MSISE90大气密度模型及其在GPS无线电掩星中的应用

本文简略介绍了MSISE90大气密度模型，它是以提高低高度大气密度计算精度为目标，基于MSIS86模式，采用不相干散射雷达和卫星质谱仪测量资料，在半经验公式的基础上进行拟合处理而成；并指出了Hedin对该模型的修正之处，并将该模型应用于GPS无线电掩星反演中性地球大气参数的先验温度序列的生成。     

Geosat卫星定轨中的大气阻力摄动

在利用卫星测高资料定轨的过程中，大气阻力摄动的影响较大。本文在比较几种常用大气密度模型误差对定轨影响的基础上，将密度改正公式引入到Geosat卫星的精密定轨中。结果显示，该公式可以有效地提高卫星的径向定轨精度。     

精密定轨用地球大气模型误差的补偿方法

本文提出了一种用于精密轨道确定的地球大气模型误差的补偿方法，这种方法采用改进 大气周日峰角的技术，有效地补偿了大气密度模型的误差，并具有较好的物理意义．与传统 的每圈改进一次加速度的方法比较，轨道确定达到了相当的径向精度，且避免了轨道改进参 数间的相关性，同时解算参数的数量也少了一半．     

大气模式动态测定的研究

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。     

J77大气模型的修订和应用

Ｊａｃｃｈｉａ １９７７大气模型（简称Ｊ７７）发表后，Ｊａｃｃｈｉａ本人对模型进行了重大修订，这两个修订都是关于地磁活动引起的大气密度变化，为了比较分析修订后模型的改进情况，本文作者更新了Ｊ７７模型的软件，对每一步修订进行了详细的数值试验，并将其应用于高度为８００公里ＥＲＳ－１卫星的轨道计算，结果表明：修订后的Ｊ７７模型比其它大气模型在测轨精度上有明显改善。     

超新星1993J4月15日光谱的模型拟合

本文利用蒙特卡罗光谱合成方法，对１９９３年由哈勃空间望远镜和里克天文台同时得到的超新星１９９３Ｊ的紫外及光学波段的光谱，进行研究并将拟合的结果与别人的模型进行了比较。假设太阳丰度及幂律为２０左右的大气密度结构，模型可以与观测较好地符合。通过计算得到光球速度为９５００ｋｍｓ－１左右，光谱的黑体温度为７９９０Ｋ。对于强线如Ｈα及ＨｅＩλ５８７６的特殊谱线轮廓，我们发现大气结构需要是双幂律的，即光球外陡降的内层大气外面，密度变化相当平缓。内外大气的幂律近似为２０和３，交界点在１３０００ｋｍｓ－１左右。外层平缓的大气同时起到了使远紫外光谱变得像观测到的那样平滑的作用。     

测定大气等密度层倾斜的方法

本文简述了大气等密度层倾斜对天体测量观测结果的影响，根据低纬子午环绝对测定瞬时大气折射的原理，提出了利用子午方向和卯酉方向交替观测，测定大气等密层倾斜的方法推导了解算倾斜量的公式，并对测定精度作了估计。     

超新星1993J4月15日光谱的模型拟合

本利用蒙特卡罗光谱合成方法，对１９９３年由哈勃空间望远镜和里克天台同时得到的超新星１９９３Ｊ的紫外及光学波段的光谱，进行研究并将拟合的结果与别人的模型进行了比较。假设太阳丰度及幂律为２０左右的大气密度结构，模型可以与观测较好地符合。通过计算得到光球速度为９５００ｋｍｓ＾－１左右，光谱的黑体温度为７９９０Ｋ。对于强线如Ｈα及ＨｅＩλ５８７６的特殊谱线轮廓，我们发现大气结构需要是双幂律的，即光球外     

DTM94大气模型及其应用

简述了ＤＴＭ９４ 大气模型, 并以其旧版本ＤＴＭ７８ 为对照进行了初步考察和分析, 其中给出了两种模型的大气密度随地磁指数ｋｐ 和太阳辐射流量（Ｓｏｌａｒ Ｒａｄｉｏ Ｆｌｕｘ） 变化的情况, 并对２０ｄ （ 天） 弧长Ａｊｉｓａｉ 卫星的全球ＳＬＲ观测资料进行处理, 结果表明ＤＴＮ９４ 对近地卫星Ａｊｉｓａｉ 的精密定轨是十分有利的。     

大气延迟模型中气象参数季节性变化的局部模型

研究了大气延迟模型中气象参数季节性变化的作用，还根据高空气象探测记录数据进一步建立了上海和乌鲁木齐两个VLBI台站的关于中性大气温度梯度和对流层顶高度的季节性变化模型，并用以改善大气延迟的精度。     

Mass density of the upper atmosphere derived from Starlette’s Precise Orbit Determination with Satellite Laser Ranging

The atmospheric mass density of the upper atmosphere from the spherical Starlette satellite’s Precise Orbit Determination is first derived with Satellite Laser Ranging measurements at 815 to 1115 km during strong solar and geomagnetic activities. Starlette’s orbit is determined using the improved orbit determination techniques combining optimum parameters with a precise empirical drag application to a gravity field. MSIS-86 and NRLMSISE-00 atmospheric density models are compared with the Starlette drag-derived atmospheric density of the upper atmosphere. It is found that the variation in the Starlette’s drag coefficient above 800 km corresponds well with the level of geomagnetic activity. This represents that the satellite orbit is mainly perturbed by the Joule heating from geomagnetic activity at the upper atmosphere. This result concludes that MSIS empirical models strongly underestimate the mass density of the upper atmosphere as compared to the Starlette drag-derived atmospheric density during the geomagnetic storms. We suggest that the atmospheric density models should be analyzed with higher altitude acceleration data for a better understanding of long-term solar and geomagnetic effects.     

Thermally driven escape from Pluto’s atmosphere: A combined fluid/kinetic model

A combined fluid/kinetic model is developed to calculate thermally driven escape of N₂ from Pluto’s atmosphere for two solar heating conditions: no heating above 1450 km and solar minimum heating conditions. In the combined model, one-dimensional fluid equations are applied for the dense part of the atmosphere, while the exobase region is described by a kinetic model and calculated by the direct simulation Monte Carlo method. Fluid and kinetic parts of the model are iteratively solved in order to maintain constant total mass and energy fluxes through the simulation region. Although the atmosphere was found to be highly extended, with an exobase altitude at ～6000 km at solar minimum, the outflow remained subsonic and the escape rate was within a factor of two of the Jeans rate for the exobase temperatures determined. This picture is drastically different from recent predictions obtained solely using a fluid model which, in itself, requires assumptions about atmospheric density, flow velocity and energy flux carried away by escaping molecules at infinity. Gas temperature, density, velocity and heat flux versus radial distance are consistent between the hydrodynamic and kinetic model up to the exobase, only when the energy flux across the lower boundary and escape rate used to solve the hydrodynamic equations is obtained from the kinetic model. This limits the applicability of fluid models to atmospheric escape problems. Finally, the recent discovery of CO at high altitudes, the effect of Charon and the conditions at the New Horizon encounter are briefly considered.     

大气、陆地水储量和海水质量分布变化与地球低阶引力场球谐系数的关系

大气、固体地球及海洋组成了一个复杂、变化的地球动力学系统，这一系统中的任一质量分布变化都将产生地球引力场变化。采用全球7000多个地面气象台站的月平均降水及温度资料、NCEP提供气压月均值、TOPEX／Poseidon卫星测高资料和WOA98海水温度及盐度模型计算了大气、陆地水储量和海水质量分布变化引起地球低阶引力场系数变化。比较综合大气、陆地水储量和海水质量分布变化对带谐项J2，J3，J4影响的计算结果和人卫激光卫星的测定结果，可以看出，大气、陆地水储量和海水质量分布变化是引起地球低阶引力场系数周年变化的重要激发源。     

A 1D microphysical cloud model for Earth,and Earth-like exoplanets: Liquid water and water ice clouds in the convective troposphere

One significant difference between the atmospheres of stars and exoplanets is the presence of condensed particles (clouds or hazes) in the atmosphere of the latter. In current 1D models clouds and hazes are treated in an approximate way by raising the surface albedo, or adopting measured Earth cloud properties. The former method introduces errors to the modeled spectra of the exoplanet, as clouds shield the lower atmosphere and thus modify the spectral features. The latter method works only for an exact Earth-analog, but it is challenging to extend to other planets.The main goal of this paper is to develop a self-consistent microphysical cloud model for 1D atmospheric codes, which can reproduce some observed properties of Earth, such as the average albedo, surface temperature, and global energy budget. The cloud model is designed to be computationally efficient, simple to implement, and applicable for a wide range of atmospheric parameters for planets in the habitable zone.We use a 1D, cloud-free, radiative–convective, and photochemical equilibrium code originally developed by Kasting, Pavlov, Segura, and collaborators as basis for our cloudy atmosphere model. The cloud model is based on models used by the meteorology community for Earth’s clouds. The free parameters of the model are the relative humidity and number density of condensation nuclei, and the precipitation efficiency. In a 1D model, the cloud coverage cannot be self-consistently determined, thus we treat it as a free parameter.We apply this model to Earth (aerosol number density 100 cm^?3, relative humidity 77%, liquid cloud fraction 40%, and ice cloud fraction 25%) and find that a precipitation efficiency of 0.8 is needed to reproduce the albedo, average surface temperature and global energy budget of Earth. We perform simulations to determine how the albedo and the climate of a planet is influenced by the free parameters of the cloud model. We find that the planetary climate is most sensitive to changes in the liquid water cloud fraction and precipitation efficiency.The advantage of our cloud model is that the cloud height and the droplet sizes are self-consistently calculated, both of which influence the climate and albedo of exoplanets.     

Numerical simulation of the general circulation of the Cytherean lower atmosphere

The principal features which distinguish the atmosphere on Venus from that of the Earth are the slow rotation of the planet, the large mass of the atmosphere, and the opacity of the atmosphere to long-wave radiation. The slow rotation of the planet gives rise, first of all, to nongeostrophuc dynamics (the atmosphere gas has a tendency to move along the pressure gradient), with the result that the region of the main influx of solar energy is located on one side of the planet, and the region of maximum cooling on the other. These considerations lead to a much simpler scheme of circulation than that in the Earth's atmosphere.The large mass of the atmosphere is the cause of a high thermal and mechanical inertia, which explains why the atmospheric circulation is asymmetrical relative to the solar-antisolar axis. The daily center of circulation is displaced to the second half of the Cytherean solar day, i.e., to the line of zero budget of thermal energy corresponding to a height of the Sun abobe the horizon of about 20°. The notions of cold and warm regions are very relative for Venus. While the horizontal temperature differences on the Earth may reach 100°, a mean horizontal temperature drop as small as 3° in the Cytherean atmosphere may be looked upon as an exceptional phenomenon. This high thermal homogeneity is due to a very large thermal inertia, with cooling at the poles never manifesting itself in the temperature fields obtained.The opacity of the Cytherean atmosphere to long-wave radiation results in vertical heat transfer by turbulence, mesoscale convection, and large-scale currents. This produces adiabatic stratification in the troposphere and a high temperature in the lower layers.These phenomena were studied in a general manner using two- and three-level models. Steps have recently been undertaken to investigate in greater detail the vertical structure of the troposphere on Venus using ten-level models. It appeared that the vertical dynamic structure of the troposphere is very much dependent on the distribution in height of the solar energy influx. In the greenhouse model, the entire atmosphere is affected by circulation. Pronounced velocity maxima are observed in the lower and upper layers. In a model with adsorption of solar radiation in the upper layer, the velocity is small in the lower layers, but it rapidly increases and changes its direction several times in the upper layers. The mean kinetic energy of the atmosphere proves to be two to three times smaller than in the greenhouse model.Attempts have been made in the calculations to find the principal modes of the statistical fluctuations. The results obtained show that atmospheric circulation may be represented by a global mean basic state following the rotation of the planet with deviations from that basic state which are indeterminate disturbances. The mean basic state exhibits a high degree of symmetry relative to the equator. On account of nonlinearity, the disturbances were observed in all the models independently of space and time resolution. This phenomenon appears to reflect the actual properties of the Cytherean atmosphere and has no bearing on the details of the numerical scheme.     

Radiative constraints on the energy budget of the tropical atmosphere

A simple one-dimensional model is presented to describe the energy budget of the tropical atmosphere. Heating of the atmosphere is associated primarily with latent energy released due to precipitation in localized regions of intense cumulonimbus activity. Air transported to upper regions of the troposphere by cumulonimbus systems is returned to the surface over a large region of descent. Heat released by subsidence is balanced primarily by emission of radiation in the infrared. The model accounts for this energy balance, exploring specifically the constraints on permissible fluxes of mass and energy.

Results suggest that the strength of the background subsidence field in the tropics may be sensitive to surface temperature and to changes in atmospheric composition, specifically variations in the altitude distribution of H₂O and changes in the abundance of greenhouse gases such as CO₂. The mean level of detrainment of deep cumulonimbus clouds is found to increase with increasing surface temperature. This behavior is shown to be sensitive to atmospheric composition. The surface temperature for an atmosphere containing twice the present level of CO₂ is predicted to increase by 1.4K, about 25% less than the change obtained with models in which the lapse rate of temperature is specified at lower altitudes, where assumptions of radiative equilibrium would lead otherwise to a statically unstable condition.

Buoyancy considerations suggest that there may be an upper limit to the range of permissible values for surface temperature in the tropics. Models in which the subsidence mass flux is assumed constant with respect to altitude are found to be unable to maintain buoyancy for rising air in the face of heat released by descent when surface temperatures exceed about 312K.     

Atmospheric erosion and replenishment induced by impacts upon the Earth and Mars during a heavy bombardment

Consequences of a heavy bombardment for the atmospheres of Earth and Mars are investigated with a stochastic model. The main result is the dominance of the accumulation. The atmospheric pressure is strongly increasing both for Earth and Mars in the course of an enhanced bombardment. The effect of atmospheric erosion is found to be minor, regarding escape during meteorite entry, in the expanding vapor plume, and ejection due to free-surface motion. The initial atmospheric surface pressure if comparable to the modern value turns out as a less important additive constant of the final pressure. Impactor retention and atmospheric erosion are parametrized in terms of scaling laws, compatible with recent numerical simulations. The dependence on impactor size, atmospheric and planetary parameters is analyzed among alternative models and numerical results. The stochastic model is fed with the net replenishment originating from impactor material and the loss of preexisting atmospheric gas. Major input parameters are the total cumulative impactor mass and the relative mass of atmophile molecules in comets and asteroids. Input size distributions of the impactor ensemble correspond to presently observed main belt asteroids and KBOs. Velocity distributions are taken from dynamical simulations for the Nice model. Depending on the composition of large cometary impactors, the Earth could acquire a more massive atmosphere, a few bars in terms of surface pressure, mostly as CO and CO₂. For Mars accumulation of 1–4 bars of CO and CO₂ requires an asteroidal ‘late veneer’ of the order of 10²⁴ g containing 2% atmophiles.     

Mid-infrared detection of large longitudinal asymmetries in Io's SO2 atmosphere

We have observed about 16 absorption lines of the ν₂ SO₂ vibrational band on Io, in disk-integrated 19-μm spectra taken with the TEXES high spectral resolution mid-infrared spectrograph at the NASA Infrared Telescope Facility in November 2001, December 2002, and January 2004. These are the first ground-based infrared observations of Io's sunlit atmosphere, and provide a new window on the atmosphere that allows better longitudinal and temporal monitoring than previous techniques. Dramatic variations in band strength with longitude are seen that are stable over at least a 2 year period. The depth of the strongest feature, a blend of lines centered at 530.42 cm⁻¹, varies from about 7% near longitude 180° to about 1% near longitude 315° W, as measured at a spectral resolution of 57,000. Interpretation of the spectra requires modeling of surface temperatures and atmospheric density across Io's disk, and the variation in non-LTE ν₂ vibrational temperature with altitude, and depends on the assumed atmospheric and surface temperature structure. About half of Io's 19-μm radiation comes from the Sun-heated surface, and half from volcanic hot spots with temperatures primarily between 150 and 200 K, which occupy about 8% of the surface. The observations are thus weighted towards the atmosphere over these low-temperature hot spots. If we assume that the atmosphere over the hot spots is representative of the atmosphere elsewhere, and that the atmospheric density is a function of latitude, the most plausible interpretation of the data is that the equatorial atmospheric column density varies from about 1.5×¹⁰¹⁷ cm⁻² near longitude 180° W to about 1.5×¹⁰¹⁶ cm⁻² near longitude 300° W, roughly consistent with HST UV spectroscopy and Lyman-α imaging. The inferred atmospheric kinetic temperature is less than about 150 K, at least on the anti-Jupiter hemisphere where the bands are strongest, somewhat colder than inferred from HST UV spectroscopy and millimeter-wavelength spectroscopy. This longitudinal variability in atmospheric density correlates with the longitudinal variability in the abundance of optically thick, near-UV bright SO₂ frost. However it is not clear whether the correlation results from volcanic control (regions of large frost abundance result from greater condensation of atmospheric gases supported by more vigorous volcanic activity in these regions) or sublimation control (regions of large frost abundance produce a more extensive atmosphere due to more extensive sublimation). Comparison of data taken in 2001, 2002, and 2004 shows that with the possible exception of longitudes near 180° W between 2001 and 2002, Io's atmospheric density does not appear to decrease as Io recedes from the Sun, as would be expected if the atmosphere were supported by the sublimation of surface frost, suggesting that the atmosphere is dominantly supported by direct volcanic supply rather than by frost sublimation. However, other evidence such as the smooth variation in atmospheric abundance with latitude, and atmospheric changes during eclipse, suggest that sublimation support is more important than volcanic support, leaving the question of the dominant atmospheric support mechanism still unresolved.     

A first look at atmospheric dynamics and temperature variations on Titan

Pollack (1973) has used a radiative equilibrium model to match radiometric data for Titan and infers the atmospheric mass, composition, opacity, and gross vertical thermal structure. These results are used to estimate the atmospheric temperature variations by means of scaling analysis, taking into account dynamics both for a baroclinic wave regime and for an axially symmetric circulation regime. Horizontal temperature variations of the atmosphere and surface are found to be very small, and the circulation is found to be weak and probably axially symmetric. The small temperature variations appear to preclude the storage of volatiles in polar caps, so that the present atmospheric methane content may be due to a balance between outgassing and photodissociation.     

Titan atmosphere profiles from Huygens engineering (temperature and acceleration) sensors

Data from several Huygens probe housekeeping sensors (an engineering accelerometer and housekeeping temperature sensors) are studied to determine how effectively such nonideal instruments may characterize the density or temperature structure of the atmosphere. While only confirming the results of the dedicated atmospheric structure instrument, this exercise is of relevance to possible future missions to various bodies which might not be equipped with such science-grade sensors able to accurately profile the atmosphere top-to-bottom. It is found that for typical engineering accelerometers with 8-bit resolution, the atmosphere density for ∼4 scale heights above the peak deceleration altitude may be recovered. If, as with Huygens, the peak deceleration exceeds the range of the accelerometers, recovery of an additional scale height or so below the peak is still possible, but relies on accurate total velocity knowledge. Engineering temperature sensors can, with care, be analyzed to recover the temperature structure of at least the lowest ∼30 km of Titan's atmosphere. Fortunately, in the case of Huygens, data from the surface after landing were available to constrain models of heat leaks which offset the observed temperature from that of the ambient air during descent; data from before and during the entry phase on other missions would be similarly useful. When corrections are made for the estimated heat transfer processes, the atmospheric temperature can be recovered to within about 3 K.