Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “terrestrial models”

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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Modelling and Laboratory Testing of Particle Resuspension and Transport for the Assessment of Terrestrial-Borne Biological Contamination of the Samples on the Mars 2020 Mission

The Mars 2020 mission will land a rover on the surface of Mars that will acquire, encapsulate, and cache scientifically selected samples of martian material for possible return to Earth by a future mission. The samples will be individually encapsulated and sealed in sample tubes. Each sample, and therefore each sample tube, must be kept clean of viable organisms with a terrestrial origin, which may adhere to the rover on their own and/or on other non-biological particles. Therefore, contrary to previous missions to the Red Planet, Mars 2020 is subject to new and more stringent biological, organic and inorganic contamination requirements. This paper reports on the analyses and testing performed to assess the various vectors that can lead to the terrestrial-borne contamination of the samples, focusing on those that are predicted to be the larger contributors. Specifically, the contamination of the sample tubes is expected to be very small prior to the commencement of the mission’s science phase since these tubes are protected by so-called Fluid Mechanical Particle Barriers. Once on the surface of Mars however the sample tubes will be removed from their FMPBs and be subject to contamination from the rover. Of specific interest is the vector by which winds dislodge some particles from the surface of the rover and transport them to the surrounding soil. Naturally, such assessments require multi-disciplinary analyses involving at minimum the physics of particle adhesion and resuspension from surfaces, fluid mechanics and aerosols. Here we provide an overview of these models. We also report on particle resuspension experiments we have performed at the Jet Propulsion Laboratory to both guide and validate the aforementioned physics models.

Steltzner, Adam↗
NASA NTRS2020

The Impact of Planetary Rotation Rate on the Reflectance and Thermal Emission Spectrum of Terrestrial Exoplanets Around Sun-L ike Stars

Robust atmospheric and radiative transfer modeling will be required to properly interpret reflected light and thermal emission spectra of terrestrial exoplanets. This will help break observational degeneracies between the numerous atmospheric, planetary, and stellar factors that drive planetary climate. Here we simulate the climates of Earth-like worlds around the Sun with increasingly slow rotation periods, from Earth-like to fully Sun-synchronous, using the ROCKE-3D general circulation model. We then provide these results as input to the Spectral Planet Model (SPM), which employs the SMART radiative transfer model to simulate the spectra of a planet as it would be observed from a future space-based telescope. We find that the primary observable effects of slowing planetary rotation rate are the altered cloud distributions, altitudes, and opacities which subsequently drive many changes to the spectra by altering the absorption band depths of biologically-relevant gas species (e.g., H2O, O2, and O3). We also identify a potentially diagnostic feature of synchronously rotating worlds in mid-infrared H2O absorption/emission lines.

Scott D Guzewich↗
NASA NTRS2012

Transforming Community Access to Space Science Models

Researching and forecasting the ever changing space environment (often referred to as space weather) and its influence on humans and their activities are model-intensive disciplines. This is true because the physical processes involved are complex, but, in contrast to terrestrial weather, the supporting observations are typically sparse. Models play a vital role in establishing a physically meaningful context for interpreting limited observations, testing theory, and producing both nowcasts and forecasts. For example, with accurate forecasting of hazardous space weather conditions, spacecraft operators can place sensitive systems in safe modes, and power utilities can protect critical network components from damage caused by large currents induced in transmission lines by geomagnetic storms.

MacNeice, Peter↗
NASA NTRS2018

Attribution of Flux Partitioning Variations Between Land Surface Models over the Continental U.S.

Accurate quantification of the terrestrial evapotranspiration (ET) components of plant transpiration (T), soil evaporation (E) and evaporation of the intercepted water (I) is necessary for improving our understanding of the links between the carbon and water cycles. Recent studies have noted that, among the modeled estimates, large disagreements exist in the relative contributions of T, E and I to the total ET. As these models are often used in data assimilation environments for incorporating and extending ET relevant remote sensing measurements, understanding the sources of inter-model differences in ET components is also necessary for improving the utilization of such remote sensing measurements. This study quantifies the contributions of two key factors explaining inter-model disagreements to the uncertainty in total ET: (1) contribution of the local partitioning and (2) regional distribution of ET. The analysis is conducted by using outputs from a suite of land surface models in the North American Land Data Assimilation System (NLDAS) configuration. For most of these models, transpiration is the dominant component of the ET partition. The results indicate that the uncertainty in local partitioning dominates the inter-model spread in modeled soil evaporation E. The inter-model differences in T are dominated by the uncertainty in the distribution of ET over the Eastern U.S. and the local partitioning uncertainty in the Western U.S. The results also indicate that uncertainty in the T estimates is the primary driver of total ET errors. Over the majority of the U.S., the contribution of the two factors of uncertainty to the overall uncertainty is non-trivial.

uncertainty↗
NASA NTRS2018

Attribution of Flux Partitioning Variations Between Land Surface Models Over the Continental U.S.

Accurate quantification of the terrestrial evapotranspiration (ET) components of plant transpiration (T), soil evaporation (E) and evaporation of the intercepted water (I) is necessary for improving our understanding of the links between the carbon and water cycles. Recent studies have noted that, among the modeled estimates, large disagreements exist in the relative contributions of T, E and I to the total ET. As these models are often used in data assimilation environments for incorporating and extending ET relevant remote sensing measurements, understanding the sources of inter-model differences in ET components is also necessary for improving the utilization of such remote sensing measurements. This study quantifies the contributions of two key factors explaining inter-model disagreements to the uncertainty in total ET: (1) contribution of the local partitioning and (2) regional distribution of ET. The analysis is conducted by using outputs from a suite of land surface models in the North American Land Data Assimilation System (NLDAS) configuration. For most of these models, transpiration is the dominant component of the ET partition. The results indicate that the uncertainty in local partitioning dominates the inter-model spread in modeled soil evaporation E. The inter-model differences in T are dominated by the uncertainty in the distribution of ET over the Eastern U.S. and the local partitioning uncertainty in the Western U.S. The results also indicate that uncertainty in the T estimates is the primary driver of total ET errors. Over the majority of the U.S., the contribution of the two factors of uncertainty to the overall uncertainty is non-trivial.

evapotranspiration partitioning; transpiration; so↗
NASA NTRS1980

Prediction of attenuation by rain

A new model is presented for the prediction of attenuation by rain on either terrestrial or slant earth-to-space propagation paths. The model was developed using geophysical observations of the statistics of point rain rate, of the horizontal structure of rainfall, and of the vertical temperature structure of the atmosphere. The model was tested by comparison with attenuation distribution observations. The results show excellent agreement; the observations differ from model predictions by less than the rms deviations predicted by the model.

Crane, R. K.↗
NASA NTRS1994

Computer Modeling Of Atomization

Improved mathematical models based on fundamental principles of conservation of mass, energy, and momentum developed for use in computer simulation of atomization of jets of liquid fuel in rocket engines. Models also used to study atomization in terrestrial applications; prove especially useful in designing improved industrial sprays - humidifier water sprays, chemical process sprays, and sprays of molten metal. Because present improved mathematical models based on first principles, they are minimally dependent on empirical correlations and better able to represent hot-flow conditions that prevail in rocket engines and are too severe to be accessible for detailed experimentation.

Giridharan, M.↗
NASA NTRS1989

Earth radiation budget and cloudiness simulations with a general circulation model

A GCM with new parameterizations of solar and terrestrial radiation, parameterized cloud optical properties, and a simple representation of the cloud liquid water feedback is used with several observational data sets to analyze the effects of cloudiness on the earth's radiation budget. The January and July results from the model are in reasonable agreement with data from Nimbus-7. It is found that the simulated cloudiness overpredicts subtropical and midlatitude cloudiness. The simulated atmospheric cloud radiative forcing is examined. The clear-sky radiation fields obtained by two methods of Cess and Potter (1987) are compared. Also, a numerical experiment was performed to determine the effects of the water vapor continuum on the model results.

HARSHVARDHAN↗
NASA NTRS1974

Geomagnetic responses to the solar wind and to solar activity

A unified overview of present knowledge of the geomagnetic response to the dynamic solar wind is reported. The formation of the magnetosphere and the magnetospheric tail is discussed the importance of electric fields is stressed, and the magnetospheric convection of plasma and frozen-in magnetic field lines under the influence of large scale magnetospheric electric fields is outlined. Ionospheric electric fields and currents are intimately related to electric fields and currents in the magnetosphere and the strong coupling between the two regions is discussed. The energy input of the solar wind to the magnetosphere and upper atmosphere is discussed in terms of the reconnection model where interplanetary magnetic field lines merge or connect with the terrestrial field on the sunward side of the magnetosphere. The merging model emphasizes the importance of the interplanetary magnetic field and especially the north-south component. The solar sector structure with its organized magnetic field and embeeded high speed plasma streams is identified as the source of recurrent geomagnetic disturbances while flare associated interplanetary shock waves are the source of most violet and sporadic geomagnetic storms.

Svalgaard, L.↗
NASA NTRS2019

Stellar Activity Effects on Moist Habitable Terrestrial Atmospheres Around M Dwarfs

Transit spectroscopy of terrestrial planets around nearby M dwarfs is a primary goal of space missions in coming decades. 3-D climate modeling has shown that slow-synchronous rotating terrestrial planets may develop thick clouds at the substellar point, increasing the albedo. For M dwarfs with T(eff) > 3000 K, such planets at the inner habitable zone (IHZ) have been shown to retain moist greenhouse conditions, with enhanced stratospheric water vapor (fH2O > 10(exp -3)) and low Earth-like surface temperatures. However, M dwarfs also possess strong UV activity, which may effectively photolyze stratospheric H2O. Prior modeling efforts have not included the impact of high stellar UV activity on the H2O. Here, we employ a 1-D photochemical model with varied stellar UV, to assess whether H2O destruction driven by high stellar UV would affect its detectability in transmission spectroscopy. Temperature and water vapor profiles are taken from published 3-D climate model simulations for an IHZ Earth-sized planet around a 3300 K M dwarf with an N2-H2O atmosphere; they serve as self-consistent input profiles for the 1-D model. We explore additional chemical complexity within the 1-D model by introducing other species into the atmosphere. We find that as long as the atmosphere is well-mixed up to 1 mbar, UV activity appears to not impact detectability of H2O in the transmission spectrum. The strongest H2O features occur in the JWST MIRI instrument wavelength range and are comparable to the estimated systematic noise floor of ~50 ppm.

Mahmuda Afrin Badhan↗
NASA NTRS2024

The SWOT Mission Will Reshape Our Understanding of the Global Terrestrial Water Cycle

Simultaneously integrating Surface Water and Ocean Topography (SWOT) measurements and those from other Earth observing satellites into hydrological modeling systems will transform our understanding of the global terrestrial water cycle. Such an opportunity comes with big challenges that the scientific community is now presented with.

Natural hazards↗
NASA NTRS2014

Water Balance in the Amazon Basin from a Land Surface Model Ensemble

Despite recent advances in land surfacemodeling and remote sensing, estimates of the global water budget are still fairly uncertain. This study aims to evaluate the water budget of the Amazon basin based on several state-ofthe- art land surface model (LSM) outputs. Water budget variables (terrestrial water storage TWS, evapotranspiration ET, surface runoff R, and base flow B) are evaluated at the basin scale using both remote sensing and in situ data. Meteorological forcings at a 3-hourly time step and 18 spatial resolution were used to run 14 LSMs. Precipitation datasets that have been rescaled to matchmonthly Global Precipitation Climatology Project (GPCP) andGlobal Precipitation Climatology Centre (GPCC) datasets and the daily Hydrologie du Bassin de l'Amazone (HYBAM) dataset were used to perform three experiments. The Hydrological Modeling and Analysis Platform (HyMAP) river routing scheme was forced with R and B and simulated discharges are compared against observations at 165 gauges. Simulated ET and TWS are compared against FLUXNET and MOD16A2 evapotranspiration datasets andGravity Recovery and ClimateExperiment (GRACE)TWSestimates in two subcatchments of main tributaries (Madeira and Negro Rivers).At the basin scale, simulated ET ranges from 2.39 to 3.26 mm day(exp -1) and a low spatial correlation between ET and precipitation indicates that evapotranspiration does not depend on water availability over most of the basin. Results also show that other simulated water budget components vary significantly as a function of both the LSM and precipitation dataset, but simulated TWS generally agrees with GRACE estimates at the basin scale. The best water budget simulations resulted from experiments using HYBAM, mostly explained by a denser rainfall gauge network and the rescaling at a finer temporal scale.

GPCP↗
NASA NTRS1974

Relating terrestrial atmospheric circulation to solar disturbances

Presented are models of two proposed mechanisms for transferring angular momentum from ionospheric heights to the vicinity of the tropopause. The first mechanism consist of a vicious coupling of the upper atmosphere to the troposphere and the second requires changes in the reflection of planetary waves by the thermosphere. This second mechanism is very appealing because it makes use only of energy derived from the lower atmosphere itself, with solar activity directly modifying only the thermospheric reflectivity.

Hines, C. O.↗
NASA NTRS1974

Bulk compositions of the moon and earth, estimated from meteorites

The present work calculates the bulk compositions of the earth and moon, based on the assumption that these planets formed by the same processes as chondrites. In terms of the model presented, the earth contains 9.2% early condensate and 1.5% carbonaceous, volatile-rich silicate. For the moon these percentages are 30.1 and 0.04, respectively. When lunar and terrestrial basalt data are normalized to these model compositions, element abundance patterns based on the percentages (assuming that each component carried its cosmic complement of trace elements) demonstrate the essential identity of igneous processes on both celestial bodies.

Ganapathy, R.↗
NASA NTRS1976

Nd isotopic variations and petrogenetic models

The isotopic composition of Nd in selected terrestrial rocks is investigated to gain information about its implications for petrogenesis and the history of the earth's crust and mantle. Chemical and mass-spectrometric measurements of the Nd-143/Nd-144 ratio in terrestrial rocks of different ages show that the Sm/Nd ratio and the rare-earth-element (REE) abundance pattern are equal within a few per cent to those of chondritic meteorites. Variations in the Nd isotopic ratio in young basalts are found to permit the identification of distinctive mantle sources and to indicate the preservation of significant heterogeneities in the mantle for times of 1 to 4 billion years ago. The isotopic data also show that mantle source regions with a Sm/Nd ratio which differs from the chondritic value by a factor of two are not preserved for more than a few hundred million years. The average continental crust material is found to have a much lower isotopic ratio than the mantle, reflecting the crust's low Sm/Nd ratio resulting from REE fractionation during crust formation from the mantle.

Depaolo, D. J.↗
NASA NTRS1977

Significance of vegetation in interpreting thermal radiation from a terrestrial surface

The regions between crop rows are modeled as infinitely long diffuse cavities. Geometrical view factors are calculated, accounting for reflected radiation emanating internal to the cavity and from the background sky. A 'cavity' emissivity dependent on local geometry is defined to allow for correcting apparent temperatures to true temperatures. The total emissivity appropriate for correcting aircraft thermal data is then calculated by averaging all emissivity components to account for soil, crop, and background. It is shown that even for the lowest crop and vegetation emissivities, if the crop height-to-spacing ratio is greater than unity, the composite emissivity is greatly increased, giving rise to a decreased error in remotely sensed temperature data.

Sutherland, R. A.↗
NASA NTRS1990

Clast sizes in terrestrial and Martian ignimbrite lag deposits

A theoretical model for predicting the sizes of clasts which may be expected in proximal ignimbrite deposits on the earth and Mars is developed. The model can provide an explanation of the eruption mechanism. It takes into account the inside and outside conditions of a vent from which a large-scale pyroclastic flow takes place. The drag forces exerted by the dusty gas on relatively large clasts are also taken into account. The sizes of the largest clasts that contribute to a proximal lag breccia deposit can thus be deduced. The analysis has shown that the pressure at the surface vent level in an ignimbrite-forming eruption is independent of the planetary atmospheric pressure; the gravity and vent size then become the major factors controlling the size of the largest clast which can be erupted.

Wilson, Lionel↗
NASA NTRS1993

Global climate change and terrestrial net primary production

A process-based model was used to estimate global patterns of net primary production and soil nitrogen cycling for contemporary climate conditions and current atmospheric CO2 concentration. Over half of the global annual net primary production was estimated to occur in the tropics, with most of the production attributable to tropical evergreen forest. The effects of CO2 doubling and associated climate changes were also explored. The responses in tropical and dry temperate ecosystems were dominated by CO2, but those in northern and moist temperate ecosystems reflected the effects of temperature on nitrogen availability.

Melillo, Jerry M.↗