2003年一次梅雨大暴雨成因的动力学研究   总被引：6，自引：5，他引：6  

张端禹  丁治英  王丛梅 《南京气象学院学报》2006,29(6):827-832

运用中尺度非静力模式MN5对2003年梅雨期一次大暴雨天气进行数值模拟，在降雨模拟基本正确的基础上分析暴雨发生原因。结果表明：该次梅雨大暴雨属于切变类暴雨，对流层低层有能量锋区、高层有惯性不稳定活动，暴雨区位于低空急流的左前方、高空急流的右前方。暴雨中心物理量要素的时间一高度演变显示：低层正涡度、辐合，高层负涡度、辐散，深厚的上升运动，等相当位温线抬升，湿位涡及其正、斜压分量3者负值加大均有利于降雨加强；暴雨减弱阶段，这些要素一般向相反方向转变。该次大暴雨的直接影响系统具有明显的中尺度时、空特点，大暴雨的发生与高层惯性不稳定和低层对流不稳定有关。  相似文献   

Inertial theory of the mean Hadley circulation under the condition of nonstatic equilibrium     

CHAO Jiping  LIU Fei 《中国科学D辑(英文版)》2006,49(5):546-553

1 Introduction The mean meridional circulation plays an important role in the transportation and balance of heat, momen- tum, vortex and vapor between different latitudes. According to the data analysis, there are three circula- tions from the equator to the polar area: the Hadley circulation, a heat-driven circulation which rises around the equator and sinks at a certain latitude; the subpolar circulation, another heat-driven circulation around the polar area; and the Ferrel circulation, an i…  相似文献   

Wavelet filter analysis of splitting and coupling of seismic normal modes below 1.5 mHz with superconducting gravimeter records after the December 26, 2004 Sumatra earthquake     

Jacques Hinderer 《中国科学D辑(英文版)》2006,49(12):1259-1269

New generation superconducting gravimeters (SGs), which have been demonstrated to be better than the best seismometers STS-1 at frequencies below 1 mHz, can be accepted as the quietest vertical seismometers for observation of long-period earth free oscillations. Wavelet filtering with narrow band-pass frequency response as shown in this paper is very helpful in removing at- mospheric pressure effects from on gravity records in long-period seismic mode frequency bands. The processing of high quality SG records after the great Sumatra earthquake (Dec. 26, 2004) with wavelet filtering leads to clear observations of all coupled toroidal modes below 1.5 mHz except these for 0T5, 0T7 and 1T1; moreover 1T2 and 1T3 are, for the first time, unambiguously revealed in the vertical components of the free oscillations. The three well-resolved splitting singlets of overtones 2S1 are observed from a single SG record for the first time.  相似文献   

Modeling errors in upward continuation for INS gravity compensation     

Christopher Jekeli  Jong-Ki Lee  Jay H. Kwon 《Journal of Geodesy》2007,81(5):297-309

Accurate upward continuation of gravity anomalies supports future precision, free-inertial navigation systems, since the latter cannot by themselves sense the gravitational field and thus require appropriate gravity compensation. This compensation is in the form of horizontal gravity components. An analysis of the model errors in upward continuation using derivatives of the standard Pizzetti integral solution (spherical approximation) shows that discretization of the data and truncation of the integral are the major sources of error in the predicted horizontal components of the gravity disturbance. The irregular shape of the data boundary, even the relatively rough topography of a simulated mountainous region, has only secondary effect, except when the data resolution is very high (small discretization error). Other errors due to spherical approximation are even less important. The analysis excluded all measurement errors in the gravity anomaly data in order to quantify just the model errors. Based on a consistent gravity field/topographic surface simulation, upward continuation errors in the derivatives of the Pizzetti integral to mean altitudes of about 3,000 and 1,500 m above the mean surface ranged from less than 1 mGal (standard deviation) to less than 2 mGal (standard deviation), respectively, in the case of 2 arcmin data resolution. Least-squares collocation performs better than this, but may require significantly greater computational resources.  相似文献   

A Ca ii H&K survey of γ Doradus candidates     

Anthony B. Kaye  & Klaus G. Strassmeier 《Monthly notices of the Royal Astronomical Society》1998,294(2):L35-L39

In an investigation of the starspot hypothesis as it applies to the 'slowly variable' F-type dwarfs, we spectroscopically observed eight promising γ Doradus candidates to search for Ca  ii H&K emission. We found that there are no significant emission reversals in the cores of these resonance lines. Based on the ceiling flux calculations of the Ca  ii K line and on calculations of the Rossby number, we conclude that there is no support for the presence of strong magnetic activity and the starspot hypothesis in these objects.  相似文献   

On the properties of strange modes     

Hideyuki Saio  Norman H. Baker  & Alfred Gautschy 《Monthly notices of the Royal Astronomical Society》1998,294(4):622-634

Properties of the so-called strange modes occurring in linear stability calculations of stellar models are discussed. The behaviour of these modes is compared for two different sets of stellar models, for very massive zero-age main-sequence stars and for luminous hydrogen-deficient stars, both with high luminosity-to-mass ratios. We have found that the peculiar behaviour of the frequencies of the strange modes with the change of a control parameter is caused by the pulsation amplitude of a particular eigenmode being strongly confined to the outer part of the envelope, around the density inversion zone. The frequency of a strange mode changes because the depth of the confinement zone changes with the control parameter. Weakly non-adiabatic strange modes tend to be overstable because the amplitude confinement quenches the effect of radiative damping. On the other hand, extremely non-adiabatic strange modes become overstable because the perturbation of radiation force (gradient of radiation pressure) provides a restoring force that can be out of phase with the density perturbation. We discuss this mechanism by using a plane-parallel two-zone model.  相似文献   

Metallicity of clusters from RRab pulsators: results of an automatic analysis     

A. Schwarzenberg-Czerny  & J. Kaluzny 《Monthly notices of the Royal Astronomical Society》1998,300(1):251-256

The stability of massive stars is re-examined with respect to an adiabatic dynamical instability discovered by Stothers & Chin. An adiabatic stability analysis is performed, its validity for the objects being considered is discussed, and the relation between the mean adiabatic index and adiabatic stability is commented on. As the results of Stothers & Chin could not be confirmed, we suspect that luminous blue variable instability is due to non-adiabatic effects.  相似文献   

On the frequency and amplitude variations of the δ Scuti star CD−24 7599 (=XX Pyx)     

G.Handler  A. A.Pamyatnykh  W.Zima  D. J.Sullivan  N.Audard  A.Nitta 《Monthly notices of the Royal Astronomical Society》1998,295(2):377-385

We present 132 h of new time-series photometric observations of the δ Scuti star CD−24 7599 acquired during 86 nights from 1993 to 1996 to study its frequency and amplitude variations. By using all published observations we demonstrate that the three dominating pulsation modes of the star can change their photometric amplitudes within one month at certain times, while the amplitudes can remain constant within the measurement errors at other times. CD−24 7599 also exhibits frequency variations, which do not show any correspondence between the different modes.   The typical time-scale for the amplitude variations is found to be several hundred days, which is of the same order of magnitude as the inverse linear growth rates of a selected model. We find no evidence for periodic amplitude modulation of two of the investigated modes ( f ₂ and f ₃), but f ₁ may exhibit periodic modulation. The latter result could be spurious and requires confirmation. The observed frequency variations may either be continuous or reflect sudden frequency jumps. No evidence for cyclical period changes is obtained.   We exclude precession of the pulsation axis and oblique pulsation for the amplitude variations. Beating of closely spaced frequencies cannot explain the amplitude modulations of two of the modes, while it is possible for the third. Evolutionary effects, binarity, magnetic field changes or avoided crossings cannot be made responsible for the observed period changes. Only resonance between different modes may be able to explain the observations. However, at this stage a quantitative comparison is not possible. More observations, especially data leading to a definite mode identification and further measurements of the temporal behaviour of the amplitudes and frequencies of CD−24 7599, are required.  相似文献   

Solar internal rotation rate and the latitudinal variation of the tachocline     

H. M. Antia  Sarbani Basu  & S. M. Chitre 《Monthly notices of the Royal Astronomical Society》1998,298(2):543-556

A new set of accurately measured frequencies of solar oscillations is used to infer the rotation rate inside the Sun, as a function of radial distance as well as latitude. We have adopted a regularized least-squares technique with iterative refinement for both 1.5D inversion, using the splitting coefficients, and 2D inversion using individual m splittings. The inferred rotation rate agrees well with earlier estimates showing a shear layer just below the surface and another one around the base of the convection zone. The tachocline or the transition layer where the rotation rate changes from differential rotation in the convection zone to an almost latitudinally independent rotation rate in the radiative interior is studied in detail. No compelling evidence for any latitudinal variation in the position and width of the tachocline is found, although it appears that the tachocline probably shifts to a slightly larger radial distance at higher latitudes and possibly also becomes thicker. However, these variations are within the estimated errors and more accurate data would be needed to make a definitive statement about latitudinal variations.  相似文献   

Determining temperature amplitude as a function of depth in the atmospheres of rapidly oscillating Ap stars     

R. Medupe  & D. W. Kurtz 《Monthly notices of the Royal Astronomical Society》1998,299(2):371-378

We present numerical models based on realistic treatment of the intensity spectrum (from model atmospheres), and demonstrate that they are consistent with Kurtz and Medupe's recent formula in showing that limb darkening is too small an effect to explain the observed sharp decline of pulsation light amplitude with wavelength in rapidly oscillating Ap stars. Kurtz and Medupe's formula is shown to be a special form of Watson's earlier general formula for non-radial light variations of a star pulsating in any mode ( l m ). Using a technique suggested by Kurtz and Medupe we derive temperature semi-amplitude as a function of depth in the atmospheres of α Cir and HR 3831, assuming that we can neglect non-adiabatic effects.  相似文献