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Understanding how and when aerosols are transported to the Arctic is crucial to evaluating the contribution of remote aerosol emissions on Arctic Amplification. Climate models show large discrepancies in long-range aerosol transport, significantly impacting estimates of local aerosol-driven forcing at the Arctic. Long-range aerosol transport is intimately linked to moisture transport. Aerosol transport is generally high during periods of low precipitation (i.e. low wet scavenging) and strong temperature inversions (with low vertical mixing). But studies have shown the importance of intense moisture intrusion events for moisture transport, with almost 30% of total annual moisture being transported during these intervals. These events are associated with warm, cloudy moist air transport that leads to strong downwelling longwave radiation and warm surface temperatures at the Arctic. Notably, the blocking patterns established during these events also give rise to favourable conditions for long-range aerosol transport from the mid-latitudes. Here, we use two reanalysis datasets – Copernicus Atmospheric Monitoring Service (CAMS) and Modern-Era Retrospective analysis for Research and Application (MERRA-2) – to investigate moisture and aerosol transport into the Arctic for a 20-year period. We present a comparison of the relative importance of intrusion events to the total annual moisture transport into to the Arctic during intrusion events for the two different datasets and whether aerosols correlate with these moisture intrusions. This comparison can advance our understanding of aerosol transport to the Arctic and improve the representation of seasonal cycle of aerosols in climate models. Finally, we investigate whether changes in aerosol transport during these events could have led to significant changes in local forcing at the Arctic.

The Arctic atmosphere is warming rapidly and its relatively pristine environment is sensitive to the long-range transport of atmospheric pollutants. While carbon dioxide is the main cause for global warming, short-lived climate forcers (SLCFs) such as methane, ozone, and particles also play a role in Arctic climate on near-term time scales. Atmospheric modelling is critical for understanding the abundance and distribution of SLCFs throughout the Arctic atmosphere, and is used as a tool towards determining SLCF impacts on climate and health in the present and in future emissions scenarios. In this study, we evaluate 18 state-of-the-art atmospheric and Earth system models, assessing their representation of Arctic and Northern Hemisphere atmospheric SLCF distributions, considering a wide range of different chemical species (methane, tropospheric ozone and its precursors, black carbon, sulfate, organic aerosol, and particulate matter) and multiple observational datasets. Model simulations over four years (2008–2009 and 2014–2015) conducted for the 2021 Arctic Monitoring and Assessment Programme (AMAP) SLCF assessment report are thoroughly evaluated against satellite, ground, ship and aircraft-based observations. The results show a large range in model performance, with no one particular model or model type performing well for all regions and all SLCF species. The multi-model mean was able to represent the general features of SLCFs in the Arctic, though vertical mixing, long-range transport, deposition, and wildfire emissions remain highly uncertain processes. These need better representation within atmospheric models to improve their simulation of SLCFs in the Arctic environment.

Clean air policies can have significant impacts on climate in remote regions. Previous modeling studies have shown that the temperature response to European sulfate aerosol reductions is largest in the Arctic. Here, we investigate the atmospheric and ocean roles in driving this enhanced Arctic warming using a set of fully‐coupled and slab‐ocean simulations (specified ocean heat convergence fluxes) with the Norwegian Earth system model (NorESM), under scenarios with high and low European aerosol emissions relative to year 2000. We show that atmospheric processes drive most of the Arctic response. The ocean pathway plays a secondary role inducing small temperature changes mostly in the opposite direction of the atmospheric response. Important modulators of the temperature response patterns are changes in sea‐ice extent and subsequent turbulent heat flux exchange, suggesting that a proper representation of Arctic sea‐ice and turbulent changes are key to predicting the Arctic response to mid‐latitude aerosol forcing.

Modeling studies have shown that changes in sulphate aerosol emissions from both Europe and North America can have an impact on remote Arctic climate. The bulk of this response is driven by atmospheric changes, rather than through changes in meridional ocean heat transport. However, these simulations have focused on the Arctic response from an equilibrium perspective; i.e. the simulations are run for 200 years and the analyses are based on means of the last 50 years. While these simulations are useful to analyze the extent of contribution of mid-latitude aerosol emission changes, they cannot be used to investigate the mechanistic processes that initiate and drive the high-latitude response. We approach this problem by conducting two sets of initial condition ensemble simulations with >30 members for each set and focus our analysis on the first 30 years. Having a large number of ensemble members improves the signal-noise ratio and allows us to distinguish the model response to emission changes from internal variability. In the first set of simulations (control set), the aerosol emissions are set to year 2000. In the second set of simulations (perturbed set), we increase the European sulphate aerosol emissions to seven times the year 2000 value. We compare the two sets of simulations to evaluate the dynamical response of the atmosphere to the change in aerosol emissions. One of the key parameters that link the mid- and high-latitudes in the equilibrium response is the change in sea-ice area in the sub-polar latitudes. Reduced sea-ice coverage and greater open ocean area with lower mid-latitude aerosol emissions leads to increased ocean-atmosphere energy exchange and impacts the atmospheric meridional heat and energy budgets in the Arctic. We present the extent and seasonality of sea-ice changes for the first 30 years of our ensemble simulations and discuss their implications in the context of the mechanistical links between the mid- and high-latitudes.

We thank NERC grant NE/N006828/1 for providing funds for the first DeepMIP meeting in Boulder, Colorado, USA, in January 2016. Daniel J. Lunt acknowledges the NERC grant “Cretaceous–Paleocene–Eocene: Exploring Climate and Climate Sensitivity” (NE/K014757/1), and advanced ERC grant “The Greenhouse Earth System” (T-GRES, project reference 340923), awarded to Rich Pancost. Matthew Huber acknowledges funding from NSF OCE-0902882. Michiel L. J. Baatsen, Henk A. Dijkstra, and Anna S. von der Heydt acknowledge support by the Netherlands Earth System Science Centre (NESSC), financially supported by the Ministry of Education, Culture and Science (OCW), 024.002.001. Past warm periods provide an opportunity to evaluate climate models under extreme forcing scenarios, in particular high (> 800ppmv) atmospheric CO2 concentrations. Although a post hoc intercomparison of Eocene (∼ 50 Ma) climate model simulations and geological data has been carried out previously, models of past high-CO2 periods have never been evaluated in a consistent framework. Here, we present an experimental design for climate model simulations of three warm periods within the early Eocene and the latest Paleocene (the EECO, PETM, and pre-PETM). Together with the CMIP6 pre-industrial control and abrupt 4 × CO2 simulations, and additional sensitivity studies, these form the first phase of DeepMIP-the Deep-time Model Intercomparison Project, itself a group within the wider Paleoclimate Modelling Intercomparison Project (PMIP). The experimental design specifies and provides guidance on boundary conditions associated with palaeogeography, greenhouse gases, astronomical configuration, solar constant, land surface processes, and aerosols. Initial conditions, simulation length, and output variables are also specified. Finally, we explain how the geological data sets, which will be used to evaluate the simulations, will be developed. Publisher PDF

The growth of Tibetan Plateau is considered to have played a key role during the evolution of Asian climate. Our understanding of the relationship between the plateau growth and Asian climate changes is limited, however, due to the scarcity of well-dated sedimentary sequences that could provide parallel information of the evolution of elevation and climate. Here, we report a high-resolution time series record of the stable hydrogen isotopic composition of leaf-wax n -alkanes ( δ D n - alk ) from a continuous Neogene stratigraphic sequence (15–1.8 Ma) from the Qaidam basin on the northern Tibetan Plateau. These data are used to reconstruct the isotopic composition of meteoric waters ( δ D m ) and subsequently applied to interpret the history of paleotopography and climate in Qaidam. Our results indicate four stages in the evolution of hydrology in the Qaidam basin. In Stage I (15 Ma to 10.4 Ma), δ D m gradually decreases from − 24.9 ‰ to − 75.5 ‰ , synchronous with a period of active tectonism. The estimated topographic growth of 2.1 ± 0.3 km is comparable to the height of Qaidam basin relative to the foreland Hexi Corridor. We note that C 3 plants were dominant in this region since the Miocene; we take this as independent evidence that this area was mountainous before the C 4 expansion in late Miocene and Pliocene. δ D m variability in subsequent stages appears to be related to shifts in dry and moist conditions and independent of topographical changes — a conclusion supported by other independent climatic records on the Tibetan Plateau. High δ D m values in Stage II (10.4 Ma to 6.9 Ma) are related to severe aridity, and Stage III (6.9 Ma to 4.1 Ma) is marked by low δ D m values, suggestive of moist conditions related to the strengthening East Asia Summer Monsoon. High δ D m values in Stage IV (4.1 Ma to 1.8 Ma) reflect a climate, drier than the present.

Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX86 values (reproducibility +/- 3-4 degrees C when translated to temperature) but a large spread in BIT measurements (reproducibility +/- 0.41 on a scale of 0-1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3 to 3.0 degrees C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the true (i.e., molar-based) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values.

Past warm periods provide an opportunity to evaluate climate models under extreme forcing scenarios, in particular high (> 800 ppmv) atmospheric CO2 concentrations. Although a post-hoc intercomparison of Eocene (~50 million years ago, Ma) climate model simulations and geological data has been carried out previously, models of past high-CO2 periods have never been evaluated in a consistent framework. Here, we present an experimental design for climate model simulations of three warm periods within the latest Paleocene and the early Eocene. Together these form the first phase of DeepMIP – the deeptime model intercomparison project, itself a group within the wider Paleoclimate Modelling Intercomparison Project (PMIP). The experimental design consists of three core paleo simulations and a set of optional sensitivity studies. The experimental design specifies and provides guidance on boundary conditions associated with palaeogeography, greenhouse gases, orbital configuration, solar constant, land surface parameters, and aerosols. Initial conditions, simulation length, and output variables are also specified. Finally, we explain how the geological datasets, which will be used to evaluate the simulations, will be developed.

article i nfo Article history: High-resolution geochemical analyses of the Lower Eocene Contessa Road section (Italy) reveal orbitally controlled ! uctuations in the percent concentration of calcium carbonate (wt.% CaCO3) that include the ETM2 (Elmo) and ETM3 ("X") hyperthermal events. Patterns of increased dissolution, negative carbon isotope excursions, and warmer global climates are intimately linked to maxima in insolation, through the global carbon cycle. Extraction of short- and long-eccentricity orbital periodicities of the wt.% CaCO3 record provides a relative cyclochronologyfortheintervalrangingfrom! 52to! 55.5 Ma.TheContessaRoadsectioniseasilyaccessibleand offers a continuous integrated stratigraphic record (stable isotopes, standard calcareous plankton biostrati- graphy, magnetostratigraphy, and cyclostratigraphy), thus providing a potential type succession for the study of Early Eocene hyperthermals.

The atmospheric transport and fate of ammonia (NH3) depend on both meteorological and chemical conditions once it is emitted into the atmosphere. The largest source contributing to NH3 emission is the agricultural production, in particular animal operation, in North Carolina (NC). In this study, three-dimensional numerical meteorological and air quality models are applied to study the transport and fate of NH3 in the atmosphere in an area in southeast US centered over NC. One summer and one winter month simulations with a 4-km horizontal grid were conducted to simulate the meteorological and chemical environments for the transport and transformation of the reduced nitrogen, NHx (=NH3+NH4+) and to examine its seasonal variations and interactions with other chemical species (e.g., ozone and fine particular matter, PM2.5). The model performance for simulated meteorology and air quality was evaluated against observations in terms of spatial distributions, temporal variations, and statistical trends. MM5/CMAQ gave an overall good performance for meteorological variables and O3 mixing ratios and a reasonably good performance for PM2.5. The simulations show that 10–40% of total NH3 was converted to NH4+ at/near source and 40–100% downwind in August, and the conversion rates were 20–50% at/near source and 50–98% downwind in December. While the 3-D atmospheric models demonstrate some skills in capturing synoptic meteorological patterns, diurnal variations of concentrations of oxidants and PM2.5, and regional transport and transformation of NHx, reproducing meteorological and chemical features at a local scale and the magnitudes of hourly concentrations of oxidants and PM2.5 remain challenging due to uncertainties in model inputs and treatments.

Agricultural air quality is an important emerging area of atmospheric sciences that represents significant challenges in many aspects of research including measurements, modeling, regulations, emission control, and operation managements. This work presents a review of current status, major challenges, and future research needs and opportunities of several important aspects of agricultural air quality modeling including chemical species, concentration and deposition measurements for model verification, emission inventories, major physical and chemical processes, model application and evaluation, and policy implications.

Paired assessments of carbon (δ 13 C lipids ) and hydrogen isotopic compositions of leaf-wax lipids (δ 2 H lipids ) from warm intervals in Earth’s history have been used to investigate the relationship between greenhouse gases, hydrological cycle and global warming. Modern studies, however, show that δ 2 H lipids can exhibit significant variability due to secondary factors including differences in biosynthetic fractionation and 2 H enrichments in soil- and leaf-water. To evaluate the intrabasinal variability of sedimentary compound specific isotopic records, we generated new carbon and hydrogen isotopic compositions of leaf wax lipids for the Paleocene–Eocene Thermal Maximum (PETM; ∼55 Ma) from Cicogna Creek (Belluno Basin, northern Italy), and compared results with published PETM records from the proximal Forada Creek section. Similar isotopic trends are observed at both localities. The magnitude of the negative carbon isotope excursion at Cicogna is ∼2.5‰. Pre-event 2 H enrichment recorded in the Forada section is missing at Cicogna, likely due to a disturbed interval at the Paleocene–Eocene boundary. A 2 H depletion of ∼10–15‰ during the body of the PETM at Cicogna is observed in several PETM sections, implicating a primary change in the global hydrological cycle. Given the proximity of Cicogna and Forada, isotopic compositions of paleo-meteoric water are expected to be similar. However, a ∼15‰ offset between the records is apparent. Possible reasons include differences in vegetation, biomarker transport and precipitation altitude, underscoring the complexity of using a single record for zonal reconstructions and data model comparisons. Ultimately, this study shows that while 2 H/ 1 H trends can be applied for paleoclimate analysis with reasonable certainty, absolute magnitudes can be biased by secondary local factors.

Earth's modern climate, characterized by polar ice sheets and large equator-to-pole temperature gradients, is rooted in environmental changes that promoted Antarctic glaciation ~33.7 million years ago. Onset of Antarctic glaciation reflects a critical tipping point for Earth's climate and provides a framework for investigating the role of atmospheric carbon dioxide (CO(2)) during major climatic change. Previously published records of alkenone-based CO(2) from high- and low-latitude ocean localities suggested that CO(2) increased during glaciation, in contradiction to theory. Here, we further investigate alkenone records and demonstrate that Antarctic and subantarctic data overestimate atmospheric CO(2) levels, biasing long-term trends. Our results show that CO(2) declined before and during Antarctic glaciation and support a substantial CO(2) decrease as the primary agent forcing Antarctic glaciation, consistent with model-derived CO(2) thresholds.

The Paleocene–Eocene Thermal Maximum is characterized by a massive perturbation of the global carbon cycle reflected in a large, negative carbon isotope excursion associated with rapid global warming and changes in the hydrologic system. The magnitude of the carbon isotope excursion from terrestrial carbonates and organic carbon is generally larger relative to marine carbonates. However, high-resolution marine and terrestrial isotopic records from the same locality for direct comparison are limited. Here we present coupled carbon isotope records from terrestrial biomarkers (δ13Cn-alkane), marine bulk carbonates (δ13Ccarbonate), and bulk organic carbon (δ13Corganic) from the continuous sedimentary record of the Forada section in northern Italy in order to evaluate the magnitude and phase relationships between terrestrial and marine environments. Consistent with previous reports, we find that the carbon isotope excursion established from δ13Cn-alkane values is more negative than those established from δ13Ccarbonate and δ13Corganic values. In contrast to the majority of PETM records, all Forada δ13C records show a sharp 13C-enrichment immediately following the onset of the carbon isotope excursion. Further, the terrestrial δ13Cn-alkane record lags δ13Ccarbonate/δ13Corganic trends by ~ 4–5 kyr—offsets that reflect the long residence time of soil organic carbon. Hydrogen isotope records from higher-plant leaf waxes (δDn-alkane) and sea-surface temperatures (TEX86) were established to assess hydrologic and ocean temperature trends. We find δDn-alkane values trend more positive, associated with higher temperatures prior to the onset of the carbon isotope excursion, and conclude that regional changes in the hydrologic cycle likely occurred before the onset of the carbon isotope anomaly.

Hot Tropical Explosion The Paleocene-Eocene Thermal Maximum (PETM), 55 million years ago, was a unique episode of rapid global warming (∼5°C), often used as an ancient analog for future global climate change. Climate alteration during the PETM has been extensively studied in the marine realm, and from a few temperate to polar terrestrial localities, but little is known about how the tropics responded to the high temperatures and high levels of CO 2 . Using evidence from pollen analysis, Jaramillo et al. (p. 957 ) show that rapid tropical forest diversification occurred during the PETM, without plant extinction or regional aridity. Unexpectedly, diversity seemed to increase at higher temperatures, contradicting previous assumptions that tropical flora will succumb if temperatures become excessive.

Gate insulator/stack scaling is arguably one of the most challenging aspects of device scaling. As gate lengths are scaled into the sub-100 nm regime, alternate materials other than SiO2 will be needed to continue device scaling. The SIA roadmap has called for introduction of high-k materials below the 100 nm technology node due to problems with direct tunneling in SiO2. However, introduction of high-k poses many challenges in the process/materials side in CMOS process integration. Also, there are device scaling issues that are equally important. When k is increased beyond a certain level, unforeseen effects come to play. A phenomenon known as fringing-induced barrier lowering (FIBL) increases Ioff and degrades the subthreshold swing of the device. This paper describes this phenomenon, and provides insight into device scaling with high k materials. A host of other tradeoffs, especially those concerning control of Ioff and speed, are examined using 2-D simulator and analytical models. Suggestions to control FIBL are also detailed.

Fringing-induced barrier lowering (FIBL), a new anomalous degradation in device turn-off/on characteristics in sub-100 nm devices with high-K gate dielectrics, is reported. FIBL is clearly evident for K>25 and worsens as K increases (without buffer oxide). With a buffer oxide, FIBL can be completely suppressed for K