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101.
102.
T. W. Thompson W. J. Roberts W. K. Hartmann R. W. Shorthill S. H. Zisk 《Earth, Moon, and Planets》1979,21(3):319-342
Radar, infrared, and photogeologic properties of lunar craters have been studied to determine whether there is a systematic difference in blocky craters between the maria and terrae and whether this difference may be due to a deep megaregolith of pulverized material forming the terra surface, as opposed to a layer of semi-coherent basalt flows forming the mare surface. Some 1310 craters from about 4 to 100 km diameter have been catalogued as radar and/or infrared anomalies. In addition, a study of Apollo Orbital Photography confirmed that the radar and infrared anomalies are correlated with blocky rubble around the crater.Analysis of the radar and infrared data indicated systematic terra—mare differences. Fresh terra craters smaller than 12 km were less likely to be infrared and radar anomalies than comparable mare craters: but terra and mare craters larger than 12 km had similar infrared and radar signatures. Also, there are many terra craters which are radar bright but not infrared anomalies.Our interpretation of these data is that while the maria are rock layers (basaltic flow units) where craters eject boulder fields, the terrae are covered by relatively pulverized megaregolith at least 2 km deep, where craters eject less rocky rubble. Blocky rubble, either in the form of actual rocks or partly consolidated blocks, contributes to the radar and infrared signatures of the crater. However, aging by impacts rapidly destroys these effects, possibly through burial by secondary debris or by disintegration of the blocks themselves, especially in terra regions.PSI Contribution No. 110. 相似文献
103.
Paleocratering of the Moon: Review of post-Apollo data 总被引:1,自引:0,他引:1
William K. Hartmann 《Astrophysics and Space Science》1972,17(1):48-64
As a result of the dating of lunar samples, we are in a position to utilize the lunar surface as a recorder of environmental conditions in the Earth-Moon neighborhood in the past. Plots of crater density vs rock age at different lunar landing sites can be used to date unexplored lunar provinces. These plots also demonstrate evolution in the population of planetesimals that struck the Moon. Prior to 4.1 aeons ago, the cratering rate on the Moon was at least 103 times the present rate, and the rate declined with a half-life less than 8×107 yr. During the interval from 4.1 to 3.2 aeons ago, the number of planetesimals showed an exponential decay with a half-life about 3×108 yr, corresponding to sweep-up of particles from solar orbits somewhat similar to those of Apollo asteroids. A more nearly constant cratering rate applied in the last three aeons. These data indicate that the Moon displays at least the final stages of an ancient accretion process; they also set certain conditions on possible capture processes relating to the Moon's origin. Pre-Apollo expectations that the Moon would provide a Rosetta Stone for interpreting solar system history and planet formation thus appear justified.Paper given at Philadelphia meeting of American Association for Advancement of Science, December, 1971. 相似文献
104.
Ulrike?WackerEmail author K.?V.?Jayaraman?Potty Christof?Lüpkes J?rg?Hartmann Matthias?Raschendorfer 《Boundary-Layer Meteorology》2005,117(2):301-336
The mesoscale weather prediction model ’Lokal-Modell’ (LM) of the Deutscher Wetterdienst is applied to the situation of an
Arctic cold air outbreak in the Fram Strait region in April 1998. Observations are available from a flight along 50E carried out during the ARTIST campaign. Initial and time-dependent boundary data for the simulation are taken from a larger
scale operational model system.
Using the standard configuration of LM, the simulation reproduced the propagation of cold air and the characteristic structure
of the atmospheric boundary layer (ABL) in fair agreement with the observations. However, a detailed comparison revealed three
basic problems. Firstly, there is evidence that the available data on sea-ice conditions were insufficient approximations
to the true state for several reasons. A modification of the sea-ice data towards observations revealed that parts of the
discrepancies were due to the original sea-ice data. Secondly, a control run with the model in its standard configuration
shows an insufficient warming of the ABL downstream of the ice edge due to underestimation of surface heat fluxes. A simple
modification of the approach for the scalar roughness length resulted in the strongest benefit, while comparative studies
showed only a slight sensitivity to different types of parametrisation of turbulent mixing or the inclusion of an additional
moist convection parametrisation. Thirdly, in all the simulations the deepening of the convective ABL downstream of the ice
edge is weaker than observed. This may be partly due to the thermal stratification above the ABL in the analysis data, which
is more stable than observed; but it may also be a hint to the fact that processes near the inversion are insufficiently parametrised
in mesoscale models with resolutions as used in LM. The simulated cloud layer in the convective ABL is similar to that observed
with respect to condensate content, a sharply defined cloud top, a diffuse lower bound, and continuous light precipitation. 相似文献
105.
Moon: Origin and evolution of multi-ring basins 总被引:2,自引:0,他引:2
This paper summarizes current data and new observations on lunar basin systems. Parts 1–4 review earlier literature and give new crater-counts used to reconstruct basin histories. Among the results are: basin rings are defined by faults, hills, craters, and/or wrinkle ridges; all of these are inter-related; 2 plays a special role in the ratios of ring diameters; flooding occurred in many basins prior to the formation of the familiar front-side maria; 3 km is a typical depth of lava flooding in basins. Parts 5–11 interpret these results in terms of origin and evolution of basins. Polar concentrations of basins and old, large craters are found (Figures 28 and 29). Basins originated by impacts of very early planetesimals left over from or created during formation of the Moon (6). Concentric fractures were produced by the impacts. Concentric rings developed along fractures during subsequent sagging of the basin into partially melted substrata, along the lines of theory and experiments by Lance and Onat (1962) (Figures 36 and 37). There is marginal empirical evidence that some rings formed significantly after their basins (8). The structure of specific rings depended on the nature of volcanic products extruded. Wrinkle ridges, peak-rings, rings of craters, concentric graben, and central peaks are all consequences of basin-forming evolutionary processes (9, Figure 41), Flooding by lava was a final stage in basin evolution. Lava extruded from concentric ring-faults, wrinkle ridges, and crater and basin rims (10). Mascons are directly correlated with the amount of mare lava, but not correlated with basin age or morphology (11). Section 12 summarizes the results and compares them to those of other authors. 相似文献
106.
William K. Hartmann 《Icarus》1984,60(1):56-74
Similarity is found in crater densities on the most heavily cratered surfaces throughout the solar system. This is hypothesized to result from a steady-state “saturation equilibrium” being approached or achieved by cratering processes. This hypothesis conflicts with some recent interpretations. However, it accounts for (1) a similarity in maximum relative crater density, below certain theoretically predicted values, on all heavily cratered surfaces; (2) a leveling off at this same relative density among 100-m scale (secondary?) craters in populations on lunar maria and other sparsely cratered lunar surfaces; (3) the approximate uniformity of maximum relative densities on Saturn satellites (in spite of dramatic variations predicted from nonsaturation models assuming heliocentric impactors). The lunar frontside upland crater population, sometimes described as a well-preserved production function useful for interpreting other planetary surfaces, is found not to be a production function. It was modified by intercrater plains formed (at least partly) by early upland basaltic lava flooding, recently confirmed spectrophotometrically. Consistent with this, counts in “pure uplands” (those lacking intercrater plains) match the proposed saturation equilibrium density. Variations among large (D > 64 km) crater populations are found, but these may involve several hypothesized mechanisms that rapidly obliterate large craters, especially on icy surfaces. Recent models, in which different populations of interplanetary bodies hit different planets, need further appraisal. 相似文献
107.
A Laser-induced Fluorescence Instrument for Detecting Tropospheric OH and HO2: Characteristics and Calibration 总被引:1,自引:0,他引:1
108.
The effect of latitudinal differential heating on the atmospheric general circulation is studied using a simple general circulation model driven by different heating rates. It is found that an increase in differential heating leads to a strengthening of the general circulation as characterized by an increase in global available potential energy, kinetic energy and atmospheric angular momentum. The strengthening of the circulation results in three circulation regimes characterized by different eddy activities. One is a zonally symmetric Hadley regime with no eddy activity while the other two are Rossby regimes dominated by eddies with intermediate and low wave numbers, respectively. Relative to other global indices, the global relative atmospheric angular momentum is superior in detecting the transition of circulation regimes. The regime changes in mid- and high-latitudes resemble the response of the atmosphere to large changes in Earths rotation rate. 相似文献
109.
J. F. Barlow G. G. Rooney S. von Hünerbein S. G. Bradley 《Boundary-Layer Meteorology》2008,127(2):173-191
Profiles of wind and turbulence over an urban area evolve with fetch in response to surface characteristics. Sodar measurements,
taken on 22 April 2002 during the Salford Experiment in the UK (Salfex), are here related to upstream terrain. A logarithmic
layer up to z = 65m was observed in all half-hour averaged profiles. Above this height the profile showed a different vertical gradient,
suggesting a change in surface cover upstream. The drag coefficient varied by a factor of two over only a 20° direction change.
Turbulence intensity (σ
x
) for each wind component (x) decreased with height, but the ratio suggested an underestimate of σ
u
compared to previous results. Mean urban and suburban cover fraction within the source area for each height decreased sharply
between z = 20 and 50m, increasing slightly above. The near-convergence of cover fractions thus occured for source areas of minimum
length ≈ 2,200 m. In comparison, the mean length scale of heterogeneity L
P was calculated from surface cover data to be 1,284 m, and the corresponding mean blending height h
b was 175 m. Finally, the mean streamline angle, α, was negative and the magnitude decreased with height. An exponential fit
to α for z ≤ 65m gave an e-folding height scale of 159 m. A simple relationship between this height scale and L
P was assumed, giving L
P ≈ 1,080 m, which is in reasonable agreement with the estimate from surface cover type. The results suggest that more emphasis
is required on modelling and measuring surface-layer flow over heterogeneous urban canopies. 相似文献
110.