Earth's Atmosphere Research Articles

Linking forest carbon opportunity costs and greenhouse gas emission substitution effects of wooden buildings: The climate optimum concept

Forests play a crucial role in achieving net-zero greenhouse gas emission targets in the coming decades, as they can act as natural carbon sinks by removing carbon dioxide from the Earth's atmosphere. The use of wood as a building material leads to lower greenhouse gas (GHG) emissions throughout its life cycle compared to other building materials and is therefore considered a valid climate change mitigation strategy. However, the impact of wood harvesting on the potential carbon storage in forests has largely been ignored. In this study, we investigated whether the use of wood as a building material is beneficial for climate change mitigation when considering carbon opportunity costs, which represent the amount of carbon prevented from accumulating in forests due to wood extraction. We introduce the climate optimum concept, which links both GHG emission substitution and associated carbon opportunity cost of wooden buildings. Application of the concept to a case study building shows that the GHG substitution benefits of wooden buildings for climate change mitigation are overshadowed by carbon opportunity costs in forests. In our analysis, no wooden scenario achieves sufficient life cycle embodied GHG emission substitution in order to compensate for the unrealized carbon storage potential in the forest system due to harvest. Wood-based GHG mitigation strategies in the building sector and beyond need to consider this unrealized carbon storage potential of forests expressed via carbon opportunity costs, in order to obtain a more comprehensive picture of the climate impact of forests and wood-based products.

Assembling algorithm for Green's tensors and absorbing boundary conditions for Galbrun's equation in radial symmetry

Solar oscillations can be modeled by Galbrun's equation which describes Lagrangian wave displacement in a self-gravitating stratified medium. For spherically symmetric backgrounds, we construct an algorithm to compute efficiently and accurately the coefficients of the Green's tensor of the time-harmonic equation in vector spherical harmonic basis. With only two resolutions, our algorithm provides values of the kernels for all heights of source and receiver, and prescribes analytically the singularities of the kernels. We also derive absorbing boundary conditions (ABC) to model wave propagation in the atmosphere above the cut-off frequency. The construction of ABC, which contains varying gravity terms, is rendered difficult by the complex behavior of the solar potential in low atmosphere and for frequencies below the Lamb frequency. We carry out extensive numerical investigations to compare and evaluate the efficiency of the ABCs in capturing outgoing solutions. Finally, as an application towards helioseismology, we compute synthetic solar power spectra that contain pressure modes as well as internal-gravity (g-) and surface-gravity (f-) ridges which are missing in simpler approximations of the wave equation. For purpose of validation, the locations of the ridges in the synthetic power spectra are compared with observed solar modes.

Hysteresis in Water Content of Ultrafine Glassy Organic Aerosol Particles

AbstractWater content of aerosol particles is atmospherically important. Water content of organic aerosol (OA) particles has been estimated by assuming thermodynamic equilibrium. Here, we discovered that the hysteresis phenomenon occurred to water content of glassy ultrafine OA particles, demonstrating that thermodynamically non‐equilibrium states need to be considered. Hygroscopic growth for monodisperse ultrafine particles (sucrose and glucose) was investigated for the temperature range from 252 to 296 K. Hysteresis was not observable at 296 K, consistent with literature data. However, hysteresis in water content was observed at sub‐273 K. The lowest relative humidity (RH), at which hygroscopic growth of particles did not depend on exposure history to water vapor, was defined as threshold RH. Threshold RH for 100 nm particles was approximately the same as the glass transition points when hysteresis clearly happened, demonstrating that water diffusion in a highly viscous matrix of organic aerosols was the key to the phenomenon. Employment of a kinetic multi‐layer model quantitatively predicted threshold RH as a function of temperature, exposure time, and the particle size. Considering the temperature and RH range of Earth's atmosphere, we hypothesize that hysteresis in water content for organic aerosols ubiquitously occurs in the upper troposphere, impacting chemical aging and cloud formation processes.

Monitoring anomalies on large-scale energy and water balance components by coupling remote sensing parameters and gridded weather data.

The SAFER (Simple Algorithm for Evapotranspiration Retrieving) algorithm was applied with MODIS images and gridded weather data from 2007 to 2021, to monitor the energy balance components and their anomalies, in the Atlantic Forest (AF) and Caatinga (CT) biomes inside the coastal agricultural growing zone, Northeast Brazil. Considering the long-term data, the Rn values between the biomes are not significantly different, however presenting distinct Rn partitions into latent (λE), sensible (H), and ground (G) heat fluxes between biomes. The Rn values annual averages are 9.40 ± 0.21 and 9.50 ± 0.23MJm-2 d-1, for AF and CT, respectively. However, for respectively AF and CT, they are respectively 5.10 ± 1.14MJm-2 d-1 and 4.00 ± 0.99MJm-2 d-1 for λE; 3.80 ± 1.12MJm-2 d-1 and 5.00 ± 1.00MJm-2 d-1 for H; 0.50 ± 0.12MJm-2 d-1 and 0.40 ± 0.10MJm-2 d-1 for G, yielding respective mean evaporative fraction (Ef = λE/(Rn - G) values of 0.60 ± 0.12 and 0.50 ± 0.15. Anomalies on λE, H, and Ef were detected through standardized index for these energy balance components by comparing the results for the years 2018 to 2021 with the long-term values from 2007 to each of these years, showing that the energy fluxes between surfaces and the lower atmosphere, and then the root-zone moisture conditions for both biomes, may strongly vary along seasons and years, with alternate positive and negative anomalies. These assessments are important for water policies as they can picture suitable periods and places for rainfed agriculture as well as the irrigation needs in irrigated agriculture, allowing rational agricultural environmental management while minimizing water competitions among other water users, under climate and land-use changes conditions.

Preparation of Hierarchical Porous Monoliths With High Surface Areas by a Solvent Knitting Strategy.

Hierarchical porous hypercrosslinked monoliths (PolyHIPE-HCP) with ultrahigh specific surface areas are prepared via a solvent knitting strategy. Compared to previous work, the solvent knitting strategy is carried out in a relatively low air-controlled atmosphere with gradient heating starting from low temperature while using DCM (Dichloromethane) as both a solvent and a cross-linker, allowing for a slow and controlled cross-linking process, thereby achieving a BET surface area ranging from 514 to 728m2g-1. Scanning electron microscopy (SEM) shows that the knitting process does not affect the presence of macroporous structure in the PolyHIPE. With the introduction of mesopores and micropores, these hierarchical porous monoliths exhibit significant potential for applications in gas adsorption and water treatment. Hence, a universal, simple and low-cost method to synthesize polymeric monoliths with hierarchically porous structure and higher surface area is proposed, which has fascinating prospects in industrialization.

Stable carbon isotope evolution of formaldehyde on early Mars

Organic matter in the Martian sediments may provide a key to understanding the prebiotic chemistry and habitability of early Mars. The Curiosity rover has measured highly variable and 13C-depleted carbon isotopic values in early Martian organic matter whose origin is uncertain. One hypothesis suggests the deposition of simple organic molecules generated from 13C-depleted CO derived from CO2 photochemical reduction in the atmosphere. Here, we present a coupled photochemistry-climate evolution model incorporating carbon isotope fractionation processes induced by CO2 photolysis, carbon escape, and volcanic outgassing in an early Martian atmosphere of 0.5–2 bar, composed mainly of CO2, CO, and H2 to track the evolution of the carbon isotopic composition of C-bearing species. The calculated carbon isotopic ratio in formaldehyde (H2CO) can be highly depleted in 13C due to CO2-photolysis-induced fractionation and is variable with changes in atmospheric CO/CO2 ratio, surface pressure, albedo, and H2 outgassing rate. Conversely, CO2 becomes enriched in 13C, as estimated from the carbonates preserved in ALH84001 meteorite. Complex organic matter formed by the polymerization of such H2CO could explain the strong depletion in 13C observed in the Martian organic matter. Mixing with other sources of organic matter would account for its unique variable carbon isotopic values.

Experimental Gas-Phase Removal of OH Radicals in the Presence of NH2C(O)H over the 11.7-353 K Range: Implications in the Chemistry of the Interstellar Medium and the Earth's Atmosphere.

Formamide (NH2C(O)H) has been observed both in the interstellar medium (ISM), being identified as a potential precursor of prebiotic molecules in space, and in the Earth's atmosphere. In these environments where temperature is very distinct, hydroxyl (OH) radicals may play an important role in the degradation of NH2C(O)H. Thus, in this work, we report for the first time the experimental study of the temperature dependence of the gas-phase removal of OH in the presence of NH2C(O)H over the 11.7-353 K range. In the lowest temperature range (11.7-177.5 K), of interest for the ISM chemistry, the kinetic study was performed using a pulsed CRESU (French acronym for Reaction Kinetics in a Uniform Supersonic Flow) apparatus, while a thermostatized slow-flow reactor was employed in the kinetic study of the OH + NH2C(O)H reaction over the 273-353 K range, of interest in the Earth's troposphere below room temperature. The pulsed laser photolysis at 248 nm of a suitable OH-precursor (hydrogen peroxide, tert-butyl hydroperoxide, or acetylacetone) was used to generate OH radicals in the reactor. The temporal evolution of OH was monitored by laser-induced fluorescence at 310 nm. An almost independent k(T) between 273 and 353 K (temperatures of the Earth's troposphere extended to T > 298 K) is reported, being the OH + NH2C(O)H reaction the major degradation route with an atmospheric lifetime of around 1 day. At lower temperatures of interest in the ISM (11.7-177.5 K), the potential formation of NH2C(O)H dimers was evaluated. Thermodynamically, under equilibrium conditions, formamide would be fully converted into the dimer in that T range. However, the qualitative agreement of the observed increase of k(T) with computational studies on the OH + NH2C(O)H reaction down to 200 K let us to report, between 177.5 and 106.0 K, the following parameters commonly used in astrochemical modeling: α = (3.76 ± 0.62) × 10-12 cm3 s-1, β = (3.07 ± 0.11), and γ = 0. At 11.7 K, a kinetic model reproducing the experimental data indicates that formamide dimerization could be important, but the OH-reaction with the monomer would be fast, 4 × 10-10 cm3 s-1, and the OH-reaction with the dimer, relatively slow [(0.1-1.0) × 10-11 cm3 s-1]. Despite that, the impact of the gas-phase OH + NH2C(O)H in the relative abundances of NH2C(O)H in a dense molecular cloud (T ∼ 10 K) and after the warm-up phase in the surroundings of hot cores/corinos (here, 10-400 K) appears to be negligible.

Investigation of micropolar dusty fluid flow in a rotational frame with magnetic field: A meshless radial basis function pseudospectral approach

AbstractRotational flow has numerous applications across a wide range of fields, including industrial processes for mixing, pumping, and processing materials, geophysical fluid dynamics for studying the Earth's atmosphere and oceans, aerospace engineering for designing and testing aircraft and spacecraft, medical imaging for creating detailed images of the human body, and environmental engineering for studying the transport of pollutants in water and air. In rotational flow, pumping power is an important parameter that measures the amount of energy required to maintain the flow of the fluid in a rotating frame. It is significant because the presence of the Coriolis force and other rotational effects can substantially alter the fluid dynamics, making it difficult to maintain a steady flow. The present study deals with the flow of micropolar dusty fluid in a rotating frame under the influence of the magnetic field, applied transversely to the flow in a horizontal channel. The fluid is induced to flow between two parallel plates by the movement of the upper plate and a constant pressure gradient. A meshless radial basis function pseudospectral approach is employed to derive a set of partial differential equations that determine the primary and secondary velocity profiles of the fluid, as well as the particle and microrotation velocities and temperature distribution. The pumping power required to sustain the flow in the absence of a pressure gradient is also calculated based on these velocity profiles. The findings provide valuable insights into the behavior of micropolar dusty fluids in a rotational channel and can potentially inform the design of industrial processes involving such fluids.

Future projection of extreme precipitation using a pseudo-global warming method: A case study of the 2013 Alberta flooding event

The June 2013 extreme precipitation event in Alberta resulted in devastating flash floods that caused significant economic losses and societal disruption. In this study, two high-resolution experiments were conducted using the Weather Research and Forecasting (WRF) model to study the change of the 2013 Alberta extreme precipitation event in a warmer climate. The control experiment was forced with 6-hourly ERA-Interim reanalysis data, while the sensitivity experiment was forced with perturbed ERA-Interim reanalysis data with climate change signals derived from ten global climate models under the Representative Concentration Pathway 8.5 emission scenario. The results indicate that the 2013 Alberta extreme precipitation event is projected to exhibit two significant characteristics in a warming climate. First, precipitation is expected to increase over the Canadian Rocky Mountain region and eastern British Columbia. Second, the precipitation is expected to decrease over the Alberta and Saskatchewan Prairies. Future changes in the extreme precipitation event are associated with changes in the cyclone evolution, moisture transport, and atmospheric stability change caused by climate change. We also found that the increase in atmospheric stability due to the decrease of relative humidity in the lower atmosphere cause less precipitation to form over the plains and later enhance the orographic precipitation in the Canadian Rockies. In addition to the general increase of precipitable water under global warming, this mechanism causes the storm's precipitation to be more concentrated near the Canadian Rockies. The findings from this study could be beneficial for understanding future changes in extreme precipitation events that share similar characteristics.

Impact sculpting of the early martian atmosphere.

Intense bombardment of solar system planets in the immediate aftermath of protoplanetary disk dissipation has played a key role in their atmospheric evolution. During this epoch, energetic collisions will have removed substantial masses of gas from rocky planet atmospheres. Noble gases are powerful tracers of this early atmospheric history, xenon in particular, which on Mars and Earth shows significant depletions and isotopic fractionations relative to the lighter noble gasses. To evaluate the effect of impacts on the loss and fractionation of xenon, we measure its ionization and recombination efficiency by laser shock and apply these constraints to model impact-driven atmospheric escape on Mars. We demonstrate that impact bombardment within the first 200 to 300 million years of solar system history generates the observed Xe depletion and isotope fractionation of the modern martian atmosphere. This process may also explain the Xe depletion recorded in Earth's deep mantle and provides a latest date for the timing of giant planet instability.

Exploring latent profiles in the relationship between learning atmosphere, negative emotions, and willingness to communicate among EFL learners

ABSTRACT The learning atmosphere, negative emotions, and willingness to communicate are pivotal in shaping learners’ experiences and fostering language proficiency. However, further exploration into these dynamics remains limited. Therefore, this study investigated latent profiles within English as a foreign language (EFL) learner and examined how they differ in terms of the relationships between the learning atmosphere, negative emotions, and willingness to communicate. A total of 591 EFL students from various universities across 19 provinces in China participated in the study. Using latent profile analysis, three distinct subgroups emerged: (1) a profile characterized by high learning atmosphere, very low negative emotions, and very high WTC; (2) a profile with moderate levels of learning atmosphere, negative emotions, and WTC; and (3) a profile marked by low learning atmosphere, high negative emotions, and moderately high WTC. The results underscore the significant positive impact of the learning atmosphere on WTC, alongside a marginal negative influence of negative emotions. These findings suggest tailored interventions and support strategies to cater to diverse learner needs, enhancing language learning environments effectively.

Interstellar computation their challenges and approaches in interplanetary cloud systems and data transmission

With the advancement of human civilisation beyond the confines of Earth's atmosphere, there has been an increasing need for efficient data processing and transmission in extraterrestrial environments. The article explores innovative strategies for resolving intricate computational challenges encountered in the context of interplanetary distances. The purpose of this study is to investigate the impact of issues such as latency, data corruption, and power consumption on classical computing paradigms in space. We examine the concept of "interplanetary cloud systems", which use distributed computation and data storage to tackle these issues. The article also covers advanced techniques for sending data, including communication systems using quantum entanglement and deep space networks. The article integrates the disciplines of astronomy, computer science, and space exploration to provide a holistic perspective on the issue. It is crucial to emphasise that the implementation of fault-tolerant systems, adaptive algorithms, and robust networking protocols is essential for the success of extrasolar computing programs. The article thoroughly explores the potential and risks that arise when space travel, astronomy, and computer science intersect. We explore the potential future of interplanetary data processing and communication technologies via the examination of fault tolerance, adaptive algorithms, and resilient networking. The importance of resolving computational issues in space increases as humanity extends its presence in the cosmos. The study results have significant ramifications for the development of forthcoming technology enabling interplanetary data transfer, hence facilitating human colonisation and scientific exploration beyond Earth.

Effect of novel aluminium titanate on mechanical, thermal and ablation performance behavior of carbon fiber reinforced phenolic resin composites

AbstractThermal Protection Systems (TPS) protect re‐entry space vehicles from the harsh heating they encounter when hypersonically flying through a planet or the earth's atmosphere. Carbon fiber‐reinforced phenolic resin composites were widely used for the thermal barrier structure of aerospace re‐entry vehicles. A Novel Aluminium Titanate (Al2TiO5/AT) micro powder‐modified Polyacrylonitrile (PAN) based Carbon Fiber Fabric‐Resorcinol Phenol Formaldehyde Resin (C‐PR) (AT‐C‐PR) composites are well prepared to meet the requirements of TPS. The AT may act as an insulating layer and anti‐ablative material due to its excellent thermal shock resistance in TPS. To understand the effectiveness of AT content on density, barcol hardness, interfacial interactions, thermal conductivity, and thermal stability, the C‐PR composites were produced with and without loading of AT with various weight percentages, namely 0 wt% (C‐PR), 1,3, and 5 wt% (AT‐C‐PR) by hot compression molding method. The microstructural and elemental change of the composites were analyzed by microscopic and spectroscopic studies. Results suggested that the Interlaminar Shear Strength (ILSS) of the composites was increased by about 14% at 1 wt% of AT loading. Mass, Linear Ablation Rates (MAR, LAR), and back‐face temperature of C‐PR and AT‐C‐PR composites were decreased to 0.15128 g/s, 0.01233 mm/s, and 405°C, respectively by loading of AT up to 1 wt%. The thermally ablated composites were also evaluated for their crystallographic phase changes. The work provided an effective way to improve the thermo‐mechanical and ablation performance characteristics of the AT‐C‐PR composites that can be potentially used in TPS of re‐entry vehicles.Highlights This investigation utilized innovative Al2TiO5/Aluminium Titanate (AT) ceramic powder as a filler in reinforcing Phenolic Resin (PR) with PAN‐based Carbon Fiber (C). It examined the impact of various loadings of AT in C‐PR composites (AT‐C‐PR) on their physical, mechanical, thermal, and anti‐ablation properties. The AT‐C‐PR composites exhibit reduced density, lower thermal conductivity, and enhanced ILSS (31 MPa) compared to the C‐PR composites. Optimal ablation resistance and thermal stability were achieved with a loading of 1 wt% AT (Mass Ablation Rate: 0.15128 g/s and Linear Ablation Rate: 0.01233 mm/s) compared to the C‐PR composites. Microstructural and elemental analysis of the composites were conducted using microscopy and energy‐dispersive spectroscopy, revealing the presence of oxides and carbides on the ablated surface. The phase transition and alterations in microstructure, coupled with the oxidation of AT, have enhanced the ablation resistance and reduced the back face temperature of different weight percentages of AT‐C‐PR composites, such as 1 wt% AT (413°C), compared to the C‐PR composites (704°C).

Bond lengths and band strengths of non-equivalent C-H bonds of 2-methyl-1,3-butadiene using density functional theory, Fourier transform IR, and cavity ringdown techniques

The C-H fundamental and overtone spectra (Δυ = 1- 4) of non-equivalent C-H bonds of isoprene (CH2=C(CH3)-CH=CH2) have been obtained using a Fourier transform infrared spectrometer. The C-H vibrational overtone spectra (Δυ = 5, 6) have been recorded using phase shift (PS) and exponential decay cavity ring down (CRD) techniques, respectively at 293 K. Theoretical density functional theory (DFT) calculations of bond lengths, harmonic, and anharmonic frequencies of isoprene and partially deuterated isoprene molecules, as well as computer deconvolution of the bands are used to identify transitions corresponding to non-equivalent C-H bonds. Harmonic frequencies ωe and anharmonicities ωexe are reported for theC-H (a) in plane and C-H (b) out of plane bonds of the methyl group, the single olefinic nonterminal C-H (o), and the four olefinic terminal C-H bonds that are defined in two groups as C-H (cis) and C-H (trans). From the Δυ = 6 peak wavenumbers, correlation functions are used to calculate C-H bond lengths, isolated frequencies, and dissociation energies. Band strengths, oscillator strengths, and transition moments are obtained experimentally for all transitions. The significance of the assigned vibrational transitions and integrated intensities of isoprene for research on Earth's atmosphere and as a potential indicator of life in exoplanets with oxygen-deprived atmospheres is examined.

Reanalysis of the Huygens GCMS dataset. I. High-resolution methane vertical profile in the atmosphere of Titan

More than 15 years after its landing on the surface of Titan, the data returned by the Huygens probe remain the only available in situ information on Titan’s lower atmosphere and its methane content. In this work, we present a reanalysis of the Huygens probe data obtained by the Gas Chromatograph Mass Spectrometer (GCMS) instrument on board Huygens. GCMS measured the atmospheric composition almost continuously during the Huygens probe descent by acquiring mass spectra between 145 km of altitude and Titan’s surface. We first focus on the recollection, reconstruction, and recalibration of the GCMS dataset to facilitate similar future work. We then reevaluate the methane vertical profile in Titan’s lower atmosphere by applying novel mass spectra data-treatment methods to this dataset. In addition to finding a slightly lower methane mixing ratio than those previously reported using GCMS measurements above the Huygens probe landing site, our work has revealed several kilometric to subkilometric-scale oscillations in the methane vertical profile below 30 km of altitude. We discuss several hypotheses that could explain these features, such as multiple layers of optically thin clouds or local convection cells, and strongly encourage the reanalysis of other Huygens datasets to further investigate these variations in the methane mixing ratio.

Unveiling spatial variations in atmospheric CO2 sources: a case study of metropolitan area of Naples, Italy

In the lower atmosphere, CO2 emissions impact human health and ecosystems, making data at this level essential for addressing carbon-cycle and public-health questions. The atmospheric concentration of CO2 is crucial in urban areas due to its connection with air quality, pollution, and climate change, becoming a pivotal parameter for environmental management and public safety. In volcanic zones, geogenic CO2 profoundly affects the environment, although hydrocarbon combustion is the primary driver of increased atmospheric CO2 and global warming. Distinguishing geogenic from anthropogenic emissions is challenging, especially through air CO2 concentration measurements alone. This study presents survey results on the stable isotope composition of carbon and oxygen in CO2 and airborne CO2 concentration in Naples’ urban area, including the Campi Flegrei caldera, a widespread hydrothermal/volcanic zone in the metropolitan area. Over the past 50 years, two major volcanic unrests (1969–72 and 1982–84) were monitored using seismic, deformation, and geochemical data. Since 2005, this area has experienced ongoing unrest, involving the pressurization of the underlying hydrothermal system as a causal factor of the current uplift in the Pozzuoli area and the increased CO2 emissions in the atmosphere. To better understand CO2 emission dynamics and to quantify its volcanic origin a mobile laboratory was used. Results show that CO2 levels in Naples’ urban area exceed background atmospheric levels, indicating an anthropogenic origin from fossil fuel combustion. Conversely, in Pozzuoli's urban area, the stable isotope composition reveals a volcanic origin of the airborne CO2. This study emphasizes the importance of monitoring stable isotopes of atmospheric CO2, especially in volcanic areas, contributing valuable insights for environmental and public health management.

Effect of microphysics scheme and data assimilation on hydrometeor and radiative flux simulations in the Arctic.

Although clouds are a major factor influencing atmospheric environments in the Arctic, numerical simulations of Arctic clouds are uncertain. In this study, the effects of microphysics scheme and data assimilation (DA) on the simulation of clouds, hydrometeors and radiative fluxes in the Arctic were investigated using the polar weather research and forecasting (WRF) model and three-dimensional variational DA. Compared with the WRF 5-class (WSM5) microphysics scheme, when the Morrison double-moment (Morrison) scheme was used, the simulated amount of cloud ice water decreased by approximately 68%. In contrast, the amount of water vapour, cloud liquid water, snow and rain in the atmosphere increased. With DA, the amount of water vapour increased, leading to increased hydrometeors. The cloud liquid water increased in the middle and low atmospheres when Morrison was used, whereas it increased in the low atmosphere when DA was used. The increase in cloud liquid water by using Morrison resulted in a decrease in the downward short-wave radiative flux at the surface, whereas using DA increased the downward long-wave radiative flux. Changing the microphysics scheme induced redistribution of the region and amounts of hydrometeors, whereas DA induced an increase in hydrometeors in specific regions by adding observation information to the model states.

Physiology, Not Nutrient Availability, May Have Limited Primary Productivity After the Emergence of Oxygenic Photosynthesis.

The evolution of oxygenic photosynthesis in Cyanobacteria was a transformative event in Earth's history. However, the scientific community disagrees over the duration of the delay between the origin of oxygenic photosynthesis and oxygenation of Earth's atmosphere, with estimates ranging from less than a hundred thousand to more than a billion years, depending on assumptions about rates of oxygen production and fluxes of reductants. Here, we propose a novel ecological hypothesis that a geologically significant delay could have been caused by biomolecular inefficiencies within proto-Cyanobacteria-ancestors of modern Cyanobacteria-that limited their maximum rates of oxygen production. Consideration of evolutionary processes and genomic data suggest to us that proto-cyanobacterial primary productivity was initially limited by photosystem instability, oxidative damage, and photoinhibition rather than nutrients or ecological competition. We propose that during the Archean era, cyanobacterial photosystems experienced protracted evolution, with biomolecular inefficiencies initially limiting primary productivity and oxygen production. Natural selection led to increases in efficiency and thus primary productivity through time. Eventually, evolutionary advances produced sufficient biomolecular efficiency that environmental factors, such as nutrient availability, limited primary productivity and shifted controls on oxygen production from physiological to environmental limitations. If correct, our novel hypothesis predicts a geologically significant interval of time between the first local oxygen production and sufficient production for oxygenation of environments. It also predicts that evolutionary rates were likely highly variable due to strong environmental selection pressures and potentially high mutation rates but low competitive interactions.

Surface Currents and Relative-Wind Stress in Coupled Ocean–Atmosphere Simulations of the Northern California Current System

Abstract The dependence of surface-current damping on the definition of surface current for the relative wind is examined in coupled ocean–atmosphere numerical simulations of the northern California Current System (nCCS) during March–October 2009. The model response is analyzed for wind stress computed from relative wind for six different choices of effective model surface velocity. Simulations without surface-current coupling are also considered. As a function of the geographically varying uppermost grid-level depth, the model uppermost grid-level velocity is found to have a wind-drift component with a log-layer structure. Mean geostrophic wind work is concentrated in the shelf and slope regions during March–May (MAM) and in the deep offshore region in June–September (JJAS). The surface-current damping effect on ocean kinetic energy depends more strongly on the parameterization of atmospheric planetary boundary layer (PBL) turbulence than on the surface-current coupling formulation: weaker PBL mixing gives stronger surface-current damping. The damping effect is stronger in the less energetic offshore region than in the more energetic region closer to the coast. During MAM, the changes in kinetic energy and geostrophic wind work in the shelf and slope regions are spatially correlated, while during JJAS, the changes in geostrophic wind work are strongly modulated by SST–stress coupling. The wind-drift-corrected surface-current formulations result in large changes in the effective wind work based on the product of stress and relative-wind surface current but result in only small changes in the kinetic energy of the circulation. Significance Statement Ocean currents and atmospheric winds are coupled by the exchange of momentum across the air–sea interface, the strength of which depends on the relative wind, the difference between the surface wind and surface current. The purpose of this work was to examine the dependence of a coupled ocean–atmosphere model of the northern California Current System (nCCS) on the representations of the relative-wind surface current and turbulent mixing in the lower atmosphere. The model surface current was found to have a shallow wind-drift response. The model ocean circulation was driven primarily by near-coast winds during the spring and by offshore winds during the summer. The ocean response depended more strongly on the atmospheric turbulent mixing than on the surface current representation.

A Data-constrained Analysis for Joule Heating as a Solar Active Region Atmosphere Heating Mechanism. I. Sunspot Umbral Light Bridge

Understanding the mechanisms underlying the heating of the solar atmosphere is a fundamental problem in solar physics. The lower atmosphere of the Sun (i.e., photosphere and chromosphere) is composed of weakly ionized plasma. This results in anisotropic dissipation of electric currents by Coulomb and Cowling resistivities. Joule heating due to dissipation of currents perpendicular to the magnetic field by Cowling resistivity has been demonstrated to be the main mechanism for the heating of a sunspot umbral light bridge located in NOAA AR 12002 on 2014 March 13. Here, we focus on the same target region and demonstrate the importance of further constraining our Joule heating model using observational data in addition to magnetic field, namely plasma temperature calculated from the inversion of spectroscopic data obtained from the Interferometric BI-dimensional Spectrometer instrument of the ground-based Dunn Solar Telescope. As a parameter in our analysis, temperature is demonstrated to have the highest sensitivity after magnetic field. We show that the heating of the light bridge is a highly dynamic event that necessitates utilization of 3D spatially resolved observational data for temperature rather than a 1D temperature stratification based on theoretical/semiempirical solar atmosphere models. Our improved data-constrained analysis using spatially resolved temperatures shows that the entire light bridge is heated by the proposed mechanism, and yields heating rate values that are consistent with our previous study.