青藏高原西部地表热通量输送的低频特征   总被引：1，自引：1，他引：0       下载免费PDF全文

张鹏飞  李国平  尹建昌 《高原气象》2009,28(3):556-563

以1997年9月-1998年10月青藏高原西部改则地区自动气象站(AWS)近地层连续观测的梯度资料为基础,计算了高原西部地面感热通量、蒸发潜热通量及地面热源强度,应用Marr小波变换重点分析了地表热通量输送以及与此相关的降水量、土壤湿度和土壤热通量的周期振荡特征.结果表明:地面感热具有明显的30～60天低频振荡,并且在夏季存在准8天的中期振荡;蒸发潜热和降水量以准双周振荡为主.土壤热通量以30～50天低频振荡为主,夏季还存在准8天的中期振荡;土壤湿度在冬季呈现明显的30～50天低频振荡,夏季则为20～30天的低频振荡.  相似文献   

青藏高原东坡理塘地区近地层湍流特征研究   总被引：7，自引：3，他引：4       下载免费PDF全文

李英  李跃清  赵兴炳 《高原气象》2009,28(4):745-753

利用中国气象局成都高原气象研究所在青藏高原东坡理塘地区建立的大气综合观测站观测资料, 以2006年1月和7月涡旋相关资料分别代表冬季和夏季, 分析和比较了该地区近地层包括风速、 风向、 大气稳定度在内的平均场特征, 以及湍流强度、 无量纲化风脉动方差相似性和地表通量变化特征,结果表明, 1月和7月稳定度基本集中在±0.5和±0.25之间; 湍流在<2 m·s-1的风速环境中发展最为旺盛, 随着风速的增大湍流强度减小迅速; 无量纲化三维风脉动方差符合Monin-Obukhov相似理论的“1/3”定律, 其最佳通用相似函数在稳定和不稳定条件下都可以拟合得到; 地表通量均表现出明显的日变化特征, 1月以感热为主, 潜热很小; 7月以潜热为主, 感热较小。  相似文献   

Aeolian bedforms, yardangs, and indurated surfaces in the Tharsis Montes as seen by the HiRISE Camera: Evidence for dust aggregates   总被引：1，自引：0，他引：1  

N.T. Bridges  M.E. Banks  F.C. Chuang  K.E. Herkenhoff  K.E. Fishbaugh  T.I. Michaels  J.J. Wray 《Icarus》2010,205(1):165-182

HiRISE images of Mars with ground sampling down to 25 cm/pixel show that the dust-rich mantle covering the surfaces of the Tharsis Montes is organized into ridges whose form and distribution are consistent with formation by aeolian saltation. Other dusty areas near the volcanoes and elsewhere on the planet exhibit a similar morphology. The material composing these “reticulate” bedforms is constrained by their remote sensing properties and the threshold curve combined with the saltation/suspension boundary, both of which vary as a function of elevation (atmospheric pressure), particle size, and particle composition. Considering all of these factors, dust aggregates are the most likely material composing these bedforms. We propose that airfall dust on and near the volcanoes aggregates in situ over time, maybe due to electrostatic charging followed by cementation by salts. The aggregates eventually reach a particle size at which saltation is possible. Aggregates on the flanks are transported downslope by katabatic winds and form linear and “accordion” morphologies. Materials within the calderas and other depressions remain trapped and are subjected to multidirectional winds, forming an interlinked “honeycomb” texture. In many places on and near the volcanoes, light-toned, low thermal inertia yardangs and indurated surfaces are present. These may represent “duststone” formed when aggregates reach a particle size below the threshold curve, such that they become stabilized and subsequently undergo cementation.  相似文献   

HiRISE observations of gas sublimation-driven activity in Mars’ southern polar regions: II. Surficial deposits and their origins     

N. Thomas  C.J. Hansen 《Icarus》2010,205(1):296-310

The High Resolution Imaging Science Experiment (HiRISE) onboard Mars Reconnaissance Orbiter (MRO) has been used to monitor the seasonal evolution of several regions at high southern latitudes and, in particular, the jet-like activity which may result from the process described by Kieffer (JGR, 112, E08005, doi:10.1029/2006JE002816, 2007) involving translucent CO₂ ice. In this work, we mostly concentrate on observations of the Inca City (81°S, 296°E) and Manhattan (86°S, 99°E) regions in the southern spring of 2007. Two companion papers, [Hansen et al. this issue] and [Portyankina et al. this issue], discuss the surface features in these regions and specific models of the behaviour of CO₂ slab ice, respectively. The observations indicate rapid on-set of activity in late winter initiating before HiRISE can obtain adequately illuminated images (Ls < 174° at Inca City). Most sources become active within the subsequent 8 weeks. Activity is indicated by the production of dark deposits surrounded by brighter bluer deposits which probably arise from the freezing out of vented CO₂ [Titus et al., 2007. AGU (abstract P41A-0188)]. These deposits originate from araneiform structures (spiders), boulders on ridges, cracks on slopes, and along linear cracks in the slab ice on flatter surfaces. The type of activity observed can often be explained qualitatively by considering the local topography. Some dark fans are observed to shorten enormously in length on a timescale of 18 days. We consider this to be strong evidence that outgassing was in progress at the time of HiRISE image acquisition and estimate a total particulate emission rate of >30 g s⁻¹ from a single typical jet feature. Brighter deposits at Inca City become increasingly hard to detect after Ls = 210°. In the Inca City region, the orientations of surficial deposits are topographically controlled. The deposition of dark material also appears to be influenced by local topography suggesting that the ejection from the vents is at low velocity (<10 m s⁻¹) and that a ground-hugging flow process (a sort of “cryo-fumarole”) may be occurring. The failure up to this point to obtain a clear detection of outgassing though stereo imaging is consistent with low level transport. The downslope orientation of the deposits may result from the geometry of the vent or from catabatic winds. At many sites, more than one ejection event appears to have occurred suggesting re-charging of the sources. Around Ls = 230°, the brightness of the surface begins to drop rapidly on north-facing slopes and the contrast between the dark deposits and the surrounding surface reduces. This indicates that the CO₂ ice slab is being lost completely in some areas at around this time. By Ls = 280°, at Inca City, the ice slab has effectively gone. CRISM band ratios and THEMIS brightness temperature measurements are consistent with this interpretation.  相似文献   

Modeling the formation of bright slope deposits associated with gullies in Hale Crater, Mars: Implications for recent liquid water     

Kelly Jean Kolb  Jon D. Pelletier  Alfred S. McEwen 《Icarus》2010,205(1):113-137

Our study investigates possible formation mechanisms of the very recent bright gully deposits (BGDs) observed on Mars in order to assess if liquid water was required. We use two models in our assessment: a one-dimensional (1D) kinematic model to model dry granular flows and a two-dimensional (2D) fluid-dynamic model, FLO-2D (O’Brien et al., 1993, FLO Engineering), to model water-rich and wet sediment-rich flows. Our modeling utilizes a high-resolution topographic model generated from a pair of images acquired by the High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter. For the 1D kinematic modeling of dry granular flows, we examine a range of particle sizes, flow thicknesses, initial velocities, flow densities, and upslope initiation points to examine how these parameters affect the flow run-out distances of the center of mass of a flow. Our 1D modeling results show that multiple combinations of realistic parameters could produce dry granular flows that travel to within the observed deposits’ boundaries. We run the 2D fluid-dynamic model, FLO-2D, to model both water-rich and wet sediment-rich flows. We vary the inflow volume, inflow location, discharge rate, water-loss rate (water-rich models only), and simulation time and examine the resulting maximum flow depths and velocities. Our 2D modeling results suggest that both wet sediment-rich and water-rich flows could produce the observed bright deposits. Our modeling shows that the BGDs are not definitive evidence of recent liquid water on the surface of Mars.  相似文献   

Indications of brine related local seepage phenomena on the northern hemisphere of Mars     

A. Kereszturi  D. Möhlmann  T. Ganti  A. Kuti  E. Szathmary 《Icarus》2010,207(1):149-743

Springtime low albedo features, called Dark Dune Spots, on the seasonal frost covered dunes on Mars between 77°N and 84°N latitude have been analyzed. Two groups of these spots have been identified: “small” and “large” ones, where large spots have diameters above 4 m, and complex internal structure. From these “large” spots branching seepage-like features emanate and grow on the steep slopes. They show a characteristic sequence of changes: first only wind-blown features emanate from them, while later a bright circular and elevated ring forms, and dark seepage-features start from the spots. These streaks grow with a speed between 0.3 m/day and 7 m/day respectively, first only from the spots, later from all along the dune crest.During this “seepage period” the temperature is between 150 K and 180 K at a 3-9 km spatial resolution scale, indicating that CO₂ ice-free parts must be present at the observed dark spots. Around the receding northern seasonal CO₂ cap, an annulus of water ice lags behind, which is probably present in the spots too where the CO₂ frost has sublimated. Our model estimates show in the present work and in Kereszturi et al. (Kereszturi, A., Möhlmann, D., Berczi, Sz., Ganti, T., Kuti, A., Sik, A., Horvath, A. [2009b]. Icarus 201, 492-503) that the warming driven by solar insolation may produce not only interfacial water, but also bulk brines around the dune grains. The brine can support the movement of liquids and dune grains, enhances the sublimation of CO₂ frost, and produce the dark features, as well as liquid modifies the optical properties of the surface.Signs of movement of dune material after the total defrosting of the terrain is also visible but it is uncertain because of the limit of resolution. In our previous work (Kereszturi et al., 2009b) we showed that resembling seepage-like streaks at the southern hemisphere might have been formed by ephemeral interfacial water, as well as these northern features. Such wet environments may have astrobiological importance too.  相似文献   

Dust devil sediment flux on Earth and Mars: Laboratory simulations     

Lynn D.V. Neakrase  Ronald Greeley 《Icarus》2010,206(1):306-318

Laboratory simulations using the Arizona State University Vortex Generator (ASUVG) were run to simulate sediment flux in dust devils in terrestrial ambient and Mars-analog conditions. The objective of this study was to measure vortex sediment flux in the laboratory to yield estimations of natural dust devils on Earth and Mars, where all parameters may not be measured. These tests used particles ranging from 2 to 2000 μm in diameter and 1300 to 4800 kg m⁻³ in density, and the results were compared with data from natural dust devils on Earth and Mars. Typically, the cores of dust devils (regardless of planetary environment) have a pressure decrease of ∼0.1-1.5% of ambient atmospheric pressure, which enhances the lifting of particles from the surface. Core pressure decreases in our experiments ranged from ∼0.01% to 5.00% of ambient pressure (10 mbar Mars cases and 1000 mbar for Earth cases) corresponding to a few tenths of a millibar for Mars cases and a few millibars for Earth cases. Sediment flux experiments were run at vortex tangential wind velocities of 1-45 m s⁻¹, which typically correspond to ∼30-70% above vortex threshold values for the test particle sizes and densities. Sediment flux was determined by time-averaged measurements of mass loss for a given vortex size. Sediment fluxes of ∼10⁻⁶-10⁰ kg m⁻² s⁻¹ were obtained, similar to estimates and measurements for fluxes in dust devils on Earth and Mars. Sediment flux is closely related to the vortex intensity, which depends on the strength of the pressure decrease in the core (ΔP). This study found vortex size is less important for lifting materials because many different diameters can have the same ΔP. This finding is critical in scaling the laboratory results to natural dust devils that can be several orders of magnitude larger than the laboratory counterparts.  相似文献   

HiRISE observations of gas sublimation-driven activity in Mars’ southern polar regions: III. Models of processes involving translucent ice     

Ganna Portyankina  Wojciech J. Markiewicz  Candice J. Hansen 《Icarus》2010,205(1):311-320

Enigmatic surface features, known as ‘spiders’, found at high southern martian latitudes, are probably caused by sublimation-driven erosion under the seasonal carbon dioxide ice cap. The Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) has imaged this terrain in unprecedented details throughout southern spring. It has been postulated [Kieffer, H.H., Titus, T.N., Mullins, K.F., Christensen, P.R., 2000. J. Geophys. Res. 105, 9653-9700] that translucent CO₂ slab ice traps gas sublimating at the ice surface boundary. Wherever the pressure is released the escaping gas jet entrains loose surface material and carries it to the top of the ice where it is carried downslope and/or downwind and deposited in a fan shape. Here we model two stages of this scenario: first, the cleaning of CO₂ slab ice from dust, and then, the breaking of the slab ice plate under the pressure built below it by subliming ice. Our modeling results and analysis of HiRISE images support the gas jet hypothesis and show that outbursts happen very early in spring.  相似文献   

Color imaging of Mars by the High Resolution Imaging Science Experiment (HiRISE)     

W. Alan Delamere  Livio L. Tornabene  Kris Becker  Nathan T. Bridges  Dennis Gallagher  Laszlo Keszthelyi  Guy K. McArthur  Moses Milazzo  Nicolas Thomas 《Icarus》2010,205(1):38-52

HiRISE has been producing a large number of scientifically useful color products of Mars and other planetary objects. The three broad spectral bands, coupled with the highly sensitive 14 bit detectors and time delay integration, enable detection of subtle color differences. The very high spatial resolution of HiRISE can augment the mineralogic interpretations based on multispectral (THEMIS) and hyperspectral datasets (TES, OMEGA and CRISM) and thereby enable detailed geologic and stratigraphic interpretations at meter scales. In addition to providing some examples of color images and their interpretation, we describe the processing techniques used to produce them and note some of the minor artifacts in the output. We also provide an example of how HiRISE color products can be effectively used to expand mineral and lithologic mapping provided by CRISM data products that are backed by other spectral datasets. The utility of high quality color data for understanding geologic processes on Mars has been one of the major successes of HiRISE.  相似文献   

Investigating gully flow emplacement mechanisms using apex slopes     

Kelly Jean Kolb  Alfred S. McEwen 《Icarus》2010,208(1):132-142

The origin of the martian gullies has been much debated since their discovery by the Mars Orbiter Camera (MOC, Malin, M.C., Edgett, K.S. [2000]. Science 288, 2330-2335). Several previous studies have looked at slope gradients in and around gullies, but none have used Digital Elevation Models (DEMs) from the High Resolution Imaging Science Experiment (HiRISE, McEwen, A.S., and 14 colleagues [2007]. J. Geophys. Res. 112 (E05), E0505S02), which has a pixel scale down to 25 cm/pixel. We use five 1 m/post HiRISE DEMs to measure gully apex slopes, the local channel gradient at the upslope extent of the gully debris apron, which marks a shift from erosion to deposition. The apex slope provides information about whether a flow was likely a typical dry granular flow (begins depositing on slopes ∼21°) or fluidized by some extra mechanism (depositing on shallower slopes). We find that 72% of the 75 gully fans studied were likely emplaced by fluidized flows. Relatively old gullies appear more likely to have hosted fluidized flows than relatively fresh gullies. This suggests a time and location dependent fluidizing agent, possibly liquid water produced in a different climate as previously proposed. Our results do not provide evidence for water-rich flows in gullies today.  相似文献