GPS无线电掩星数据处理系统     

郭鹏徐会作   《中国科学院上海天文台年刊》2006,(1):118-128

GPS无线电掩星技术能提供高精度、高分辨率、全球覆盖的地球电离层和中性层大气剖面。它具有全天候、低费用、无系统长期漂移等优点。从1995年4月至1997年3月,首次GPS／MET试验的成功显示了GPS掩星技术对监测全球大气能够发挥重要的作用,从而成为当前空间探测技术的研究热点之一。该文主要叙述了无线电掩星技术的数据处理系统的有关情况,并介绍了美国UCAR的掩星数据处理系统CDAAC的概况,可作为我国开展无线电掩星计划有关工作的借鉴。  相似文献   

Hubble Space Telescope imaging polarimetry of Mars during the 2003 opposition     

Yu. Shkuratov  M. Kreslavsky  V. Kaydash  J. Bell III  M. Hubbard  A. Lubenow 《Icarus》2005,176(1):1-11

We report results of polarimetric imaging observations of Mars with the Hubble Space Telescope during the 2003 opposition. Through careful calibration, the observations with the ACS camera allow measurements of the polarization degree with an absolute accuracy better than 0.5% and detection of features with polarization degree contrast as small as 0.2%. The general distribution of linear polarization parameters over the Mars disk and their dependence on phase angle and wavelength are well explained qualitatively by a combination of scattering separately by the martian surface and atmosphere. We have discovered transient polarization phenomena interpreted as clouds that are best observed in ultraviolet light. These clouds are optically thin but strongly polarizing, and their origin may be related to atmospheric ice condensation processes.  相似文献   

Gravity waves in Jupiter's stratosphere, as measured by the Galileo ASI experiment     

Leslie A. Young  Roger V. Yelle  Alvin Seiff  Donn B. Kirk 《Icarus》2005,173(1):185-199

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双波长卫星激光测距     

张忠萍  李人东  杨福民  扈荆夫 《天文学进展》2005,23(2):99-109

双波长卫星激光测距不必借助大气改正模型，利用双波长往返时间差就可以进行大气折射改正，采用皮秒级事件计时器等技术测量往返时间差，修正精度可以达到毫米量级，介绍了这一领域的研究进展、双波长大气改正的基本原理，分析了双波长激光测距的精度，最后对双波长卫星激光测距前景进行了展望。  相似文献   

Numerical simulations of very large impacts on the Earth     

Vladimir V. Svetsov 《Planetary and Space Science》2005,53(12):1205-1220

Vertical impacts on the Earth of asteroids 500-3000 km in diameter at 15 km/s have been numerically modelled using the hydrodynamic SOVA code. This code has been modified for the spherical system of coordinates well suited for simulations of very large impacts when the entire Earth is involved in motion. The simulations include cratering process, upward motion of deep mantle layers, fall of ejecta on the Earth, escape of matter to space, and formation of rock vapour atmospheres. The calculations were made for the period preceding disappearance of rock vapour atmospheres caused by radiation several years after the largest impacts. For very large vertical impacts at 15 km/s, escaping masses proved to be negligibly small. Quantities of kinetic, internal, potential, and radiated away energies are obtained as functions of time and space. After the impacts, a global layer of condensed ejecta covers the whole of the Earth's surface and the ejecta energy is sufficient to vaporise an ocean 3 km deep. The mass of rock vapour atmosphere is 10-23% of the impactor mass. This atmosphere has a greater mass than the water atmosphere if impactor is 2000 km in diameter or larger.  相似文献   

A three-dimensional model of moist convection for the giant planets II: Saturn's water and ammonia moist convective storms     

Ricardo Hueso  Agustín Sánchez-Lavega 《Icarus》2004,172(1):255-271

Moist convective storms constitute a key aspect in the global energy budget of the atmospheres of the giant planets. Among them, Saturn is known to develop the largest scale convective storms in the Solar System, the Great White Spots (GWS) which occur rarely and have been detected once every 30 years approximately. On the average, Saturn seems to show much less convective storms than Jupiter with smaller size and reduced frequency and intensity. Here we present detailed simulations of the onset and development of storms at the Equator and mid-latitudes of Saturn. These are the regions where most of the recent convective activity of the planet has been observed. We use a 3D anelastic model with parameterized microphysics (Hueso and Sánchez-Lavega, 2001, Icarus 151, 257) studying the onset and evolution of water and ammonia moist convective storms up to sizes of a few hundred km. Water storms, while more difficult to initiate than in Jupiter, can be very energetic, arriving to the 150 mbar level and developing vertical velocities on the order of 150 m s⁻¹. Ammonia storms develop easier but with a much smaller intensity unless very large abundances of ammonia (10 times solar) are present in Saturn's atmosphere. The Coriolis forces play a major role in the morphology and properties of water based storms.  相似文献   

一个中小型抛射的精细结构观测——太阳低层大气磁重联的证据     

张延安  宋慕陶  季海生 《天文学报》2002,43(2):155-159,T001,T002

2000年6月18日中国科学院紫金山天文台赣榆观测站观测到太阳西边缘一个小型抛射现象，寿命仅15^m，不属于耀斑的后期抛射现象，可看到十发精细的螺旋结构。用低层大气磁重联提供的初速约100kg/s，在略骈劳伦兹力情况下，给出了准均匀密度抛射柱所能达到的高度，和观测值一致。  相似文献   

大气模式动态测定的研究     

吴连大 《天文学进展》2001,19(2):277-278

利用12万组大气阻力资料，对DTM－1994模式进行改造，获得了一个新的大气模式，该模式的特点是：1．利用2阶周日峰效应，代替了原来模式中的复杂的周日效应表达式，减少了模式参数（少于50个），并使模式参数均具有明确的物理意义，2．分清了模式的主要参数和次要参数，在主要参数中，又分清了利用了阻力资料可以改进的参数和可能改不好的参数．3．与MSIS－1990和DTM－1994模式相比，其互差可以被接受，说明使用卫星阻力资料可以进行大气模式动态改正，不仅能测定大气总密度，并且能测定大气的分密度，4．与卫星轨道相比较，改进有显优于MSIS－1990模式，在120km轨道附近，改进模式密度比MSIS－1990模式大10％，同时我们在卫星陨落期预报中发现，MSIS－1990模式密度比实际大气密度小9％，这说明改进模式的密度与实际大气的密度基本接近。  相似文献   

Latitudinal variations of CO and OCS in the lower atmosphere of Venus from near-infrared nightside spectro-imaging     

Emmanuel Marcq  Bruno Bézard  Mirel Birlan 《Icarus》2005,179(2):375-386

Spectro-imaging of Venus' nightside in the 2.3-μm window provides a powerful means of probing the lower atmosphere in the 25-40 km altitude range. We present observations recorded at the NASA/IRTF in February 2003 and August 2004, using the SpeX spectro-imager in the 2.1-2.5-μm region. Abundances of CO and OCS have been derived as a function of latitude for different longitudes. The CO abundance increases by about 15% between the equatorial region and higher latitudes (±40°). No longitudinal or temporal variations are observed. The OCS abundance shows the opposite variation in observational sets with sufficient S/N. These variations and anticorrelation are consistent with upwelling motions in the equatorial region and downwelling at higher latitudes.  相似文献   

Search for spatial variation in the jovian N/N ratio from Cassini/CIRS observations     

Thierry Fouchet  Patrick G.J. Irwin  Simon B. Calcutt  Conor A. Nixon 《Icarus》2004,172(1):50-58

We have used the spectra obtained by the Composite Infrared Spectrometer (CIRS) onboard the Cassini spacecraft to search for latitudinal variation in the ¹⁵N/¹⁴N ratio on Jupiter. We found no variations statistically significant given the observational and model uncertainties. The absence of latitudinal variations demonstrates that ¹⁵NH₃ is not fractionated in Jupiter's atmosphere, and that the measured ¹⁵N/¹⁴N represents Jupiter's global value. Our mean value for the global jovian ¹⁵N/¹⁴N ratio of (2.22±0.52)×10⁻³ agrees with previous measurements made by Fouchet et al. (2000, Icarus 143, 223-243) and Owen et al. (2001, Astrophys. J. 553, L77-L79). We argue that the jovian isotopic ¹⁵N/¹⁴N ratio must represent the solar nitrogen isotopic composition. The solar ¹⁵N/¹⁴N ratio hence significantly differs from the terrestrial value: (¹⁵N/¹⁴N)_⊕=3.68×10⁻³. This supports the proposition that terrestrial nitrogen originates from a nitrogen reservoir isolated from the main nitrogen reservoir in the proto-solar nebula. The origin and carrier of this isolated reservoir are still unknown.  相似文献