Correction to: Multilevel Graph Partitioning for Three-Dimensional Discrete Fracture Network Flow Simulations

Mathematical Geosciences - The publication of this article unfortunately contained a mistake. The assignment to the affiliations of author Satish Karra was not correct     

Significance of glacio-morphological factors in glacier retreat: a case study of part of Chenab basin,Himalaya

A study has been carried out in part of Chenab basin,Himalaya to understand the relationship between glacio-morphological factors and change in glacial area. Initially change in areal extent of glaciers was derived for two time frames(1962-2001/02 and 2001/02-2010/11). The study comprised of 324 glaciers for the monitoring period of 1962-2001/02 for,which 11% loss in glacial area was observed. Two hundred and thirty-eight glaciers were further monitored between 2001/02 and 2010/11. These glaciers showed an area loss of 1.1%. The annual deglaciation has been found to be higher during the period of 1962-2001/02 compared to 2001/02-2010/11. The spatial and temporal variability in deglaciation was also addressed usingglacio-morphic parameters. Area,length,percentage of debris cover,and various elevation parameters of glaciers were observed to have significant controls on relationships to the rate of glacial shrinkage. Largerarea and longer glaciers show a lower percentage of retreat than smaller and shorter ones. Moreover,glaciers located at lower altitudes and having gentle slopes show more area retreat. The results of area retreat in debris covered and debris free glaciers supports that the glaciers covered by debris retard ice melting at some extent. 158 glaciers were observed having no debris cover,and these exhibit 14% of loss in surface area. In glaciers having 40% debris cover,8% of deglaciation was observed. The glaciers located below equilibrium line altitude(ELA) have experienced 4.6% of deglaciation for the time frame 2001/02 – 2010/11 whereas it was found to be 1.1% for the glaciers occurring above ELA. However,theorientation of glaciers did not show any considerable influence on glacial change based on hypothesis.     

The granulitic impactite suite: Impact melts and metamorphic breccias of the early lunar crust

Abstract— An important and poorly understood group of rocks found in the ancient lunar highlands is called “feldspathic granulitic impactites.” Rocks of the granulite suite occur at most of the Apollo highlands sites as hand samples, rake samples, clasts in breccias, and soil fragments. Most lunar granulites contain 70–80% modal plagioclase, but they can range from anorthosite to troctolite and norite. Previous studies have led to different interpretations for the thermal history of these rocks, including formation as igneous plutons, long-duration metamorphism at high temperatures, and short-duration metamorphism at low temperatures. This paper reports on a study of 24 polished thin sections of lunar granulites from the Apollo 15, 16, and 17 missions. We identify three different textural types of granulitic breccias: poikilitic, granoblastic, and poikilitic-granoblastic breccias. These breccias have similar equilibration temperatures (1100 ± 50 °C), as well as common compositions. Crystal size distributions in two granoblastic breccias reveal that Ostwald ripening took place during metamorphism. Solid-state grain growth and diffusion calculations indicate relatively rapid cooling during metamorphism (0.5 to 50 °C/year), and thermal modeling shows that they cooled at relatively shallow depths (<200 m). In contrast, we conclude that the poikilitic rocks formed by impact melting, whereas the poikilitic-granoblastic rocks were metamorphosed and may have partially melted. These results indicate formation of lunar granulites in relatively small craters (30–90 km in diameter), physically associated with the impact-melt breccia pile, and possibly from fine-grained fragmental precursor lithologies.     

Possible Impacts of Global Warming on the Hydrology of the Ogallala Aquifer Region

The Ogallala or High Plains aquifer provides water for about 20% of the irrigated land in the United States. About 20 km³ (16.6 million acre-feet) of water are withdrawn annually from this aquifer. In general, recharge has not compensated for withdrawals since major irrigation development began in this region in the 1940s. The mining of the Ogallala has been pictured as an analogue to climate change in that many GCMs predict a warmer and drier future for this region. In this paper we attempt to anticipate the possible impacts of climate change on the sustainability of the aquifer as a source of water for irrigation and other purposes in the region. We have applied HUMUS, the Hydrologic Unit Model of the U.S. to the Missouri and Arkansas-White-Red water resource regions that overlie the Ogallala. We have imposed three general circulation model (GISS, UKTR and BMRC) projections of future climate change on this region and simulated the changes that may be induced in water yields (runoff plus lateral flow) and ground water recharge. Each GCM was applied to HUMUS at three levels of global mean temperature (GMT) to represent increasing severity of climate change (a surrogate for time). HUMUS was also run at three levels of atmospheric CO₂ concentration (hereafter denoted by [CO₂]) in order to estimate the impacts of direct CO₂ effects on photosynthesis and evapotranspiration. Since the UKTR and GISS GCMs project increased precipitation in the Missouri basin, water yields increase there. The BMRC GCM predicts sharply decreased precipitation and, hence, reduced water yields. Precipitation reductions are even greater in the Arkansas basin under BMRC as are the consequent water yield losses. GISS and UKTR climates lead to only moderate yield losses in the Arkansas. CO₂-fertilization reverses these losses and yields increase slightly. CO₂ fertilization increases recharge in the base (no climate change) case in both basins. Recharge is reduced under all three GCMs and severities of climate change.     

An Observational Study of Wind Profiles in the Baroclinic Convective Mixed Layer

A comprehensive planetary boundary-layer (PBL) and synoptic data set is used to isolate the mechanisms that determine the vertical shear of the horizontal wind in the convective mixed layer. To do this, we compare a fair-weather convective PBL with no vertical shear through the mixed layer (10 March 1992), with a day with substantial vertical shear in the north-south wind component (27 February). The approach involves evaluating the terms of the budget equations for the two components of the vertical shear of the horizontal wind; namely: the time-rate-of-change or time-tendency term, differential advection, the Coriolis terms (a thermal wind term and a shear term), and the second derivative of the vertical transport of horizontal momentum with respect to height (turbulent-transport term). The data, gathered during the 1992 STorm-scale Operational and Research Meteorology (STORM) Fronts Experiments Systems Test (FEST) field experiment, are from gust-probe aircraft horizontal legs and soundings, 915-MHz wind profilers, a 5-cm Doppler radar, radiosondes, and surface Portable Automated Mesonet (PAM) stations in a roughly 50 × 50 km boundary-layer array in north-eastern Kansas, nested in a mesoscale-to-synoptic array of radiosondes and surface data.We present evidence that the shear on 27 February is related to the rapid growth of the convective boundary layer. Computing the shear budget over a fixed depth (the final depth of the mixed layer), we find that the time-tendency term dominates, reflecting entrainment of high-shear air from above the boundary layer. We suggest that shear within the mixed layer occurs when the time-tendency term is sufficiently large that the shear-reduction terms – namely the turbulent-transport term and differential advection terms – cannot compensate. In contrast, the tendency term is small for the slowly-growing PBL of 10 March, resulting in a balance between the Coriolis terms and the turbulent-transport term. Thus, the thermal wind appears to influence mixed-layer shear only indirectly, through its role in determining the entrained shear.     

Complexly zoned chromium‐aluminum spinel found in situ in the Allende meteorite

Abstract— In addition to the Mg‐, Al‐, ¹⁶O‐rich spinels that are known to occur in refractory inclusions, the Murchison meteorite contains Cr‐rich, ¹⁶O‐poor spinels, most of whose sources are unknown because they are rarely found in situ. Here we report the in situ occurrence in Allende of Cr‐rich spinels, found in 13 chondrules and 4 “olivine‐rich objects”. The Allende spinels exhibit major and minor element contents, isotopic compositions, and zoning of Cr₂O₃ contents like those of the Cr‐spinels from Murchison. Some chondrules contain patchy‐zoned spinel (Simon et al., 1994), which suggests that such grains did not form by sintering but perhaps by formation of overgrowths on relic grains. Unlike the olivine‐rich objects, phases in all three chondrules that were analyzed by ion microprobe have uniform, near‐normal O‐isotopic compositions. One olivine‐rich object, ALSP1, has a huge (1 mm) fragment of chevron‐zoned spinel. This spinel has near‐normal O‐isotopic compositions that are quite distinct from those of adjacent forsteritic olivine, which are relatively ¹⁶O‐rich and plot on the calcium‐aluminum‐inclusion (CAI) line, like some isolated forsterite grains found in Allende. The spinel and olivine in this object are therefore not genetically related to each other. Another olivine‐rich object, ALSP11A, contains a rectangular, 150 ×s 100 μm, homogeneous spinel grain with 50 wt% Cr₂O₃ and 23 wt% FeO in a vuggy aggregate of finer‐grained (5–90 μm), FeO‐rich (Fo_47–55) olivine. The magnesian core of one olivine grain has a somewhat ¹⁶O‐rich isotopic composition like that of the large spinel, whereas the FeO‐rich olivine is relatively ¹⁶O‐poor. The composition of the spinel in ALSP11A plots on the CAI line, the first Cr‐rich spinel found to do so. Chevron‐zoned spinel has not been observed in chondrules, and it is unlikely that either ALSP1 or ALSP11A were ever molten. Calculations show that a spinel with the composition of that in ALSP1 can condense at 1780 K at a P^tot of 10^?3 atm and a dust/gas ratio of 100 relative to solar. The Cr‐rich spinel in ALSP11A could condense at ～1420 K, but this would require a dust/gas enrichment of 1000 relative to solar. The data presented here confirm that, as in Murchison, the coarse Cr‐rich spinels in Allende are relatively ¹⁶O‐depleted and are isotopically distinct from the ¹⁶O‐enriched MgAl₂O₄ from CAIs. Sample ALSP11A may represent a third population, one that is Cr‐rich and plots on the CAI line. That the O‐isotopic composition of ALSP1 is like those of Cr‐rich spinels from chondrules indicates that O‐isotopic compositions cannot be used to distinguish whether grains from such unequilibrated objects are condensates or are fragments from a previous generation of chondrules.     

Infrasonic tracking of large bubble bursts and ash venting at Erebus Volcano,Antarctica

Explosive degassing at Erebus Volcano produces infrasound that can be used to locate, characterize, and quantify eruptive activity from multiple vents. We use a three element distributed microphone network to pinpoint eruption sources and track the activity at the prominent vents through time. Eruptive mechanisms for both source types are analyzed in conjunction with the telemetered time-synced video imagery. We identify two commonly active vents corresponding to the large (often > 10-m diameter) bubble bursts at the free surface of a persistent phonolitic lava lake (‘Ray Lake’), and the less frequent ash-rich eruptions from a constricted vent (‘Active Vent’) located ∼ 80 m from the lava lake. During a 3-month study interval from 6 January to 13 April 2006 we identified and mapped more than 350 eruptive sources from the lava lake and 20 sources from the ash vent. Lava lake events are characterized by high-amplitude infrasonic transients that reflect rapid (less than a few s) acceleration and rupture of magma bubble films followed by an explosion of pressurized gases. Precise infrasonic localization of the lava lake events to accuracies of a few m indicates variable bubble source locations across a 40 by 50-m region spanning the lava lake. Spatial variability is corroborated by the video data. In contrast, degassing from the ash vent produces longer-duration (tens of s), lower amplitude transients that reflect diminished impulsivity and an extended degassing duration, features that are corroborated by video. Because infrasound networks can operate continuously in all weather conditions and during both diurnal and seasonal polar darkness, and are easily incorporated into automatic processing, they significantly contribute to the completeness and quantification of eruption catalogues for Erebus.     

Mechanisms of lateral and linear extension of gullies (dongas) in a subhumid grassland of South Africa

The formation of deep gullies (called ‘dongas’ locally) in rangeland in KwaZulu-Natal Province in South Africa is a natural phenomenon. These U-shaped, very wide gullies have considerable lateral expansion due to the episodic collapse of sidewalls. The dongas have developed in duplex soils such as Luvisols and Lixisols formed on Permian sedimentary rocks or unconsolidated Quaternary colluvium. This study combined morphological, mineralogical and chemical characterization with measurements of grain-size content, structural stability and the complete shrinkage curve to detect changes in soil properties of the different horizons located in the gully banks. The different soil horizons present clear and sharp differences in physical and mineralogical properties. The topsoil with complete grass cover is very resistant to soil detachment. However, the leached E horizon and the BC horizon have low structural stability. The soil profile down to and including the Bt horizon contains exclusively illite in the clay fraction, while the BC colluvial layer and the C horizon (mudstone) contain expandable interstratified illite–smectite. The Bt horizon has a high water content at saturation and high shrinkage, while the BC and C horizons have a high residual shrinkage and a very low water content at saturation. Because this type of gully expansion is not significantly linked to slope value or the stream power index (SPI) at the gully head, to land-use change, high rainfall intensities or the threshold of concentrated runoff being exceeded at the gully head, other causes were investigated. It was concluded that the heterogeneity between horizons with different mineralogical properties and structural stabilities, soil types and parent material, anisotropic water-saturation and shrink-swell properties are of major importance. This heterogeneity between different soil horizon morphologies and their physical properties can explain why the relationship between the critical slope and the drainage area for gully initiation showed a threshold for gullying much lower than that found elsewhere. © 2020 John Wiley & Sons, Ltd.     

The Representation of Tropospheric Water Vapor Over Low-Latitude Oceans in (Re-)analysis: Errors,Impacts, and the Ability to Exploit Current and Prospective Observations

This paper addresses the representation of lower tropospheric water vapor in the meteorological analyses—fully detailed estimates of atmospheric state—providing the wide temporal and spatial coverage used in many process studies. Analyses are produced in a cycle combining short forecasts from initial conditions with data assimilation that optimally estimates the state of the atmosphere from the previous forecasts and new observations, providing initial conditions for the next set of forecasts. Estimates of water vapor are among the less certain aspects of the state because the quantity poses special challenges for data assimilation while being particularly sensitive to the details of model parameterizations. Over remote tropical oceans observations of water vapor come from two sources: passive observations at microwave or infrared wavelengths that provide relatively strong constraints over large areas on column-integrated moisture but relatively coarse vertical resolution, and occultations of Global Positioning System provide much higher accuracy and vertical resolution but are relatively spatially coarse. Over low-latitude oceans, experiences with two systems suggest that current analyses reproduce much of the large-scale variability in integrated water vapor but have systematic errors in the representation of the boundary layer with compensating errors in the free troposphere; these errors introduce errors of order 10% in radiative heating rates through the free troposphere. New observations, such as might be obtained by future observing systems, improve the estimates of water vapor but this improvement is lost relatively quickly, suggesting that exploiting better observations will require targeted improvements to global forecast models.