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NASA NTRS1986

A cloud model-radiative model combination for determining microwave TB-rain rate relations

The development of a cloud model-radiative transfer model combination for computing average brightness temperature, T(B), is discussed. The cloud model and radiative transfer model used in this study are described. The relations between rain rate, cloud and rain water, cloud and precipitation ice, and upwelling radiance are investigated. The effects of the rain rate relations on T(B) under different climatological conditions are examined. The model-derived T(B) results are compared to the 92 and 183 GHz aircraft observations of Hakkarinen and Adler (1984, 1986) and the radar-estimated rain rate of Hakkarinen and Adler (1986); good correlation between the data is detected.

Szejwach, Gerard↗

NASA NTRS1989

Proposed reference models for atomic oxygen in the terrestrial atmosphere

A provisional Atomic Oxygen Reference model was derived from average monthly ozone profiles and the MSIS-86 reference model atmosphere. The concentrations are presented in tabular form for the altitude range 40 to 130 km.

Llewellyn, E. J.↗

NASA NTRS1992

Model capabilities, 2-D

Two dimensional (2-D) atmospheric models provide results for altitude versus latitude as a function of time and are developed primarily for two reasons: to help understand atmospheric occurrences and to give assessments and/or make predictions of future changes in the atmosphere. Historically, the formulation of transport in 2-D models has been a difficult problem. Most current 2-D models have a transport that is either an Eulerian mean circulation with large stratospheric eddy diffusion or a residual (diabatic or Lagragian) mean circulation which typically is accompanied with small stratospheric eddy diffusion. Because of the assumption of zonal averaging, 2-D models are primarily useful in making predictions of atmospheric changes of time scales longer than a season. Although decadel atmospheric changes may be reasonably well represented with a 2-D model, the year to year changes which result from interannual transport differences, stratospheric warmings, semiannual oscillations, or quasi-biennial oscillations may not be well represented in the stratosphere and troposphere.

Jackman, Charles H.↗

NASA NTRS1976

Pioneer 10 and 11 and ground-based infrared data on Jupiter - The thermal structure and He-H2 ratio

Temperature profiles for four midlatitude regions on Jupiter and an improved value of the H2 molar mixing ratio are obtained from Pioneer 11 IR radiometer data and ground-based IR spectral data. The investigated regions include two in the Southern Hemisphere and two in the Northern Hemisphere, all of which consist of an adjacent belt and zone. The temperature profiles for the pressure regime between 0.1 and 1.0 bar are plotted along with the emitted net flux, flux divergence, and cooling rate for a temperature profile that is an average of those derived for the South Equatorial Belt and a 'cloudy' model of the South Tropical Zone. Averaging of the results obtained with clear and cloudy zone models yields a weighted mean value of 0.88 for the H2 molar mixing ratio, which corresponds to a He/H2 ratio of 0.14. It is emphasized that this value depends on perfect validity of the adopted opacity model, the absence of systematic errors in the data, and other factors. Local effective temperatures for each region are found to range from 124.2 to 127.6 K, which are close to the model-independent global average of 125 K.

Orton, G. S.↗

NASA NTRS1979

Monte Carlo simulation of lunar megaregolith and implications

A realistic Monte Carlo model closely simulating the evolution of the lunar megaregolith over a large area of 67 million sq. km of the front surface of the moon is presented. Craters larger than 100 km in diameter observed over the entire surface of the moon and those less than 100 km lying in the referenced area are included in the simulation. A total of 21,664 craters are processed. The model predicts the average thickness of the megaregolith to be about 1.9-2.0 km. Curves for the variation of the regolith thickness across the simulated area are given and show that about 50% of the area is covered with regolith less than 1 km thick. The model produces crater structures similar to the ones observed in the lunar highlands, it partially supports the layering theory for crater structures that the variations in strength and density of target materials may be responsible for the observed differences in the morphologies of lunar craters, and rules out the possibility that all craters when formed are bowl-shaped with a fixed depth/diameter ratio characteristic of small craters.

Aggarwal, H. R.↗

NASA NTRS2018

(GO)2-SIM: a GCM-Oriented Ground-Observation Forward-Simulator Framework for Objective Evaluation of Cloud and Precipitation Phase

General circulation model (GCM) evaluation using ground-based observations is complicated by inconsistencies in hydrometeor and phase definitions. Here we describe (GO)2-SIM, a forward simulator designed for objective hydrometeor-phase evaluation, and assess its performance over the North Slope of Alaska using a 1-year GCM simulation. For uncertainty assessment, 18 empirical relationships are used to convert model grid-average hydrometeor (liquid and ice, cloud, and precipitation) water contents to zenith polarimetric micropulse lidar and Ka-band Doppler radar measurements, producing an ensemble of 576 forward-simulation realizations. Sensor limitations are represented in forward space to objectively remove from consideration model grid cells with undetectable hydrometeor mixing ratios, some of which may correspond to numerical noise.Phase classification in forward space is complicated by the inability of sensors to measure ice and liquid signals distinctly. However, signatures exist in lidarâ€“radar space such that thresholds on observables can be objectively estimated and related to hydrometeor phase. The proposed phase-classification technique leads to misclassification in fewer than 8% of hydrometeor-containing grid cells. Such misclassifications arise because, while the radar is capable of detecting mixed-phase conditions, it can mistake water- for ice-dominated layers. However, applying the same classification algorithm to forward-simulated and observed fields should generate hydrometeor-phase statistics with similar uncertainty. Alternatively, choosing to disregard how sensors define hydrometeor phase leads to frequency of occurrence discrepancies of up to 40%. So, while hydrometeor-phase maps determined in forward space are very different from model "reality" they capture the information sensors can provide and thereby enable objective model evaluation.

Lamer, K.↗

NASA NTRS2018

Average Versus High Surface Ozone Levels over the Continental USA: Model Bias, Background Influences, and Interannual Variability

US background ozone (O3) includes O3 produced from anthropogenic O3 precursors emitted outside of the USA, from global methane, and from any natural sources. Using a suite of sensitivity simulations in the GEOS-Chem global chemistry transport model, we estimate the influence from individual background sources versus US anthropogenic sources on total surface O3 over 10 continental US regions from 2004 to 2012. Evaluation with observations reveals model biases of +0-19ppb in seasonal mean maximum daily 8h average (MDA8) O3, highest in summer over the eastern USA. Simulated high-O3 events cluster too late in the season. We link these model biases to excessive regional O3 production (e.g., US anthropogenic, biogenic volatile organic compounds (BVOCs), and soil NOx, emissions), or coincident missing sinks. On the 10 highest observed O3 days during summer (O3_top10obs_JJA), US anthropogenic emissions enhance O3 by 5-11ppb and by less than 2ppb in the eastern versus western USA. The O3 enhancement from BVOC emissions during summer is 1-7 ppb higher on O3_top10obs_JJA days than on average days, while intercontinental pollution is up to 2ppb higher on average versus on O3_top10obs_JJA days. During the summers of 2004-2012, monthly regional mean US background O3 MDA8 levels vary by up to 15ppb from year to year. Observed and simulated summertime total surface O3 levels on O3_top10obs_JJA days decline by 3ppb (averaged over all regions) from 2004-2006 to 2010-2012, reflecting rising US background (+2ppb) and declining US anthropogenic O3 emissions (6ppb) in the model. The model attributes interannual variability in US background O3 on O3_top10obs days to natural sources, not international pollution transport. We find that a 3-year averaging period is not long enough to eliminate interannual variability in background O3 on the highest observed O3 days.

Guo, Jean J.↗

NASA NTRS2014

Twin Jet Effects on Noise of Round and Rectangular Jets: Experiment and Model

Many subsonic and supersonic aircraft concepts proposed by NASA's Fundamental Aeronautics Program have asymmetric, integrated propulsion systems. The asymmetries in the exhaust of these propulsion systems create an asymmetric acoustic field. The asymmetries investigated in the current study are from twin jets and rectangular nozzles. Each effect produces its own variation of the acoustic field. An empirical model was developed to predict the acoustic field variation from round twin jets with twin jet spacing from 2.6 to 5.6, where s is the center-to-center spacing over the jet diameter. The model includes parameters to account for the effects of twin jet spacing, jet static temperature ratio, flight Mach number, frequency, and observer angle (both polar and azimuthal angles). The model was then applied to twin 2:1 and 8:1 aspect ratio nozzles to determine the impact of jet aspect ratio. For the round and rectangular jets, the use of the model reduces the average magnitude of the error over all frequencies, observation angles, and jet spacings by approximately 0.5dB when compared against the assumption of adding two jets incoherently.

Noise↗

NASA NTRS2017

Historic Global Biomass Burning Emissions for CMIP6 (BB4CMIP) Based on Merging Satellite Observations with Proxies and Fire Models (1750-2015)

Fires have influenced atmospheric composition and climate since the rise of vascular plants, and satellite data has shown the overall global extent of fires. Our knowledge of historic fire emissions has progressively improved over the past decades due mostly to the development of new proxies and the improvement of fire models. Currently there is a suite of proxies including sedimentary charcoal records, measurements of fire-emitted trace gases and black carbon stored in ice and firn, and visibility observations. These proxies provide opportunities to extrapolate emissions estimates based on satellite data starting in 1997, but each proxy has strengths and weaknesses regarding, for example, the spatial and temporal extents over which they are representative. We developed a new historic biomass burning emissions dataset starting in 1750 that merges the satellite record with several existing proxies, and uses the average of six models from the Fire Model Intercomparison Project (FireMIP) protocol to estimate emissions when the available proxies had limited coverage. According to our approach, global biomass burning emissions were relatively constant with 10-year averages varying between 1.8 and 2.3 petagrams of carbon per year. Carbon emissions increased only slightly over the full time period and peaked during the 1990's after which they decreased gradually. There is substantial uncertainty in these estimates and patterns varied depending on choices regarding data representation, especially on regional scales. The observed pattern in fire carbon emissions is for a large part driven by African fires, which accounted for 58 percent of global fire carbon emissions. African fire emissions declined since about 1950 due to conversion of savanna to cropland, and this decrease is partially compensated for by increasing emissions in deforestation zones of South America and Asia. These global fire emissions estimates are mostly suited for global analyses and will be used in the Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations.

Biomass burning; Satellite observations; computer ↗

NASA NTRS2002

Scale Dependence of Statistics of Spatially Averaged Rain Rate Seen in TOGA COARE Comparison with Predictions from a Stochastic Model

A characteristic feature of rainfall statistics is that they in general depend on the space and time scales over which rain data are averaged. As a part of an earlier effort to determine the sampling error of satellite rain averages, a space-time model of rainfall statistics was developed to describe the statistics of gridded rain observed in GATE. The model allows one to compute the second moment statistics of space- and time-averaged rain rate which can be fitted to satellite or rain gauge data to determine the four model parameters appearing in the precipitation spectrum - an overall strength parameter, a characteristic length separating the long and short wavelength regimes and a characteristic relaxation time for decay of the autocorrelation of the instantaneous local rain rate and a certain 'fractal' power law exponent. For area-averaged instantaneous rain rate, this exponent governs the power law dependence of these statistics on the averaging length scale $L$ predicted by the model in the limit of small $L$. In particular, the variance of rain rate averaged over an $L \times L$ area exhibits a power law singularity as $L \rightarrow 0$. In the present work the model is used to investigate how the statistics of area-averaged rain rate over the tropical Western Pacific measured with ship borne radar during TOGA COARE (Tropical Ocean Global Atmosphere Coupled Ocean Atmospheric Response Experiment) and gridded on a 2 km grid depends on the size of the spatial averaging scale. Good agreement is found between the data and predictions from the model over a wide range of averaging length scales.

Kundu, Prasun K.↗

NASA NTRSDate not supplied

An Artificial Neural Network Approach to Predict Rotor-Airframe Acoustic Waveforms

A surrogate artificial neural network/machine learning model was developed to predict the acoustic interaction for a fixed-pitch rotor in proximity to a downstream cylindrical airframe typical of small Unmanned Aerial System (sUAS) platforms. The model was trained to predict the acoustic waveform under representative hover conditions as a function of rotational speed, airframe proximity, and observer angle. Training data were acquired in an anechoic chamber on both isolated rotors and rotor-airframe configurations. Acoustic amplitude and phase of the revolution-averaged interaction were predicted, which required up to 25 harmonics to capture the impulse event caused by the blade’s approach and departure from the airframe. Prediction performance showed, on average, that the models could estimate the acoustic amplitude and phase over the relevant harmonics for unseen conditions with 86% and 75% accuracy, respectively, enabling a time domain reconstruction of the waveform for the range of geometric and flow parameters tested.

acoustics↗

NASA NTRSDate not supplied

An Artificial Neural Network Approach to Predict Rotor-Airframe Acoustic Waveforms

acoustics↗

NASA NTRS2004

A new Mars radiation environment model with visualization

A new model for the radiation environment to be found on the planet Mars due to Galactic Cosmic Rays (OCR) has been developed at the NASA Langley Research Center. Solar modulated primary particles rescaled for Mars conditions are transported through the Martian atmosphere, with temporal properties modeled with variable timescales, down to the surface, with altitude and backscattering patterns taken into account. The Martian atmosphere has been modeled by using the Mars Global Reference Atmospheric Model--version 2001 (Mars-GRAM 2001). The altitude to compute the atmospheric thickness profile has been determined by using a model for the topography based on the data provided by the Mars Orbiter Laser Altimeter (MOLA) instrument on board the Mars Global Surveyor (MGS) spacecraft. The Mars surface composition has been modeled based on averages over the measurements obtained from orbiting spacecraft and at various landing sites, taking into account the possible volatile inventory (e.g., CO2 ice, H2O ice) along with its time variation throughout the Martian year. Particle transport has been performed with the HZETRN heavy ion code. The Mars Radiation Environment Model has been made available worldwide through the Space Ionizing Radiation Effects and Shielding Tools (SIREST) website, a project of NASA Langley Research Center. c2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

NASA Center LaRC↗

NASA NTRS1988

Evolution of the Antarctic polar vortex in spring: Response of a GCM to a prescribed Antarctic ozone hole

The possible effect of the Antartic ozone hole on the evolution of the polar vortex during late winter and spring using a general circulation model (GCM) is examined. The GCM is a version of the NCAR Community Climate Model whose domain extends from the surface to the mesosphere and is similar to that described on Boville and Randel (1986). Ozone is not a predicted variable in the model. A zonally averaged ozone distribution is specified as a function of latitude, pressure and month for the radiation parameterization. Rather that explicitly address reasons for the formation of the ozone hole, researchers postulate its existence and ask what effect it has on the subsequent evolution of the vortex. The evolution of the model when an ozone hole is imposed is then discussed.

Boville, B. A.↗

NASA NTRS1990

Numerical analysis of secondary flow in a two-stage turbine

The three-dimensional viscous average passage flow in the Pratt and Whitney alternate design Space Shuttle Main Engine fuel turbine has been simulated. The effect of secondary flows generated by upstream blade rows on the performance of downstream blade rows is studied. The numerical results are compared to the design intent to validate improved models in the average passage equations. Analysis of the results centers on the primary spanwise mixing mechanism in this low aspect ratio turbine. A multigrid method has also been incorporated to improve the overall convergence rate of the numerical algorithm.

Kirtley, K. R.↗

NASA NTRS2014

Additional Evidence Supporting a Model of Shallow, High-Speed Supergranulation

Recently, Duvall and Hanasoge (Solar Phys. 287, 71, 2013) found that large distance separation [delta] travel-time differences from a center to an annulus [deltat(sub oi)] implied a model of the average super granular cell that has a peak upflow of 240 ms(exp −1) at a depth of 2.3 Mm and a corresponding peak outward horizontal flow of 700 ms(exp −1) at a depth of 1.6 Mm. In the present work, this effect is further studied by measuring and modeling center-to-quadrant travel-time differences [deltat(sub qu)], which roughly agree with this model. Simulations are analyzed that show that such a model flow would lead to the expected travel-time differences. As a check for possible systematic errors, the center-to-annulus travel-time differences [deltat(sub oi)] are found not to vary with heliocentric angle. A consistency check finds an increase of deltat(sub oi) with the temporal frequency [ν] by a factor of two, which is not predicted by the ray theory.

Helioseismology↗

NASA NTRS1990

Dynamic crystallization study of barred olivine chondrules

The 'classic' barred olivine (BO) texture was defined by Donaldson (1976) as a single-plate dendrite which shares the entire chondrule with the remaining glass or subsequent crystallization products. This paper describes experiments in which BO textures were produced experimentally from two starting compositions: one modeled after the average BO chondrule composition in L-chondrites determined by Weisberg (1987), and the other after an olivine-rich composition (CH-1) studied by Lofgren (1989). It is shown that most of the textural features observed in natural BO chondrules are replicated in the experimentally produced chondrules. Several new constraints on models for the chondrule-forming process are proposed.

Lofgren, Gary↗

NASA NTRS2009

Hybrid Reynolds-Averaged/Large-Eddy Simulations of a Co-Axial Supersonic Free-Jet Experiment

Reynolds-averaged and hybrid Reynolds-averaged/large-eddy simulations have been applied to a supersonic coaxial jet flow experiment. The experiment utilized either helium or argon as the inner jet nozzle fluid, and the outer jet nozzle fluid consisted of laboratory air. The inner and outer nozzles were designed and operated to produce nearly pressure-matched Mach 1.8 flow conditions at the jet exit. The purpose of the computational effort was to assess the state-of-the-art for each modeling approach, and to use the hybrid Reynolds-averaged/large-eddy simulations to gather insight into the deficiencies of the Reynolds-averaged closure models. The Reynolds-averaged simulations displayed a strong sensitivity to choice of turbulent Schmidt number. The baseline value chosen for this parameter resulted in an over-prediction of the mixing layer spreading rate for the helium case, but the opposite trend was noted when argon was used as the injectant. A larger turbulent Schmidt number greatly improved the comparison of the results with measurements for the helium simulations, but variations in the Schmidt number did not improve the argon comparisons. The hybrid simulation results showed the same trends as the baseline Reynolds-averaged predictions. The primary reason conjectured for the discrepancy between the hybrid simulation results and the measurements centered around issues related to the transition from a Reynolds-averaged state to one with resolved turbulent content. Improvements to the inflow conditions are suggested as a remedy to this dilemma. Comparisons between resolved second-order turbulence statistics and their modeled Reynolds-averaged counterparts were also performed.

Baurle, R. A.↗