGAbasic level ill daily wind analyses on a 2.5 degree square grid around the global zone from 20°S-30°N at 200 hpa for92-day periods covering June, July and August of 1988 are used. Kinetic energy is gained at high frequencies and lostat low frequencies.In the planetary scale dynamics over tropics, barotropic nonlinear energy transfer plays a negativerole.Low frequency wave of period 45 day loses maximum amount of energy when it interacted with frequencies ofperiods 92 day and 30 day.45 day cycle is also the main source of energy for other frequencies. Distrubances of periodl 5 day gain maximum amount of energy.The major contribution comes from the triad interaction of the frequencies<7,l,6>.North of 20'N low frequency waves of period 30 to 92--day gain energy through nonlinear triadinteraction with the maximum gain at 22.5'N. The study may help to investigate the rapid loss of predictability of lowfrequency modes over tropics.展开更多
A method of extracting normal mode attenuation coefficient from low frequency reverberation signal has been proposed.Pseudo-inverse normal mode filtering method is implemented to get single mode reverberation field fi...A method of extracting normal mode attenuation coefficient from low frequency reverberation signal has been proposed.Pseudo-inverse normal mode filtering method is implemented to get single mode reverberation field firstly.Based on the assumption of separability of modal back-scattering matrix,effective back-scattering matrix element can be calculated using single mode average reverberation intensity.Finally,mode attenuation coefficient is extracted by comparing effective back-scattering matrix elements at different ranges.The extracted mode attenuation coefficients are used to predict sound transmission loss at the same experiment area. Results show that the predicted transmission loss agrees well with the measured data.This method avoids the difficult of treating the coupling between bottom scattering attenuation and normal mode propagation attenuation.Research on extraction of mode attenuation coefficient from low frequency reverberation signal is useful for both geoacoustic inversion and rapid underwater environment assessment.展开更多
文摘In order to determine nonlinear energy exchanges into individual triad interactions in the frequency domain,spectral formulas are derived by use of the cross-spectral technique. First time attempt has been made to understandthe problem of maintenance of low frequency waves for tropical weather system by using this technique.The TOGAbasic level ill daily wind analyses on a 2.5 degree square grid around the global zone from 20°S-30°N at 200 hpa for92-day periods covering June, July and August of 1988 are used. Kinetic energy is gained at high frequencies and lostat low frequencies.In the planetary scale dynamics over tropics, barotropic nonlinear energy transfer plays a negativerole.Low frequency wave of period 45 day loses maximum amount of energy when it interacted with frequencies ofperiods 92 day and 30 day.45 day cycle is also the main source of energy for other frequencies. Distrubances of periodl 5 day gain maximum amount of energy.The major contribution comes from the triad interaction of the frequencies<7,l,6>.North of 20'N low frequency waves of period 30 to 92--day gain energy through nonlinear triadinteraction with the maximum gain at 22.5'N. The study may help to investigate the rapid loss of predictability of lowfrequency modes over tropics.
文摘A method of extracting normal mode attenuation coefficient from low frequency reverberation signal has been proposed.Pseudo-inverse normal mode filtering method is implemented to get single mode reverberation field firstly.Based on the assumption of separability of modal back-scattering matrix,effective back-scattering matrix element can be calculated using single mode average reverberation intensity.Finally,mode attenuation coefficient is extracted by comparing effective back-scattering matrix elements at different ranges.The extracted mode attenuation coefficients are used to predict sound transmission loss at the same experiment area. Results show that the predicted transmission loss agrees well with the measured data.This method avoids the difficult of treating the coupling between bottom scattering attenuation and normal mode propagation attenuation.Research on extraction of mode attenuation coefficient from low frequency reverberation signal is useful for both geoacoustic inversion and rapid underwater environment assessment.
