The upper limit of glaciation in the Himalayas

On the slopes of Himalayan Mountains there is a reduction and culmination of glaciation at 7000–7200 m asl. The presumed cause for this is that the surface temperatures on these slopes are too low for glaciation. This working hypothesis was verified with temperature measurements using collected infra-red radiation. The regression analysis of the measurements taken in the Mt. Everest region during sunny weather conditions of the post-monsoon season resulted in a 0°C line at 7000–7200 m asl. The coincidence of the 0°C line with the upper limit of glaciation is causally definable with the copula between the function of temperature and snow metamorphism: since it is too cold above 7000–7200 m asl, metamorphism into perennial or galcial ice through settling or sintering is absent or simply too slow. High relief and drifting hinder here the processes of ice-formation through pressure compaction of the dry-snow accumulation caused by molecular diffusion and recrystallization. Above 7200 m only continuous leeward accumulations of shifting snow on wall sections with moderate inclination lead to the formation of seracs. However, glaciation generally ceases at this level. This additionally confirms another study. It has been proven that Himalayan glaciers with catchment areas over 7000 m do not extend further downward than those glaciers whose catchment areas just reach this altitude. A break in balance at 7100 m asl is thereby confirmed, and the upper glacial limit is proven. Above the glacial region a rocky zo ne adjoins with pergelic conditions even in the surface layer. This zone is covered by snow during monsoon season only. Here, the weathering processes take place in an arid environment without thawing and purely by means of temperature variations below 0°C. They could correspond to those occurring on a larger scale on the planets of our solar system.A lowering of the upper glacial limit by at least 660 or 1200 m respectively, analogous to the Pleistocene snow-line depression reconstructed in S Tibet and the Central Himalayas, is assumed during the Ice Age.The author gratefully acknowledges the translation of this paper rendered by Dr. J. A. Hellen, Newcastle-upon-Tyne.     

The petrography of Southern Tibet

Summary Mineralogical investigations of rock samples from the Transhimalaya and Tibetan Himalaya allow the conclusion that during the last glaciations in this area there was long distance glacial transport. The samples from the Mt. Everest group, the highest region of the continental crust, provide an account of the petrological data collected from this area. They depict a juxtaposition of sedimentary series and granitic intrusive bodies and also extreme tectonic action deep into their cystalline structure.     

Simulations of a Line W-based observing system for the Atlantic meridional overturning circulation

In a series of observing system simulations, we test whether the Atlantic meridional overturning circulation (AMOC) can be observed based on the existing Line W deep western boundary array. We simulate a Line W array, which is extended to the surface and to the east to cover the basin to the Bermuda Rise. In the analyzed ocean circulation model ORCA025, such an extended Line W array captures the main characteristics of the western boundary current. Potential trans-basin observing systems for the AMOC are tested by combining the extended Line W array with a mid-ocean transport estimate obtained from thermal wind “measurements” and Ekman transport to the total AMOC (similarly to Hirschi et al., Geophys Res Lett 30(7):1413, 2003). First, we close Line W zonally supplementing the western boundary array with several “moorings” in the basin (Line W-32°N). Second, we supplement the western boundary array with a combination of observations at Bermuda and the eastern part of the RAPID array at 26°N (Line W-B-RAPID). Both, a small number of density profiles across the basin and also only sampling the eastern and western boundary, capture the variability of the AMOC at Line W-32°N and Line W-B-RAPID. In the analyzed model, the AMOC variability at both Line W-32°N and Line W-B-RAPID is dominated by the western boundary current variability. Away from the western boundary, the mid-ocean transport (east of Bermuda) shows no significant relation between the two Line W-based sections and 26°N. Hence, a Line W-based AMOC estimate could yield an estimate of the meridional transport that is independent of the 26°N RAPID estimate. The model-based observing system simulations presented here provide support for the use of Line W as a cornerstone for a trans-basin AMOC observing system.     

Quasi-static and Quasi-dynamic Modeling of Earthquake Failure at Intermediate Scales

We present a model for earthquake failure at intermediate scales (space: 100 m–100 km, time: 100 m/v _shear- 1000’s of years). The model consists of a segmented strike–slip fault embedded in a 3-D elastic solid as in the framework of Ben-Zion and Rice (1993). The model dynamics is governed by realistic boundary conditions consisting of constant velocity motion of the regions around the fault, static/kinetic friction laws with possible gradual healing, and stress transfer based on the solution of Chinnery (1963) for static dislocations in an elastic half-space. As a new ingredient, we approximate the dynamic rupture on a continuous time scale using a finite stress propagation velocity (quasi–dynamic model) instead of instantaneous stress transfer (quasi–static model). We compare the quasi–dynamic model with the quasi–static version and its mean field approximation, and discuss the conditions for the occurrence of frequency-size statistics of the Gutenberg–Richter type, the characteristic earthquake type, and the possibility of a spontaneous mode switching from one distribution to the other. We find that the ability of the system to undergo a spontaneous mode switching depends on the range of stress transfer interaction, the cell size, and the level of strength heterogeneities. We also introduce time-dependent log (t) healing and show that the results can be interpreted in the phase diagram framework. To have a flexible computational environment, we have implemented the model in a modular C++ class library.     

Evaluation of Probe-Induced Flow Distortion of Campbell CSAT3 Sonic Anemometers by Numerical Simulation

The Campbell CSAT3 sonic anemometer is one of the most popular instruments for turbulence measurements in basic micrometeorological research and ecological applications. While measurement uncertainty has been characterized by field experiments and wind-tunnel studies in the past, there are conflicting estimates, which motivated us to conduct a numerical experiment using large-eddy simulation to evaluate the probe-induced flow distortion of the CSAT3 anemometer under controlled conditions, and with exact knowledge of the undisturbed flow. As opposed to wind-tunnel studies, we imposed oscillations in both the vertical and horizontal velocity components at the distinct frequencies and amplitudes found in typical turbulence spectra in the surface layer. The resulting flow-distortion errors for the standard deviations of the vertical velocity component range from 3 to 7%, and from 1 to 3% for the horizontal velocity component, depending on the azimuth angle. The magnitude of these errors is almost independent of the frequency of wind speed fluctuations, provided the amplitude is typical for surface-layer turbulence. A comparison of the corrections for transducer shadowing proposed by both Kaimal et al. (Proc Dyn Flow Conf, 551–565, 1978) and Horst et al. (Boundary-Layer Meteorol 155:371–395, 2015) show that both methods compensate for a larger part of the observed error, but do not sufficiently account for the azimuth dependency. Further numerical simulations could be conducted in the future to characterize the flow distortion induced by other existing types of sonic anemometers for the purposes of optimizing their geometry.     

Assessing parameter identifiability for multiple performance criteria to constrain model parameters

ABSTRACT

Reliable simulations of hydrological models require that model parameters are precisely identified. In constraining model parameters to small ranges, high parameter identifiability is achieved. In this study, it is investigated how precisely model parameters can be constrained in relation to a set of contrasting performance criteria. For this, model simulations with identical parameter samplings are carried out with a hydrological model (SWAT) applied to three contrasting catchments in Germany (lowland, mid-range mountains, alpine regions). Ten performance criteria including statistical metrics and signature measures are calculated for each model simulation. Based on the parameter identifiability that is computed separately for each performance criterion, model parameters are constrained to smaller ranges individually for each catchment. An iterative repetition of model simulations with successively constrained parameter ranges leads to more precise parameter identifiability and improves model performance. Based on these results, a more consistent handling of model parameters is achieved for model calibration.     

Late Quaternary glacier and sea-ice history of northern Wijdefjorden,Svalbard

The deglaciation history and Holocene environmental evolution of northern Wijdefjorden, Svalbard, are reconstructed using sediment cores and acoustic data (multibeam swath bathymetry and sub-bottom profiler data). Results reveal that the fjord mouth was deglaciated prior to 14.5±0.3 cal. ka BP and deglaciation occurred stepwise. Biomarker analyses show rapid variations in water temperature and sea ice cover during the deglaciation, and cold conditions during the Younger Dryas, followed by minimum sea ice cover throughout the Early Holocene, until c. 7 cal. ka BP. Most of the glaciers in Wijdefjorden had retreated onto land by c. 7.6±0.2 cal. ka BP. Subsequently, the sea-ice extent increased and remained high throughout the last part of the Holocene. We interpret a high Late Holocene sediment accumulation rate in the northernmost core to reflect increased sediment flux to the site from the outlet of the adjacent lake Femmilsjøen, related to glacier growth in the Femmilsjøen catchment area. Furthermore, increased sea ice cover, lower water temperatures and the re-occurrence of ice-rafted debris indicate increased local glacier activity and overall cooler conditions in Wijdefjorden after c. 0.5 cal. ka BP. We summarize our findings in a conceptual model for the depositional environment in northern Wijdefjorden from the Late Weichselian until present.     

Reconstruction of an approximately complete Quaternary Tibetan inland glaciation between the Mt. Everest- and Cho Oyu Massifs and the Aksai Chin. A new glaciogeomorphological SE–NW diagonal profile through Tibet and its consequences for the glacial isostasy and Ice Age cycle

Studies were done on new geomorphological and quaternary-geological profiles through representative reliefs of Tibet from the Central Himalaya as far as the Kuenlun. Thus, further detailed investigations on the prehistoric glaciation could be carried out. Youngest historical to neoglacial ice margin positions could be recorded. Their mapping took place in a downward direction from the modern glacier margins. They confirm snow line (ELA) depressions from decametres up to ca. 100–250 m. At distances of several kilometres to many decakilometres (depending on the relief) from the modern glaciers, névé shields and perennial snow fields, end moraines and later just remnants of lateral moraines and kame complexes of the Late Glacial (ca. Stadia IV-II) have been localized in an increasing disrupted succession and samples have been taken. The recorded, inter- and extrapolated lowest ice margin positions allowed the reconstruction of accompanying depressions of the snow line which, due to the altitude of the Tibetan plateau plains, attained a maximum of 400–700 m. Accordingly, the early Late Glacial (Stadia I to II) and High Glacial glacier traces (Riss or pre-LGM and Würm or LGM = Stadia −I and/or 0) occurred over a horizontal distance of 1620 km across the plateau with an average height of 4700 m asl without showing the key forms of ice margin positions. From the profiles introduced here, running from Mt. Everest/Cho Oyu (Central Himalaya) in the SE via Gertse (Kaitse; Central Tibet) as far as the Lingzi Thang and Aksai Chin and from there into the Kuenlun, as well as from a parallel section of the Gurla Mandhata (central S Tibet) to the currently very arid Nako Tso, located centrally in the W, sediment samples have been analysed which provide evidence for a ground moraine genesis. Thus, the macroscopic field observations are confirmed. Only the relatively small basin of Shiquanha (Ali) – like the Indus valley chamber of Leh – may have been free of ice during the High Glacial (LGM). Forms of glacial horns, as well as roches moutonnées and large, several metres-high round-polished mountain ridges with slight debris covers, flank polishings, abraded mountain spurs at intermediate valley ridges and high-lying erratics document the widespread ice cover. Important ice thicknesses of at least 1300–1400 m have been recognized by means of transfluences. Especially by and in the Nako Tso (lake) the limnic undercutting of roches moutonnées provides evidence only of a postglacial filling into a primary glacial relief. The glacial ice cover (with the LGM at the end) testified here for a further area of Tibet, is the foundation of the relief-specific hypothesis on the development of the Ice Ages, based on the global radiation geometry: accordingly, the last great geological event, the early Pleistocene plate-tectonically induced uplift of Tibet above the snow line, has brought about a glaciation which, owing to its high albedo, reflected the subtropical radiation energy into space, so that it could not be exploited for the heating of the atmosphere. This may have triggered the Ice Ages. The repeated interglacial warming-up is to be reduced to the positive radiation anomalies by the variations of the parameters of the earth's orbit – which take place rhythmically – and the overlying glacio-isostatic lowering of Tibet and the other inland ice areas. This revised version was published online in July 2006 with corrections to the Cover Date.     

Neutron star mergers in the context of the hadron–quark phase transition

The long awaited event of the detection of a gravitational wave from a binary neutron star merger and its electromagnetic counterparts marked the beginning of a new era in observational astrophysics. The brand-new field of gravitational wave astronomy combined with multi-messenger observations will uncover violent, highly energetic astrophysical events that could not be explored before by humankind. This article focuses on the presumable appearance of a hadron–quark phase transition and the formation of regions of deconfined quark matter in the interior of a neutron star merger product. The evolution of density and temperature profiles inside the inner region of the produced hypermassive/supramassive neutron star advises an incorporation of a hadron–quark phase transition in the equation of state of neutron star matter. The highly densed and hot neutron star matter of the remnant populate regions in the QCD phase diagram where a non neglectable amount of deconfined quark matter is expected to be present. If a strong hadron–quark phase transition would happen during the post-merger phase, it will be imprinted in the spectral properties of the emitted gravitational wave signal and might give an additional contribution to the dynamically emitted outflow of mass.