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NASA NTRS2004

Activities of NASA's Global Modeling Initiative (GMI) in the Assessment of Subsonic Aircraft Impact

The Intergovernmental Panel on Climate Change estimated a peak increase in ozone ranging from 7-12 ppbv (zonal and annual average, and relative to a baseline with no aircraft), due to the subsonic aircraft in the year 2015, corresponding to aircraft emissions of 1.3 TgN/year. This range of values presumably reflects differences in model input (e.g., chemical mechanism, ground emission fluxes, and meteorological fields), and algorithms. The model implemented by the Global Modeling Initiative allows testing the impact of individual model components on the assessment calculations. We present results of the impact of doubling the 1995 aircraft emissions of NOx, corresponding to an extra 0.56 TgN/year, utilizing meteorological data from NASA's Data Assimilation Office (DAO), the Goddard Institute for Space Studies (GISS), and the Middle Atmosphere Community Climate Model, version 3 (MACCM3). Comparison of results to observations can be used to assess the model performance. Peak ozone perturbations ranging from 1.7 to 2.2 ppbv of ozone are calculated using the different fields. These correspond to increases in total tropospheric ozone ranging from 3.3 to 4.1 Tg/Os. These perturbations are consistent with the IPCC results, due to the difference in aircraft emissions. However, the range of values calculated is much smaller than in IPCC.

Rodriquez, J. M.↗
NASA NTRS2020

Toward Coupled Data Assimilation in NASA’s GEOS: Developments in the Ocean Context

The Global Modeling & Assimilation Office (GMAO) at NASA GSFC produces analyses and predictions of the Earth system using various configurations of the Goddard Earth Observing System (GEOS) model and assimilation system. The current sub-seasonal-to-seasonal prediction system (GEOS-S2S) is based on a coupled atmosphere-ocean-land-ice configuration of GEOS which includes the Modular Ocean Model version 5 (MOM5) run at approximately 50-km resolution and a de-coupled OI-based ocean analysis that uses an initialization of MOM5 forced by the MERRA-2 reanalysis. GMAO will soon implement an updated GEOS-S2S system that will run at 25-km resolution and adopt aspects of the hybrid four-dimensional ensemble-variational (H4DEnVar) system already running in the production-version atmospheric analysis system, including a Local Ensemble Transform Kalman Filter (LETKF) to provide initial conditions for the oceanic state. This presentation will focus on developments to sustain the GMAO's systems on longer time horizons, where more radical transformations will be required to adapt to advanced computing environments, higher resolution and more diverse model components, and new observations for the Earth system. Results will describe progress toward a version of the GEOS coupled system that will be based around the Joint Effort for Data assimilation Integration (JEDI) framework being developed within Joint Center for Satellite Data Assimilation (JCSDA) and include an updated ocean model, MOM6. Discussion will focus specifically on the use of a Unified Forward Operator (UFO) for simulating observations and the Object Oriented Prediction System (OOPS) for providing the state estimate. These features are being developed as a multi-agency effort under the auspices of the JCSDA and are being adopted in the GMAO for all its applications of coupled data assimilation including S2S, numerical weather prediction, and reanalysis.

Mahajan, Rahul↗
NASA NTRS2023

A Surface Radiation Balance Data Set from Siple Dome in West Antarctica for Atmospheric and Climate Model Evaluation

A field campaign at Siple Dome in West Antarctica during the austral summer 2019-2020 offers an opportunity to evaluate climate model performance, particularly cloud microphysical simulation. Over Antarctic ice sheets and ice shelves, clouds are a major regulator of the surface energy balance, and in the warm season their presence occasionally induces surface melt that can gradually weaken an ice shelf structure. This dataset from Siple Dome, obtained using transportable and solar-poweredequipment, includes surface energy balance measurements, meteorology and cloud remote sensing. To demonstrate how these data can be used to evaluate model performance, comparisons are made with meteorological reanalysis known to give generally good performance over Antarctica (ERA5). Surface albedo measurements show expected variability with observed cloud amount, and can be used to evaluate a model's snowpack parameterization. One case study discussed involves a squall with northerly winds, during which ERA5 fails to produce cloud cover throughout one of the days. A second case study illustrates how shortwave spectroradiometer measurements that encompass the 1.6-micron atmospheric window reveal cloud phase transitions associated with cloud lifecycle. Here, continuously precipitating mixed-phase clouds become mainly liquid water clouds from local morning through the afternoon, not reproduced by ERA5. We challenge researchers to run their various regional or global models in a manner that has the large-scale meteorology follow the conditions of this field campaign, compare cloud and radiation simulations with this Siple Dome dataset, and potentially investigate why cloud microphysical simulations or other model components might produce discrepancies with these observations.

cloud remote sensing↗
NASA NTRSDate not supplied

The Flight Dynamics Risk Assessment of Artemis I

With launch vehicles and spacecraft, it is necessary to dynamically test the structure to validate structural models. These validated models are then used to determine a launch vehicle's control stability margin and the loads on the structure. While often a dedicated structural test article is used to correlate the integrated structure in preparation for the final analysis cycles, the Artemis I flight is using an approach where the components of the launch vehicle are dynamically tested and the component models validated. The fully integrated vehicle is not tested until a few months before launch, which limits the ability to fully correlate a model prior to launch. This paper introduces the Flight Dynamics Risk Assessment of the vehicle, which is the process being used to determine the adequacy of the vehicle structural model after the Integrated Modal Test. This work outlines the process of quickly tuning a model post-test then determining any control margin violations and increases in loads due to that tuned model.

Eric C Stewart↗
NASA NTRSDate not supplied

The Flight Dynamics Risk Assessment of Artemis I

With launch vehicles and spacecraft, it is necessary to dynamically test the structure to validate structural models. These validated models are then used to determine a launch vehicle's control stability margin and the loads on the structure. While often a dedicated structural test article is used to correlate the integrated structure in preparation for the final analysis cycles, the Artemis I flight is using an approach where the components of the launch vehicle are dynamically tested and the component models validated. The fully integrated vehicle is not tested until a few months before launch, which limits the ability to fully correlate a model prior to launch. This paper introduces the Flight Dynamics Risk Assessment of the vehicle, which is the process being used to determine the adequacy of the vehicle structural model after the Integrated Modal Test. This work outlines the process of quickly tuning a model post-test then determining any control margin violations and increases in loads due to the tuning of the model.

Eric C Stewart↗
NASA NTRS1993

Enhancements to the Engine Data Interpretation System (EDIS)

The Engine Data Interpretation System (EDIS) expert system project assists the data review personnel at NASA/MSFC in performing post-test data analysis and engine diagnosis of the Space Shuttle Main Engine (SSME). EDIS uses knowledge of the engine, its components, and simple thermodynamic principles instead of, and in addition to, heuristic rules gathered from the engine experts. EDIS reasons in cooperation with human experts, following roughly the pattern of logic exhibited by human experts. EDIS concentrates on steady-state static faults, such as small leaks, and component degradations, such as pump efficiencies. The objective of this contract was to complete the set of engine component models, integrate heuristic rules into EDIS, integrate the Power Balance Model into EDIS, and investigate modification of the qualitative reasoning mechanisms to allow 'fuzzy' value classification. The results of this contract is an operational version of EDIS. EDIS will become a module of the Post-Test Diagnostic System (PTDS) and will, in this context, provide system-level diagnostic capabilities which integrate component-specific findings provided by other modules.

Hofmann, Martin O.↗
NASA NTRS1993

Enhancements to the Engine Data Interpretation System (EDIS)

The Engine Data Interpretation System (EDIS) expert system project assists the data review personnel at NASA/MSFC in performing post-test data analysis and engine diagnosis of the Space Shuttle Main Engine (SSME). EDIS uses knowledge of the engine, its components, and simple thermodynamic principles instead of, and in addition to, heuristic rules gathered from the engine experts. EDIS reasons in cooperation with human experts, following roughly the pattern of logic exhibited by human experts. EDIS concentrates on steady-state static faults, such as small leaks, and component degradations, such as pump efficiencies. The objective of this contract was to complete the set of engine component models, integrate heuristic rules into EDIS, integrate the Power Balance Model into EDIS, and investigate modification of the qualitative reasoning mechanisms to allow 'fuzzy' value classification. The result of this contract is an operational version of EDIS. EDIS will become a module of the Post-Test Diagnostic System (PTDS) and will, in this context, provide system-level diagnostic capabilities which integrate component-specific findings provided by other modules.

Hofmann, Martin O.↗
NASA NTRS1993

Population II Li-6 as a probe of nucleosynthesis and stellar structure and evolution

We discuss the importance of Population II Li-6 as a diagnostic for models of primordial nucleosynthesis, cosmic-ray nucleosyntheses in the early Galaxy, and the structure and evolution of metal-poor solar-type stars. The observation of Li-6 in the subdwarf HD 84937 is shown to be consistent with the existing Population II LiBeB data within the context of a simple three-component model: (1) standard big bang nucleosynthesis, (2) Population II cosmic-ray nucleosynthesis, (3) standard (nonrotating) stellar LiBeB depletion. If this interpretation is correct, we predict a potentially detectable boron abundance for this star: about 2 x 10 exp -12. Subsequent Population II LiBeB observations, and in particular further observations of Population II Li-6, are shown to be crucial to our understanding of the primordial and early galactic creation and destruction mechanisms for light elements.

Steigman, Gary↗
NASA NTRS1997

Revised Simulation Model of the Control System, Displays, and Propulsion System for a ASTOVL Lift Fan Aircraft

This report describes revisions to a simulation model that was developed for use in piloted evaluations of takeoff, transition, hover, and landing characteristics of an advanced short takeoff and vertical landing lift fan fighter aircraft. These revisions have been made to the flight/propulsion control system, head-up display, and propulsion system to reflect recent flight and simulation experience with short takeoff and vertical landing operations. They include nonlinear inverse control laws in all axes (eliminating earlier versions with state rate feedback), throttle scaling laws for flightpath and thrust command, control selector commands apportioned based on relative effectiveness of the individual controls, lateral guidance algorithms that provide more flexibility for terminal area operations, and a simpler representation of the propulsion system. The model includes modes tailored to the phases of the aircraft's operation, with several response types which are coupled to the aircraft's aerodynamic and propulsion system effectors through a control selector tailored to the propulsion system. Head-up display modes for approach and hover are integrated with the corresponding control modes. Propulsion system components modeled include a remote lift fan and a lift-cruise engine. Their static performance and dynamic responses are represented by the model. A separate report describes the subsonic, power-off aerodynamics and jet induced aerodynamics in hover and forward flight, including ground effects.

Franklin, James A.↗
NASA NTRS2010

Agricultural Productivity Forecasts for Improved Drought Monitoring

Water stresses on agricultural crops during critical phases of crop phenology (such as grain filling) has higher impact on the eventual yield than at other times of crop growth. Therefore farmers are more concerned about water stresses in the context of crop phenology than the meteorological droughts. However the drought estimates currently produced do not account for the crop phenology. US Department of Agriculture (USDA) and National Oceanic and Atmospheric Administration (NOAA) have developed a drought monitoring decision support tool: The U.S. Drought Monitor, which currently uses meteorological droughts to delineate and categorize drought severity. Output from the Drought Monitor is used by the States to make disaster declarations. More importantly, USDA uses the Drought Monitor to make estimates of crop yield to help the commodities market. Accurate estimation of corn yield is especially critical given the recent trend towards diversion of corn to produce ethanol. Ethanol is fast becoming a standard 10% ethanol additive to petroleum products, the largest traded commodity. Thus the impact of large-scale drought will have dramatic impact on the petroleum prices as well as on food prices. USDA's World Agricultural Outlook Board (WAOB) serves as a focal point for economic intelligence and the commodity outlook for U.S. WAOB depends on Drought Monitor and has emphatically stated that accurate and timely data are needed in operational agrometeorological services to generate reliable projections for agricultural decision makers. Thus, improvements in the prediction of drought will reflect in early and accurate assessment of crop yields, which in turn will improve commodity projections. We have developed a drought assessment tool, which accounts for the water stress in the context of crop phenology. The crop modeling component is done using various crop modules within Decision Support System for Agrotechnology Transfer (DSSAT). DSSAT is an agricultural crop simulation system, which integrates the effects of soil, crop phenotype, weather, and management options. It has been in use for more than 15 years by researchers, growers and has become a de-facto standard in crop modeling communities spanning over 100 countries. The meteorological forcings to DSSAT are provided by NASA s National Land Data Assimilation System (NLDAS) datasets. NLDAS is a framework that incorporates atmospheric forcing and land parameter values along with land surface models to diagnose and predict the state of the land surface.

Limaye, Ashutosh↗
NASA NTRS2016

A Unified Model for GRB Prompt Emission from Optical to Gamma-Rays; Exploring GRBs as Standard Candles

The origin of prompt emission from gamma-ray bursts (GRBs) remains to be an open question. Correlated prompt optical and gamma-ray emission observed in a handful of GRBs strongly suggests a common emission region, but failure to adequately fit the broadband GRB spectrum prompted the hypothesis of different emission mechanisms for the low- and high-energy radiations. We demonstrate that our multi-component model for GRB -ray prompt emission provides an excellent fit to GRB 110205A from optical to gamma-ray energies. Our results show that the optical and highest gamma-ray emissions have the same spatial and spectral origin, which is different from the bulk of the X- and softest gamma-ray radiation. Finally, our accurate redshift estimate for GRB 110205A demonstrates promise for using GRBs as cosmological standard candles.

acceleration of particles – black hole physics â↗
NASA NTRS2010

Attempts to Simulate Anisotropies of Solar Wind Fluctuations Using MHD with a Turning Magnetic Field

We examine a "two-component" model of the solar wind to see if any of the observed anisotropies of the fields can be explained in light of the need for various quantities, such as the magnetic minimum variance direction, to turn along with the Parker spiral. Previous results used a 3-D MHD spectral code to show that neither Q2D nor slab-wave components will turn their wave vectors in a turning Parker-like field, and that nonlinear interactions between the components are required to reproduce observations. In these new simulations we use higher resolution in both decaying and driven cases, and with and without a turning background field, to see what, if any, conditions lead to variance anisotropies similar to observations. We focus especially on the middle spectral range, and not the energy-containing scales, of the simulation for comparison with the solar wind. Preliminary results have shown that it is very difficult to produce the required variances with a turbulent cascade.

Ghosh, Sanjoy↗
NASA NTRS1990

Spatially resolved optical and near infrared spectroscopy of I Zw 18

For a long time, I Zw 18 has been recognized as the lowest abundance extra-galactic HII region (with the possible recent exception of SBS 0335-052; Izotov 1989). As such, it is important for many studies, including the determination of the primordial helium abundance. Recent imaging studies of I Zw 18 have revealed a more complex structure to I Zw 18 than the simple two-component model previously assumed. This has given rise to concern about the reliability of chemical abundance measurements derived for I Zw 18. Researchers have obtained long-slit spectra covering the wavelength range lambda 3650 to lambda 10,000, which allow us to measure physical parameters and chemical abundances as a function of position. With these new data we can investigate the SE component, which has not been studied previously, and we can address some of the concerns about abundance uncertainties.

Skillman, Evan D.↗
NASA NTRS1991

Observations of the Galactic center 511 keV line

A review of observations of the positron annihilation 511 keV line from the Galactic center and plane is presented. Emphasis is given to the new data from balloon observations in 1988 and 1989. The positron annihilation source in the direction of the center was found to be turned on again in 1988 October after being observed in a quiescent state since the early 1980s. There is evidence for variability between May and October in 1988. The new observations give the first data in which the line is spectrally resolved and in which the Galactic center and plane components of the annihilation radiation are independently measured. These data support the two-component model of the emission with a variable point source near the center and a steady-state source distributed along the galactic plane. Comparing measurements of narrow and wide field instruments in the 1980s gives a flux of about 8 x 10 exp -4 photons/sq cm/s for the point source in its high state and a flux of about 1.2 x 10 exp-3 photons/sq cm/s/rad for the galactic plane component with a relatively flat distribution over the central radian. The line width for the point source component is about 3 keV FWHM.

Gehrels, Neil↗
NASA NTRS2010

Using Leaf Chlorophyll to Parameterize Light-Use-Efficiency Within a Thermal-Based Carbon, Water and Energy Exchange Model

Chlorophylls absorb photosynthetically active radiation and thus function as vital pigments for photosynthesis, which makes leaf chlorophyll content (C(sub ab) useful for monitoring vegetation productivity and an important indicator of the overall plant physiological condition. This study investigates the utility of integrating remotely sensed estimates of C(sub ab) into a thermal-based Two-Source Energy Balance (TSEB) model that estimates land-surface CO2 and energy fluxes using an analytical, light-use-efficiency (LUE) based model of canopy resistance. The LUE model component computes canopy-scale carbon assimilation and transpiration fluxes and incorporates LUE modifications from a nominal (species-dependent) value (LUE(sub n)) in response to short term variations in environmental conditions, However LUE(sub n) may need adjustment on a daily timescale to accommodate changes in plant phenology, physiological condition and nutrient status. Day to day variations in LUE(sub n) were assessed for a heterogeneous corn crop field in Maryland, U,S.A. through model calibration with eddy covariance CO2 flux tower observations. The optimized daily LUE(sub n) values were then compared to estimates of C(sub ab) integrated from gridded maps of chlorophyll content weighted over the tower flux source area. The time continuous maps of daily C(sub ab) over the study field were generated by focusing in-situ measurements with retrievals generated with an integrated radiative transfer modeling tool (accurate to within +/-10%) using at-sensor radiances in green, red and near-infrared wavelengths acquired with an aircraft imaging system. The resultant daily changes in C(sub ab) within the tower flux source area generally correlated well with corresponding changes in daily calibrated LUE(sub n) derived from the tower flux data, and hourly water, energy and carbon flux estimation accuracies from TSEB were significantly improved when using C(sub ab) for delineating spatio-temporal variations in LUE(sub n). The results demonstrate the synergy between thermal infrared and shortwave reflective wavebands in producing valuable remote sensing data for operational monitoring of carbon and water fluxes.

Houlborg, Rasmus↗
NASA NTRS1983

The quiescent chromospheres and transition regions of active dwarf stars - What are we learning from recent observations and models?

Progress in understanding active dwarf stars based on recent IUE, Einstein, and ground-based observations is reviewed. The extent of magnetic field control over nonflare phenomena in active dwarf stars is considered, and the spatial homogeneity and time variability of active dwarf atmospheres is discussed. The possibility that solar like flux tubes can explain enhanced heating in active dwarf stars in examined, and the roles of systematic flows in active dwarf star atmospheres are considered. The relation between heating rates in different layers of active dwarf stars is summarized, and the mechanism of chromosphere and transition region heating in these stars are discussed. The results of one-component and two-component models of active dwarf stars are addressed.

Linsky, J. L.↗
NASA NTRS1997

Direct Aerosol Radiative Forcing: Calculations and Measurements from the Tropospheric

Radiative forcing is defined as the change in the net (downwelling minus upwelling) radiative flux at a given level in the atmosphere. This net flux is the radiative power density available to drive climatic processes in the earth-atmosphere system below that level. Recent research shows that radiative forcing by aerosol particles is a major source of uncertainty in climate predictions. To reduce those uncertainties, TARFOX was designed to determine direct (cloud-free) radiative forcing by the aerosols in one of the world's major industrial pollution plumes--that flowing from the east coast of the US over the Atlantic Ocean. TARFOX measured a variety of aerosol radiative effects (including direct forcing) while simultaneously measuring the chemical, physical, and optical properties of the aerosol particles causing those effects. The resulting data sets permit a wide variety of tests of the consistency, or closure, among the measurements and the models that link them. Because climate predictions use the same or similar model components, closure tests help to assess and reduce prediction uncertainties. In this work we use the TARFOX-determined aerosol, gas, and surface properties to compute radiative forcing for a variety of aerosol episodes, with inadvisable optical depths ranging from 0.07 to 0.6. We calculate forcing by several techniques with varying degrees of sophistication, in part to test the range of applicability of simplified techniques--which are often the only ones feasible in climate predictions by general circulation models (GCMs). We then compare computed forcing to that determined from: (1) Upwelling and downwelling fluxes (0.3-0.7 mm and 0.7-3.0 mm) measured by radiometers on the UK MRF C-130. and (2) Daily average cloud-free absorbed solar and emitted thermal radiative flux at the top of the atmosphere derived from the AVHRR radiometer on the NOAA- 14 satellite. The calculations and measurements all yield aerosol direct radiative forcing in the range -50 to -190 W sq m per unit inadvisable optical depth. The magnitudes are about 15 to 100 times larger than the global-average direct forcing expected for the global-average sulfate aerosol optical depth of 0.04. The reasons for the larger forcing in TARFOX include the relatively large optical depths and the focus on cloud-free, daytime conditions over the dark ocean surface. These are the conditions that produce the actual major radiative forcing events that contribute to any global-average climate effect. Detailed comparisons of calculated and measured forcings for specific events are used for more refined tests of closure.

Russell, P. B.↗
NASA NTRS1991

Basic research in solar physics

This grant, dating back more than 20 years has supported a variety of investigations of the chromospheres and coronae of the Sun and related cool stars by the Principal Investigator, his postdocs and graduate students, and colleagues at other institutions. This work involved studies of radiative transfer and spectral line formation theory, and the application of these techniques to the analysis of spectra obtained from space and ground-based observatories in the optical, ultraviolet, x-ray and radio portions of the spectrum. Space observations have included the analysis of spectra from OSO-7, Skylab, SMM, and the HRTS rocket experiments. Recent work has concentrated on the interaction of magnetic fields, plasma and radiation in the outer atmospheres of the Sun and other magnetically active stars with different fundamental parameters. Our study of phenomena common to the Sun and stars, the 'solar-stellar connection', can elucidate the fundamental physics, because spatially-resolved observations of the Sun provide us with the 'groundtruth,' while interpretation of stellar data permit us to isolate those parameters critical to stellar activity. Recently, we have studied the differences in physical properties between solar regions of high magnetic flux density and the surrounding plasma. High-resolution CN and CO spectroheliograms have been used to model the thermal inhomogeneities driven by unstable CO cooling, and we have analyzed spatially resolved UV spectra from HRTS to model the thermal structure and energy balance of small-scale structures. The study of nonlinear relations between atmospheric radiative losses and the photospheric magnetic flux density has been continued. We have also proposed a new model for the decay of plages by random walk diffusion of magnetic flux. Our analysis of phenomena common to the Sun and stars included the application of available spectroscopic diagnostics, establishing evidence that the atmospheres of the least active stars are heated at a 'basal' rate that is also found in the centers of solar supergranules, and using the Doppler-imaging technique to measure the position, size, and brightness of stellar active regions. We are computing multi-component models for solar and stellar atmospheres, and models for coronal loops and for the transition-region down flows. The study of solar and stellar flares permits us to assess the role of turbulent energy transport, to pinpoint the mechanism behind Type I radio bursts, to determine whether plasma radiation or cyclotron maser is responsible for microwave flares on M dwarfs, and to extend our knowledge of the basic physics pertinent to cyclotron-maser processes operating on the Sun.

Linsky, Jeffrey L.↗