火星表面风沙物理过程及沙尘暴的起动风速

通过建立风吹动地表沙粒运动的模型并根据大气湍流边界层风速廓线规律,计算了火星上沙尘暴的起动风速和沙尘暴发生时空中悬浮沙尘粒径的大小,并对沙粒从地面跳起进入气流的方式进行了验证.发现当大气为中性层结时,火星沙尘暴的起动需要离地面2m高处的风速达到28.7m·s-1.在起动临界风速下,地表沙粒需要滚动一个粒径的距离才能跳起,沙尘暴发生后,火星大气中悬浮沙尘的粒径小于30μm.      

Martian cloud systems: Current knowledge and future observations

In this paper we summarise the current understanding of Martian condensate and dust clouds. The paper is particularly concerned with the spatial, temporal and seasonal characteristics of the clouds. The condensate clouds are composed of water and ice particles and occasionally CO₂ particles. Dust clouds are composed of material from the surface and redistributed over the planet through the weather systems. The apparent lack of annual reproductivity of these dust storms forms a major unresolved problem. We discuss in this paper the types of observations needed in future space missions, in particular the requirements for the NASA Mars Geochemical Climatology Orbiter Mission planned for the end of this decade.     

Dust ring/torus around Mars,waiting for detection by NOZOMI

Two small satellites of Mars, Phobos and Deimos, can be dust sources around Mars. Orbits of circummartian dust particles are controlled by solar radiation pressure as well as Martian oblateness. Their orbital eccentricity and inclination can be enhanced greatly by the orbital resonance. Particles from Phobos would form a thin dust ring where dust radius is dominant in 20–200μm. On the other hand, particles from Deimos would form an extended dust torus. Collisions of ring particles on Phobos and Deimos may be the most important dust source. The upper limit of dust production from this self-sustaining mechanism can be estimated from the erosion rate of Phobos. Japanese Mars mission NOZOMI (PLANET-B) could discover dust ring/torus through direct detection by MDC (Mars Dust Counter).     

The MAGO experiment for dust environment monitoring on the Martian surface

Among the main directions identified for future Martian exploration, the study of the properties of dust dispersed in the atmosphere, its cycle and the impact on climate are considered of primary relevance. Dust storms, dust devils and the dust “cycle” have been identified and studied by past remote and in situ experiments, but little quantitative information is available on these processes, so far. The airborne dust contributes to the determination of the dynamic and thermodynamic evolution of the atmosphere, including the large-scale circulation processes and its impact on the climate of Mars. Moreover, aeolian erosion, redistribution of dust on the surface and weathering processes are mostly known only qualitatively. In order to improve our knowledge of the airborne dust evolution and other atmospheric processes, it is mandatory to measure the amount, mass-size distribution and dynamical properties of solid particles in the Martian atmosphere as a function of time. In this context, there is clearly a need for the implementation of experiments dedicated to study directly atmospheric dust. The Martian atmospheric grain observer (MAGO) experiment is aimed at providing direct quantitative measurements of mass and size distributions of dust particles, a goal that has never been fully achieved so far. The instrument design combines three types of sensors to monitor in situ the dust mass flux (micro balance system, MBS) and single grain properties (grain detection system, GDS + impact sensor, IS). Technical solutions and science capabilities are discussed in this paper.     

Dust storms detection over the Indo-Gangetic basin using multi sensor data

Dust storms are common during the summer season over the Indo-Gangetic basin and are considered to be a major health hazard to millions of people living in the basin. In countries like India, there is no early warning made for dust outbreaks and as a result the day-to-day life is affected by these dust events. In this paper, efforts have been made to utilize multi sensor data to study the characteristics of dust storms. Moderate Resolution Imaging Spectroradiometer and Multiangle Imaging SpectroRadiometer images clearly show dust storm events over the Indo-Gangetic basin. The Total Ozone Mapping Spectroradiometer (TOMS) Aerosol Index and the Advanced Microwave Sounding Unit (AMSU) data over the western end of the Indo-Gangetic basin have been analyzed. These data show characteristic behavior of brightness temperature and Aerosol Index due to dust, which change significantly as dust migrates towards east over Kanpur. The TOMS Aerosol Index and the AMSU brightness temperature (T_b) show a characteristic anti-correlation, which confirms the presence of a dust storm over Indo-Gangetic basin.     

Spectroscopic observation of Mars

Visible and near-infrared reflectance spectroscopy has proven a powerful tool for exploring the geology of Mars. Most of this data has been obtained from Earth, but the technique is ideally suited to orbital application, as proposed for the U.S. Mars Geoscience/Climatology Orbiter mission. Spectral reflectance in the near-UV and visible is highly diagnostic of ferric-iron mineralogy, and has shown that Fe³⁺ in the ubiquitous bright dust and soil is amorphous or poorly-crystalline. Other iron-oxide minerals, indicative of other modes or episodes of crustal alteration, may be found in spatially localized deposits. Clay minerals (hydroxylated silicates) have diagnostic vibrational absorptions throughout the near-infrared. While some form of bound water and/or OH has been known on Mars for many years, a new result presented here is the identification of structural OH in a dilute or poorly crystalline magnesian clay. Salts such as carbonates, sulfates, and nitrates have not yet been detected in martian soils but have diagnostic spectral features in the 3- to 4-μm region, best suited to Mars-orbital observation. Analysis of reflectance spectra of low-albedo regions is a primary source of evidence for a basaltic or ultramafic crust, with identification of abundant clinopyroxene and possible detection of other mafic minerals. The distinctive near-infrared spectral shape of dark regions indicates that the dark materials commonly consist of relatively unaltered rocks or rock fragments very thinly coated by (or mixed with) bright oxidized material similar to the global dust. Visible and near-infrared reflectance spectroscopy is also a sensitive technique for detecting and analyzing water ice, as has been demonstrated on Mars by observations of the north polar cap.     

South polar permanent CO2 ice cap presentation in the Global Mars Multiscale Model

The atmospheric influence caused by the Martian permanent south CO₂ ice cap is examined to improve the Global Mars Multiscale Model (GM3) to see if it can significantly improve the representation of south polar meteorology. However, the seasonal carbon dioxide ice in the polar regions is presented in the surface ice simulation by the Global Mars Multiscale Model but the model does not produce a permanent south CO₂ ice cap, and the physics code must modify to capture the realistic physical such as ice process detail; probably makes a bias in terms of total CO₂ ice and meteorological processes in the model aside from ice formation. The permanent south CO₂ ice cap in the model can significantly improve the representation of south polar meteorology for example in predicted surface temperatures, surface pressures, horizontal and zonal winds over the south cap and possible initiation of dust storms at south polar region during the southern summer period.     

火星尘埃与探测

火星表面尘埃与太阳辐射、热辐射的相互作用直接影响火星大气的结构、热平衡和动力学过程,并会产生改变火星表面反照率和火星地貌的长期效应.火星尘埃环境还对登陆于火星表面的着陆器能源系统和光学载荷等系统构成影响.为此需开展火星大气尘埃的直接就位探测.在介绍了火星的尘埃特性与主要探测方法基础上,提出了采用微质量计技术开展火星表面尘埃就位探测的综合探测器方案.探测器包含3种传感器.尘埃累积传感器通过设置其敏感晶体表面朝上,可以探测火星表面尘埃的沉积质量与速率;荷电尘埃传感器通过加置不同极性的偏置电压,可以探测荷正电尘埃和荷负电尘埃的累积特性;磁尘传感器通过在敏感晶体后加设小型永久磁铁,可以探测磁性尘埃的累积特性.传感器感测质量范围为10^-11~10^-4g.火星尘埃综合探测器可应用于未来的火星着陆探测计划.     

Annual solar UV exposure and biological effective dose rates on the Martian surface.

The ultraviolet (UV) environment of Mars has been investigated to gain an understanding of the variation of exposure throughout a Martian year, and link this flux to biological effects and possible survival of organisms at the Martian surface. To gain an idea of how the solar UV radiation varies between different regions, including planned landing sites of two future Mars surface missions, we modelled the total solar UV surface flux throughout one Martian year for two different dust scenarios. To understand the degree of solar UV stress on micro-organisms and/or molecules essential for life on the surface of Mars, we also calculated the biologically effective dose (BED) for T7 and Uracil in relevant wavelength regions at the Martian surface as a function of season and latitude, and discuss the biological survival rates in the presence of Martian solar UV radiation. High T7/Uracil BED ratios indicate that even at high latitudes where the UV flux is significantly reduced, the radiation environment is still hostile for life due to the persisting UV-C component of the flux.     

火星尘埃对太阳电池阵的影响与电帘除尘研究

火星表面大量尘埃在太阳电池阵表面的累积将会导致其输出功率下降,甚至使太阳电池阵功能失效。近年来,电帘除尘方法被认为是在火星着陆任务中进行尘埃防护最有效的手段之一。本文开展了火星尘埃累积对三结砷化镓太阳电池性能影响的实验研究,得到了火星尘埃累积量与太阳电池电压、电流和相对输出功率数值模型;通过除尘技术分析,确定电帘除尘装置构型;依据制备得到的除尘电帘,对不同火星尘埃累积下电帘的除尘效率进行了研究,为火星着陆太阳电池阵遥测数据分析和开发自适应除尘太阳电池阵提供有力的技术支持。     

Scientific Objectives and Payloads of Chinese First Mars Exploration

China plans to implement the first Mars exploration mission in 2020. It will conduct global and comprehensive exploration of Mars and high precision and fine resolution detection of key areas on Mars through orbiting, landing and roving. The scientific objectives include studying the Martian morphology and geological structure characteristics, studying the soil characteristics and the water-ice distribution on the Martian surface, studying the material composition on the Martian surface, studying the atmosphere ionosphere and surface climate and environmental characteristics of Mars, studying the physical field and internal structure of Mars and the Martian magnetic field characteristics. The mission equips 12 scientific payloads to achieve these scientific objectives. This paper mainly introduces the scientific objectives, exploration task, and scientific payloads.      

Global MGS TES data and Mars-GRAM validation

Mars Global Reference Atmospheric Model (Mars-GRAM 2001) is an engineering-level Mars atmosphere model widely used for many Mars mission applications. From 0 to 80 km, it is based on NASA Ames Mars General Circulation Model (MGCM), while above 80 km it is based on University of Michigan Mars Thermospheric General Circulation Model. Mars-GRAM 2001 and MGCM use surface topography from Mars Global Surveyor Mars Orbiter Laser Altimeter (MOLA). Validation studies are described comparing Mars-GRAM with a global summary data set of Mars Global Surveyor Thermal Emission Spectrometer (TES) data. TES averages and standard deviations were assembled from binned TES data which covered surface to ∼40 km, over more than a full Mars year (February 1999–June 2001, just before start of a Mars global dust storm). TES data were binned in 10° × 10° latitude–longitude bins (36 longitude bins, centered at 5°–355°, by 18 latitude bins, centered at −85° to +85°), and 12 seasonal bins (based on 30° increments of L_s angle). Bin averages and standard deviations were assembled at 23 data levels (temperature at 21 pressure levels, plus surface temperature and surface pressure). Two time-of-day bins were used: local time near 2 or 14 h. Two dust optical depth bins were used: infrared optical depth, either less than or greater than 0.25 (which corresponds to visible optical depth less than or greater than about 0.5). For interests in aerocapture and precision entry and landing, comparisons focused on atmospheric density. TES densities versus height were computed from TES temperature versus pressure, using assumptions of perfect gas law and hydrostatics. Mars-GRAM validation studies used density ratio (TES/Mars-GRAM) evaluated at data bin center points in space and time. Observed average TES/Mars-GRAM density ratios were generally 1 ± 0.05, except at high altitudes (15–30 km, depending on season) and high latitudes (>45°N), or at most altitudes in the southern hemisphere at L_s ∼ 90° and 180°. Compared to TES averages for a given latitude and season, TES data had average density standard deviation about the mean of ∼2.5% for all data, or ∼1–4%, depending on time of day and dust optical depth. Average standard deviation of TES/Mars-GRAM density ratio was 8.9% for local time 2 h and 7.1% for local time 14 h. Thus standard deviation of observed TES/Mars-GRAM density ratio, evaluated at matching positions and times, is about three times the standard deviation of TES data about the TES mean value at a given position and season.     

Optical properties of dust and the opacity of the Martian atmosphere

Particulate component of the Mars atmosphere composed by micron-sized products of soil weathering and water ice clouds strongly affects the current climate of the planet. In the absence of a dust storm so-called permanent dust haze with τ ≈ 0.2 in the atmosphere of Mars determines its thermal structure. Dust loading varies substantially with the season and geographic location, and only the data of mapping instruments are adequate to characterize it, such as TES/MGS and IRTM/Viking. In spite of vast domain of collected data, no model is now capable to explain all observed spectral features of dust aerosol. Several mineralogical and microphysical models of the atmospheric dust have been proposed but they cannot explain the pronounced systematic differences between the IR data (τ = 0.05–0.2) and measurements from the surface (Viking landers, Pathfinder) which give the typical “clear” optical depth of τ ≈ 0.5 from one side, and ground-based observations in the UV–visible range showing much more transparent atmosphere, on the other side. Also the relationship between τ₉ and the visible optical depth is not well constrained experimentally so far. Future focused measurements are therefore necessary to study Martian aerosol.     

火星信道衰落特性对通信链路预算的影响

对火星星体段的信道衰落特性进行研究.通过对近火段自然环境因素的分析,提取影响火星通信性能的因素,重点分析火星的大气、云雾、沙尘对通信信道的衰落作用机理;并以NASA实际火星探测任务为例,针对以上衰落因素对UHF,S,X和Ka频段下的通信链路影响情况进行仿真;结合实际探测数据对地球通信链路预算模型进行修正,提出一种适用于火星通信链路预算的模型;明确火星大气衰落、云雾衰落、沙尘衰落的取值范围.研究结果可作为火星及其他深空探测任务的通信系统设计与链路复核复算的参考.      

Climatology of global,hemispheric and regional electron content variations during the solar cycles 23 and 24

We present the results of study on the variations of ionospheric total electron content (TEC) by using global, hemispheric, and regional electron contents computed from the global ionospheric maps (GIMs) for the period from 1999 to 2020. For a low and moderate solar activity, the global and regional electron contents vary linearly with solar 10.7 cm radio flux and EUV flux. While a saturation effect in the electron content verses EUV and F10.7 is found during the high solar activity periods at all regions, the maximum effect is observed at low-latitudes followed by high and mid-latitudes region. The extent of saturation effect is more pronounced for F10.7 as compared to EUV. A wavelet transform is applied to global and hemispheric electron contents to examine the relative strength of different variations. The semi-annual variations dominate in the northern hemisphere, whereas annual variations dominate in the southern counterpart. The amplitude of annual variations in southern hemisphere is found to be higher than northern counterpart at all latitudes. This asymmetry in the amplitude of annual variation is maximum at low-latitudes, followed by mid and high-latitudes, respectively. The semi-annual variations are in-phase in both hemisphere and follow the solar cycle. The northern hemisphere depicts relatively large amplitude of semi-annual variations and exhibit the maximum effect at high-latitudes.     

一种基于GNSS数据的全球电离层不规则结构活动表征方法

针对如何利用GNSS(Global Navigation Satellite System)数据进行电离层扰动监测的问题,提出了一种基于GNSS数据表征全球电离层扰动的方法.利用大约400个GNSS地面站点的观测数据,计算总电子含量(Total Electron Content,TEC)变化率的标准差——ROTI(Ra...     

利用CRISM数据探测火星表面含水矿物及其演化

火星表层矿物识别是了解火星大气环境变化、表层地质环境的关键因素。通过确定火星表层矿物,分析矿物特性,了解火星的环境状态、地质演化以及火星的未来适居性。火星勘测轨道器(Mars reconnaissance orbiter,MRO)上搭载的紧凑型侦察成像仪(compact reconnaissance imaging spectrometer for Mars,CRISM)是针对火星矿物探测的最新的高光谱成像仪,以很高的光谱分辨率覆盖可见光至近红外波段,为火星表面的矿物分布及区域填图提供了可能。通过光谱匹配及计算CRISM光谱参数综合产品,分析了火星Jezero以及Holden撞击坑内的矿物成分及其演化。Jezero与Holden因其复杂而关键的地质特征,被列为火星2020登陆任务的备选登陆点。对这两个地点的矿物探测与填图分析不仅可进一步分析火星典型地质特征以及演化,而且还可以为未来的火星登陆点分析提供现实意义。在研究区域已检测到与水成蚀变相关的含水硅酸盐类以及碳酸盐类与含水硫酸盐类。水合矿物增加了这些区域曾经含水的可能性,且矿物的多样性表明研究区地质环境经历了不同的变化,其中Jezero地区不同于火星的绝大多数地区从中性环境到酸性环境的演化,有可能经历了从中性环境到碱性环境的演化。     

火星地形对火星大气运动的影响及火星尘暴发生的可能机制

本文在准地转模式的假定下,讨论了火星地形对火星大气的影响,并根据文章所提供的信息对火星尘暴发生的物理机制作了粗略的解释。