Observational evidence of changing cloud macro-physical properties under warming climate over the Indian summer monsoon region

The cloud responses to global warming are captured in various global climate models with distinct inferences on changes in cloud vertical structure as function of surface warming. However, long term observational evidences are scarce to validate the model outputs. Here, we have studied the changes in radiosonde derived cloud macro-physical properties and their association with other atmospheric variables during the period 2000-2019 in response to warming climate over the Indian summer monsoon region. We have observed a statistically significant increase in the frequency of cloudy days (∼13 % decade-1), high-level clouds (HLCs ∼11 % decade-1) and simultaneous decrease in low-level clouds (LLCs ∼8 % decade-1) over the Indian region during the monsoon season. The multiple linear regression, principle component analyses and further correlation analyses suggest significant associations between cloud vertical structure variations and large-scale climate indicators, such as global warming and El Niño-Southern Oscillation. The vertical extension of the tropospheric column and the upward shift of clouds, attributed to global warming, explain the changes observed in both HLCs and LLCs. These results contribute to a deeper understanding of the dynamic interplay between global climate change and regional cloud dynamics, with implications for weather and climate modeling.

Estimation and characterization of atmospheric turbulence in the free atmosphere above the Tibetan Plateau using the Thorpe method

Understanding turbulence in the free atmosphere is important for analyzing atmospheric pollution, forecasting weather, and light transmission. In this paper, we have tried to estimate the atmospheric refractive index structure constant C n2, the turbulent dissipation rate ε, and the turbulent diffusion coefficient K simultaneously during the experiment time over Lhasa, using the sounding data coupled with the Thorpe method. The result shows that the C n2 estimation gives a better performance with the correlation coefficients and the average relative error when compared with C n2 estimated by Dewan and HMNSP99. Besides this, the measured and estimated C n2, estimated ε, and K all show larger values in the troposphere, especially near the tropopause. It is worth noting that C n2 and ε are similar in terms of height distribution. These attempts at estimation all suggest that the Thorpe method can be used to estimate the intensity of turbulence in the free atmosphere over Lhasa.

Physical-Optical Properties of Marine Aerosols over the South China Sea: Shipboard Measurements and MERRA-2 Reanalysis

Aerosols play an important role in the Earth–atmosphere system. Their impacts on the weather and climate are highly dependent on spatiotemporal distributions as well as physical-optical properties. Physical-optical properties of the aerosols over the Asian continent have been widely investigated, but there are relatively few observations in maritime locations, especially the South China Sea (SCS). Here, with the combination of in situ ship-based observations from June and July 2019 as well as long-term MERRA-2 reanalysis datasets from January 2012 to December 2021, the physical and optical properties of marine aerosols in the SCS are explored. The impacts of meteorological factors, particularly frontal systems, on the aerosol properties are further analyzed based on detailed observations. The observed results show that aerosols are vertically concentrated below 3 km and the extinction coefficient reaches the maximum value of 0.055 km−1 near 480 m. Moreover, the particles are composed of an accumulation and a coarse particle mode, and they conform to the lognormal distribution. The synoptic-scale case study demonstrates that both the cold front and stationary front lead to an increase in aerosol optical thickness (AOD), which is due to the enhanced wind speed and the hygroscopic growth of fine particles, respectively. The long-term analysis indicates that AOD decreases from northwest to southeast with the increasing distance away from the continent, and it reflects higher values in spring and winter than in summer and autumn. Sulfate and sea salt dominate AOD in this region when compared with other components. The overall AOD shows a significant negative trend of −0.0027 year−1. This work will help us further understand the physical and optical properties of marine aerosols over the SCS and then contribute to quantifying the aerosol radiative forcing in the future.

In Situ Observations of Interstellar Pickup Ions from 1 au to the Outer Heliosphere

Interstellar pickup ions are an ubiquitous and thermodynamically important component of the solar wind plasma in the heliosphere. These PUIs are born from the ionization of the interstellar neutral gas, consisting of hydrogen, helium, and trace amounts of heavier elements, in the solar wind as the heliosphere moves through the local interstellar medium. As cold interstellar neutral atoms become ionized, they form an energetic ring beam distribution comoving with the solar wind. Subsequent scattering in pitch angle by intrinsic and self-generated turbulence and their advection with the radially expanding solar wind leads to the formation of a filled-shell PUI distribution, whose density and pressure relative to the thermal solar wind ions grows with distance from the Sun. This paper reviews the history of in situ measurements of interstellar PUIs in the heliosphere. Starting with the first detection in the 1980s, interstellar PUIs were identified by their highly nonthermal distribution with a cutoff at twice the solar wind speed. Measurements of the PUI distribution shell cutoff and the He focusing cone, a downwind region of increased density formed by the solar gravity, have helped characterize the properties of the interstellar gas from near-Earth vantage points. The preferential heating of interstellar PUIs compared to the core solar wind has become evident in the existence of suprathermal PUI tails, the nonadiabatic cooling index of the PUI distribution, and PUIs' mediation of interplanetary shocks. Unlike the Voyager and Pioneer spacecraft, New Horizon's Solar Wind Around Pluto (SWAP) instrument is taking the only direct measurements of interstellar PUIs in the outer heliosphere, currently out to ∼ 47 au from the Sun or halfway to the heliospheric termination shock.

Cloud-Top Height Comparison from Multi-Satellite Sensors and Ground-Based Cloud Radar over SACOL Site

Cloud-top heights (CTH), as one of the representative variables reflecting cloud macro-physical properties, affect the Earth–atmosphere system through radiation budget, water cycle, and atmospheric circulation. This study compares the CTH from passive- and active-spaceborne sensors with ground-based Ka-band zenith radar (KAZR) observations at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) site for the period 2013–2019. A series of fundamental statistics on cloud probability in different limited time and areas at the SACOL site reveals that there is an optimal agreement for both cloud frequency and fraction derived from space and surface observations in a 0.5° × 0.5° box area and a 40-min time window. Based on the result, several facets of cloud fraction (CF), cloud overlapping, seasonal variation, and cloud geometrical depth (CGD) are investigated to evaluate the CTH retrieval accuracy of different observing sensors. Analysis shows that the CTH differences between multi-satellite sensors and KAZR decrease with increasing CF and CGD, significantly for passive satellite sensors in non-overlapping clouds. Regarding passive satellite sensors, e.g., Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua, the Multi-angle Imaging SpectroRadiometer (MISR) on Terra, and the Advanced Himawari Imager on Himawari-8 (HW8), a greater CTH frequency difference exists between the upper and lower altitude range, and they retrieve lower CTH than KAZR on average. The CTH accuracy of HW8 and MISR are susceptible to inhomogeneous clouds, which can be reduced by controlling the increase of CF. Besides, the CTH from active satellite sensors, e.g., Cloud Profiling Radar (CPR) on CloudSat, and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), agree well with KAZR and are less affected by seasonal variation and inhomogeneous clouds. Only CALIPSO CTH is higher than KAZR CTH, mainly caused by the low-thin clouds, typically in overlapping clouds.

Reference carbon cycle dataset for typical Chinese forests via colocated observations and data assimilation

Chinese forests cover most of the representative forest types in the Northern Hemisphere and function as a large carbon (C) sink in the global C cycle. The availability of long-term C dynamics observations is key to evaluating and understanding C sequestration of these forests. The Chinese Ecosystem Research Network has conducted normalized and systematic monitoring of the soil-biology-atmosphere-water cycle in Chinese forests since 2000. For the first time, a reference dataset of the decadal C cycle dynamics was produced for 10 typical Chinese forests after strict quality control, including biomass, leaf area index, litterfall, soil organic C, and the corresponding meteorological data. Based on these basic but time-discrete C-cycle elements, an assimilated dataset of key C cycle parameters and time-continuous C sequestration functions was generated via model-data fusion, including C allocation, turnover, and soil, vegetation, and ecosystem C storage. These reference data could be used as a benchmark for model development, evaluation and C cycle research under global climate change for typical forests in the Northern Hemisphere.

Rapid indirect solar responses observed in the lower atmosphere

Establishing clear evidence of solar-induced lower atmosphere effects is hampered by the small 11-year solar cycle responses, typically swamped by meteorological variability. Strong 27-day cyclic changes are exploited here instead. During the 2007/8 minimum in solar activity, regular 27-day lighthouse-like sweeps of energetic particles crossed the heliosphere and Earth, followed by a burst of solar ultraviolet radiation. Averaging the atmospheric responses at UK sites reveals immediate cooling in the troposphere after the peak energetic particle flux, followed by warming in the stratosphere. Regionally, this is accompanied by zonal wind changes, and temperature changes beneath cloud at the same time. Of two possible rapid distinct routes of solar influence—photochemical (through ozone) and atmospheric electrical (through low level clouds)—the ozone route does not provide a phase-locked response but the electrical route is supported by observed phase-locked thickening of low level clouds. These findings have potential value to weather forecasting.

An automated common algorithm for planetary boundary layer retrievals using aerosol lidars in support of the U.S. EPA Photochemical Assessment Monitoring Stations Program

A unique automated planetary boundary layer (PBL) retrieval algorithm is proposed as a common cross-platform method for use with commercially available ceilometers for implementation under the redesigned U.S. Environmental Protection Agency Photochemical Assessment Monitoring Stations program. This algorithm addresses instrument signal quality and screens for precipitation and cloud layers before the implementation of the retrieval methodology using the Haar wavelet covariance transform method. Layer attribution for the PBL height is supported with the use of continuation and time-tracking parameters, and uncertainties are calculated for individual PBL height retrievals. Commercial ceilometer retrievals are tested against radiosonde PBL height and cloud-base height during morning and late afternoon transition times, critical to air quality model prediction and when retrieval algorithms struggle to identify PBL heights. A total of 58 radiosonde profiles were used and retrievals for nocturnal stable layers, residual layers and mixing layers were assessed. Overall good agreement was found for all comparisons with one system showing limitations for the cases of nighttime surface stable layers and daytime mixing layer. It is recommended that nighttime shallow stable layer retrievals be performed with a recommended minimum height or with additional verification. Retrievals of residual layer heights and mixing layer comparisons revealed overall good correlations to radiosonde heights (correlation coefficients, r², ranging from 0.89 - 0.96 and bias ranging from ~ -131 to +63 m, and r² from 0.88 - 0.97 and bias from -119 to +101 m, respectively).

Spatio-temporal discrimination of molecular, aerosol and cloud scattering and polarization using a combination of a Raman lidar, Doppler cloud radar and microwave radiometer

The combined data from the ESA Mobile Raman Polarization and Water Vapor Lidar (EMORAL), the LATMOS Bistatic Doppler Cloud Radar System for Atmospheric Studies (BASTA), and the INOE Microwave Radiometer (HATPRO-G2) have been used to explore the synergy for the spatio-temporal discrimination of polarization and molecular, aerosol and cloud scattering. The threshold-based methodology is proposed to perform an aerosol-cloud typing using the three instruments. It is demonstrated for 24 hours of observations on 10 June 2019 in Rzecin, Poland. A new scheme for target classification, developed collaboratively by the FUW and the OUC, can help determine molecules, aerosol (spherical, non-spherical, fine, coarse), cloud phase (liquid, ice, supercooled droplets) and precipitation (drizzle, rain). For molecular, aerosol, and cloud discrimination, the thresholds are set on the backward scattering ratio, the linear particle depolarization ratio and the backscatter colour ratio, all calculated from lidar signals. For the cloud phase and precipitation categorization, the thresholds are set on the reflectivity and the Doppler velocity derived from cloud radar signals. For boundary layer particles, precipitation, and supercooled droplets separation, the thresholds are set on the profiles of temperature and relative humidity obtained by the microwave radiometer. The algorithm is able to perform separation even under complicated meteorological situation, as in the presented case study.

Non-linear interaction modulates global extreme sea levels, coastal flood exposure, and impacts

We introduce a novel approach to statistically assess the non-linear interaction of tide and non-tidal residual in order to quantify its contribution to extreme sea levels and hence its role in modulating coastal protection levels, globally. We demonstrate that extreme sea levels are up to 30% (or 70 cm) higher if non-linear interactions are not accounted for (e.g., by independently adding astronomical and non-astronomical components, as is often done in impact case studies). These overestimates are similar to recent sea-level rise projections to 2100 at some locations. Furthermore, we further find evidence for changes in this non-linear interaction over time, which has the potential for counteracting the increasing flood risk associated with sea-level rise and tidal and/or meteorological changes alone. Finally, we show how accounting for non-linearity in coastal impact assessment modulates coastal exposure, reducing recent estimates of global coastal flood costs by ~16%, and population affected by ~8%.

Statistical Analysis of Turbulence Characteristics over the Tropical Western Pacific Based on Radiosonde Data

The tropical region is a key area for the interaction between the stratosphere and troposphere. The strong convective activity in the troposphere produces a series of gravity wave activities, which result in strong and widespread turbulence over the region. Therefore, studying the turbulent activity in the western Pacific is essential for understanding the characteristics of atmospheric disturbance over this region, which has the world’s most complex circulation system. In this paper, we explore the characteristics of atmospheric turbulence distribution over Guam in this region, and the Thorpe sorting method is used to study one-second resolution radiosonde data from the US. On the basis of the background field and local instability, the turbulence generation mechanism is discussed in detail. Results show that the US high-resolution balloon data are efficacious for tropospheric turbulence retrieval but increasingly affected by instrument noise as altitude increases. It is also found that there is a strong turbulent mixing band caused by both shear instability and static instability near the tropopause, where the turbulence activity is markedly enhanced and characterized by annual oscillation, reaching the maximum from July to September.

Retrieval and Analysis of the Strongest Mixed Layer in the Troposphere

In this article, Thorpe analysis, which often retrieves the characteristics of mixing in the free atmosphere from balloon sounding data, is applied to the data of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC). We find that the COSMIC data can well retrieve the strongest mixed layer in the troposphere (SMLT) altitude, and can reveal the basic variation trend of the SMLT thickness and Thorpe scale L T . We use COSMIC data to reveal the global spatial and temporal distribution of the SMLT from 2007 to 2015 and analyze the fluctuation period of the SMLT altitude with Hilbert–Huang transform (HHT), we find that the variation of the SMLT altitude is influenced by the dual effects of terrain and solar radiation.

Hygroscopicity of Different Types of Aerosol Particles: Case Studies Using Multi-Instrument Data in Megacity Beijing, China

Water uptake by aerosol particles alters its light-scattering characteristics significantly. However, the hygroscopicities of different aerosol particles are not the same due to their different chemical and physical properties. Such differences are explored by making use of extensive measurements concerning aerosol optical and microphysical properties made during a field experiment from December 2018 to March 2019 in Beijing. The aerosol hygroscopic growth was captured by the aerosol optical characteristics obtained from micropulse lidar, aerosol chemical composition, and aerosol particle size distribution information from ground monitoring, together with conventional meteorological measurements. Aerosol hygroscopicity behaves rather distinctly for mineral dust coarse-mode aerosol (Case I) and non-dust fine-mode aerosol (Case II) in terms of the hygroscopic enhancement factor, f β ( R H , λ 532 ) , calculated for the same humidity range. The two types of aerosols were identified by applying the polarization lidar photometer networking method (POLIPHON). The hygroscopicity for non-dust aerosol was much higher than that for dust conditions with the f β ( R H , λ 532 ) being around 1.4 and 3.1, respectively, at the relative humidity of 86% for the two cases identified in this study. To study the effect of dust particles on the hygroscopicity of the overall atmospheric aerosol, the two types of aerosols were identified and separated by applying the polarization lidar photometer networking method in Case I. The hygroscopic enhancement factor of separated non-dust fine-mode particles in Case I had been significantly strengthened, getting closer to that of the total aerosol in Case II. These results were verified by the hygroscopicity parameter, κ (Case I non-dust particles: 0.357 ± 0.024; Case II total: 0.344 ± 0.026), based on the chemical components obtained by an aerosol chemical speciation instrument, both of which showed strong hygroscopicity. It was found that non-dust fine-mode aerosol contributes more during hygroscopic growth and that non-hygroscopic mineral dust aerosol may reduce the total hygroscopicity per unit volume in Beijing.

The First Observation of Turbulence in Northwestern China by a Near-Space High-Resolution Balloon Sensor

Based on a new type of sensor mounted on a near-space balloon released in Hami, Xinjiang, the Thorpe method was used to analyze turbulence. The method was applied for the first time to northwest China (the mid-latitude region), and almost no radiosonde data above 40 km have been used to study turbulence hitherto. The feasibility of analyzing turbulence characteristics using radiosonde data based on the Beidou positioning system by the Thorpe method was thus verified. The distribution characteristics of turbulence scale, turbulence intensity, and turbulence kinetic energy dissipation rate, and the turbulence diffusion coefficient, were analyzed and discussed. The relationship between turbulence fraction, turbulence intensity, and stratified instability was also investigated. The results show that over 35 km, the influence of instrument noise on turbulence detection is significantly enhanced, which lead to an overestimation of turbulence in that region. The turbulence fraction was defined to reflect the degree of turbulence internal mixing, which is closely related to atmospheric instability. It was found that when the turbulence fraction reached 60%–80%, the turbulence reached its strongest intensity, and when the turbulence fraction exceeded 80%, the turbulence could not be maintained and began to decay.

Dynamic Drivers of TIFe Diurnal Cycle in Antarctica

The discovery of the thermosphere-ionosphere Fe (TIFe) layers has opened a door to exploring the least understood thermosphere and ionosphere region between 100 and 200 km with ground-based lidar instruments. The characteristics of the polar TIFe layers, and the impacts of the atmosphere neutral dynamics, electrodynamics, and metallic chemistry on the formation of TIFe layers deserve further investigation, especially the diurnal cycles of TIFe layers observed by lidar. This paper aims at investigating the major driving forces with 1-D Thermosphere-Ionosphere Fe/Fe+ (TIFe) model. A main question to answer is whether neutral dynamics like tidal winds or electrodynamics like the convection electric fields and currents in the magnetosphere and ionosphere are responsible for the diurnal cycle of TIFe layers.

Features of the Cloud Base Height and Determining the Threshold of Relative Humidity over Southeast China

Clouds play a critical role in adjusting the global radiation budget and hydrological cycle; however, obtaining accurate information on the cloud base height (CBH) is still challenging. In this study, based on Lidar and aircraft soundings, we investigated the features of the CBH and determined the thresholds of the environmental relative humidity (RH) corresponding to the observed CBHs over Southeast China from October 2017 to September 2018. During the observational period, the CBHs detected by Lidar/aircraft were commonly higher in cold months and lower in warm months; in the latter, 75.91% of the CBHs were below 2000 m. Overall, the RHs at the cloud base were mainly distributed between 70 and 90% for the clouds lower than 1000 m, in which the most concentrated RH was approximately 80%. In addition, for the clouds with a cloud base higher than 1000 m, the RH thresholds decreased dramatically with increasing CBH, where the RH thresholds at cloud bases higher than 2000 m could be lower than 60%. On average, the RH thresholds for determining the CBHs were the highest (72.39%) and lowest (63.56%) in the summer and winter, respectively, over Southeast China. Therefore, to determine the CBH, a specific threshold of RH is needed. Although the time period covered by the collected CBH data from Lidar/aircraft is short, the above analyses can provide some verification and evidence for using the RH threshold to determine the CBH.

Retrieval and Validation of Cloud Top Temperature from the Geostationary Satellite INSAT-3D

Investigation of cloud top temperature (CTT) and its diurnal variation is highly reliant on high spatial and temporal resolution satellite data, which is lacking over the Indian region. An algorithm has been developed for detection of clouds and retrieval of CTT from the geostationary satellite INSAT-3D. These retrievals are validated (inter-compared) with collocated in-situ (satellite) measurements with specific intent to generate climate-quality data. The cloud detection algorithm employs nine different tests, in accordance with solar illumination, satellite angle and surface type conditions to generate pixel-resolution cloud mask. Validation of cloud mask with cloud-aerosol lidar with orthogonal polarization (CALIOP) shows that probability of detection (POD) of cloudy (clear) sky is 81% (85%), with 83% hit rate. The algorithm is also implemented on similar channels of moderate resolution imaging spectroradiometer (MODIS), which provides 88% (83%) POD of cloudy (clear) sky, with 86% hit rate. CTT retrieval is done at the pixel level, for all cloud pixels, by employing appropriate methods for various types of clouds. Comparison of CTT with radiosonde and cloud-aerosol lidar and infrared pathfinder satellite observations (CALIPSO) shows mean absolute error less than 3%. The study also examines sensitivity of retrieved CTT to the cloud classification scheme and retrieval criteria. Validation results and their close agreements with those of similar satellites demonstrate the reliability of the retrieved product for climate studies.

Global geochemical fingerprinting of plume intensity suggests coupling with the supercontinent cycle

Plate tectonics and mantle plumes are two of the most fundamental solid-Earth processes that have operated through much of Earth history. For the past 300 million years, mantle plumes are known to derive mostly from two large low shear velocity provinces (LLSVPs) above the core-mantle boundary, referred to as the African and Pacific superplumes, but their possible connection with plate tectonics is debated. Here, we demonstrate that transition elements (Ni, Cr, and Fe/Mn) in basaltic rocks can be used to trace plume-related magmatism through Earth history. Our analysis indicates the presence of a direct relationship between the intensity of plume magmatism and the supercontinent cycle, suggesting a possible dynamic coupling between supercontinent and superplume events. In addition, our analysis shows a consistent sudden drop in MgO, Ni and Cr at ~3.2–3.0 billion years ago, possibly indicating an abrupt change in mantle temperature at the start of global plate tectonics.

The links between plate tectonics and deep mantle structure remain unclear. Here, the authors demonstrate that transition elements (Ni, Cr, and Fe/Mn) in basaltic rocks can be used as a tool to trace plume-related magmatism through Earth history, and their results indicate the presence of a direct relationship between the intensity of plume magmatism and the supercontinent cycle.

Estimation of Turbulence Parameters in the Lower Troposphere from ShUREX (2016–2017) UAV Data

Turbulence parameters in the lower troposphere (up to ~4.5 km) are estimated from measurements of high-resolution and fast-response cold-wire temperature and Pitot tube velocity from sensors onboard DataHawk Unmanned Aerial Vehicles (UAVs) operated at the Shigaraki Middle and Upper atmosphere (MU) Observatory during two ShUREX (Shigaraki UAV Radar Experiment) campaigns in 2016 and 2017. The practical processing methods used for estimating turbulence kinetic energy dissipation rate ε and temperature structure function parameter C T 2 from one-dimensional wind and temperature frequency spectra are first described in detail. Both are based on the identification of inertial (−5/3) subranges in respective spectra. Using a formulation relating ε and C T 2 valid for Kolmogorov turbulence in steady state, the flux Richardson number R f and the mixing efficiency χ m are then estimated. The statistical analysis confirms the variability of R f and χ m around ~ 0.13 − 0.14 and ~ 0.16 − 0.17 , respectively, values close to the canonical values found from some earlier experimental and theoretical studies of both the atmosphere and the oceans. The relevance of the interpretation of the inertial subranges in terms of Kolmogorov turbulence is confirmed by assessing the consistency of additional parameters, the Ozmidov length scale L O , the buoyancy Reynolds number R e b , and the gradient Richardson number Ri. Finally, a case study is presented showing altitude differences between the peaks of N 2 , C T 2 and ε , suggesting turbulent stirring at the margin of a stable temperature gradient sheet. The possible contribution of this sheet and layer structure on clear air radar backscattering mechanisms is examined.

Enhancement of gasworks groundwater remediation by coupling a bio-electrochemical and activated carbon system

Here, we show the electrical response, bacterial community, and remediation of hydrocarbon-contaminated groundwater from a gasworks site using a graphite-chambered bio-electrochemical system (BES) that utilizes granular activated carbon (GAC) as both sorption agent and high surface area anode. Our innovative concept is the design of a graphite electrode chamber system rather than a classic non-conductive BES chamber coupled with GAC as part of the BES. The GAC BES is a good candidate as a sustainable remediation technology that provides improved degradation over GAC, and near real-time observation of associated electrical output. The BES chambers were effectively colonized by the bacterial communities from the contaminated groundwater. Principal coordinate analysis (PCoA) of UniFrac Observed Taxonomic Units shows distinct grouping of microbial types that are associated with the presence of GAC, and grouping of microbial types associated with electroactivity. Bacterial community analysis showed that β-proteobacteria (particularly the PAH-degrading Pseudomonadaceae) dominate all the samples. Rhodocyclaceae- and Comamonadaceae-related OTU were observed to increase in BES cells. The GAC BES (99% removal) outperformed the control graphite GAC chamber, as well as a graphite BES and a control chamber both filled with glass beads.

Evaluating the Roles of Rainout and Post-Condensation Processes in a Landfalling Atmospheric River with Stable Isotopes in Precipitation and Water Vapor

Atmospheric rivers (ARs), and frontal systems more broadly, tend to exhibit prominent “V” shapes in time series of stable isotopes in precipitation. Despite the magnitude and widespread nature of these “V” shapes, debate persists as to whether these shifts are driven by changes in the degree of rainout, which we determine using the Rayleigh distillation of stable isotopes, or by post-condensation processes such as below-cloud evaporation and equilibrium isotope exchange between hydrometeors and surrounding vapor. Here, we present paired precipitation and water vapor isotope time series records from the 5–7 March 2016, AR in Bodega Bay, CA. The stable isotope composition of surface vapor along with independent meteorological constraints such as temperature and relative humidity reveal that rainout and post-condensation processes dominate during different portions of the event. We find that Rayleigh distillation controls during peak AR conditions (with peak rainout of 55%) while post-condensation processes have their greatest effect during periods of decreased precipitation on the margins of the event. These results and analyses inform critical questions regarding the temporal evolution of AR events and the physical processes that control them at local scales.

Long-term variation of satellite-based PM2.5 and influence factors over East China

With the explosive economic development of China over the past few decades, air pollution has attracted increasing global concern. Using satellite-based PM_2.5 data from 2000 to 2015, we found that the available emissions of atmospheric compositions show similar yearly variation trends to PM_2.5, even if the synchronization is not met for each composition, implying that the intensity of anthropogenic emissions dominates the temporal variation of PM_2.5 in East China. Empirical orthogonal function analysis demonstrates that the dominant variability in the seasonal PM_2.5 is closely associated with climate circulation transformation, incarnated as the specific climate index such as the Asia Polar Vortex intensity in spring, the Northern Hemisphere Subtropical High Ridge Position for the leading mode and the Kuroshio Current SST for the second mode in summer, the Asia Polar Vortex Area for the leading mode and the Pacific Polar Vortex Intensity for the second mode in autumn, the NINO A SSTA for the leading mode and the Pacific Decadal Oscillation for the second mode in winter. Therefore, apart from anthropogenic emissions effects, our results also provide robust evidence that over the past 16 years the climate factor has played a significant role in modulating PM_2.5 in eastern China.

Monte Carlo simulations of the backscattering measurements for associated uncertainty

Three-dimensional simulations using the Monte Carlo method are implemented to analyze and quantify the uncertainty and the influence of absorption on the measurement of light backscattering by ECO-BB9 (WET Labs) sensor for a wide variety of optically complex and open ocean waters. The analytical investigation of the geometrical configuration revealed a distinct effective path length which contributes towards an accurate assessment of absorption effect on the backscattering measurement. The present study proposes the application of a non-linear relationship to determine the measured parameter from the detector counts more accurately than the conventional method that applies the scale factor. It was found that the mean centroid angle of the instrument shows marginal variations for varying absorption and backscattering coefficients. Nevertheless, the mean centroid angle for the instrument over the entire course of the simulation study was found to be 124° which conforms well with the study of Doxaran et al. [Opt. Express 24, 3615 (2016)].

Seasonal Response of North Western Pacific Marine Ecosystems to Deposition of Atmospheric Inorganic Nitrogen Compounds from East Asia

The contribution of the atmospheric deposition of inorganic nitrogen compounds produced in East Asia to the marine ecosystems of the North Western Pacific Ocean (NWPO) was investigated in this study using a 3-D lower trophic-marine ecosystem model (NEMURO) combined with an atmospheric regional chemical transport model (WRF-CMAQ). The monthly mean values for the wet and dry deposition of nitrogen compounds, including gases (HNO₃ and NH₃) and aerosol particles (NO₃⁻ and NH₄⁺), were determined using the WRF-CMAQ for the NWPO from 2009–2016. These values were input into the NEMURO as an additional nitrogen source. The NEMURO indicated that the annual average chlorophyll mass concentration at the surface in the subtropical region (20°N–30°N; 125°E–150°E) of the NWPO increased from 0.04 to 0.10 mg/m³. Similarly, the gross primary productivity, integrated over sea depths of 0–200 m, increased from 85 to 147 mg C/m²/day because of this deposition. This study indicates that the supply of atmospheric inorganic nitrogen compounds from East Asia to the NWPO could have a high nutrient impact on the marine ecosystem in the subtropical region.

Vertical variations in optical properties of the waters in the Yellow Sea and Bohai Sea at seasonal scales and their influencing mechanisms

This research used the profile data measured extensively in the Yellow Sea and Bohai Sea (YSBS) to explain the temporal and spatial distribution characteristics of optical properties and systematically analyzed the influencing mechanisms of the seasonal variations of optical properties in the YSBS in conjunction with synchronously measured hydrological and biogeochemical data in vertical profiles. The main conclusions obtained are as follows: the vertical variations in the optical properties in the YSBS are mainly influenced by the stratification effect, vertical mixing function, and phytoplankton growth process; and the variations of optical properties are dominated by the change of particle characteristics. The backscattering ratio can be used to discriminate particle types as a proxy of particulate bulk refractive index. In the YSBS, for waters with a backscattering ratio of less than 0.012, the variations of optical properties are dominated by the phytoplankton particles. For waters with a backscattering ratio greater than 0.012, the variations of optical properties are dominated by inorganic sediment particles. In addition, for the YSBS, the variations in optical properties of upper surface layer waters can be elucidated well by the vertical variations.

Compositionally-distinct ultra-low velocity zones on Earth's core-mantle boundary

The Earth’s lowermost mantle large low velocity provinces are accompanied by small-scale ultralow velocity zones in localized regions on the core-mantle boundary. Large low velocity provinces are hypothesized to be caused by large-scale compositional heterogeneity (i.e., thermochemical piles). The origin of ultralow velocity zones, however, remains elusive. Here we perform three-dimensional geodynamical calculations to show that the current locations and shapes of ultralow velocity zones are related to their cause. We find that the hottest lowermost mantle regions are commonly located well within the interiors of thermochemical piles. In contrast, accumulations of ultradense compositionally distinct material occur as discontinuous patches along the margins of thermochemical piles and have asymmetrical cross-sectional shape. Furthermore, the lateral morphology of these patches provides insight into mantle flow directions and long-term stability. The global distribution and large variations of morphology of ultralow velocity zones validate a compositionally distinct origin for most ultralow velocity zones.

Ultralow velocity zones are detected on the core-mantle boundary, but their origin is enigmatic. Here, the authors find that the global distribution and large variations of morphology of ultralow velocity zones are consistent with most having a compositionally-distinct origin.

Geologically-inspired strong bulk ceramics made with water at room temperature

Dense ceramic materials can form in nature under mild temperatures in water. By contrast, man-made ceramics often require sintering temperatures in excess of 1,400 °C for densification. Chemical strategies inspired by biomineralization processes have been demonstrated but remain limited to the fabrication of thin films and particles. Besides biomineralization, the formation of dense ceramic-like materials such as limestone also occurs in nature through large-scale geological processes. Inspired by the geological compaction of mineral sediments in nature, we report a room-temperature method to produce dense and strong ceramics within timescales comparable to those of conventional manufacturing processes. Using nanoscale powders and high compaction pressures, we show that such cold sintering process can be realized with water at room temperature to result in centimetre-sized bulk parts with specific strength that is comparable to, and occasionally even higher than, that of traditional structural materials like concrete.

Milder conditions for processing ceramics is of interest for a range of uses. Here authors report room temperature sintering of nanoparticulate powders using a solution-assisted route, yielding parts with centimetre-sized bulk parts with specific strength comparable to and possibly surpassing that of traditional structural materials like concrete.

Unravelling raked linear dunes to explain the coexistence of bedforms in complex dunefields

Raked linear dunes keep a constant orientation for considerable distances with a marked asymmetry between a periodic pattern of semi-crescentic structures on one side and a continuous slope on the other. Here we show that this shape is associated with a steady-state dune type arising from the coexistence of two dune growth mechanisms. Primary ridges elongate in the direction of the resultant sand flux. Semi-crescentic structures result from the development of superimposed dunes growing perpendicularly to the maximum gross bedform-normal transport. In the particular case of raked linear dunes, these two mechanisms produces primary and secondary ridges with similar height but with different orientations, which are oblique to each other. The raked pattern develops preferentially on the leeward side of the primary ridges according to the direction of propagation of the superimposed bedforms. As shown by numerical modelling, raked linear dunes occur where both these oblique orientations and dynamics are met.

Origin and evolution of the deep thermochemical structure beneath Eurasia

A unique structure in the Earth's lowermost mantle, the Perm Anomaly, was recently identified beneath Eurasia. It seismologically resembles the large low-shear velocity provinces (LLSVPs) under Africa and the Pacific, but is much smaller. This challenges the current understanding of the evolution of the plate–mantle system in which plumes rise from the edges of the two LLSVPs, spatially fixed in time. New models of mantle flow over the last 230 million years reproduce the present-day structure of the lower mantle, and show a Perm-like anomaly. The anomaly formed in isolation within a closed subduction network ∼22,000 km in circumference prior to 150 million years ago before migrating ∼1,500 km westward at an average rate of 1 cm year⁻¹, indicating a greater mobility of deep mantle structures than previously recognized. We hypothesize that the mobile Perm Anomaly could be linked to the Emeishan volcanics, in contrast to the previously proposed Siberian Traps.

The Perm anomaly is found in the lower mantle beneath Eurasia, but how this structure formed has remained unclear. Here, the authors show that the anomaly has been mobile since it formed in isolation within a closed subduction network and propose that the anomaly is linked to the Emeishan volcanics.

High nitrogen deposition in an agricultural ecosystem of Shaanxi, China

Atmospheric nitrogen (N) deposition plays an important role in the global N cycle. Data for dry and wet N deposition in agricultural ecosystem of Shaanxi in China is still imperfect; in this study, we continuously measured concentrations and fluxes of dry N deposition from 2010 to 2013 in Yangling district of Shaanxi province and wet N deposition from 2010 to 2012. The average annual concentrations of NH3, NO2, HNO3, particulate ammonium, and nitrate (pNH4 (+) and pNO3 (-)) varied among 3.9-9.1, 6.6-8.0, 1.2-1.4, 3.1-4.3, and 3.3-4.8 μg N m(-3), respectively, with mean values of 6.0, 7.2, 1.3, 3.8, and 4.1 μg N m(-3), respectively, during the entire monitoring period. The annual NH4 (+)-N and NO3 (-)-N concentrations in precipitation ranged 3.9-4.3 and 2.8-3.4 mg N L(-1) with the mean values of 4.1 and 3.3 mg N L(-1). The NH4 (+)-N/NO3 (-)-N ratio in rainfall averaged 1.2. Dry N deposition flux was determined to be 19.2 kg N ha(-1) year(-1) and the wet N deposition flux was 27.2 kg N ha(-1) year(-1). The amount of total atmospheric N deposition (dry plus wet) reached 46.4 kg N ha(-1) year(-1), in which dry deposition accounted 41 %. Gaseous N deposition comprised over 75 % of the dry deposition, and the proportion of oxidized N in dry deposition was equal to the reduced N. Therefore, the results suggest that more stringent regional air pollution control policies are required in the target area and that N deposition is an important nutrient resource from the atmosphere that must be taken into consideration in nutrient management planning of agricultural ecosystems.

Clouds enhance Greenland ice sheet meltwater runoff

The Greenland ice sheet has become one of the main contributors to global sea level rise, predominantly through increased meltwater runoff. The main drivers of Greenland ice sheet runoff, however, remain poorly understood. Here we show that clouds enhance meltwater runoff by about one-third relative to clear skies, using a unique combination of active satellite observations, climate model data and snow model simulations. This impact results from a cloud radiative effect of 29.5 (±5.2) W m(-2). Contrary to conventional wisdom, however, the Greenland ice sheet responds to this energy through a new pathway by which clouds reduce meltwater refreezing as opposed to increasing surface melt directly, thereby accelerating bare-ice exposure and enhancing meltwater runoff. The high sensitivity of the Greenland ice sheet to both ice-only and liquid-bearing clouds highlights the need for accurate cloud representations in climate models, to better predict future contributions of the Greenland ice sheet to global sea level rise.

Phase diagrams of dune shape and orientation depending on sand availability

New evidence indicates that sand availability does not only control dune type but also the underlying dune growth mechanism and the subsequent dune orientation. Here we numerically investigate the development of bedforms in bidirectional wind regimes for two different conditions of sand availability: an erodible sand bed or a localized sand source on a non-erodible ground. These two conditions of sand availability are associated with two independent dune growth mechanisms and, for both of them, we present the complete phase diagrams of dune shape and orientation. On an erodible sand bed, linear dunes are observed over the entire parameter space. Then, the divergence angle and the transport ratio between the two winds control dune orientation and dynamics. For a localized sand source, different dune morphologies are observed depending on the wind regime. There are systematic transitions in dune shape from barchans to linear dunes extending away from the localized sand source, and vice-versa. These transitions are captured fairly by a new dimensionless parameter, which compares the ability of winds to build the dune topography in the two modes of dune orientation.

Stability of active mantle upwelling revealed by net characteristics of plate tectonics

Viscous convection within the mantle is linked to tectonic plate motions and deforms Earth's surface across wide areas. Such close links between surface geology and deep mantle dynamics presumably operated throughout Earth's history, but are difficult to investigate for past times because the history of mantle flow is poorly known. Here we show that the time dependence of global-scale mantle flow can be deduced from the net behaviour of surface plate motions. In particular, we tracked the geographic locations of net convergence and divergence for harmonic degrees 1 and 2 by computing the dipole and quadrupole moments of plate motions from tectonic reconstructions extended back to the early Mesozoic era. For present-day plate motions, we find dipole convergence in eastern Asia and quadrupole divergence in both central Africa and the central Pacific. These orientations are nearly identical to the dipole and quadrupole orientations of underlying mantle flow, which indicates that these 'net characteristics' of plate motions reveal deeper flow patterns. The positions of quadrupole divergence have not moved significantly during the past 250 million years, which suggests long-term stability of mantle upwelling beneath Africa and the Pacific Ocean. These upwelling locations are positioned above two compositionally and seismologically distinct regions of the lowermost mantle, which may organize global mantle flow as they remain stationary over geologic time.

Resolving the interactions between population density and air pollution emissions controls in the San Joaquin Valley, USA

The effectiveness of emissions control programs designed to reduce concentrations of airborne particulate matter with an aerodynamic diameter < 2.5 microm (PM2.5) in California's San Joaquin Valley was studied in the year 2030 under three growth scenarios: low, medium, and high population density. Base-case inventories for each choice of population density were created using a coupled emissions modeling system that simultaneously considered interactions between land use and transportation, area source, and point source emissions. The ambient PM2.5 response to each combination of population density and emissions control was evaluated using a regional chemical transport model over a 3-week winter stagnation episode. Comparisons between scenarios were based on regional average and population-weighted PM2.5 concentrations. In the absence of any emissions control program, population-weighted concentrations of PM2.5 in the future San Joaquin Valley are lowest undergrowth scenarios that emphasize low population density. A complete ban on wood burning and a 90% reduction in emissions from food cooking operations and diesel engines must occur before medium- to high-density growth scenarios result in lower population-weighted concentrations of PM2.5. These trends partly reflect the fact that existing downtown urban cores that naturally act as anchor points for new high-density growth in the San Joaquin Valley are located close to major transportation corridors for goods movement. Adding growth buffers around transportation corridors had little impact in the current analysis, since the 8-km resolution of the chemical transport model already provided an artificial buffer around major emissions sources. Assuming that future emissions controls will greatly reduce or eliminate emissions from residential wood burning, food cooking, and diesel engines, the 2030 growth scenario using "as-planned" (medium) population density achieves the lowest population-weighted average PM2.5 concentration in the future San Joaquin Valley during a severe winter stagnation event.

IMPLICATIONS

The San Joaquin Valley is one of the most heavily polluted air basins in the United States that are projected to experience strong population growth in the coming decades. The best plan to improve air quality in the region combines medium- or high-density population growth with rigorous emissions controls. In the absences of controls, high-density growth leads to increased population exposure to PM2.5 compared with low-density growth scenarios (urban sprawl).