Hemisphere Temperature Research Articles

Changes in Northern Hemisphere temperature variability shaped by regional warming patterns

Global warming involves changes not only in the mean atmospheric temperature, but also in its variability and extremes. Here, we use a feature-tracking technique to investigate the dynamical contribution to temperature anomalies in the Northern Hemisphere in climate-change simulations from the Coupled Model Intercomparison Project – Phase 5 (CMIP5). We develop a simple theory to explain how temperature variance and skewness changes are generated dynamically from mean temperature gradient changes, and demonstrate the crucial role of regional warming patterns in shaping the distinct response of cold and warm anomalies. We also show that skewness changes must be taken into account, in addition to variance changes, to correctly capture the projected temperature variability response. Our findings suggest that the world may experience not only a warmer mean climate in the coming decades, but also changes in the likelihood of temperature anomalies within that climate. Regional warming patterns control temperature variance and skewness changes in the Northern Hemisphere, suggests analysis of tracked temperature anomalies.

Multiplicative error model on northern hemispheric volcanic sulfate and European temperature anomalies

It is generally accepted that volcanic eruptions may have a climatic impact involving overall cooling of the troposphere, as the sulfur injected into the stratosphere is transformed into sulfate. However, it is intrinsically difficulty to distinguish this impact because of natural climate variability. In this paper, we look for a relationship between sulfate in the Northern Hemisphere (NH) and European temperature during the last 500 years using two independent data sets: stratospheric sulfate retrieved from ice cores and European seasonally and annually averaged temperature. Relationships between temperature and sulfate are obtained as a function of the season (summer and winter) and location (tropics vs extra‐tropics) one and two years after the sulfate record year. After one year, we always find a negative correlation in the winter for both tropical and extra‐tropical eruptions. A correlation value of ‐0.56 is obtained for the relationship between sulfate and annually averaged temperature anomalies after one year, and a linear regression predicts a cooling of 1 °C for an eruption of 100 Tg of sul‐ fate, an amount similar to that estimated to have been emitted by the Laki eruption in 1783.The variability of the cooling effect after one year is evaluated by introducing a multiplicative error model for sulfate that accounts for sys‐ tematic as well as random errors in retrieved sulfate. To evaluate the impact of sulfate uncertainties on the regression slope, a resampling approach with 104 simulations is applied. Results indicate that when uncertainties in sulfate are introduced, the variability of cooling is in the order of several 10‐3 °C/Tg. Temperature anomaly uncertainties impact slope uncertainty but have little influence on slope variability.

How Does Temperature Vary Over Time?: Evidence on the Stationary and Fractal Nature of Temperature Fluctuations

SummaryThe paper analyses temperature data from 96 selected weather stations world wide, and from reconstructed northern hemisphere temperature data over the last two millennia. Using a non-parametric test, we find that the stationarity hypothesis is not rejected by the data. Subsequently, we investigate further properties of the data by means of a statistical model known as the fractional Gaussian noise (FGN) model. Under stationarity FGN follows from the fact that the observed data are obtained as temporal aggregates of data generated at a finer (basic) timescale where temporal aggregation is taken over a ‘large’ number of basic units. The FGN process exhibits long-range dependence. Several tests show that both the reconstructed and most of the observed data are consistent with the FGN model.

Effects of B2O3 on Melting Characteristics and Temperature-Dependent Viscosity of High-Basicity CaO-SiO2-FeOx-MgO Slag.

In order to reduce the amount of fluorite during the steelmaking process for environmental protection, it is essential to investigate the fluorine-free slag system. Thus, high-basicity CaO–SiO2–FeOx–MgO slag with B2O3 content from 0% to 15% was designed, and its melting characteristics and viscosity were investigated. The influence of B2O3 content on the phase diagram of the slag system was calculated using FactSage 7.3, and the break temperature was determined from the curves of temperature-dependent viscosity. The results show that, with the increase in B2O3 content, the melting characteristics of the CaO–SiO2–FeOx–MgO/B2O3 slag system, including liquidus temperature, flow temperature, softening temperature, and hemispheric temperature, all decreased; the main phase of the slag system transformed from Ca2SiO4 into borosilicate, and finally into borate; the viscous flow activation energy reduced from 690 kJ to 130 kJ; the break temperature reduced from 1590 °C to 1160 °C. Furthermore, the melting characteristics and the break temperature of the slag system with 5% and 8% B2O3 content were found to be the closest to the values of fluorine-containing steel slag.

Evaluation of ash composition and deposition tendencies of biomasses and torrefied products from woody and shrubby feedstocks: SRC poplar clones and common broom

This work intended to compare ash composition and deposition tendencies biomasses and of torrefied products of SRC poplar clones and common broom. These biomasses were assessed in a previous study as these delivering torrefied products with better fuel quality. Ash analysis for quantification of inorganic major and minor ash elements of biomasses and torrefied products was performed with an inductively coupled plasma- optical emission spectrometer (ICP-OES). The ash melting profiles were experimentally determined. These results allowed the calculation of empirical indexes for evaluation of slagging and fouling tendencies. Independence was established between torrefaction dynamics properties such as mass loss, fixed carbon, volatiles and ash inorganic components for biomasses and torrefied products and with physical–chemical deposition indexes. Results showed that biomasses and torrefied products of common broom and in a lesser extent of AF2 and AF8 poplar clones were prone to a silicate melt induced slagging pattern, whilst the other poplar clones’ feedstocks should exhibit an alkali induced slagging profile. Correlation analysis showed different patterns of interconnectedness of ash elements and physical properties for biomasses and torrefied products. For example, initial deformation, hemispheric and flow temperature and alkali indexes were shown with higher relevance for characterization of slag/foul tendencies in biomasses and ash fusibility index, although fundamental for both feedstocks, were more influenced by oxides in torrefied biomasses. In non-torrefied products the major interaction of temperature indexes was observed with alkali indexes. The two databases generated in this work on ash composition and properties of biomasses and torrefied products can contribute to planning of research actions on biomass torrefaction as a tool for upgrading of solid biofuel qualities.

Late Holocene monsoon precipitation changes in southern China and their linkage to Northern Hemisphere temperature

Observations and models suggest a latitudinal redistribution of precipitation as a result of ongoing global climatic warming. However, the dynamic link between temperature and regional precipitation in the course of natural climatic variability during the current interglacial period remains unclear, especially in the monsoon regions of China. Here we present a reconstruction of a ∼5 year-resolution summer monsoon rainfall record for the past 3200 years, based on 622 pairs of δ18O and δ13C and 29 230Th dates from a stalagmite (Wu37) from Wulu Cave in southern China. A close similarity between the δ18O and δ13C records on centennial to decadal timescales suggests that calcite δ18O is most likely a proxy associated with monsoon precipitation. The record reveals that the Little Ice Age (650 - 100 yr B.P.) was a relatively humid period, with two centennial-scale wet events, compared with the Medieval Warm Period (1050 - 650 yr B.P.). In contrast with previous observations in India and northern China, monsoon precipitation variations indicated by our record and other cave records nearby were inversely related to changes in Northern Hemisphere (NH) temperature over the past two millennia, in particular to variations in the thermal gradient between the Northern and Southern hemispheres. This suggests that NH temperature has an important influence on summer precipitation in southern China, via the interhemispheric thermal gradient and land-ocean thermal contrast. In addition, we find that variations of monsoon rainfall in southern China on multi-centennial to centennial timescales are inversely correlated with observed rainfall in the core monsoon region of India and in the northern fringe of the Asian summer monsoon region in China. This spatial pattern of rainfall variability can be interpreted as a result of the migration of the intertropical convergence zone that is likely dominated by the interhemispheric thermal gradient via cross-equatorial airflows.

Prediction of rice straw ash fusion behaviors and improving its ash fusion properties by layer manure addition

As rice straw has high levels of SiO2 and alkali metals, which tend to form low temperature eutectics during thermo-conversion, by blending Ca-rich biomass, the ash fusion behavior of rice straw may be improved. Ash fusion behavior could not be measurable online, it can be beneficial to use a quickly measured ash composition and predict the ash fusion behavior instantly. In this study, the ash fusibility prediction of rice straw-based ash composition and the effect of Ca-containing layer manure addition on rice straw ash fusibility were investigated. Several significant correlations between ash fusion temperatures of rice straw and ash composition were identified. All the developed equations for AFTs of rice straw ash based on ash composition presented high accuracy with average absolute error < 4%. The deformation and softening temperature of rice straw increased more than 200 °C after adding the layer manure. The layer manure was beneficial for improving rice straw ash fusion characteristics and could replace chemical additives, combing the improved effect of both P and Ca on the ash fusion temperatures. Together with the improvement for the deformation, softening, hemispherical, and flow temperatures of rice straw ash, the 30% mass ration of layer manure could be optimum selection.

CMIP5 Climate Models Overestimate Cooling by Volcanic Aerosols

AbstractWe compare projections of the observed hemispherical mean surface temperature (HadCRUT4.6.0.0) and the ensemble mean of CMIP5 climate models' simulations on a set of standard regression model forcing variables. We find that the volcanic aerosol regression coefficients of the CMIP5 simulations are consistently significantly larger (by 40–49%) than the volcanic aerosol coefficients of the observed temperature. The probability that the observed differences are caused just by chance is much less than 0.01. The overestimate is due to the climate models' response to volcanic aerosol radiative forcing. The largest overestimate occurs in the winter season of each hemisphere. We hypothesize that the models' parameterization of aerosol‐cloud interactions within ice and mixed phase clouds is a likely source of this discrepancy. Furthermore, the models significantly underestimate the effect of solar variability on temperature for both hemispheres.

Influence of TiO2 on the melting property and viscosity of Cr-containing high-Ti melting slag

A study on the melting and viscosity properties of the chromium-containing high-titanium melting slag (CaO-SiO2-MgO-Al2O3-TiO2-Cr2O3) with TiO2 contents ranging from 38.63wt% to 42.63wt% was conducted. The melting properties were investigated with a melting-point apparatus, and viscosity was measured using the rotating cylinder method. The FactSage 7.1 software and X-ray diffraction, in combination with scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS), were used to characterize the phase equilibrium and microstructure of chromium-containing high-titanium melting slags. The results indicated that an increase in the TiO2 content led to a decrease in the viscosity of the chromium-containing high-titanium melting slag. In addition, the softening temperature, hemispheric temperature, and flowing temperature decreased with increasing TiO2 content. The amount of crystallized anosovite and sphene phases gradually increased with increasing TiO2 content, whereas the amount of perovskite phase decreased. SEM observations revealed that the distribution of the anosovite phase was dominantly influenced by TiO2.

Estimating the influence of thermal inertia and feedbacks in the atmosphere–ocean system on the variability of global surface temperature

The present climate is characterized not only by the trend due to the increase in the concentrations of greenhouse gases in the atmosphere, but also by fluctuations covering a wide range of frequencies and scales. The global climate variability, calculated via the computational results from the Coupled Model Intercomparison Project Phase 5 of the World Climate Research Program, show significant inter-model differences. In particular, inter-model distinctions in decadal anomalies of the global and hemispheric temperatures reach four times the value. However, unlike the inter-model differences in climate sensitivity, the reasons for a wide range of estimates of climate variability are still unclear. Based on the two-component energy-balance stochastic model, the paper analyzes the inter-annual and inter-decadal variability of the mean global surface temperature (GST) to feedback and the thermal inertia of the atmosphere-ocean system, assuming that the external forcing is random fluctu-ations of the radiation balance at the top of the atmosphere. Using the obtained ab-solute and relative sensitivity functions, the influence of thermal inertia and feed-backs in the climate system on the inter-annual and inter-decimal variability (variance) of the GST and its spectrum is estimated.

Midlatitude Southern Hemisphere Temperature Change at the End of the Eocene Greenhouse Shortly Before Dawn of the Oligocene Icehouse

AbstractThe Eocene‐Oligocene transition (EOT) marked the initiation of large‐scale Antarctic glaciation. This fundamental change in Cenozoic climate state is recorded in deep‐sea sediments by a rapid benthic foraminiferal δ18O increase and appearance of ice‐rafted debris in the Southern Ocean. However, we know little about the magnitude of cooling associated with the EOT in shallow water environments, particularly at middle to high latitudes. Here we present new stratigraphic records of the C13r/C13n magnetochron boundary and the EOT in the clay‐rich Blanche Point Formation, South Australia. The Blanche Point Formation was deposited in a shallow shelf setting (water depths of &lt;100 m) at a paleolatitude of ~51°S. We present high‐resolution δ18O, δ13C, and Mg/Ca records of environmental change from well‐preserved benthic foraminifera of latest Eocene age at this site. A marked, negative δ13C excursion occurs immediately before EOT Step 1 and may be a globally representative signal. An ~2 °C cooling of shallow shelf seawater is evident from benthic foraminiferal Mg/Ca across Step 1. This cooling signal is both sufficient to account fully for the δ18O increase in our data and is of similar amplitude to that documented in published records for shallow shelf and upper water column open ocean settings, which suggests no obvious polar amplification of this cooling signal. Our results strengthen the evidence base for attributing EOT Step 1 to global cooling with little contribution from ice volume growth and contradict the mechanism suggested to explain the inferred northward migration of the intertropical convergence zone in the contemporaneous equatorial Pacific Ocean.

Contribution of SST change to multidecadal global and continental surface air temperature trends between 1910 and 2013

The global mean surface air temperature (GMST) shows multidecadal variability over the period of 1910–2013, with an increasing trend. This study quantifies the contribution of hemispheric surface air temperature (SAT) variations and individual ocean sea surface temperature (SST) changes to the GMST multidecadal variability for 1910–2013. At the hemispheric scale, both the Goddard Institute for Space Studies (GISS) observations and the Community Earth System Model (CESM) Community Atmosphere Model 5.3 (CAM5.3) simulation indicate that the Northern Hemisphere (NH) favors the GMST multidecadal trend during periods of accelerated warming (1910–1945, 1975–1998) and cooling (1940–1975, 2001–2013), whereas the Southern Hemisphere (SH) slows the intensity of both warming and cooling processes. The contribution of the NH SAT variation to the GMST multidecadal trend is higher than that of the SH. We conduct six experiments with different ocean SST forcing, and find that all the oceans make positive contributions to the GMST multidecadal trend during rapid warming periods. However, only the Indian, North Atlantic, and western Pacific oceans make positive contributions to the GMST multidecadal trend between 1940 and 1975, whereas only the tropical Pacific and the North Pacific SSTs contribute to the GMST multidecadal trend between 2001 and 2013. The North Atlantic and western Pacific oceans have important impacts on modulating the GMST multidecadal trend across the entire 20th century. Each ocean makes different contributions to the SAT multidecadal trend of different continents during different periods.

Estimating the Influence of Thermal Inertia and Feedbacks in the Atmosphere–Ocean System on the Variability of the Global Surface Air Temperature

The modern climate of our planet is characterized not only by a trend caused by an increase in the concentration of greenhouse gases in the atmosphere, but also by fluctuations covering a wide range of frequencies and scales. The global climate variability based on the modeling results of the Coupled Model Intercomparison Project Phase 5 of the World Climate Research Program is characterized by significant differences between models. In particular, for the decadal-scale anomalies of the global and hemispheric temperatures, the standard deviation differences between models are as high as fourfold. However, in contrast to the differences in climate sensitivity between models, the causes of a wide range of the estimates of climate variability are still not entirely understood. The research in this paper is based on two-component energy-balance stochastic model. We analyze the sensitivity of interannual and interdecade variability of the mean global surface temperature (GST) to the feedback and thermal inertia of the atmosphere–ocean system under the assumption that the main external forcing factor is random fluctuations of the radiation balance at the upper boundary of the atmosphere. We estimate the influence of thermal inertia and feedback in the climate system on the interannual and interdecade variability (variance) of the GST and the spectrum of its fluctuations using the absolute and relative sensitivity functions derived in the research.

Nonlinear response of Northern Hemisphere stratospheric polar vortex to the Indo\u2013Pacific warm pool (IPWP) Ni\xf1o

Variations in tropical sea surface temperatures (SST) have pronounced impacts on the stratospheric polar vortex, with the role of El Niño being the focus of much research interest. However, the Indo–Pacific warm pool (IPWP), which is the warmest body of seawater in the world, has received less attention. The IPWP has been warming in recent years. This paper presents for the first time the remarkable nonlinearity in Northern Hemisphere (NH) stratospheric circulation and temperature response to IPWP warming (the so-called IPWP Niño) in boreal winter. The magnitude of NH stratospheric vortex weakening is strong and significant in case of moderate IPWP Niño, but is weak and insignificant in strong IPWP Niño case. This phenomenon is robust in both the historical simulations and observations. An idealized model experiments forced with linear varying SST forcing in the IPWP region isolate the nonlinearities arising from IPWP Niño strength. Westward extension of precipitation into the Maritime Continent drives attenuation and westward shift of extratropical waves during strong IPWP Niño events. Linear wave interference analysis reveals this leads to weak interference between the climatological and anomalous stationary waves and thereby a weak response of the stratospheric vortex. These findings imply a distinct stratospheric vortex response to the IPWP Niño, and provide extended implications for the surface climate in the NH.

Characterizing late Quaternary lake-level variability in Lago de Tota, Colombian Andes, with CHIRP seismic stratigraphy

Geophysical analysis of lacustrine sediment stratigraphy at Lago de Tota (Tota), Boyaca, Colombia provided evidence for significant lake-level fluctuations through the late Quaternary and produced a record that potentially spans the last 60 ka. CHIRP data collected in 2015 from this large, high-elevation lake in the Eastern Cordillera of the northern hemisphere Colombian Andes reveal a series of off-lap and on-lap sequences in the upper ~ 20 m of the lake’s sediment column that indicate large amplitude changes in lake level. Because 14C dated sediment cores are only available for the upper 3 m of the sediment column, known Holocene sedimentation rates were extrapolated in order to assign preliminary ages to the off-lap and on-lap sequence boundaries below 3 m depth. These data suggest that lake levels at Tota were lower than present during marine isotope stage (MIS) 4 between 60 and 57 ka, relatively high during MIS 3 between 57 and 29 ka, fell to their lowest levels during MIS 2 between 29 and 14 ka, and gradually rose to the modern high stand through a series of transgressions during MIS 1 and the Holocene from ~ 14 ka to the present. These fluctuations are broadly consistent with trends observed in other lake-level reconstructions from the northern (in phase) and southern (out of phase) hemisphere Andes, possibly supporting the idea that millennial-to-orbital-scale South American hydroclimate variability is linked to shifts in the mean latitude of the intertropical convergence zone due to the influence of insolation- and ocean circulation-driven hemispheric temperature gradients during glacial/stadial and interglacial/interstadial events. Although additional geochronological data will be needed to better resolve the timing of the Tota lake-level changes and their relationships with other records, these preliminary results from Tota, as well as the presence of a thick (> 300 m) sedimentary archive, indicate that this site has significant potential to produce high-resolution, quantitative, paleo-hydroclimate data spanning much of the last 1 million years. Because geophysical surveys and long paleoclimate records from northern hemisphere South America are exceedingly rare, these data provide critical insight into regional hydroclimate trends through the Late Quaternary. Additional work, such as the collection of sediment cores spanning the depth interval represented in the CHIRP data, is required, however, in order to place firmer chronological constraints on the hypothesized timing of lake-level fluctuations at Tota and to investigate their paleo-hydroclimatic implications.

Viscosity and Structure of a CaO-SiO2-FeO-MgO System during a Modified Process from Nickel Slag by CaO.

There is a high iron content in nickel slag that mainly exists in the fayalite phase. Basic oxide can destroy the stable structure of fayalite which is beneficial to the treatment and comprehensive utilization of nickel slag. The research was based on the composition of the raw nickel slag, taking the CaO-SiO2-FeO-MgO system as the object and CaO as a modifier. The effect of basicity on the melting characteristics, viscosity and structure of the CaO-SiO2-FeO-MgO system was studied. The relationship between the viscosity and structure of the CaO-SiO2-FeO-MgO system was also explored. The results show as follows: (1) When the basicity is lower than 0.90, the primary phase of the slag system is olivine phase. When the basicity is greater than 0.90, the primary phase of the slag system transforms into monoxide. When the basicity is 0.90, olivine and monoxide precipitate together as the temperature continues to decrease. At the same time, the liquidus temperature, softening temperature, hemispherical temperature, and flow temperature all reach the lowest value. (2) With the increase of basicity, the critical viscosity temperature of the CaO-SiO2-FeO-MgO system decreases first and then increases. Critical viscosity temperature is the lowest at the basicity of 0.90, which is 1295 °C. (3) When the slag system is heterogeneous, the viscosity of the molten slag increases rapidly because of the quantity of solid phase precipitated from the CaO-SiO2-FeO-MgO system. (4) When the slag system is in a homogeneous liquid phase, the molar fraction of O0 decreases with the increase of basicity and the mole fraction of O−, and O2− increases continuously at the basicity of 0.38~1.50. The silicate network structure is gradually depolymerized into simple monomers, resulting in the degree of polymerization, and the viscosity, being reduced. The mole fraction of different kinds of oxygen atoms is converged to a constant value when the basicity is above 1.20.

A major hydrobiological change in Dasht-e Arjan Wetland (southwestern Iran) during the late glacial – early Holocene transition revealed by subfossil chironomids

The late glacial – early Holocene transition is a key period in the earth’s history. However, although this transition is well studied in Europe, it is not well constrained in the Middle East and palaeohydrological records with robust chronologies remain scarce from this region. Here we present an interesting hydrobiological record showing a major environmental change occurring in the Dasht-e Arjan Wetland (southwestern Iran, near to Persepolis) during the late glacial – early Holocene transition (ca. 11 650 years cal BP). We use subfossil chironomids (Insecta: Diptera) as a proxy for hydrological changes and to reconstruct lake-level fluctuations. The Arjan wetland was a deep lake during the Younger Dryas marked by a dominance of Chironomus plumosus/anthracinus-type, taxa adapted to anoxic conditions of deep waters. At the beginning of the Holocene, a drastic decrease (more than 80% to less than 10%) of Chironomus plumosus/anthracinus-type, combined with diversification of littoral taxa such as Polypedilum nubeculosum-type, Dicrotendipes nervosus-type, and Glyptotendipes pallens-type, suggests a lake-level decrease and a more vegetalized aquatic environment. We compare and contrast the chironomid record of Arjan with a similar record from northwestern Iran. The palaeoclimatic significance of the record, at a local and regional scale, is subsequently discussed. The increase in Northern Hemisphere temperatures, inferred by geochemical data from NGRIP, at the beginning of the Holocene best explains the change from the Younger Dryas highstand to early Holocene lowstand conditions in the Dasht-e Arjan wetland. However, a contribution of the meltwater inflow from small local glaciers in the catchment basin is not excluded.

Searching for solar-like interannual to bidecadal effects on temperature and precipitation over a Southern Hemisphere location

Precipitation and temperature over Tucuman (26.8°S, 65.2°W), a province located in the Northwestern region of Argentina, is analyzed for the interval 1889–2018 in search of any plausible statistical associations with impacts and responses from solar variability. The aim of the study was to contribute data to the controversial issue of climate variations in response to both anthropogenic and natural forcings. The long-term behavior of Tucuman climatic series involves overall warming and augmented precipitation tendencies, possibly linked to the increasing greenhouse gases concentration or even other local man-made factors like increasing urbanization. In addition, we identified sporadic ~4 and ~8-year periodicities, and a ~20-year oscillation after the 1950–1960's. Based on the physical hint that bidecadal periodicities detected in climate parameters are probably not linked to the solar 11-year-like irradiance cycles, we expand our scope of investigations to include another effect which has been recently considered in the dynamics of large rivers as “the planetary hypothesis of the solar cycles”. This new hypothesis supposes that the barycentric dynamics of the Sun could be involved in modulations of the intrinsic solar magnetic and radiative output cycles and therefore Earth-bound climatic responses. Thus, we present a wide-ranging statistical analysis of correlation, cross spectrum, and coherence between Tucuman's climatic series and solar orbital parameters, including also the analysis of hemispheric mean temperatures. Our results show significant coherence at the ~20-year cycle, which is clearly present in the Sun's barycentric dynamic that could in turn be linked to some features of the quasi-decadal solar activity variations.

Orbital controls on Namib Desert hydroclimate over the past 50,000 years

Abstract Despite being one of the world’s oldest deserts, and the subject of decades of research, evidence of past climate change in the Namib Desert is extremely limited. As such, there is significant debate regarding the nature and drivers of climate change in the low-latitude drylands of southwestern Africa. Here we present data from stratified accumulations of rock hyrax urine that provide the first continuous high-resolution terrestrial climate record for the Namib Desert spanning the past 50,000 yr. These data, spanning multiple sites, show remarkably coherent variability that is clearly linked to orbital cycles and the evolution and perturbation of global boundary conditions. Contrary to some previous predictions of southwestern African climate change, we show that orbital-scale cycles of hydroclimatic variability in the Namib Desert region are in phase with those of the northern tropics, with increased local summer insolation coinciding with periods of increased aridity. Supported by climate model simulations, our analyses link this to variations in position and intensity of atmospheric pressure cells modulated by hemispheric and land-sea temperature gradients. We conclude that hydroclimatic variability at orbital time scales is driven by the combined influence of direct low-latitude insolation forcing and the influence of remote controls on the South Atlantic anticyclone, with attendant impacts on upwelling and sea-surface temperature variations.

The role of residual char on ash flow behavior, Part 2: Effect of SiO2/Al2O3 on ash fusibility and carbothermal reaction

SiO2/Al2O3 weight ratio (Si/Al) in the ash content is always regarded as the key factor on ash fouling and sintering in the gasifier, and residual char is often found in gasification slag. The effect of Si/Al on the fusibility of ash containing different contents of residual char (5–15%) was investigated in this work. The residual char was added into five ash samples with different Si/Al from 1.0 to 3.0. The results show that the residual char content shows a significant effect on the AFTs and the fusion temperature range (ΔT = FT-DT) when the Si/Al of the ash is higher than 1.0, especially for the ash with more than 10% residual carbon. Carbothermal reaction products (SiC and Fe3Si) have obvious influence on hemispherical temperature and flow temperature of ash with a high Si/Al. For the ash with Si/Al of 1.0, anorthite, corundum and mullite are the major minerals at high temperatures, and formation of SiC and Fe3Si shows a slight effect on the ash fusion temperatures. However, there are less anorthite and SiO2 at high temperatures in the ashes with Si/Al of 2.0 and 3.0. Besides, Si/Al mainly affects the formation of SiC, while it does not influence formation of Fe3Si. The formation rate of SiC in ash with Si/Al = 2.0 is slower than that of the ash with Si/Al = 1.0 and Si/Al = 3.0. Furthermore, it demonstrates that a high amorphous content and less SiO2 in the ash are detrimental to carbothermal reaction (3C + SiO2 = SiC + 2CO).