On the “rotational angular momentum” of the oceans and the corresponding polar motion

Periodic polar motions caused by ocean tides are predicted. In the Liouville equations for rotational motion the complete excitation functions for the ocean tides have to be used. This does not depend on the fact that hydrodynamical ocean tide models do not consider the centrifugal acceleration. The observable polar motion of the Celestial Ephemeris Pole CEP (more exactly: the terrestrial location of the CEP) is tabulated for the ten ocean tides M₂, S₂, N₂, K₁, O₁, P₁, M f, M f′, M m, Ssa. Typical amplitudes for the largest ocean tides are 0.4 milliarcseconds. This is within the reach of geodetic VLBI and SLR observations.     

2×CO2 Eastern Asia regional responses in the RSM/CCM3 modeling system

A global to regional modeling system has been developed to evaluate precipitation under doubled CO₂. The National Centers for Environmental Prediction (NCEP) regional spectral model (RSM) is initialized and forced by current and doubled CO₂ simulations from the NCAR community climate model (CCM3). Three RSM simulations, RSM0, RSM1, and RSM2, with resolution of 280, 50 and 15 km, are examined. The RSM0 setup resolution matches the T42 CCM3 simulations. The RSM2 simulation is centered over Taiwan. Due to incompatibility of the model physics, noticeable differences between RSM0 and CCM3 are found, especially in wintertime, which suggests that simulation from RSM0, rather than CCM3, should be used to contrast high-resolution regional variations produced by RSM1 or RSM2 simulations.While the spatial distributions of RSM1 and RSM2 simulations over Taiwan are greatly improved over the CCM3 simulation, the intensity of the unique wintertime drizzle is overestimated, especially in RSM2. There is also a spurious northward extension of the precipitation pattern from the subtropical warm-pool region. Thus the regional response to doubled CO₂, which consists of more summerlike wintertime precipitation characteristics over the northeastern and eastern sides of Taiwan, with increased intensity mostly in the extreme events, is still in doubt and must be examined with improved global and regional models.     

Issues related to low resolution modeling of soil moisture: experience with the PLACE model

This study documents the new PLACE soil hydrology model, and examines the effects of various parameterization schemes on the solution of the Richards equation. Richards equation is the basis upon which many of the land surface schemes participating in the PILPS experiments model soil water transport. Generally, the integration is carried out using a coarse model grid, which makes the solution more sensitive to particulars of the parameterization scheme. Parameterization schemes for the lower boundary condition, lateral interflow, and for moisture fluxes between model layers are tested in PLACE using both high and low resolution grids. Simulations were made using PILPS-HAPEX forcing data and soil and vegetation parameters. The soil hydrology model is validated against the annual observed HAPEX soil moisture profiles. The predicted evapotranspiration is also compared to a value computed from the PILPS-HAPEX forcing data using the Penman-Monteith equation.When testing a low-resolution soil grid typical of land surface schemes, predicted soil moisture was found to be highly sensitive to the interpolation method for computing vertical moisture fluxes between model layers. A new interpolation method for low resolution models is proposed and tested. It reproduces the high resolution model results more faithfully, over the entire range of soil moisture, than two methods commonly applied in the literature. Further tests demonstrate that by varying the parameterizations for lower boundary condition and the treatment of lateral flow (collectively called drainage), the predicted total annual evapotranspiration may range between 74% and 97% of the incident precipitation in this case. Both of these parameterizations involve one free parameter, and both are largely unconstrained by the available observations. Good overall agreement between the PLACE predicted and HAPEX observed soil moisture profiles was attained by varying these two PLACE drainage parameters over their respective ranges for a series of model simulations. Root-mean square error tests were then used to determine the set of parameters which corresponded to the best predicted soil moisture profile. However, the best predicted soil moisture profiles do not correspond with the best predicted evapotranspiration. This inconsistency occurs not only for PLACE, but, to varying degrees, for all of the land-surface schemes participating in PILPS-HAPEX.     

Petrogenesis of Grove Mountains 020090: An enriched “lherzolitic” shergottite

Grove Mountains (GRV) 020090 is a “lherzolitic” shergottite found in the Grove Mountains, Antarctica. It exhibits two distinct textures: poikilitic and nonpoikilitic. In poikilitic areas, large pyroxene oikocrysts enclose subhedral olivine and chromite chadacrysts. Pyroxene oikocrysts are zoned from pigeonite cores to augite rims. In nonpoikilitic areas, olivine, pyroxene, and interstitial maskelynite occur as major phases, and minor phases include chromite and merrillite. Compared with typical “lherzolitic” shergottites, GRV 020090 contains a distinctly higher abundance of maskelynite (19 vol%). Olivine and pyroxene are more ferroan (Fa_28–40, En_57–72Fs_24–31Wo_4–14 and En_46–53Fs_17–21Wo_26–35), and maskelynite is more alkali‐rich (Ab_43–65Or_2–7). The major phases, whole‐rock (estimated) and fusion crust of GRV 020090, are relatively enriched in light rare earth elements (LREE), similar to those of the geochemically enriched basaltic shergottites, but distinct from those of LREE‐depleted “lherzolitic” shergottites. Combined with a high oxygen fugacity of log fO₂ = QFM ? 1.41 ± 0.04 (relative to the quartz‐fayalite‐magnetite buffer), it is clear that GRV 020090 sampled from an oxidized and enriched mantle reservoir similar to those of other enriched shergottites. The calculated REE abundances and patterns of the melts in equilibrium with the cores of major phases are parallel to but higher than that of the whole rock, suggesting that GRV 020090 originated from a single parent magma and experienced progressive fractional crystallization in a closed system. The crystallization age recorded by baddeleyite is 192 ± 10 (2σ) Ma, consistent with the young internal isochron ages of enriched shergottites. Baddeleyite dating results further demonstrated that the young ages, rather than ancient ages (>4 Ga), appear to represent the crystallization of Martian surface lava flow. GRV 020090 shares many similarities with Roberts Massif (RBT) 04261/2, the first enriched “lherzolitic” shergottite. Detailed comparisons suggest that these two rocks are petrologically and geochemically closely related, and probably launch paired.     

Modeling the total and polarized emission in evolving galaxies: “Spotty” magnetic structures

Future radio observations with the Square Kilometre Array (SKA) and its precursors will be sensitive to trace spiral galaxies and their magnetic field configurations up to redshift z ≈ 3. We suggest an evolutionary model for the magnetic configuration in star‐forming disk galaxies and simulate the magnetic field distribution, the total and polarized synchrotron emission, and the Faraday rotation measures for disk galaxies at z ≲ 3. Since details of dynamo action in young galaxies are quite uncertain, we model the dynamo action heuristically relying only on well‐established ideas of the form and evolution of magnetic fields produced by the mean‐field dynamo in a thin disk. We assume a small‐scale seed field which is then amplified by the small‐scale turbulent dynamo up to energy equipartition with kinetic energy of turbulence. The large‐scale galactic dynamo starts from seed fields of 100 pc and an averaged regular field strength of 0.02 μG, which then evolves to a “spotty” magnetic field configuration in about 0.8 Gyr with scales of about one kpc and an averaged regular field strength of 0.6 μG. The evolution of these magnetic spots is simulated under the influence of star formation, dynamo action, stretching by differential rotation of the disk, and turbulent diffusion. The evolution of the regular magnetic field in a disk of a spiral galaxy, as well as the expected total intensity, linear polarization and Faraday rotation are simulated in the rest frame of a galaxy at 5GHz and 150 MHz and in the rest frame of the observer at 150 MHz. We present the corresponding maps for several epochs after disk formation. Dynamo theory predicts the generation of large‐scale coherent field patterns (“modes”). The timescale of this process is comparable to that of the galaxy age. Many galaxies are expected not to host fully coherent fields at the present epoch, especially those which suffered from major mergers or interactions with other galaxies. A comparison of our predictions with existing observations of spiral galaxies is given and discussed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

“New” lunar meteorites: Impact melt and regolith breccias and large‐scale heterogeneities of the upper lunar crust

Abstract— We have analyzed nine highland lunar meteorites (lunaites) using mainly INAA. Several of these rocks are difficult to classify. Dhofar 081 is basically a fragmental breccia, but much of its groundmass features a glassy‐fluidized texture that is indicative of localized shock melting. Also, much of the matrix glass is swirly‐brown, suggesting a possible regolith derivation. We interpret Dar al Gani (DaG) 400 as an extremely immature regolith breccia consisting mainly of impact‐melt breccia clasts; we interpret Dhofar 026 as an unusually complex anorthositic impact‐melt breccia with scattered ovoid globules that formed as clasts of mafic, subophitic impact melt. The presence of mafic crystalline globules in a lunar material, even one so clearly impact‐heated, suggests that it may have originated as a regolith. Our new data and a synthesis of literature data suggest a contrast in Al₂O₃‐incompatible element systematics between impact melts from the central nearside highlands, where Apollo sampling occurred, and those from the general highland surface of the Moon. Impact melts from the general highland surface tend to have systematically lower incompatible element concentration at any given Al₂O₃ concentration than those from Apollo 16. In the case of Dhofar 026, both the bulk rock and a comparatively Al‐poor composition (14 wt% Al₂O₃, 7 μg/g Sm) extrapolated for the globules, manifest incompatible element contents well below the Apollo 16 trend. Impact melts from Luna 20 (57°E) distribute more along the general highland trend than along the Apollo 16 trend. Siderophile elements also show a distinctive composition for Apollo 16 impact melts: Ni/Ir averaging ?1.8x chondritic. In contrast, lunaite impact‐melt breccias have consistently chondritic Ni/Ir. Impact melts from Luna 20 and other Apollo sites show average Ni/Ir almost as high as those from Apollo 16. The prevalence of this distinctive Ni/Ir ratio at such widely separated nearside sites suggests that debris from one extraordinarily large impact may dominate the megaregolith siderophile component of a nearside region 2300 km or more across. Highland polymict breccia lunaites and other KREEP‐poor highland regolith samples manifest a strong anticorrelation between Al₂O₃ and mg. The magnesian component probably represents the chemical signature of the Mg‐suite of pristine nonmare rocks in its most “pure” form, unaltered by the major KREEP‐assimilation that is so common among Apollo Mg‐suite samples. The average composition of the ferroan anorthositic component is now well constrained at Al₂O₃ ?29–30 wt% (implying about 17–19 wt% modal mafic silicates), in good agreement with the composition predicted for flotation crust over a “ferroan” magma ocean (Warren 1990).     

“Stickiness” in mappings and dynamical systems

We present results of a study of the so-called “stickiness” regions where orbits in mappings and dynamical systems stay for very long times near an island and then escape to the surrounding chaotic region. First we investigated the standard map in the form x_i+1 = x_i+y_i+1 and y_i+1 = y_i+K/2π · sin(2πx_i) with a stochasticity parameter K = 5, where only two islands of regular motion survive. We checked now many consecutive points—for special initial conditions of the mapping—stay within a certain region around the island. For an orbit on an invariant curve all the points remain forever inside this region, but outside the “last invariant curve” this number changes significantly even for very small changes in the initial conditions. In our study we found out that there exist two regions of “sticky” orbits around the invariant curves: A small region I confined by Cantori with small holes and an extended region II is outside these cantori which has an interesting fractal character. Investigating also the Sitnikov-Problem where two equally massive primary bodies move on elliptical Keplerian orbits, and a third massless body oscillates through the barycentre of the two primaries perpendicularly to the plane of the primaries—a similar behaviour of the stickiness region was found. Although no clearly defined border between the two stickiness regions was found in the latter problem the fractal character of the outer region was confirmed.     

Scenarios of land cover in China

A method for surface modeling of land cover change (SMLC) is developed on the basis of establishing transition probability matrixes between land cover types and HLZ types. SMLC is used to simulate land cover scenarios of China for the years 2039, 2069 and 2099, for which HLZ scenarios are first simulated in terms of HadCM3 climatic scenarios that are downscaled in zonal model of spatial climate change in China. This paper also analyzes spatial distribution of land cover types, area change and mean center shift of each land cover type, ecotope diversity, and patch connectivity under the land cover scenarios. The results show that cultivated land would decrease and woodland would expand greatly with climatic change, which coincides with consequences expected by implementation of Grain-for-Green policy. Nival area would shrink, and desertification area would expand at a comparatively slow rate in future 100 years. Climate change would generally cause less ecotope diversity and more patch connectivity. Ecosystems in China would have a pattern of beneficial cycle after efficient ecological conservation and restoration. However, if human activities would exceed regulation capacity of ecosystems themselves, the ecosystems in China might deteriorate more seriously.     

Insolation in Titan’s troposphere

Seasonality in Titan’s troposphere is driven by latitudinally varying insolation. We show that the latitudinal distributions of insolation in the troposphere and at the surface, based on Huygens DISR measurements, can be approximated analytically with nonzero extinction optical depths τ, and are not equivalent to that at the top of the atmosphere (τ = 0), as has been assumed previously. This has implications for the temperature distribution and the circulation, which we explore with a simple box model. The surface temperature maximum and the upwelling arm of thermally-direct meridional circulation reach the midlatitudes, not the poles, during summertime.     

Possible Interpretations of B2 and 5C Quasar Candidate Counts and the “Cut off” in Quasar Density

Optical quasar candidate counts in the far reaching radio surveys B₂ and 5C are consistent either with a luminosity function containing a high percentage of low luminosity objects and a cut off in quasar density or, more probably, with a normal number of quasars at high redshifts and a less steep luminosity function. The absence of high redshifted objects in currently available samples is to be expected of q₀ ≈︂ o and if some of the few quasars observed at z>2.2 are exceptionally bright intrinsically and not typical for the bulk.     

Detecting crater ejecta‐blanket boundaries and constraining source crater regions for boulder tracks and elongated secondary craters on Eros

Abstract– We present results of a numerical model of the dynamics of ejecta emplacement on asteroid 433 Eros. Ejecta blocks represent the coarsest fraction of Eros’ regolith and are important, readily visible, “tracer particles” for crater ejecta‐blanket units that may be linked back to specific source craters. Model results show that the combination of irregular shape and rapid rotation of an asteroid can result in markedly asymmetric ejecta blankets (and, it follows, ejecta block spatial distribution), with locally very sharp/distinct boundaries. We mapped boulder number densities in NEAR‐Shoemaker MSI images across a portion of a predicted sharp ejecta‐blanket boundary associated with the crater Valentine and confirm a distinct and real ejecta‐blanket boundary, significant at least at the 3‐sigma level. Using our dynamical model, we “back track” the landing trajectories of three ejecta blocks with associated landing tracks in an effort to constrain potential source regions where those blocks were ejected from Eros’ surface in impact events. The observed skip distances of the blocks upon landing on Eros’ surface and the landing speeds and elevation angles derived from our model allow us to estimate the coefficient of restitution, ε, of Eros’ surface for impacts of 10‐m‐scale blocks at approximately 5 m s^?1 impact speeds. We find mean values of ε of approximately 0.09–0.18.     

Interannual variability of regional climate and its change due to the greenhouse effect

Interannual variability of regional climate was investigated on a seasonal basis. Observations and two global climate model (GCM) simulations were intercompared to identify model biases and climate change signals due to the enhanced greenhouse effect. Observed record length varies from 40 to 100 years, while the model output comes from two 100-year equilibrium climate simulations corresponding to atmospheric greenhouse gas concentrations at observed 1990 and projected 2050 levels. The GCM includes an atmosphere based on the NCAR CCM1 with the addition of the radiative effects of CH₄, N₂O and CFCs, a bulk layer land surface and a mixed-layer ocean with thermodynamic sea-ice and fixed meridional oceanic heat transport.Because comparisons of interannual variability are sensitive to the time period chosen, a climate ensemble technique has been developed. This technique provides comparisons between variance ratios of two time series for all possible contiguous sub-periods of a fixed length. The time autocorrelation is thus preserved within each sub-period. The optimal sub-period length was found to be 30 years, based on which robust statistics of the ensemble were obtained to identify substantial differences in interannual variability that are both physically important and statistically significant.Several aspects of observed interannual variability were reproduced by the GCM. These include: global surface air temperature; Arctic sea-ice extent; and regional variability of surface air temperature, sea level pressure and 500 mb height over about one quarter of the observed data domains. Substantial biases, however, exist over broad regions, where strong seasonality and systematic links between variables were identified. For instance, during summer substantially greater model variability was found for both surface air temperature and sea-level pressure over land areas between 20–50°N, while this tendency was confined to 20–30°N in other seasons. When greenhouse gas concentrations increase, atmospheric moisture variability is substantially larger over areas that experience the greatest surface warming. This corresponds to an intensified hydrologic cycle and, hence, regional increases in precipitation variability. Surface air temperature variability increases where hydrologic processes vary greatly or where mean soil moisture is much reduced. In contrast, temperature variability decreases substantially where sea-ice melts completely. These results indicate that regional changes in interannual variability due to the enhanced greenhouse effect are associated with mechanisms that depend on the variable and season.     

The land-surface flux model PROGSURF

The land-surface flux model (PROGSURF) designed jointly at the Universities of Vienna and Budapest is reviewed; it belongs to the broad spectrum of PILPS¹ models. PROGSURF comprises one vegetation layer and three soil layers. Temperature prediction is made by the heat conduction equation in conjunction with the force-restore method. Turbulent heat fluxes are parameterized by gradient laws using the resistance concept. The formula for the canopy surface resistance involves both a parameter describing atmospheric demand and one describing moisture availability. Soil moisture prediction is made with Richards' equation. PROGSURF is tested in off-line mode for the Cabauw data set. The observed annual mean values of the state and flux quantities at the earth's surface are well reproduced. For example, the model yields latent and sensible heat fluxes of −35.3 and −2.4 W/m², respectively; evapotranspiration and runoff is −449 and 326 mm/yr; and root zone soil moisture content is 0.344 m³/m³. Further, the seasonal changes of water and energy balance components are well simulated. The sensitivity of PROGSURF to the canopy resistance formulation is analysed. We find that the atmospheric demand is largely represented by the saturation value of the evapotranspiration/soil moisture curve with maximum summer impact upon the annual value and further that the moisture availability is represented by the slope of the evapotranspiration curve. Both saturation value and slope control the amplitude of the seasonal fluctuation of the water balance components; at Cabauw site the saturation value is the governing parameter. These results fit satisfactorily into the other PILPS models. In particular, we are able to reproduce with PROGSURF the total variability of most other PILPS models by simply changing the atmospheric demand and soil moisture availability parameters. PROGSURF presently serves to simulate observed surface fluxes for an atmospheric diagnostic model.     

Influence of ice rheology and dust content on the dynamics of the north-polar cap of Mars

The evolution and dynamics of the north-polar cap (residual-ice-cap/layered-deposits complex) of Mars is simulated with a thermomechanical ice-sheet model. We consider a scenario with ice-free initial conditions at 5 Ma before present due to the large obliquities which prevailed prior to this time. The north-polar cap is then built up to its present shape, driven by a parameterized climate forcing (surface temperature, surface mass balance) based on the obliquity and eccentricity history. The effects of different ice rheologies and different dust contents are investigated. It is found that the build-up scenarios require an accumulation rate of approximately 0.15-0.2 mm a⁻¹ at present. The topography evolution is essentially independent of the ice dynamics due to the slow ice flow. Owing to the uncertainties associated with the ice rheology and the dust content, flow velocities can only be predicted within a range of two orders of magnitude. Likely present values are of the order of 0.1-1 mm a⁻¹, and a strong variation over the climatic cycles is found. For all cases, computed basal temperatures are far below pressure melting.     

Solar dynamo models with α ‐effect and turbulent pumping from local 3D convection calculations

Results from kinematic solar dynamo models employing α ‐effect and turbulent pumping from local convection calculations are presented. We estimate the magnitude of these effects to be around 2–3 m s^–1, having scaled the local quantities with the convective velocity at the bottom of the convection zone from a solar mixing‐length model. Rotation profile of the Sun as obtained from helioseismology is applied in the models; we also investigate the effects of the observed surface shear layer on the dynamo solutions. With these choices of the small‐ and large‐scale velocity fields, we obtain estimate of the ratio of the two induction effects, C _α /C _Ω ≈ 10^–3, which we keep fixed in all models. We also include a one‐cell meridional circulation pattern having a magnitude of 10–20 m s^–1 near the surface and 1–2 m s^–1 at the bottom of the convection zone. The model essentially represents a distributed turbulent dynamo, as the α ‐effect is nonzero throughout the convection zone, although it concentrates near the bottom of the convection zone obtaining a maximum around 30° of latitude. Turbulent pumping of the mean fields is predominantly down‐ and equatorward. The anisotropies in the turbulent diffusivity are neglected apart from the fact that the diffusivity is significantly reduced in the overshoot region. We find that, when all these effects are included in the model, it is possible to correctly reproduce many features of the solar activity cycle, namely the correct equatorward migration at low latitudes and the polar branch at high latitudes, and the observed negative sign of B _r B _ϕ . Although the activity clearly shifts towards the equator in comparison to previous models due to the combined action of the α ‐effect peaking at midlatitudes, meridional circulation and latitudinal pumping, most of the activity still occurs at too high latitudes (between 5° … 60°). Other problems include the relatively narrow parameter space within which the preferred solution is dipolar (A0), and the somewhat too short cycle lengths of the solar‐type solutions. The role of the surface shear layer is found to be important only in the case where the α ‐effect has an appreciable magnitude near the surface. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Future desertification and climate change: The need for land-surface system evaluation improvement

In already drought-stressed areas and places with the potential for desertification as a result of greenhouse-induced change, high quality model-derived climate projections are essential for sustainable management. Today's challenge is how to select from the plethora of models and proposed new analyses the tools most likely to be valid for areas already water-stressed and those threatened by future surface moisture reduction. Here, the land-surface skills of models involved in the IPCC Fourth Assessment Report and new techniques of isotopic enrichment of components of evapotranspiration are analyzed. Both are found to have shortcomings. Surprisingly poor reporting of fundamental components of the land-surface system in standard model output was the largest challenge for widely accepted models. We show that very few of a large group (20) of today's climate models report land-surface water and energy budgets correctly in a well-controlled international experiment and that most fail basic conservation tests. Our analysis of a smaller (5) experiment suggests that isotopic techniques employed in arid zone irrigation management may not transition to evaluation and model improvement. Land-surface conditions important for policy are found to be poorly reported which raises questions about equal weighting given by international assessments to all models: good and bad.     

Mid–late Holocene monsoon climate retrieved from seasonal Sr/Ca and δO records of Porites lutea corals at Leizhou Peninsula, northern coast of South China Sea

South China Sea (SCS) is a major moisture source region, providing summer monsoon rainfall throughout Mainland China, which accounts for more than 80% total precipitation in the region. We report seasonal to monthly resolution Sr/Ca and δ¹⁸O data for five Holocene and one modern Porites corals, each covering a growth history of 9–13 years. The results reveal a general decreasing trend in sea surface temperature (SST) in the SCS from 6800 to 1500 years ago, despite shorter climatic cycles. Compared with the mean Sr/Ca–SST in the 1990s (24.8 °C), 10-year mean Sr/Ca–SSTs were 0.9–0.5 °C higher between 6.8 and 5.0 thousand years before present (ky BP), dropped to the present level by 2.5 ky BP, and reached a low of 22.6 °C (2.2 °C lower) by 1.5 ky BP. The summer Sr/Ca–SST maxima, which are more reliable due to faster summer-time growth rates and higher sampling resolution, follow the same trend, i.e. being 1–2 °C higher between 6.8 and 5.0 ky BP, dropping to the present level by 2.5 ky BP, and reaching a low of 28.7 °C (0.7 °C lower) by 1.5 ky BP. Such a decline in SST is accompanied by a similar decrease in the amount of monsoon moisture transported out of South China Sea, resulting in a general decrease in the seawater δ¹⁸O values, reflected by offsets of mean δ¹⁸O relative to that in the 1990s. This observation is consistent with general weakening of the East Asian summer monsoon since early Holocene, in response to a continuous decline in solar radiation, which was also found in pollen, lake-level and loess/paleosol records throughout Mainland China. The climatic conditions 2.5 and 1.5 ky ago were also recorded in Chinese history. In contrast with the general cooling trend of the monsoon climate in East Asia, SST increased dramatically in recent time, with that in the 1990s being 2.2 °C warmer than that 1.5 ky ago. This clearly indicates that the increase in the concentration of anthropogenic greenhouse gases played a dominant role in recent global warming, which reversed the natural climatic trend in East Asian monsoon regime.     

Thermophysical analysis of infrared observations of asteroids

Abstract— Visual photometry, which measures reflected solar radiation, can be combined with infrared radiometry, which measures absorbed and re‐radiated solar energy, to determine key properties of small solar system objects. This method can be applied via thermophysical model concepts not only for albedo and diameter determination, but also for studies of thermal parameters like thermal inertia, surface roughness or emissivity. Hence, a detailed analysis of the asteroid surface is possible and topics like surface mineralogy, the density of the regolith or the presence of a rocky surface, lightcurve influences due to shape or albedo, porosity of the surface material, etc. can be addressed. The “radiometric technique” based on a recently developed thermophysical model is presented. The model was extensively tested against observations from the infrared space observatory, including spectroscopic and photometric measurements at infrared wavelengths between 2 and 200 μm of more than 40 asteroids. The possible model applications are discussed in terms of the different levels of knowledge for individual asteroids. The effects of the thermal parameters are illustrated and methods are presented as to how to separate different aspects. Possibilities and limitations are evaluated for the possible transfer of this model to near‐Earth asteroids. In the long run, this kind of study of near‐Earth asteroids may provide answers to questions about their surface properties which are crucial to develop mitigation scenarios.     

Primordial noble gases in “phase Q” in carbonaceous and ordinary chondrites studied by closed‐system stepped etching

Abstract— The HF/HCI‐resistant residues of the chondrites CM2 Cold Bokkeveld, CV3 (ox.) Grosnaja, CO3.4 Lancé, CO3.7 Isna, LL3.4 Chainpur, and H3.7 Dimmitt have been measured by closed‐system stepped etching (CSSE) in order to better characterise the noble gases in “phase Q”, a major carrier of primordial noble gases. All isotopic ratios in phase Q of the different meteorites are quite uniform, except for (²⁰Ne/²²Ne)_Q. As already suggested by precise earlier measurements (Schelhaas et al., 1990; Wieler et al., 1991, 1992), (²⁰Ne/²²Ne)_Q is the least uniform isotopic ratio of the Q noble gases. The data cluster ～10.1 for Cold Bokkeveld and Lancé and 10.7 for Chainpur, Grosnaja, and Dimmitt, respectively. No correlation of (²⁰Ne/²²Ne)_Q with the classification or the alteration history of the meteorites has been found. The Ar, Kr, and Xe isotopic ratios for all six samples are identical within their uncertainties and similar to earlier Q determinations as well as to Ar‐Xe in ureilites. Thus, an unknown process probably accounts for the alteration of the originally incorporated Ne‐Q. The noble gas elemental compositions provide evidence that Q consists of at least two carbonaceous carrier phases “Q1” and “Q2” with slightly distinct chemical properties. Ratios (Ar/Xe)_Q and (Kr/Xe)_Q reflect both thermal metamorphism and aqueous alteration. These parent‐body processes have led to larger depletions of Ar and Kr relative to Xe. In contrast, meteorites that suffered severe aqueous alteration, such as the CM chondrites, do not show depletions of He and Ne relative to Ar but rather the highest (He/Ar)_Q and (Ne/Ar)_Q ratios. This suggests that Q1 is less susceptible to aqueous alteration than Q₂. Both subphases may well have incorporated noble gases from the same reservoir, as indicated by the nearly constant, though very large, depletion of the lighter noble gases relative to solar abundances. However, the elemental ratios show that Q₁ and Q₂ must have acquired (or lost) noble gases in slightly different element proportions. Cold Bokkeveld suggests that Q₁ may be related to presolar graphite. Phases Q₁ and Q₂ might be related to the subphases that have been suggested by Gros and Anders (1977). The distribution of the ²⁰Ne/²²Ne ratios cannot be attributed to the carriers Q₁ and Q₂. The residues of Chainpur and Cold Bokkeveld contain significant amounts of Ne‐E(L), and the data confirm the suggestion of Huss (1997) that the ²²Ne‐E(L) content, and thus the presolar graphite abundances, are correlated with the metamorphic history of the meteorites.     

Subsurface temperature—depth profiles, anomalies due to climatic ground surface temperature changes or groundwater flow effects

Climatic temperature changes at the ground surface propagate downward to the subsurface creating transient disturbances to the temperature—depth (T(z)) profile. Due to the poor thermal diffusivity of rocks the disturbances are preserved long times in the bedrock, and in a conductive regime it is possible to reveal the ground surface temperature (GST) history from borehole temperature data with inversion techniques. Geothermal temperature measurements thus provide a source of palaeoclimatic information which so far has not been utilized extensively. Inversion of GST history is, however, not straightforward and any disturbing effects should be excluded before the data can be utilized in inversion. Groundwater flow is of special importance in this respect because it is a common phenomenon in bedrock and convection often produces temperature—depth profiles resembling those affected by palaeoclimatic GST changes. In interpreting temperature—depth (T(z)) logs it is therefore not always clear whether the recorded vertical gradient variations should be attributed to the effects of palaeoclimatic ground surface temperature (GST) changes or to groundwater circulation. Using several synthetic T(z) profiles and applying general least squares inversion techniques we simulate a situation of “misinterpreting” the curvature of the T(z) profile in terms of palaeoclimatic GST changes, although it is actually produced by convective heat transfer due to groundwater flow. For comparison the opposite case is also studied, namely, genuine palaeoclimatic effects are misinterpreted as being due to disturbances caused by groundwater flow. A homogeneous half-space model is used to model T(z) profiles disturbed conductively by GST changes during the time interval 10–10000 yr B.P. and a one-dimensional porous layer model is applied for convective heat transfer calculations. The results indicate that a given T(z) profile can be attributed to either of these effects with reasonable parameter values. In addition to the synthetic T(z) profiles, a case history from a 958 m deep drill hole at Lavia, southwestern Finland, is presented. Special care is needed in analyzing T(z) data. A knowledge of geothermal data, such as temperature, thermal conductivity and diffusivity is not necessarily adequate for determining which of the phenomena (or whether a combination of them) provides the most probable interpretation of a T(z) profile. Additional information on the hydrogeological properties of the drilled strata is essential.