Three decades of slope streak activity on Mars   总被引：1，自引：0，他引：1  

N. Schorghofer  O. Aharonson  L. Tatsumi 《Icarus》2007,191(1):132-140

Slope streaks are surficial mass movements that are abundant in the dust-covered regions of Mars. Targeting of slope streaks seen in Viking images with the Mars Orbiter Camera provides observations of slope streak dust activity over two to three decades. In all study areas, new and persisting dark slope streaks are observed. Slope streaks disappeared in one area, with persisting streaks nearby. New slope streaks are found to be systematically darker than persisting streaks, which indicates gradual fading. Far more slope streaks formed at the study sites than have faded from visibility. The rate of formation at the study sites was 0.03 new slope streaks per existing streak per Mars year. Bright slope streaks do not presently form in sudden events as dark slope streaks do. Instead, bright streaks might form from old dark slope streaks, perhaps transitioning through a partially faded stage.  相似文献   

On the sublimation of ice particles on the surface of Mars; with applications to the 2007/8 Phoenix Scout mission     

Peter A. Taylor  Konstantin Baibakov  Michael H. Hecht  P.-Y. Li  Luis Prieto 《Icarus》2006,181(2):375-387

Experimental studies related to the sublimation of ice, in bulk or as small particles, alone or mixed with dust similar to that expected on the surface of Mars, are reported. The experiments, a cloud physics particle sublimation model, and a convection model presented by Ingersoll, all indicate a strong dependence of sublimation rate on temperature, and this appears to be the dominant factor, assuming that the relative humidity of the air is fairly low. In addition the rate of loss of water vapour appears to depend primarily on exposed surface area and less on particle size and the total mass of the sample, or the mass of ice in the sample. The 2007/8 Phoenix Scout mission plans to obtain and analyse samples of sub-surface ice from about 70° N on Mars. A concern is that these samples, in the form of ice chips of size about 1 mm diameter, could be prone to sublimation when exposed for prolonged periods (many hours) to a relatively warm and dry atmosphere. Our laboratory simulations confirm that this could be a problem if particles are simply left lying on the surface, but also indicate that samples kept suitably cold and collected together in confined piles will survive long enough for the collection and delivery (to the analysis instruments) procedure to be completed.  相似文献   

基于自动观测的天气现象电码自动编制实现流程     

陈冬冬  王力  施丽娟  张鑫 《气象科技》2015,43(1):70-75

实现地面气象要素自动观测是近年来我国气象观测领域的发展趋势,观测自动化给地面观测业务和观测数据的应用推广带来较大改变。本文研究了基于自动观测的天气现象代码表WMO4680,分析得出WMO4680简化了视程障碍和降水阵性的代码分类,比WMO4677编码更适合自动观测设备的特点。结合我国业务天气现象电码编制原则,设计实现了现在天气现象电码和过去天气现象电码的自动编制。根据我国目前可自动化观测的要素数目,经过流程设计和当前最新业务改革内容,可以实现46个天气电码的自动编报。  相似文献   

Mesoscale dynamics and its application in torrential rainfall systems in China     

Shouting Gao  Zhemin Tan  Sixiong Zhao  Zhexian Luo  Hancheng Lu  Donghai Wang  Chunguang Cui  Xiaopeng Cui  Jianhua Sun 《大气科学进展》2015,32(2):192-205

Progress over the past decade in understanding moisture-driven dynamics and torrential rain storms in China is reviewed in this paper. First, advances in incorporating moisture effects more realistically into theory are described, including the development of a new parameter, generalized moist potential vorticity(GMPV) and an improved moist ageostrophic Q vector(Qum). Advances in vorticity dynamics are also described, including the adoption of a "parcel dynamic" approach to investigate the development of the vertical vorticity of an air parcel; a novel theory of slantwise vorticity development, proposed because vorticity develops easily near steep isentropic surfaces; and the development of the convective vorticity vector(CVV)as an effective new tool. The significant progress in both frontal dynamics and wave dynamics is also summarized, including the geostrophic adjustment of initial unbalanced flow and the dual role of boundary layer friction in frontogenesis, as well as the interaction between topography and fronts, which indicate that topographic perturbations alter both frontogenesis and frontal structure. For atmospheric vortices, mixed wave/vortex dynamics has been extended to explain the propagation of spiral rainbands and the development of dynamical instability in tropical cyclones. Finally, we review wave and basic flow interaction in torrential rainfall, for which it was necessary to extend existing theory from large-scale flows to mesoscale fields, enriching our knowledge of mesoscale atmospheric dynamics.  相似文献   

2015年4月大气环流和天气分析   总被引：1，自引：1，他引：0  

周康辉  方翀 《气象》2015,41(7):915-920

2015年4月环流特征如下：极涡为偶极型环流,极涡主体位于格陵兰西侧与加拿大之间,另一中心位于亚洲的东北部;两个极涡中心较常年平均偏低4~8 dagpm,乌拉尔山高压脊偏高8~12 dagpm;副热带高压面积偏大、西脊点偏西,南支槽位置与强度接近常年平均;4月全国平均气温11.6℃,较常年同期（11℃）偏高0.6℃;全国平均降水量43 mm,接近常年同期（44.7 mm）,我国中东部长江以北地区降水偏多,江南、华南降水偏少。4月全国强对流天气过程频发,1—4、19—20和28—29日出现了范围较大的强对流天气。北方地区出现2次沙尘天气。  相似文献   

环境磁学在城市环境污染监测中的应用和进展   总被引：15，自引：4，他引：15       下载免费PDF全文

张春霞  黄宝春 《地球物理学进展》2005,20(3):705-711

环境磁学是一门介于地球科学、环境科学和磁学之间的边缘科学，已广泛应用于很多领域.本文在简述了环境磁学参数和不同环境中磁性矿物变迁和演化过程的基础上,介绍了环境磁学在城市环境污染的不同方面所取得的进展,探讨了环境磁学在土壤污染和大气等城市环境污染研究中的不足,提出了环境磁学在城市环境污染研究领域的发展趋势.  相似文献   

Probability distribution functions for the Sun's magnetic field     

J.O. Stenflo 《Astronomische Nachrichten》2010,331(6):585-588

Magnetoconvection structures the Sun's magnetic field cover a vast range of scales, down to the magnetic diffusion scale that is orders of magnitude smaller than the resolution of current telescopes. The statistical properties of this structuring are governed by probability density functions (PDFs) for the flux densities and by the angular distribution functions for the orientations of the field vectors. The magnetic structuring on sub‐pixel scales greatly affects the field properties averaged over the resolution element due to the non‐linear relation between polarization and magnetic field. Here we use a Hinode SOT/SP data set for the quiet Sun disk center to explore the complex behavior of the 6301–6302 Å Stokes line profile system and identify the observables that allow us to determine the distribution functions in the most robust and least model dependent way. The angular distribution is found to be strongly peaked around the vertical direction for large flux densities but widens with decreasing flux density to become isotropic in the limit of zero flux density. The noise‐corrected PDFs for the vertical, horizontal, and total flux densities all have a narrowly peaked maximum at zero flux density that can be fitted with a stretched exponential, while the extended wings decline quadratically (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

IR spectroscopy of COmosphere dynamics with the CO ?rst overtone band     

T.A. Schad  M.J. Penn 《Astronomische Nachrichten》2010,331(6):589-592

We discuss observations of the weak ?rst overtone (Δν = 2) CO absorption band near 2300 nm with the U.S. National Solar Observatory Array Camera (NAC), a modern mid‐infrared detector. This molecular band provides a thermal diagnostic that forms lower in the atmosphere than the stronger fundamental band near 4600 nm. The observed center‐to‐limb increase in CO line width qualitatively agrees with the proposed higher temperature shocks or faster plasma motions higher in the COmosphere. The spatial extent of chromospheric shock waves is currently at or below the diffraction limit of the available CO lines at existing telescopes. Five minute period oscillations in line strength and measured Doppler shifts are consistent with the p‐mode excitation of the photospheric gas. We also show recent efforts at direct imaging at 4600 nm. We stress that future large‐aperture solar telescopes must be teamed with improved, dynamic mid‐infrared instruments, like the NAC, to capitalize on the features that motivate such facilities (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

The origin of cutoff frequencies for torsional tube waves propagating in the solar atmosphere     

R. Hammer  Z.E. Musielak  S. Routh 《Astronomische Nachrichten》2010,331(6):593-595

Torsional waves supported by magnetic flux tubes have long been thought to bear a high potential for supplying energy and momentum to the upper solar atmosphere, thereby contributing to its heating and to the driving of dynamic events like spicules. This hope rested on the belief that their propagation is not impeded by cutoff restrictions, unlike longitudinal and kink waves. We point out that this applies only to thin, isothermal tubes. When they widen in the chromosphere, and as a result of temperature gradients, cutoff restrictions arise. We compare them to recent observational reports of such waves and of vortex motions and find that their long period components are already affected by cutoff restrictions. An observational strategy is proposed that should permit the derivation of better information on vortex flows from off‐center observations with next generation telescopes (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Abundances of Jupiter's trace hydrocarbons from Voyager and Cassini     

C.A. Nixon  R.K. Achterberg  P.N. Romani  X. Zhang  P.G.J. Irwin 《Planetary and Space Science》2010,58(13):1667-1680

The flybys of Jupiter by the Voyager spacecraft in 1979, and over two decades later by Cassini in 2000, have provided us with unique datasets from two different epochs, allowing the investigation of seasonal change in the atmosphere. In this paper we model zonal averages of thermal infrared spectra from the two instruments, Voyager 1 IRIS and Cassini CIRS, to retrieve the vertical and meridional profiles of temperature, and the abundances of the two minor hydrocarbons, acetylene (C₂H₂) and ethane (C₂H₆). The spatial variation of these gases is controlled by both chemistry and dynamics, and therefore their observed distribution gives us an insight into both processes. We find that the two gases paint quite different pictures of seasonal change. Whilst the 2-D cross-section of C₂H₆ abundance is slightly increased and more symmetric in 2000 (northern summer solstice) compared to 1979 (northern fall equinox), the major trend of equator to pole increase remains. For C₂H₂ on the other hand, the Voyager epoch exhibits almost no latitudinal variation, whilst the Cassini era shows a marked decrease polewards in both hemispheres. At the present time, these experimental findings are in advance of interpretation, as there are no published models of 2-D Jovian seasonal chemical variation available for comparison.  相似文献