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Previous analytical and simulation‐based analyses suggest that deeper land surface models are needed to realistically simulate the terrestrial thermal state in climate models, with implications for land‐atmosphere interactions. Analytical approaches mainly focused on the subsurface propagation of harmonics such as the annual temperature signal, and a direct comparison with climate‐change model output has been elusive. This study addresses the propagation of a harmonic pulse fitted to represent the timescale and amplitude of anthropogenic warming. Its comparison to land model simulations with stepwise increased bottom boundary depth leads to an agreement between the simulation‐based and analytical frameworks for long‐term climate trends. Any depth increase gradually decreases the relative error in the subsurface thermodynamics, and a minimum depth of 170 m is recommended to simulate the ground climate adequately. The approach provides an accurate estimate of the required land‐model depth for climate‐change simulations and assesses the relative bias in insufficiently deep land models. Many current‐generation climate models have land components that are too shallow. Under climate change conditions, the long‐term warming trend at the surface propagates deeper into the ground than the commonly used 3–10 m. Shallow models alter the terrestrial heat storage and distribution of temperatures in the subsurface, influencing the simulated land‐atmosphere interactions. Previous studies focusing on annual timescales suggest that deeper models are required to match subsurface‐temperature observations and the classic analytical heat conduction solution. However, for a systematic investigation of land‐model deepening in the frame of anthropogenic climate change, the classic analytical solution is inaccurate because it does not mimic the timescale and amplitude of the simulated warming trend. This study intends to bridge the gap between analytical and simulation‐based estimates of the subsurface thermodynamic state by adapting the classic analytical framework to mimic long‐term anthropogenic warming. The analysis shows that a land‐model depth of at least 170 m is recommended for a proper simulation of the post‐1850 ground climate, which differs up to 30% from the estimate of the classic approach. Compared to previous studies, this provides an accurate estimate of the required land model depth for long‐term climate‐change simulations and indicates the relative bias in insufficiently deep land models. Heat conduction from analytical and numerical estimates suggests a required land‐model depth of 170 m for climate change simulationsAgreement between numerical and analytical estimates on climate change timescales gives more confidence for the required land‐model depthStepwise land‐model depth increase gradually reduces the relative error of shallow models in climate‐change simulations Heat conduction from analytical and numerical estimates suggests a required land‐model depth of 170 m for climate change simulations Agreement between numerical and analytical estimates on climate change timescales gives more confidence for the required land‐model depth Stepwise land‐model depth increase gradually reduces the relative error of shallow models in climate‐change simulations

A dynamical mechanism of sufficient strength to maintain the stability of the observed annual mean global climate against the destabilizing influence of the positive lower tropospheric water vapour/infrared radiative (WVIR) feedback on SST perturbations has recently been proposed (Bates, 1999). The mechanism consists of an evaporative negative feedback associated with the atmospheric angular momentum (AM) cycle and the surface winds which it induces. The mechanism was found from an analysis of a simple two‐zone model of the climate system. Numerical experiments with an atmospheric GCM aimed at testing the conclusions of the simple model are here described. Aquaplanet boundary conditions with a prescribed latitudinally‐varying SST distribution are adopted. An equinoctial distribution of solar radiation is assumed. An equilibrium climate for the GCM is established and perturbation experiments with a uniform 2 K increase in the SST are carried out. In the equilibrium and basic perturbation experiments, the GCM is run with all fields evolving freely. Further perturbation experiments are then carried out with the cloud fields held fixed, and with both the cloud and water vapour fields held fixed, in the GCM's radiation package. These experiments allow the relative influence of cloud and water vapour in the infrared and solar radiative feedbacks at the surface to be estimated. The results of the experiments are compared with those predicted by the simple model for a similar SST perturbation. The GCM results are found to be consistent with the basic assumptions and conclusions of the simple model. In particular, they indicate that a positive WVIR feedback exists in both the tropical and extratropical zones and confirm the existence of a negative evaporative feedback associated with the AM cycle that is of sufficient strength to overcome it. The experiments support the conclusion based on the simple model that it is necessary to consider both the wind factor and the humidity factor in evaluating the evaporative feedback. The cloud/infrared radiative feedback in the GCM is found to be small compared with the WVIR feedback. The experiments suggest that the feedback resulting from the absorbtion of solar radiation by water vapour (which was not included in the simple model) provides a significant additional stabilizing influence on SST perturbations.

Abstract—An analysis of the distribution of 3He and 4He in L and H chondrites has shown that the parent body of L chondrites underwent a catastrophic collision in space 340 ± 50 Ma ago. This age differs considerably from the collision age of 520 ± 60 Ma given previously (Heymann, 1967). The parent body of H chondrites may also have undergone local heating and degassing ∼200 Ma ago. Data for L chondrites argue in favour of Antarctic and non‐Antarctic meteorites having originated from a common parent body.

This paper presents study of microstructure of the material (tool steel 150Cr14) produced by the selective laser melting (SLM) technology. The chemical composition analysis and grain size measurements of the initial powder tool steel 150Cr14 were performed. The bulk density and flowability of the powder were investigated. Specimens were built under various building parameters such as laser scanning speed and laser power and tested on uniaxial tension. In this study, the effect of the SLM parameters on the mechanical properties of tool steel is investigated. Due to less surface quality limitations of SLM technology compared with conventional production techniques specimens were subjected to set of tests including measurement of surface roughness, inspection of inner structure which are influenced from building parameters.

This work presents the results of research of the impact of layer-by-layer growing of workpieces made of 316L steel on their machinability. The results of determination of residual stresses and measurement of hardness of the workpieces grown have been demonstrated. A series of experimental studies has been performed in order to determine the cutting force which occurs in the process of machining. The microstructure of the workpieces grown has been examined. It has been shown that the workpieces machined using Selective Laser Melting technology have the microstructure which is a totality of 'microwelded seams', which have a significant influence on the behavior of deformation processes in case of machining. The studies have shown that in case of lateral milling of the horizontally grown workpiece, the codirectional microwelded borders prevent any significant deformation of the misalignment which increases the cutting force by up to 10% as compared with milling of the vertically grown workpiece.