易帆
中、高层大气遥感探测和数值建模研究
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 姓名：易帆
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运筹学
 研究兴趣：中、高层大气遥感探测和数值建模研究
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易帆， Shaodong Zhang， and Fan Yi
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, D07106，0001，（）：
1年11月30日
By using a fullimplicitcontinuousEulerian (FICE) scheme and taking a set of basic atmospheric motion equations in spherical coordinates as governing equations, z fully nonlinear numerical model for the dynamics of the middle and upper atmosphere is established to numerically study the nonlinear global propagations and amplitude growths of largescale gravity wave packets. The simulation results show that the newly established model can successfully exhibit the essential characteristics of the global propagations of gravity waves: wave energies propagate upward along the ray paths derived from the hnear gravity wave theory, and wave disturbance amplitudes increase with the increasing heights. During the upward propagation of gravity wave packets, there occurs evident enhancement of background wind along the propagation direction. Moreover, our simulation demonstrates that Earth rotation has little influences on the wave energy propagations and amplitude growths. However, the primary nonlinear curvature terms (uvr tan0 and u2r tan0) play an important role in the growths of gravity wave amplitudes, which causes a evident latitudinal dependence of wave amplitude growth. In the Northern Hemisphere, with the same spatial scales and initial zonal dislurbance amplitudes, the waves propagating in lowerlatitude regions have larger disturbance amplitudes.

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易帆， Shao Dong Zhang a， b， *， Fan Yia， Xiong Huc
Journal of Atmospheric and SolarTerrestrial Physics 66 (2004) 1525，0001，（）：
1年11月30日
Data obtatmed from the medlunfrequency radar at Wuhan (30°N, 114°E} from Ⅱ to 25 February and frum 28 February to 13 March have been used to study the mean wind and tidal ogcillations at mesopause (8O98km) region over Wuhan to 13 Minter The observed zonal and meridional mean winds show obvious temporal variation and usually decrease widl the mcreasing heighls in most observational time. the zonal mean wind is eastward A Aynamic spectral analysis of disturbance amplutudc illustratcs a promincnt peak at a period of 24h al all hcighls and alines! uninterrupted, and there are occasionally shghlly stong senlldiurnal and weak lerdiurnal tidal disturbarces, indicating that in Ihe midlalitude regions. the diurnal tide is Ihe dominant tidal disturbance at tnesopausc in winter. The temporal variation of tidal ampbtudes and their wave kinematical cncrgies iffustrates that there may bc sigmificant resonant interaction among the diurnal, semidiurnal and terdiurnal rides A quantitative compariosn with Ihe globalscale wave model (GSWM) demonslrates that the observed diuulal and semidiurnal tidal amplitudes are less 3nd larger than lhe results of GSWM02. respectively Tbe essentially linear GSWM carmot predicl Ihe decrease ot diurnal tidal anplitude at higher heigbts. which muy be due to several possible nonlinear processes. such at waveWave interaction aad wave break. Although the height vanations of tidal phases are Consistenly well with the prediction of GSWM. there are evident pbase differenees between our observation and tile model. The profiles of the diunanl tidal phases show nbvious decreasc trond with Ihe increasiong height, indicalmg the observed diurnal tide is propagating upward The vertical wavelength of Ihe observed diurnal tide is estimated to be about 37km. and die eorresponding downward phase velocity is about 15km1h.
MF radar observation， Mesopause， Mean wind， Tides

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【期刊论文】Lidar observations of sporadic Na layer over Wuhan (30.5
易帆， Fan Yi， Shaodong Zhang， Haijian Zeng， Yujin He， Xianchang Yue， Jinbo Liu， Hongfang Lv， and Donghui Xiong
GEPIJUSOCA; RESEARCJ; ETTERS. VOL. 29, NO.9.，0001，（）：
1年11月30日
Based on lidar measurements beteen March and September 2001, the charccteristics of sporadic Na layers (Na, layers) over wuhan (30.5

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易帆， Shao Dong Zhang， and Fan Yi
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO.D14，0001，（）：
1年11月30日
By using a twodimensional, fullimplicitcontinuousEulerian (FICE) scheme, we simulated the nonlinear propagation and evolution of gravity wave paekels in a compressible, nonisothermal and dissipative atmosphere. The numerical results show that when an upgoing gravity wave packet is generated in the lower mesosphere, it can propagate along gs ray path until it reaches lower thermosphere. However, upon reaching the lower thennosphere, the wave packet and associated energy propagate ahnost horizontally, which departs obviously from the prediction of linear gravity wave theory under WKB approximation in the nondissipative case. Further discussion indicates that the influences of nonlinearity and background temperature are not strong enough to restrict completely the upward energy propagation of the wave packet and that the influence of constant molecular viscosity on the characteristics (energy propagation path and wave parameters) of gravity waves is insignificant. It is the vertical inhomogeneity of molecular viscosity that causes the restriction of upward energy propagation of the gravity wave packet Moreover, througheut propagation, the donlgrant vertical wavelength of the wave packet decreases with time, as it is affected by the joint actions of nonlinearity, background temperature, and dissipation. These results indicate that the molecular viscosity, especially the vertical inhomogeneity of molecular viscosity, plays an important talc in the nonlinear propagation of gravity wave packets.

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易帆， Fan Yi*
Journal of Atmospheric and SolarTerrestrat Physics 63 (2001) 749757，0001，（）：
1年11月30日
Data obtained from the mobile SOUSY VHF rodar at Andoya/Norway (69
Shimterm variability， Temporary structure， Tides and mean wind， Mesosphcre

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【期刊论文】Resonant interactions between propagating gravity wave packets
易帆， Fan Yi*
Journal of Atmospheric and SolarTerrestrat Physics 61 (1999) 675691，0001，（）：
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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【期刊论文】A numerical study of nonlinear propagation of a gravitywave packet in compressible atmosphere
易帆， Shao Dong Zhang， and Fan Yi
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 104, NO.D12, PAGES 14, 26114, 270, JUNE 27, 1999，0001，（）：
1年11月30日
By using a twodimentional fugimplicitcontinuousEuleri&n scheme, numerical sLm ulation for nonlinear propagation of Gaussian gravitywave packets in a compressible and isothermal a~osphere are carried out. The numerical analyses show that for an inkiaUy given upgomg gravitywave packet whose disturbance velocity is much less than ambient wind velocity, although there exists nonlinear interaction, during the propagation, the whole wave packet and the waveassociated energy keep moving upward, while the wave front keeps moving downward, Waveassociated perturbation velocity increases with the increasing height, and the mean flow shows obvious enhancement when the wave packet passes. After a long time propagation (several periods), waveassociated perturbation and energy can still concentrate in a limited region that is comparable in size to that given initially, The propagation path of wave energy coincides well with the ray path predicted by the linear gravity wave theory, but the magnitude of wave energy propagation velocity is evidently smaller than the group velocity derived from the linear gravity wave theory. This indicates that once gravity waves are generated, they propagate almost freely along their rays, and the nonlinear effect will only lower the propagation velocity of the wave associated energy While gravitywave packets propagate in a nonlsothermal atmosphere, the nonlinar propagation paths of wave energy depart clearly from the ray paths derived from the Fncer gravity wave theory under the WKB approximation, which indicates that the linear gravitywave theory under the UKB approximation can not predict the nonlinear propagation of gravitywave packet in a nonisothennal atmosphere.

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易帆， Fan Yi， and Zuo Xiao
Joural of Atmaspheric and SolarTerrestrtal Physics, Vol. 59, No.3, pp. 305317, 1997.，0001，（）：
1年11月30日
We examine the evolution of threegravdywave 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 onehail 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， Alan Manson， Fan Yi， ， Greg Hall， and Chris Meek
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 101, NO.D23, PAGES 29, 55329, 563, DECEMBER 27, 1996，0001，（）：
1年11月30日
Winds and waves measured by the Medium Frequency Radars (MFR) at Saskatoon (52N, 107W), Robsart (49N, lg9W), and Sylvan Lake (52N, 114w), and the FabryPerot Interferometer (FPI) at Saskatoon are compared. Particular care has been taken to exclude FPI airglow (558 nm, green line) contamination by aurora or scatter from clouds; radar data were setected from high slgnaltonoise conditions. Comparisons between the MFR/FPI in seasonal wind climatologies (at a radar height of 98km) and wind speed ratios and directiondifference histograms for the Saskatoon systems show excellent agreement. Zonal and meridional wind comparisons (scatter plots) also show no significant differences in mean winds between the FPI and MFR. Differences between instantaneous measurements, as seen on 91 individual days, are categorized into four types of events, depending upon FPI/MFR similarities and differences and the dominance of the solar tide A gravity wave model is then used to demonstrate the effects of waves, with scales from hundreds to several thousand of kilometers, upon such optical and radar systems, each of which has a different inherent spatial averaging. The model is largely successful in explaining the differences between the instantaneous MFR and FPI measurements. The relevance of such comparisons to satellite/groundbased collaborations is briefly discussed.

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易帆， Fan Yi， Jfirgen Klostermeyer， and Rudiger Ruster
GEOPHYSICAL RESEARCH LETTERS, VOL. 18, NO.4, PAGES 697700, 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, quasimanochromatic 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 wavecritical 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 smallscale structure in the electron gas.

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