Insolation Variations Research Articles

Model-based orbital-scale precipitation δ18O variations and distinct mechanisms in Asian monsoon and arid regions

The past Asian precipitation δ18O (δ18Op) records from stalagmites and other deposits have shown significant orbital-scale variations, but their climatic implications and regional differences are still not fully understood. This study, as the first attempt of a 300-kyr transient stable isotope-enabled simulation, investigated the characteristics and mechanisms of the orbital-scale δ18Op variations in three representative regions of Asia: arid Central Asia (CA), monsoonal South Asia (SA) and monsoonal East Asia (EA). The modelling results showed that the variations in the CA, SA and EA annual δ18Op exhibited significant but asynchronous 23-kyr precession cycles. Further analyses revealed that although the precession-induced insolation variation was the ultimate cause of the δ18Op variation in all three regions, the dominant mechanisms and the involved physical processes were distinct among them. For the CA region, the rainy-season (November-March) temperature effect and water vapour transport by the westerly circulation were identified as the key precession-scale processes linking the October-February boreal mid-latitude insolation to the rainy-season or annual δ18Op. In the SA region, the rainy-season (June-September) precipitation amount effect and upstream depletion of the monsoonal water vapour δ18O served as the main mechanisms linking the rainy-season or annual δ18Op to the April-July insolation variation at the precession scale. For the EA region, however, the precession-scale annual δ18Op was mainly controlled by the late-monsoon (August-September) and pre-monsoon (April-May) water vapour transport patterns, which were driven by the July-August insolation and the global ice volume, respectively. These results suggest that the climatic implications of the orbital-scale Asia δ18Op variations are sensitive to their geographic locations as determined by the combined effects of insolation and regional circulation patterns associated with the respective rainy seasons. This study provides new insights into understanding the regional differences and formation mechanisms of the Asian orbital-scale δ18Op variations.

Holocene environmental change along the central Namib Desert escarpment derived from hyrax and owl dung

Fossil pollen and geochemical sequences from a series of hyrax dung deposits from rock shelters along the eastern margin of the central Namib Desert shed light on the Holocene environmental history of Namibia. Grassy pollen assemblages suggest relatively humid conditions during the early Holocene between ca. 9.6 and 7.7 ka. A series of stepwise changes follows, including the prominence of different pioneer plant communities of which changes in ratios between grassy and shrub pollen types suggests moisture oscillations. The development of more C4 plants around ca. 4.5 ka, as indicated by isotope concentrations and persistent grass pollen percentages, point to the development of a different climatic regime than that in the early Holocene, which extended the area of subtropical savanna towards the south at ca. 24°S. This transition can in part be interpreted as a vegetation response to a shift in the rainfall distribution from an early even seasonal distribution to the current late Holocene summer rainfall regime. Climate changes may have been driven by variations in austral summer and winter solar insolation with changes in total solar irradiance (TSI) superimposed upon them. Through its link to Bond events in the North Atlantic, and thus Atlantic Meridional Overturning Circulation (AMOC), TSI may have affected SSTs in the SE Atlantic and SW Indian Ocean, which influence both summer and winter rainfall in southern Africa.

Environmental and Hydrological Changes of Lake Coatetelco in Central Mesoamerica (Southwest Mexico) Over the Holocene and Comparison With Climatic Forcing

Elemental composition of the inorganic fraction, carbon isotopes, and C/N of organic matter from a new radiocarbon-dated sedimentary sequence collected from Lake Coatetelco (960 m asl) extend information about the environmental and hydrological conditions of central Mesoamerica from the earliest Holocene to the interval of first human settlements in the lake vicinity and nearby streams. Proxy-based reconstructions of erosion/runoff (Ti), water column salinity (CaCO3), sediment–water interactions (PIA), and provenance of organics (δ13Corg and C/N) showed similarities with the summer insolation modulated ITCZ position between ∼11.5 and 4.2 cal ka BP, and more frequent ENSO between ∼4.2 and 2.1 cal ka BP. After a possible depositional hiatus between ∼11.2 and 10.2 cal ka BP, the moderate-to-extremely altered sediments were deposited with enhanced erosion/runoff during the wetter ∼10.2–6 cal ka BP and the organic matter was dominantly autochthonous. Comparison of δ13Corg and C/N suggested that the contribution of C4 plants to organic matter increased over the drier ∼6–4.2 cal ka BP. Sediments representing this middle- Holocene drought-like condition showed geochemical similarity with sediments of the Post-Classic drought (∼1–0.4 cal ka BP), coeval with abandonment of the Xochicalco culture. Variation in seasonal insolation at orbital scales might have forced frequent droughts between ∼6 and 4.2 cal ka BP and the ENSO related short-lived storms possibly led to an unstable hydroclimate after ∼4.2 cal ka BP when the first Olmec settlements commenced in the region. Dissimilarity between this lacustrine archive and speleothems from southwest Mexico for the later part of the Holocene reflected different sensitivities of the geological records to seasonal and-annual precipitation.

Thermal performance enhancement of solar air heater using louvered fins collector

Solar air heater is one of the important device for heating the air which is mainly used for space heating, timber seasoning, crop/vegetable drying, etc.. To improve the performance of solar air collectors, the fin plays an important role to increases the performances. Due to this reason in the present work, a novel type of solar air heater has been constructed with louvered fins and performed experiments to evaluate its thermal performance. The louvered fins have been attached to the bottom of the absorber plate to steer the flowing air and increase the heat transfer rate. To achieve this aim, the solar collector has been designed with the value of louvered angle, louvered length, louvered pitch & height taken to be 20°, 2.5 cm, 2.5 cm, and 3.5 cm, respectively, and conducted experiments with mass flow rate 0.007 kg/s to 0.0158 kg/s. The variations of insolation and fin spacing on the thermal efficiency and temperature rise have been also studied in the present experimental study. The results indicate that thermal efficiency increase with increasing flow rate, for a mass flow rate of 0.0158 kg/s and 0.007 kg/s, thermal efficiency and outlet temperature obtained a maximum of 70% and 58.66 °C respectively for spacing of 2 cm. further, observed that the thermal efficiency of louvered fin spacing 2 cm and 5 cm is higher as compared to plane solar air heater which is 106.7% and 59.45% respectively. The thermal performance of the louvered fins solar air heater is significantly enhanced as compared to that of the plane solar air heater.

Orbital insolation variations, intrinsic climate variability, and Quaternary glaciations

Abstract. The relative role of external forcing and of intrinsic variability is a key question of climate variability in general and of our planet's paleoclimatic past in particular. Over the last 100 years since Milankovic's contributions, the importance of orbital forcing has been established for the period covering the last 2.6 Myr and the Quaternary glaciation cycles that took place during that time. A convincing case has also been made for the role of several internal mechanisms that are active on timescales both shorter and longer than the orbital ones. Such mechanisms clearly have a causal role in Dansgaard–Oeschger and Heinrich events, as well as in the mid-Pleistocene transition. We introduce herein a unified framework for the understanding of the orbital forcing's effects on the climate system's internal variability on timescales from thousands to millions of years. This framework relies on the fairly recent theory of non-autonomous and random dynamical systems, and it has so far been successfully applied in the climate sciences for problems like the El Niño–Southern Oscillation, the oceans' wind-driven circulation, and other problems on interannual to interdecadal timescales. Finally, we provide further examples of climate applications and present preliminary results of interest for the Quaternary glaciation cycles in general and the mid-Pleistocene transition in particular.

Plio-Pleistocene environmental variability in Africa and its implications for mammalian evolution

Understanding the climatic drivers of environmental variability (EV) during the Plio-Pleistocene and EV’s influence on mammalian macroevolution are two outstanding foci of research in African paleoclimatology and evolutionary biology. The potential effects of EV are especially relevant for testing the variability selection hypothesis, which predicts a positive relationship between EV and speciation and extinction rates in fossil mammals. Addressing these questions is stymied, however, by 1) a lack of multiple comparable EV records of sufficient temporal resolution and duration, and 2) the incompleteness of the mammalian fossil record. Here, we first compile a composite history of Pan-African EV spanning the Plio-Pleistocene, which allows us to explore which climatic variables influenced EV. We find that EV exhibits 1) a long-term trend of increasing variability since ∼3.7 Ma, coincident with rising variability in global ice volume and sea surface temperatures around Africa, and 2) a 400-ky frequency correlated with seasonal insolation variability. We then estimate speciation and extinction rates for fossil mammals from eastern Africa using a method that accounts for sampling variation. We find no statistically significant relationship between EV and estimated speciation or extinction rates across multiple spatial scales. These findings are inconsistent with the variability selection hypothesis as applied to macroevolutionary processes.

Renewable energy based charging station with power quality features for multi EV spots using maximum correntropy sub-band adaptive technique

ABSTRACT Here, a photovoltaic (PV)-based multi-spots electric vehicles (EVs) charging station (CS) is presented by using maximum correntropy criteria with affine projection sub-band adaptive filter (MCC-APSAF). The presented CS also includes the features of power quality at nonlinear loads connected at the point of common coupling (PCC). This CS comprises a battery bank, multi-EV batteries, and ultra-capacitor (UC) charging spots. However, a dramatic increase of EVs and charging stations in the existing grid has raised the issues related to the harmonics, voltage fluctuations, reactive power, and burden on the grid. These issues are addressed in the presented charging station. Moreover, the ultra-capacitor can provide fast charging, which minimizes the high inrush current of the CS. Therefore, the batteries during the high EVs load at the CS are protected by the ultra-capacitor spots. To stabilize the DC bus voltage, separate cascaded controllers for ultra-capacitor and battery spots are used. The CS shows the multifunctional capabilities, which include PV array to grid (PV2G), PV array to the EV battery (S2EVB), EV battery to grid (EVB2G), and PV array to home (PV2H) when PV source is present. The various EVB2G, G2EVB, battery to home (EVB2H), and grid to home (G2H) behaviors are also presented. This CS shows good dynamic efficacy under insolation variation, EVB2G, G2EVB modes, load throw, and load reconnection operations. The grid current THD using the proposed current control is 1.44%, which is in accordance with the IEEE-519 standard. Moreover, the maximum power obtained from the PV generation is 63 kW, which is successfully distributed in the battery bank and six EV batteries (30 kW), in nonlinear load (14 kW), and the rest of the power is injected to the grid (29 kW). This CS is simulated in the MATLAB/Simulink library and test results are obtained using the experimental workbench with OPAL-RT (OP5600) in the laboratory.

Asynchronous variations of East Asian summer monsoon, vegetation and soil formation at Yulin (North China) in the Holocene

ABSTRACTIn the East Asian monsoon region, Chinese speleothem δ18O records exhibit a maximum monsoon strength during the early Holocene. However, other proxy data from lakes or loess, interpreted as monsoon rainfall, show a mid‐Holocene monsoon optimum. This discrepancy may come from specific climate interpretation of different proxies. Here we report multiproxy records from a single loess–palaeosol sequence at Yulin in the monsoon marginal northern China, based on an independent and high‐precision chronology. Our long‐chain n‐alkane δD values, together with related biomarker proxies including the average chain length and concentration of long‐chain n‐alkanes, reveal a weakening trend in monsoon strength and less woody vegetation since ~6 ka. However, other soil formation‐related proxies, such as magnetic susceptibility, grain‐size distribution and total organic carbon, show a decreasing trend since 4–3 ka. We find that monsoon and vegetation are controlled by insolation variation, while soil formation is more related to temperature and humidity changes. Our multiple proxy comparison reveals different controlling mechanisms leading to different interpretations in monsoon, vegetation and soil formation reconstructions. This finding suggests that previous debates on Holocene monsoon changes in East Asia probably stem from the specific proxy interpretation.

Optimal planning of solar PV and battery storage with energy management systems for Time‐of‐Use and flat electricity tariffs

This paper determines the optimal capacity of solar photovoltaic (PV) and battery energy storage (BES) with novel rule-based energy management systems (EMSs) under flat and time-of-use (ToU) tariffs. Four schemes are investigated based on the combinations of flat and ToU tariffs for buying and selling the electricity: (1) Flat-Flat, (2) ToU-Flat, (3) Flat-ToU, and (4) ToU-ToU. For each scheme, two configurations are evaluated: (i) PV only, and (ii) PV-BES. The optimization of the grid-connected household is evaluated based on one-year realistic data. An uncertainty analysis is presented based on the variations of insolation, temperature, and load. Sensitivity analyses are implemented based on the average daily load, the grid constraint, and the costs of PV and BES. The operational analyses for 48 h in summer and winter are carried out to evaluate the dynamic performance of the systems for high and low solar insolation. The effectiveness of the proposed model is verified by comparing the results with that of common EMS based on the net metering scheme. It is found that the COE of the proposed EMS for a PV-BES house with ToU-Flat scheme (as the best option) is 2 ¢/kWh lower than that of the net metering scheme.

Orbital controls on eastern African hydroclimate in the Pleistocene

Understanding eastern African paleoclimate is critical for contextualizing early human evolution, adaptation, and dispersal, yet Pleistocene climate of this region and its governing mechanisms remain poorly understood due to the lack of long, orbitally-resolved, terrestrial paleoclimate records. Here we present leaf wax hydrogen isotope records of rainfall from paleolake sediment cores from key time windows that resolve long-term trends, variations, and high-latitude effects on tropical African precipitation. Eastern African rainfall was dominantly controlled by variations in low-latitude summer insolation during most of the early and middle Pleistocene, with little evidence that glacial–interglacial cycles impacted rainfall until the late Pleistocene. We observe the influence of high-latitude-driven climate processes emerging from the last interglacial (Marine Isotope Stage 5) to the present, an interval when glacial–interglacial cycles were strong and insolation forcing was weak. Our results demonstrate a variable response of eastern African rainfall to low-latitude insolation forcing and high-latitude-driven climate change, likely related to the relative strengths of these forcings through time and a threshold in monsoon sensitivity. We observe little difference in mean rainfall between the early, middle, and late Pleistocene, which suggests that orbitally-driven climate variations likely played a more significant role than gradual change in the relationship between early humans and their environment.

Mitigation of Cross-Coupling Effects in PV String-Integrated-Converters Employing SEPIC Converter with P&O MPPT Technique

Photovoltaic (PV) string-integrated-converter (S-I-C) topology allows each PV string to operate at their respective maximum power point (MPP) corresponding to the variations in solar insolation. The S-I-C topology comprises an individual DC–DC converter integrated into each PV string. The output terminals of the S-I-Cs are connected either in the series or parallel configuration. There are certain limitations in each of the series/parallel configured PV S-I-Cs. By employing DC–DC boost converter as an S-I-C, cross-coupling effect is the main limitation of a series configured S-I-Cs. The cross-coupling effect causes the deviation in operating points (MPPs) of the shaded & unshaded PV strings and this leads to power consumption by the boost type S-I-Cs instead of delivering to the load. This article presents the mitigation of cross-coupling effects by employing a single-ended primary inductor converter (SEPIC) as an S-I-C in a series configuration of S-I-Cs. The conventional perturb & observe (P&O) MPPT technique is used to track the maximum power from PV strings. The results of the series configuration of SEPIC converter-based S-I-Cs are compared with the boost converter-based series configuration along with the mathematical analysis under uneven-row, uneven-column, diagonal, and long & narrow shading patterns.

Applied Mathematical Model for Solar Energy Collection and Thermal Storage

Solar thermal storage systems (STSS) are renewable energy systems that provide a continuous, controllable source of heat for many applications. The inherent variability of solar insolation poses a challenge to the use of direct solar power for continuous operations. A dynamic non-linear model of the STSS was initialised via a steady state analysis and verified by drying 1000 kg of cocoa beans per batch from 60% to 8% moisture content. Ambient temperature and insolation data for Trinidad in 2017 were used as inputs. This was achieved by modifying flow rates, varying aspect ratio of the storage tank, and observing their effect on storage tank temperature profiles and drying air temperatures. The steady state analysis determined the tank volume as 12.57 m3 and a required mass airflow rate of 1020 kg/h. A dynamic model of the STSS revealed an optimal tank aspect ratio of 2:4 m (D: H) and that three AE-40 solar collectors were sufficient. The effect of the circulation rate between the storage tank and solar collectors on energy storage was found to be negligible. The need for temperature control was demonstrated and a control strategy developed. A pilot plant was built using recommended specifications, albeit without temperature control. As predicted, drying was more than sufficient, but poor control led to burnt cocoa beans. The application of this work extends well beyond the cocoa bean test case, and the open-source models built can be applied to optimise the design of any solar heating application.

Study of Impact of Meteorological Parameters on Atmospheric Transmittance of Solar Radiation over Jumla

This paper reports the variation of atmospheric transmittance with meteorological parameters over Jumla (Lat.29.28° N, Long.:82.16° E and Alt.: 2300 m above sea level) from2011 to 2013 (three years) by using CMP6 pyranometer and satellite data. The trends of monthly and seasonal variations of atmospheric transmittance, solar insolation and clearness index have been analyzed. The result exemplifies that during the study period, average value of global solar radiation, solar insolation and clearness index are 19.26 ±3.88 MJ/m2/day , 4.95 ± 1.14 kWh/m2/day and 0.59 ±0.12 respectively. The average value of atmospheric transmittance during the whole study period is 0.60 ± 0.11. The average value of atmospheric transmittance of ozone, Rayleigh scattering, gas mixture, water vapor and aerosol are 0.9830 ±0.0007, 0.8999 ±0.0178, 0.9875 ± 0.0007, 0.8839 ±0.0101 and 0.7836 ±0.0909 respectively. There is positive correlation of relative sunshine hour and negative correlation of rain fall with atmospheric transmittance. Result of this research work is beneficial for the further analysis of solar radiation at different places improving life of flora and fauna and protecting the whole environment.

Seasonal variability in temperature trends and atmospheric circulation systems during the Eemian (Last Interglacial) based on n-alkanes hydrogen isotopes from Northern Finland

The Last Interglacial warm period, the Eemian (ca. 130–116 thousand years ago), serves as a reference for projected future climate in a warmer world. However, there is a limited understanding of the seasonal characteristics of interglacial climate dynamics, especially in high latitude regions. In this study, we aim to provide new insights into seasonal trends in temperature and moisture source location, linked to shifts in atmospheric circulation patterns, for northern Fennoscandia during the Eemian. Our study is based on the distribution and stable hydrogen isotope composition (δD) of n-alkanes in a lake sediment sequence from the Sokli paleolake in NE Finland, placed in a multi-proxy framework. The δD values of predominantly macrophyte-derived mid-chain n-alkanes are interpreted to reflect lake water δD variability influenced by winter precipitation δD (δDprec), ice cover duration and deuterium (D)-depleted meltwater. The δD values of terrestrial plant-derived long-chain n-alkanes primarily reflect soil water δD variability modulated by summer δDprec and by the evaporative enrichment of soil and leaf water. The δDprec variability in our study area is mostly attributed to the temperature effect and the moisture source location linked to the relative dominance between D-depleted continental and polar air masses and D-enriched North Atlantic air masses. The biomarker signal further corroborates earlier diatom-based studies and pollen-inferred January and July temperature reconstructions from the same sediment sequence. Three phases of climatic changes can be identified that generally follow the secular variations in seasonal insolation: (i) an early warming trend succeeded by a period of strong seasonality (ii) a mid-optimum phase with gradually decreased seasonality and cooler summers, and (iii) a late climatic instability with a cooling trend. Superimposed on this trend, two abrupt cooling events occur in the early and late Eemian. The Sokli δD variability is generally in good agreement with other North Atlantic and Siberian records, reflecting major changes in the atmospheric circulation patterns during the Eemian as a response to orbital and oceanic forcings.

An energy-autonomous UAV swarm concept to support sea-rescue and maritime patrol missions in the Mediterranean sea

PurposeFor the crews and assets of the European Union’s (EU’s) Joint Operations available today, but a vast area in the Mediterranean Sea to monitor, detection of small boats and rafts in distress can take up to several days or even fail at all. This study aims to outline how an energy-autonomous swarm of Unmanned Aerial System can help to increase the monitored sea area while minimizing human resource demand.Design/methodology/approachA concept for an unattended swarm of solar powered, unmanned hydroplanes is proposed. A swarm operations concept, vehicle conceptual design and an initial vehicle sizing method is derived. A microscopic, multi-agent-based simulation model is developed. System characteristics and surveillance performance is investigated in this delimited environment number of vehicles scale. Parameter variations in insolation, overcast and system design are used to predict system characteristics. The results are finally used for a scale-up study on a macroscopic level.FindingsMiniaturization of subsystems is found to be essential for energy balance, whereas power consumption of subsystems is identified to define minimum vehicle size. Seasonal variations of solar insolation are observed to dominate the available energy budget. Thus, swarm density and activity adaption to solar energy supply is found to be a key element to maintain continuous aerial surveillance.Research limitations/implicationsThis research was conducted extra-occupationally. Resources were limited to the available range of literature, computational power number and time budget.Practical implicationsA proposal for a probable concept of operations, as well as vehicle preliminary design for an unmanned energy-autonomous, multi-vehicle system for maritime surveillance tasks, are presented and discussed. Indications on path planning, communication link and vehicle interaction scheme selection are given. Vehicle design drivers are identified and optimization of parameters with significant impact on the swarm system is shown.Social implicationsThe proposed system can help to accelerate the detection of ships in distress, increasing the effectiveness of life-saving rescue missions.Originality/valueFor continuous surveillance of expanded mission theatres by small-sized vehicles of limited endurance, a novel, collaborative swarming approach applying in situ resource utilization is explored.

Variability of Diffuse Daylight Due to the Diversity of Cloud Arrays

Illuminance modeling that allows us to mimic or even replicate the dynamics of daylight changes is increasingly becoming a challenge for the development of more accurate prediction systems of natural light availability in building interiors or variations of insolation at arbitrarily oriented façades. We demonstrate that illuminance amplitude due to random cloud arrangement can vary over a wide range even when other atmospheric parameters remain unchanged. It follows from our systematic numerical modeling that diffuse illuminance predictions can be significantly improved by incorporating cloud coverage, mean cloud size, and cloud base altitude into daylight models. We show that any model of homogeneous luminance patterns would fail in modeling the illuminance amplitudes we can expect on horizontal and vertical planes under partial cloud coverage with individual clouds distributed randomly. However, these situations occur with high frequency in most of regions worldwide, thus the modeling results we obtained here are of high relevance to daylight modeling and solar energy systems as well.

Variations in seasonal solar insolation are associated with a history of suicide attempts in bipolar I disorder

BackgroundBipolar disorder is associated with circadian disruption and a high risk of suicidal behavior. In a previous exploratory study of patients with bipolar I disorder, we found that a history of suicide attempts was associated with differences between winter and summer levels of solar insolation. The purpose of this study was to confirm this finding using international data from 42% more collection sites and 25% more countries.MethodsData analyzed were from 71 prior and new collection sites in 40 countries at a wide range of latitudes. The analysis included 4876 patients with bipolar I disorder, 45% more data than previously analyzed. Of the patients, 1496 (30.7%) had a history of suicide attempt. Solar insolation data, the amount of the sun’s electromagnetic energy striking the surface of the earth, was obtained for each onset location (479 locations in 64 countries).ResultsThis analysis confirmed the results of the exploratory study with the same best model and slightly better statistical significance. There was a significant inverse association between a history of suicide attempts and the ratio of mean winter insolation to mean summer insolation (mean winter insolation/mean summer insolation). This ratio is largest near the equator which has little change in solar insolation over the year, and smallest near the poles where the winter insolation is very small compared to the summer insolation. Other variables in the model associated with an increased risk of suicide attempts were a history of alcohol or substance abuse, female gender, and younger birth cohort. The winter/summer insolation ratio was also replaced with the ratio of minimum mean monthly insolation to the maximum mean monthly insolation to accommodate insolation patterns in the tropics, and nearly identical results were found. All estimated coefficients were significant at p < 0.01.ConclusionA large change in solar insolation, both between winter and summer and between the minimum and maximum monthly values, may increase the risk of suicide attempts in bipolar I disorder. With frequent circadian rhythm dysfunction and suicidal behavior in bipolar disorder, greater understanding of the optimal roles of daylight and electric lighting in circadian entrainment is needed.

Holocene moisture evolution and its response to atmospheric circulation recorded by aeolian deposits in the southern Tibetan Plateau

The pattern of changes in Holocene moisture conditions in the southern Tibetan Plateau (TP) and the associated driving mechanism are still controversial. Here, we present the results of an analysis of an aeolian sedimentary sequence from the Yarlung Zangbo River valley in the southern TP, which potentially provides a record of changes in moisture conditions during the Holocene, and hence changes in the atmospheric circulation process. Optically stimulated luminescence dating with the single-aliquot regeneration protocol was used to establish the chronology for the sequence, and geochemical and granulometric measurements were used to reconstruct the Holocene moisture history. The results indicate that moisture conditions were strongly influenced by the early Holocene maximum in summer insolation (30°N) and hence by the Indian summer monsoon (ISM), under which the weathering intensity was relatively high. However, at ∼7.6 ka the climate abruptly became drier, probably due to the weakening of the ISM. Subsequently, with the further decrease in summer insolation and increase in winter insolation, the variations in ISM-related moisture delivery to the southern TP were regulated by the enhanced winter mid-latitude Westerlies (MLW), resulting in increasing weathering intensity. Thus, the Holocene evolution of moisture conditions in the southern TP was mainly controlled by changes in the relative intensities of the ISM and the winter MLW, which depended on the variations of summer and winter insolation at 30°N. Overall, our results provide an improved understanding of the driving mechanism of climate change in the southern TP during the Holocene.

Earth’s Albedo and Its Symmetry

AbstractThe properties of Earth's albedo and its symmetries are analyzed using twenty years of space‐based Energy Balanced And Filled product of Clouds and the Earth's Radiant Energy System measurements. Despite surface asymmetries, top of the atmosphere temporally &amp; hemispherically averaged reflected solar irradiance appears symmetric over Northern/Southern hemispheres. This is confirmed with the use of surrogate time‐series, which provides margins of for possible hemispheric differences supported by Clouds and Earth's Radiant System data. time‐series are further analyzed by decomposition into a seasonal (yearly and half yearly) cycle and residuals. Variability in the reflected solar irradiance is almost entirely (99%) due to the seasonal variations, mostly due to seasonal variations in insolation. The residuals of hemispherically averaged are not only small, but also indistinguishable from noise, and thus not correlated across hemispheres. This makes yearly and sub‐yearly timescales unlikely as the basis for a symmetry‐establishing mechanism. The residuals however contain a global trend that is large, as compared to expected albedo feedbacks. It is also hemispherically symmetric, and thus indicates the possibility of a symmetry enforcing mechanism at longer timescales. To pinpoint precisely which parts of the Earth system establish the hemispheric symmetry, we create an energetically consistent cloud‐albedo field from the data. We show that the surface albedo asymmetry is compensated by asymmetries between clouds over extra‐tropical oceans, with southern hemispheric storm‐tracks being 11% cloudier than their northern hemisphere counterparts. This again indicates that, assuming the albedo symmetry is not a result of chance, its mechanism likely operates on large temporal and spatial scales.

Low-latitude forcing: A new insight into paleo-climate changes

Low-latitude forcing: A new insight into paleo-climate changes