By means of the numerical method,the tropical air-sea interaction waves are studied.The results show that when the Kelvin waves are filtered out and only the equatorial Rossby waves are reserved both in the atmosphere...By means of the numerical method,the tropical air-sea interaction waves are studied.The results show that when the Kelvin waves are filtered out and only the equatorial Rossby waves are reserved both in the atmosphere and in the ocean,the disturbances can also propagate eastward because of the air-sea interaction.The critical wavelength of the eastward propagating waves is related to the intensity of the air-sea interaction.The stronger the air-sea interaction,the larger the eastward propagating components of the air-sea interaction waves.The results of the numerical experiments are in good agreement with those of the theoretical analysis(Chao and Zhang,1988).展开更多
The effects of hurricane forward speed(V)and approach angle(θ)on storm surge are important and a systematic investigation covering possible and continuous ranges of these parameters has not been done before.Here we p...The effects of hurricane forward speed(V)and approach angle(θ)on storm surge are important and a systematic investigation covering possible and continuous ranges of these parameters has not been done before.Here we present such a study with a numerical experiment using the Finite Volume Community Ocean Model(FVCOM).The hurricane track is simplified as a straight line,such that V andθfully define the motion of the hurricane.The maximum surge is contributed by both free waves and a forced storm surge wave moving with the hurricane.Among the free waves,Kelvin-type waves can only propagate in the down-coast direction.Simulations show that those waves can only have a significant positive storm surge when the hurricane velocity has a down-coast component.The optimal values of V andθthat maximize the storm surge in an idealized semi-circular ocean basin are functions of the bathymetry.For a constant bathymetry,the maximum surge occurs when the hurricane approaches the coast from the normal direction when the free wave generation is minimal;for a stepped bathymetry,the maximum surge occurs at a certain acute approach angle which maximizes the duration of persistent wind forcing;a step-like bathymetry with a sloped shelf is similar to the stepped bathymetry,with the added possibility of landfall resonance when the free and forced waves are moving at about the same velocity.For other cases,the storm surge is smaller,given other parameters(hurricane size,maximum wind speed,etc.)unchanged.展开更多
The mechanisms of establishment and adjustment of the basin-scale circulation in the South China Sea (SCS) during the monsoon-forced spin-up are investigated using a high resolu-tion circulation model in this paper. T...The mechanisms of establishment and adjustment of the basin-scale circulation in the South China Sea (SCS) during the monsoon-forced spin-up are investigated using a high resolu-tion circulation model in this paper. The process, in which the upper layer in the SCS evolved from the motionless state to the one when the basin-scale circulation initially established, was described, and the participation of various Kelvin and Rossby waves and their traveling time scales in differ-ent stages was revealed. It shows that the coastal trapped Kelvin waves and the westward propa-gating Rossby waves play important roles in the adjustment of the basin-scale circulation. Fur-thermore, the characteristic timescale of establishment for the basin-scale circulation in the upper layer of the SCS was obtained.展开更多
GPS radio occultation（GPS RO） method,an active satellite-to-satellite remote sensing technique,is capable of producing accurate,all-weather,round the clock,global refractive index,density,pressure,and temperature pr...GPS radio occultation（GPS RO） method,an active satellite-to-satellite remote sensing technique,is capable of producing accurate,all-weather,round the clock,global refractive index,density,pressure,and temperature profiles of the troposphere and stratosphere.This study presents planetary-scale equatorially trapped Kelvin waves in temperature profiles retrieved using COSMIC（Constellation Observing System for Meteorology,Ionosphere,and Climate） satellites during 2006-2009 and their interactions with background atmospheric conditions.It is found that the Kelvin waves are not only associated with wave periods of higher than 10 days（slow Kelvin waves） with higher zonal wave numbers（either 1 or 2）,but also possessing downward phase progression,giving evidence that the source regions of them are located at lower altitudes.A thorough verification of outgoing longwave radiation（OLR） reveals that deep convection activity has developed regularly over the Indonesian region,suggesting that the Kelvin waves are driven by the convective activity.The derived Kelvin waves show enhanced（diminished） tendencies during westward（eastward） phase of the quasi-biennial oscillation（QBO） in zonal winds,implying a mutual relation between both of them.The El Nino and Southern Oscillation（ENSO） below 18 km and the QBO features between 18 and 27km in temperature profiles are observed during May 2006-May 2010 with the help of an adaptive data analysis technique known as Hilbert Huang Transform（HHT）.Further,temperature anomalies computed using COSMIC retrieved temperatures are critically evaluated during different phases of ENSO,which has revealed interesting results and are discussed in light of available literature.展开更多
The influence of E1 Nifio-Southern Oscillation （ENSO） on the convectively coupled Kelvin waves over the tropical Pacific is investigated by comparing the Kelvin wave activity in the eastern Pacific （EP） E1 Nifio, ...The influence of E1 Nifio-Southern Oscillation （ENSO） on the convectively coupled Kelvin waves over the tropical Pacific is investigated by comparing the Kelvin wave activity in the eastern Pacific （EP） E1 Nifio, central Pacific （CP） E1 Nifio, and La Nifia years, respectively, to 30-yr （1982 2011） mean statistics. The convectively coupled Kelvin waves in this study are represented by the two leading modes of empirical orthogonal function （EOF） of 2-25-day band-pass filtered daily outgoing longwave radiation （OLR）, with the estimated zonal wavenumber of 3 or 4, period of 8 days, and eastward propagating speed of 17 m s-1. The most significant impact of ENSO on the Kelvin wave activity is the intensification of the Kelvin waves during the EP E1 Nifios. The impact of La Nifia on the reduction of the Kelvin wave intensity is relatively weaker, reflecting the nonlinearity of tropical deep convection and the associated Kelvin waves in response to ENSO sea surface temperature （SST） anomalies. The impact of the CP E1 Nifio on the Kelvin waves is less significant due to relatively weaker SST anomalies and smaller spatial coverage. ENSO may also alter the frequency, wavelength, and phase speed of the Kelvin waves. This study demonstrates that low- frequency ENSO SST anomalies modulate high-frequency tropical disturbances, an example of weather- climate linkage.展开更多
Based on the observed equatorial ocean dynamic characteristics, the effects of a sloping thermocline and Rayleigh friction on the equatorially trapped free Kelvin waves were theoretically studied with a linear one and...Based on the observed equatorial ocean dynamic characteristics, the effects of a sloping thermocline and Rayleigh friction on the equatorially trapped free Kelvin waves were theoretically studied with a linear one and one half layer reduced gravity model, the multiple scale method and a small parameter expansion technique. Assuming that main thermocline depth (MTD) variations are slow, i.e. the changes of MTD over one wavelength are smaller than that of the wave amplitude and that wave reflections are negligible, the authors showed by their analytical results that the wavelengths and amplitudes of Kelvin waves are significantly modified by the MTD variations and Rayleigh friction. The results also showed that for an eastward shallowing thermocline, the zonal velocity of the Kelvin waves varies with thermocline depth to the power -7/8. The eastward shallowing of the thermocline depth strengthens Kelvin wave entrapment at the equator. Rayleigh friction reduces the Kelvin wave’s eastward velocity while the thermocline acts in the opposite way. The friction causes dispersion of the Kelvin wave, whose dissipation factor does not depend on its wavelength. The friction increases the lateral decay length and causes phase lines of Kelvin waves to slant westward in parabolic arcs.展开更多
本文研究了层云降水加热对于激发热带大气季节内振荡(Madden-Julian oscillation,简称MJO)所起到的作用。将层云加热作用引入到非线性的CISK(Conditional Instability of Second Kind)-Kelvin波方程组,并分别利用截谱方法和四阶Runge-Ku...本文研究了层云降水加热对于激发热带大气季节内振荡(Madden-Julian oscillation,简称MJO)所起到的作用。将层云加热作用引入到非线性的CISK(Conditional Instability of Second Kind)-Kelvin波方程组,并分别利用截谱方法和四阶Runge-Kutta方法对该方程组进行了简化和数值求解,结果发现,单纯的层云加热同积云加热一样也可以激发出MJO。如果考虑两者共同的作用,相比于仅考虑积云的情况,能够在很大程度上扩大加热强度的取值范围,从而使热带大气更容易发生MJO。层云作用的引入还使得波动多以波群传播,波动形式更规律,周期性也更显著。展开更多
文摘By means of the numerical method,the tropical air-sea interaction waves are studied.The results show that when the Kelvin waves are filtered out and only the equatorial Rossby waves are reserved both in the atmosphere and in the ocean,the disturbances can also propagate eastward because of the air-sea interaction.The critical wavelength of the eastward propagating waves is related to the intensity of the air-sea interaction.The stronger the air-sea interaction,the larger the eastward propagating components of the air-sea interaction waves.The results of the numerical experiments are in good agreement with those of the theoretical analysis(Chao and Zhang,1988).
基金The National Key R&D Project under contract No.2017YFC1404201
文摘The effects of hurricane forward speed(V)and approach angle(θ)on storm surge are important and a systematic investigation covering possible and continuous ranges of these parameters has not been done before.Here we present such a study with a numerical experiment using the Finite Volume Community Ocean Model(FVCOM).The hurricane track is simplified as a straight line,such that V andθfully define the motion of the hurricane.The maximum surge is contributed by both free waves and a forced storm surge wave moving with the hurricane.Among the free waves,Kelvin-type waves can only propagate in the down-coast direction.Simulations show that those waves can only have a significant positive storm surge when the hurricane velocity has a down-coast component.The optimal values of V andθthat maximize the storm surge in an idealized semi-circular ocean basin are functions of the bathymetry.For a constant bathymetry,the maximum surge occurs when the hurricane approaches the coast from the normal direction when the free wave generation is minimal;for a stepped bathymetry,the maximum surge occurs at a certain acute approach angle which maximizes the duration of persistent wind forcing;a step-like bathymetry with a sloped shelf is similar to the stepped bathymetry,with the added possibility of landfall resonance when the free and forced waves are moving at about the same velocity.For other cases,the storm surge is smaller,given other parameters(hurricane size,maximum wind speed,etc.)unchanged.
基金the MOST Programs (Grant No. 1999043806 2001DIA50041) and the CAS Knowledge Innovation Project (Grant No. KZCX2-202)
文摘The mechanisms of establishment and adjustment of the basin-scale circulation in the South China Sea (SCS) during the monsoon-forced spin-up are investigated using a high resolu-tion circulation model in this paper. The process, in which the upper layer in the SCS evolved from the motionless state to the one when the basin-scale circulation initially established, was described, and the participation of various Kelvin and Rossby waves and their traveling time scales in differ-ent stages was revealed. It shows that the coastal trapped Kelvin waves and the westward propa-gating Rossby waves play important roles in the adjustment of the basin-scale circulation. Fur-thermore, the characteristic timescale of establishment for the basin-scale circulation in the upper layer of the SCS was obtained.
基金Supported by the Science Council of Taiwan(NSC-101-2811-M-008-012)
文摘GPS radio occultation（GPS RO） method,an active satellite-to-satellite remote sensing technique,is capable of producing accurate,all-weather,round the clock,global refractive index,density,pressure,and temperature profiles of the troposphere and stratosphere.This study presents planetary-scale equatorially trapped Kelvin waves in temperature profiles retrieved using COSMIC（Constellation Observing System for Meteorology,Ionosphere,and Climate） satellites during 2006-2009 and their interactions with background atmospheric conditions.It is found that the Kelvin waves are not only associated with wave periods of higher than 10 days（slow Kelvin waves） with higher zonal wave numbers（either 1 or 2）,but also possessing downward phase progression,giving evidence that the source regions of them are located at lower altitudes.A thorough verification of outgoing longwave radiation（OLR） reveals that deep convection activity has developed regularly over the Indonesian region,suggesting that the Kelvin waves are driven by the convective activity.The derived Kelvin waves show enhanced（diminished） tendencies during westward（eastward） phase of the quasi-biennial oscillation（QBO） in zonal winds,implying a mutual relation between both of them.The El Nino and Southern Oscillation（ENSO） below 18 km and the QBO features between 18 and 27km in temperature profiles are observed during May 2006-May 2010 with the help of an adaptive data analysis technique known as Hilbert Huang Transform（HHT）.Further,temperature anomalies computed using COSMIC retrieved temperatures are critically evaluated during different phases of ENSO,which has revealed interesting results and are discussed in light of available literature.
文摘The influence of E1 Nifio-Southern Oscillation （ENSO） on the convectively coupled Kelvin waves over the tropical Pacific is investigated by comparing the Kelvin wave activity in the eastern Pacific （EP） E1 Nifio, central Pacific （CP） E1 Nifio, and La Nifia years, respectively, to 30-yr （1982 2011） mean statistics. The convectively coupled Kelvin waves in this study are represented by the two leading modes of empirical orthogonal function （EOF） of 2-25-day band-pass filtered daily outgoing longwave radiation （OLR）, with the estimated zonal wavenumber of 3 or 4, period of 8 days, and eastward propagating speed of 17 m s-1. The most significant impact of ENSO on the Kelvin wave activity is the intensification of the Kelvin waves during the EP E1 Nifios. The impact of La Nifia on the reduction of the Kelvin wave intensity is relatively weaker, reflecting the nonlinearity of tropical deep convection and the associated Kelvin waves in response to ENSO sea surface temperature （SST） anomalies. The impact of the CP E1 Nifio on the Kelvin waves is less significant due to relatively weaker SST anomalies and smaller spatial coverage. ENSO may also alter the frequency, wavelength, and phase speed of the Kelvin waves. This study demonstrates that low- frequency ENSO SST anomalies modulate high-frequency tropical disturbances, an example of weather- climate linkage.
文摘Based on the observed equatorial ocean dynamic characteristics, the effects of a sloping thermocline and Rayleigh friction on the equatorially trapped free Kelvin waves were theoretically studied with a linear one and one half layer reduced gravity model, the multiple scale method and a small parameter expansion technique. Assuming that main thermocline depth (MTD) variations are slow, i.e. the changes of MTD over one wavelength are smaller than that of the wave amplitude and that wave reflections are negligible, the authors showed by their analytical results that the wavelengths and amplitudes of Kelvin waves are significantly modified by the MTD variations and Rayleigh friction. The results also showed that for an eastward shallowing thermocline, the zonal velocity of the Kelvin waves varies with thermocline depth to the power -7/8. The eastward shallowing of the thermocline depth strengthens Kelvin wave entrapment at the equator. Rayleigh friction reduces the Kelvin wave’s eastward velocity while the thermocline acts in the opposite way. The friction causes dispersion of the Kelvin wave, whose dissipation factor does not depend on its wavelength. The friction increases the lateral decay length and causes phase lines of Kelvin waves to slant westward in parabolic arcs.
文摘本文研究了层云降水加热对于激发热带大气季节内振荡(Madden-Julian oscillation,简称MJO)所起到的作用。将层云加热作用引入到非线性的CISK(Conditional Instability of Second Kind)-Kelvin波方程组,并分别利用截谱方法和四阶Runge-Kutta方法对该方程组进行了简化和数值求解,结果发现,单纯的层云加热同积云加热一样也可以激发出MJO。如果考虑两者共同的作用,相比于仅考虑积云的情况,能够在很大程度上扩大加热强度的取值范围,从而使热带大气更容易发生MJO。层云作用的引入还使得波动多以波群传播,波动形式更规律,周期性也更显著。
