Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Formation factor”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

ISCCP reduced resolution satellite radiance data

The International Satellite Cloud Climatology Project (ISCCP) is the first active project of the World Climate Research Program. It is a multinational data collection project focused on collecting a data set that will improve the ability to predict and/or simulate the radiative effects of clouds on climate. For specified cloud parameters, the goals are to archieve values for 3-hour periods over the whole globe for 5 years at 30 km resolution. The task of collecting and processing radiance data from both geosynchronous and polar orbiting satellites began in July 1983. A diagram was shown illustrating the flow of data from the transmitting satellites to the various receiving institutions that handle it. The various stages of processing were then explained in detail, emphasizing Level B3-normalized, reformatted, reduced raw satellite data. The reduction of data by sampling is an essential step in the flow. By the time the ISCCP data reaches the Global Processing Center at Goddard Institute for Space Studies (GISS), the volume has been reduced by a factor of 1000. The Pilot Climate Data System (PLDS) will provide access to the ISCCP data set. It should prove to be one of the cleanest satellite data sets because it will have been through three filters--that of the operational agency, the Global Processing Center, and the PCDS. The ISCCP data set also includes other correlative data sets delivered in compatible format.

Rossow, W.↗
NASA NTRS1986

A diagnostic study of baroclinic disturbances in polar air streams

Quasi-Lagrangian budgets of mass, vorticity and heat are calculated following disturbances that form within polar air streams. Observed cases are extracted from the European Centre for Medium-range Weather Forecasts analyses during the First GARP Global Experiment. Model-generated cases are extracted from the simulations of extratropical cyclogenesis by Sandgathe. These polar lows grow primarily through basic baroclinic instability processes and exhibit many features of larger maritime extratropical cyclones. Polar lows that originate on the poleward (or Cyclonic - Type C) side of the jet and have considerable midtropospheric positive vorticity advection at formation time are contrasted with lows that form on the equatorward (or Anticyclonic - Type A) side of a nearly straight upper-level jet. The midtropospheric positive vorticity advection must be present to enhance the vertical circulation when the large surface fluxes that are associated with strong outbreaks act to damp the thermal wave amplification. Although latent heat release is an important factor in both types, it is an essential energy source for the Type A low developments on the equatorward side. Although the vorticity balance is initially different for the two types of polar lows, the vorticity budgets during later stages are similar. The heat budget and the thickness tendency equation demonstrated that the self-development process that is present in larger maritime cyclones is also important for polar low intensification. The absence of favorable coupling to a jet stream is the missing factor in a model-generated Type A polar low that failed to develop. Consequently, the mid- and upper-tropospheric wind fields determine which polar lows will intensify to significant amplitudes.

Sinclair, Mark R.↗
NASA NTRS1991

Optically thin cirrus clouds over oceans and possible impact on sea surface temperature of warm pool in western Pacific

Over the convectively active tropical ocean regions, the measurement made from space in the IR and visible spectrum have revealed the presence of optically thin cirrus clouds, which are quite transparent in the visible and nearly opaque in the IR. The Nimbus-4 IR Interferometer Spectrometer (IRIS), which has a field of view (FOV) of approximately 100 km, was utilized to examine the IR optical characteristics of these cirrus clouds. From the IRIS data, it was observed that these optically thin cirrus clouds prevail extensively over the warm pool region of the equatorial western Pacific, surrounding Indonesia. It is found that the seasonal cloud cover caused by these thin cirrus clouds exceeds 50 percent near the central regions of the warm pool. For most of these clouds, the optical thickness in the IR is less than or = 2. It is deduced that the dense cold anvil clouds associated with deep convection spread extensively and are responsible for the formation of the thin cirrus clouds. This is supported by the observation that the coverage of the dense anvil clouds is an order of magnitude less than that of the thin cirrus clouds. From these observations, together with a simple radiative-convective model, it is inferred that the optically thin cirrus can provide a greenhouse effect, which can be a significant factor in maintaining the warm pool. In the absence of fluid transports, it is found that these cirrus clouds could lead to a runaway greenhouse effect. The presence of fluid transport processes, however, act to moderate this effect. Thus, if a modest 20 W/sq m energy input is considered to be available to warm the ocean, then it is found that the ocean mixed-layer of a 50-m depth will be heated by approximately 1 C in 100 days.

Prabhakara, C.↗
NASA NTRS1994

MODIS Technical Report Series. Volume 4: MODIS data access user's guide: Scan cube format

The software described in this document provides I/O functions to be used with Moderate Resolution Spectroradiometer (MODIS) level 1 and 2 data, and could be easily extended to other data sources. This data is in a scan cube data format: a 3-dimensional ragged array containing multiple bands which have resolutions ranging from 250 to 1000 meters. The complexity of the data structure is handled internally by the library. The I/O calls allow the user to access any pixel in any band through 'C' structure syntax. The high MODIS data volume (approaching half a terabyte per day) has been a driving factor in the library design. To avoid recopying data for user access, all I/O is performed through dynamic 'C' pointer manipulation. This manual contains background material on MODIS, several coding examples of library usage, in-depth discussions of each function, reference 'man' type pages, and several appendices with details of the included files used to customize a user's data product for use with the library.

Kalb, Virginia L.↗
NASA NTRS1997

HIRES Dust Imaging of the NGC 6334 Star Forming Complex

We present here our final report for the NASA grant "HIRES Dust Imaging of the NGC 6334 Star Forming Complex." This project was designed to study the photodissociation regions surrounding several OB stars in this cloud complex. NGC 6334 is unique in having at least seven distinct massive star forming regions in the same molecular cloud complex. The obvious advantage of studying young stars in the same molecular complex is that the stars all formed in the same global environment. Consequently, global factors like density waves, abundances, global magnetic field strength, and age of the parental molecular cloud cannot contribute to the differences among the star forming regions. Instead, the differences must arise only from local effects such as the mass, age, and UV fields of the individual stars. A study of NGC 6334 will greatly simplify the general problem of comparing different star formation regions by eliminating global effects.

Jackson, James M.↗
NASA NTRS2002

Micromechanics Modeling of Fracture in Nanocrystalline Metals

Nanocrystalline metals have very high theoretical strength, but suffer from a lack of ductility and toughness. Therefore, it is critical to understand the mechanisms of deformation and fracture of these materials before their full potential can be achieved. Because classical fracture mechanics is based on the comparison of computed fracture parameters, such as stress intlmsity factors, to their empirically determined critical values, it does not adequately describe the fundamental physics of fracture required to predict the behavior of nanocrystalline metals. Thus, micromechanics-based techniques must be considered to quanti@ the physical processes of deformation and fracture within nanocrystalline metals. This paper discusses hndamental physicsbased modeling strategies that may be useful for the prediction Iof deformation, crack formation and crack growth within nanocrystalline metals.

Glaessgen, E. H.↗
NASA NTRS1999

Delayed translational silencing of ceruloplasmin transcript in gamma interferon-activated U937 monocytic cells: role of the 3' untranslated region

Ceruloplasmin (Cp) is an acute-phase protein with ferroxidase, amine oxidase, and pro- and antioxidant activities. The primary site of Cp synthesis in human adults is the liver, but it is also synthesized by cells of monocytic origin. We have shown that gamma interferon (IFN-gamma) induces the synthesis of Cp mRNA and protein in monocytic cells. We now report that the induced synthesis of Cp is terminated by a mechanism involving transcript-specific translational repression. Cp protein synthesis in U937 cells ceased after 16 h even in the presence of abundant Cp mRNA. RNA isolated from cells treated with IFN-gamma for 24 h exhibited a high in vitro translation rate, suggesting that the transcript was not defective. Ribosomal association of Cp mRNA was examined by sucrose centrifugation. When Cp synthesis was high, i.e., after 8 h of IFN-gamma treatment, Cp mRNA was primarily associated with polyribosomes. However, after 24 h, when Cp synthesis was low, Cp mRNA was primarily in the nonpolyribosomal fraction. Cytosolic extracts from cells treated with IFN-gamma for 24 h, but not for 8 h, contained a factor which blocked in vitro Cp translation. Inhibitor expression was cell type specific and present in extracts of human cells of myeloid origin, but not in several nonmyeloid cells. The inhibitory factor bound to the 3' untranslated region (3'-UTR) of Cp mRNA, as shown by restoration of in vitro translation by synthetic 3'-UTR added as a "decoy" and detection of a binding complex by RNA gel shift analysis. Deletion mapping of the Cp 3'-UTR indicated an internal 100-nucleotide region of the Cp 3'-UTR that was required for complex formation as well as for silencing of translation. Although transcript-specific translational control is common during development and differentiation and global translational control occurs during responses to cytokines and stress, to our knowledge, this is the first report of translational silencing of a specific transcript following cytokine activation.

NASA Discipline Regulatory Physiology↗
NASA NTRS2017

A Synthesis of Experimental Data Describing the Partitioning of Moderately Volatile Elements in Major Rock Forming Minerals: Implications for the Moon

Highly volatile elements [condensation temperatures below about 700 K] and water are highly informative about lunar bulk composition (hence origin), differentiation and magmatic evolution, and the role of impacts in delivering volatiles to the Moon. Fractionation of volatile elements compared to moderately volatile and refractory elements are informative about high-temperature conditions that operated in the proto-lunar disk. Existing data show clearly that the Moon is depleted in volatile elements compared to the bulk silicate Earth. For example, K/Th is ~400-700 in the Moon compared to 2800-3000 in Earth. A complicating factor is that the abundances of the highly volatile elements in major lunar lithologies vary by approximately two orders of magnitude. Perhaps most interesting, H2O is not correlated with the concentration of volatile elements, indicating a decoupling of highly volatile elements from the even more volatile H2O. We contend that this decoupling could be a significant tracer of processes operating during lunar formation, differentiation, and bombardment, and the combination of analyzing both volatile elements and water is likely to provide significant insight into lunar geochemical history. This variation and lack of correlation raises the question: what were the relative contributions of crystallization in the magma ocean, subsequent mantle overturn, production of secondary magmas, and addition of volatiles by large impacts in producing this apparently large range in volatile abundances? This current study will produce new partitioning data relevant to the role and distribution of the volatile and non-volatile, yet geochemically significant elements (Co, Ni, Zn, Se, Rb, Sr, Mo, Ag, Cd, In, Sb, Ce, Yb, Tl, Pb, Bi) during the thermal and magmatic evolution of the Moon.

Vander Kaaden, Kathleen E.↗
NASA NTRS2022

Crater Population on Asteroid (101955) Bennu Indicates Impact Armouring and a Young Surface

The impactor-to-crater size scaling relationships that enable estimates of planetary surface ages rely on an accurate formulation of impactor–target physics. An armouring regime, specific to rubble-pile surfaces, has been proposed to occur when an impactor is comparable in diameter to a target surface particle (for example, a boulder). Armouring is proposed to reduce crater diameter, or prevent crater formation in the asteroid surface, at small crater diameters. Here, using measurements of 1,560 craters on the rubble-pile asteroid (101955) Bennu, we show that the boulder population controls a transition from crater formation to armouring at crater diameters ~2–3 m, below which crater formation in the bulk surface is increasingly rare. By combining estimates of impactor flux with the armouring scaling relationship, we find that Bennu’s crater retention age (surface age derived from crater abundance) spans from 1.6–2.2 Myr for craters less than a few meters to ~10–65 Myr for craters >100 m in diameter, reducing the maximum surface age by a factor of >15 relative to previous estimates. The range of crater retention ages, together with latitudinal variations in large-crater spatial density, indicate that ongoing resurfacing processes render the surface many times younger than the bulk asteroid.

Asteroids↗
NASA NTRS2000

Factors Contributing to Pilot Valve Fuel Seal Extrusion in Orbiter PRCS Thrusters

Extrusion of the polytetrafluoroethylene (PTFE) pilot seal used in the monomethylhydrazine (fuel) valve of the Orbiter Primary Reaction Control System (PRCS) thrusters has been implicated in numerous on-orbit thruster failures and on-ground valve failures. Two extrusion mechanisms have been proposed, one or both may be occurring. The first mechanism is attributed to thermal expansion mismatch between adjacent PTFE and metal parts used in the fuel valve, and is referred to as thermal extrusion. The second mechanism is attributed to nitrogen tetroxide (oxidizer) leakage from the adjacent oxidizer valve on the same thruster during ground turnaround, and is referred to as oxidizer-induced extrusion. Model calculations of PTFE pilot seal in an exact pilot valve configuration show that extrusion can be caused by differential thermal expansion, without the intervening influence of oxidizer. Experimental data on semitrapped PTFE and TFM (modified PTFE) specimens simulating a fuel pilot valve configuration show that thermal extrusion 1) is incremental and irreversible, 2) increases with the size of the thermal excursion, 3) decreases with successive thermal cycling, and 4) is accompanied by gap formation. Both PTFE and TFM exhibit a higher affinity for oxidizer than fuel. The property changes associated with oxidizer uptake may explain why oxidizer seals do not exhibit extrusion. Impression replicas of fuel pilot seals removed from the Orbiter fleet show two types of extrusion: extrusion of the entire seal (loaded extrusion), or extrusion of non-sealing surface (unloaded extrusion). Both extrusion types may arise from differences in service history, rather than in failure mechanism. The plausibility oxidizer-induced extrusion was evaluated. Preliminary calculations suggest that enough energy, heat, or gas may be liberated under certain operational scenarios to cause catastrophic extrusion. However, given the lack of supporting data, conclusions implicating oxidizer leakage as a factor in extrusion must be made with caution.

Waller, J.M.↗
NASA NTRS2014

Nanophase Carbonates on Mars: Implications for Carbonate Formation and Habitability

Despite having an atmosphere composed primarily of CO2 and evidence for abundant water in the past, carbonate minerals have only been discovered in small amounts in martian dust [1], in outcrops of very limited extent [2, 3], in soils in the Northern Plains (the landing site of the 2007 Phoenix Mars Scout Mission) [4] and may have recently been detected in aeolian material and drilled and powdered sedimentary rock in Gale Crater (the Mars Science Laboratory [MSL] landing site) [5]. Thermal analysis of martian soils by instruments on Phoenix and MSL has demonstrated a release of CO2 at temperatures as low as 250-300 degC, much lower than the traditional decomposition temperatures of calcium or magnesium carbonates. Thermal decomposition temperature can depend on a number of factors such as instrument pressure and ramp rate, and sample particle size [6]. However, if the CO2 released at low temperatures is from carbonates, small particle size is the only effect that could have such a large impact on decomposition temperature, implying the presence of extremely fine-grained (i.e., "nanophase" or clay-sized) carbonates. We hypothesize that this lower temperature release is the signature of small particle-sized (clay-sized) carbonates formed by the weathering of primary minerals in dust or soils through interactions with atmospheric water and carbon dioxide and that this process may persist under current martian conditions. Preliminary work has shown that clay-sized carbonate grains can decompose at much lower temperatures than previously thought. The first work took carbonate, decomposed it to CaO, then flowed CO2 over these samples held at temperatures >100 degC to reform carbonates. Thermal analysis confirmed that carbonates were indeed formed and transmission electron microsopy was used to determine crystal sized were on the order of 10 nm. The next step used minerals such as diopside and wollastonite that were sealed in a glass tube with a CO2 and H2O source. After reacting these materials for a number of hours, thermal analysis demonstrated the formations of carbonates that decomposed at temperatures as low as 500 degC [7]. Further work is underway to carry out the weathering process under more Mars-like conditions (low pressure and low temperature) to determine if the carbonate decomposition temperature can be shifted to even lower temperatures, consistent with what has been detected by thermal analysis instruments on Mars.

Archer, P. Douglas, Jr.↗
DOE OSTI2024

A tailored deep eutectic solvent for high-yield conversion of poplar residues to bio-based building blocks at mild conditions

The generation of condensed compounds in a deep eutectic solvent (DES) pretreatment has become a paramount factor that inhibits the further conversion of pretreated cellulose-rich substrate. Here, this study proposed a novel three-constituent DES system for the value-added utilization of poplar residues by efficiently suppressing hemicellulose derived condensation reactions. The results showed that adding ethanol into the DES system could effectively deconstruct the recalcitrant structure of poplar residues, simultaneously hindering the condensed composition formation. Under optimum ethanol addition (30%), the maximum xylan and lignin removal of 87.94% and 90.99% could be achieved, with more than 90.47% of glucan being preserved. With this, the glucan enzymatic hydrolysis efficiency was remarkably improved to 100% under the pretreatment conditions of 100 °C for 60 min, which was 84.69 times higher than the regular DES-pretreated poplar residues (1.17%). The working mechanism of relieving condensation reactions was characterized by Py-GC–MS, NMR, SEM, FTIR, and others. The results demonstrated that the addition of ethanol could regulate the degradation/conversion pathway of hemicellulose and lignin precipitation, thus inhibit the formation of condensed compounds during the pretreatment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Hydroxypyridinone-based stabilization of Np(IV) enabling efficient U/Np/Pu separations in the Adapted PUREX process

The classical process to recover uranium (U) and plutonium (Pu) from used nuclear fuel using tributyl phosphate (TBP), namely the Plutonium Uranium Redox EXtraction (PUREX) process, is complicated by the persistent presence of neptunium (Np) and thus requires extra purification steps. The concept of Adapted PUREX seeks to achieve Np recovery by adjusting the valence of the metal more effectively, thereby controlling its behavior more precisely. This study introduces the use of an aqueous hydroxypyridinone chelator, 3,4,3-LI(1,2-HOPO) (abbreviated as HOPO), to dictate the behavior of Np for recovery and meanwhile simplify cumbersome reprocessing steps. The interactions between Np and HOPO were probed mechanistically by way of absorption spectrophotometry, in conjunction with cyclic voltammetry. UV–Vis-NIR spectra illustrated the reduction of NpO 2 2+ to Np 4+ , with a fast reaction rate. Cyclic voltammetry revealed quasi-reversible processes between the oxidized and reduced forms of the ligand and its Np complexes. The corresponding heterogeneous rate constants (k 0 ) were estimated from the peak-to-peak separation potentials (ΔE p ), at ~ 4 – 35 μm/s for both HOPO and NpHOPO, with scan rates of 0.01 – 0.4 V/s. Meanwhile, the electromotive force (E MF ) as well as the change of Gibbs free energy (ΔG) were assessed from the half-wave potential (E 1/2 ), demonstrating the completeness of NpO 2 2+ reduction to Np 4+ by HOPO. The cumulative formation constant of the resulting NpHOPO complex (logβ 101 ) was determined by metal competition titration to be 42.0 ± 0.6, corroborating the extraordinarily high affinity of HOPO to tetravalent metal ions. Here, the prowess of valence control by HOPO and the high stability of the formed complex resulted in enhanced separations of Np from U and of Pu from U, with a maximum separation factor of ~7000 for both, nearly 90- and 10300-fold higher, respectively, than the values obtained using conventional PUREX formulae.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2024

Evaluation of Autoconversion Representation in E3SMv2 Using an Ensemble of Large-Eddy Simulations of Low-Level Warm Clouds

In numerical atmospheric models that treat cloud and rain droplet populations as separate condensate categories, precipitation initiation in warm clouds is often represented by an autoconversion rate (Au), which is the rate of formation of new rain droplets through the collisions of cloud droplets. Being a function of the cloud droplet size distribution (DSD), the local Au is commonly parameterized as a function of DSD moments: cloud droplet number (n c ) and mass (q c ) concentrations. When applied in a large-scale model, the grid-mean Au must also include a correction, or enhancement factor, to account for the horizontal variability of the cloud properties across the model grid. In this study, we evaluate the Au representation in the Energy Exascale Earth System Model version 2 (E3SMv2) climate model using large-eddy simulations (LES), which explicitly resolve cloud droplet spectra, and therefore the local Au, as well as its spatial variability. The analysis of an ensemble of warm low-level cloud cases shows that the E3SMv2 formulation represents the Au reasonably well compared to the horizontally averaged explicitly computed rate from LES. The agreement, however, comes from a combination of an underestimated E3SM-tuned local Au rate and an overestimated subgrid cloud variability enhancement factor. The latter bias is traced to neglecting the horizontal variability of n c and its co-variability with q c in parameterizing the grid-mean Au.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Harmonized geospatial data to support infrastructure siting feasibility planning for energy system transitions

Climate change, energy system transitions, and socioeconomic change are compounding influences affecting the growth of electricity demand. While energy efficiency initiatives and distributed resources can address a significant amount of this demand, the United States will likely still need new utility-scale generation resources. The energy sector uses capacity expansion planning models to determine the aggregate need for new generation, but these models are typically at the state or regional scale and are not equipped to address the wide range of location- and technology-specific issues that are increasingly a factor in power plant siting. To help address these challenges, we have developed the Geospatial Raster Input Data for Capacity Expansion Regional Feasibility (GRIDCERF) data package, a high-resolution product to evaluate siting suitability for renewable and non-renewable power plants in the conterminous United States. GRIDCERF offers 264 suitability layers for use with 56 power plant technologies in a harmonized format that can be easily ingested by geospatially-enabled modeling software allowing for customization to robustly address science objectives when evaluating varying future conditions.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2021

FAIR Interfaces for Geospatial Scientific Data Searches

Several factors must be considered in designing a highly accurate, reliable, scalable, and user-friendly geospatial data search interfaces. This paper examines four critical questions that ought to be considered during design phase: (1) Is the search interface or API that provides the search capability useable by both humans and machines? (2) Are the results consistent and reliable? (3) Is the output response format free to use, community-defined, and non-propriety? (4) Does the API clearly state the usage clauses? This paper discusses how certain data repositories at the US Department of Energy's Oak Ridge National Laboratory apply FAIR data principles to enable geospatial searches and address the above-mentioned questions.

Devarakonda, Ranjeet↗
DOE OSTI2025

Environmental Conditions Affecting Global Mesoscale Convective System Occurrence

Abstract The ERA5 environments of mesoscale convective systems (MCSs), tracked from satellite observations, are assessed over a 20-yr period. The use of a large set of MCS tracks allows us to robustly test the sensitivity of the results to factors such as region, latitude, and diurnal cycle. We aim to provide novel information on environments of observed MCSs for assessments of global atmospheric models and to improve their ability to simulate MCSs. Statistical analysis of all tracked MCSs is performed in two complementary ways. First, we investigate the environments when an MCS has occurred at different spatial scales before and after MCS formation. Several environmental variables are found to show marked changes before MCS initiation, particularly over land. The vertically integrated moisture flux convergence shows a robust signal across different regions and when considering MCS initiation diurnal cycle. We also found spatial scale dependence of the environments between 200 and 500 km, providing new evidence of a natural length scale for use with MCS parameterization. In the second analysis, the likelihood of MCS occurrence for given environmental conditions is evaluated, by considering all environments and determining the probability of being in an MCS core or shield region. These are compared to analogous non-MCS environments, allowing discrimination between conditions suitable for MCS and non-MCS occurrence. Three environmental variables are found to be useful predictors of MCS occurrence: total column water vapor, midlevel relative humidity, and total column moisture flux convergence. Such relations could be used as trigger conditions for the parameterization of MCSs, thereby strengthening the dependence of the MCS scheme on the environment. Significance Statement Large storm systems called mesoscale convective systems form across Earth. These are collections of thunderstorms, with associated high-level clouds that produce substantial, lighter rainfall and modulate Earth’s energy balance. They produce hazardous weather conditions, such as floods and high winds, and are responsible for a high percentage of rainfall in many regions globally. We investigate the environmental conditions under which they form, so that we can understand the spatial extent of the environment which is important for their formation, and also where and when the effects of these storms might be felt. The novel information generated here should help improve the representation of these storms in weather and climate models, improving the prediction of rainfall, thunderclouds, and high-level clouds.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Data for Microbial-Explicit Processes and Refined Perennial Plant Traits Improve Modeled Ecosystem Carbon Dynamics

Globally, soils hold approximately half of ecosystem carbon and can serve as a source or sink depending on climate, vegetation, management, and disturbance regimes. Understanding how soil carbon dynamics are influenced by these factors is essential to evaluate proposed natural climate solutions and policy regarding net ecosystem carbon balance. Soil microbes play a key role in both carbon fluxes and stabilization. However, biogeochemical models often do not specifically address microbial-explicit processes. Here, we incorporated microbial-explicit processes into the DayCent biogeochemical model to better represent large perennial grasses and mechanisms of soil carbon formation and stabilization. We also take advantage of recent model improvements to better represent perennial grass structural complexity and life-history traits. Specifically, this study focuses on: 1) a plant sub-model that represents perennial phenology and more refined plant chemistry with downstream implications for soil organic matter (SOM) cycling though litter inputs, 2) live and dead soil microbe pools that influence routing of carbon to physically protected and unprotected pools, 3) Michaelis-Menten kinetics rather than first-order kinetics in the soil decomposition calculations, and 4) feedbacks between decomposition and live microbial pools. We evaluated the performance of the plant sub-model and two SOM cycling sub-models, Michaelis-Menten (MM) and first-order (FO), using observations of net ecosystem production, ecosystem respiration, soil respiration, microbial biomass, and soil carbon from long-term bioenergy research plots in the mid-western United States. The MM sub-model represented seasonal dynamics of soil carbon fluxes better than the FO sub-model which consistently overestimated winter soil respiration. While both SOM sub-models were similarly calibrated to total, physically protected, and physically unprotected soil carbon measurements, the models differed in future soil carbon response to disturbance and climate, most notably in the protected pools. Adding microbial-explicit mechanisms of soil processes to ecosystem models will improve model predictions of ecosystem carbon balances but more data and research are necessary to validate disturbance and climate change responses and soil pool allocation.

Field Data↗