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NASA NTRS2020

Neptune Global Reference Atmospheric Model (Neptune-GRAM): User Guide

This Technical Memorandum (TM) presents the Neptune Global Reference Atmospheric Model (Neptune-GRAM) and its updated features. Neptune-GRAM is an engineering-oriented atmospheric model that estimates mean values and statistical variations of atmospheric properties for Neptune. This TM summarizes the atmospheric data model in Neptune-GRAM and provides a guide for the user to obtain, set up, and run the code in various configurations. Additional details regarding the Neptune-GRAM input and output files and how to interpret Neptune-GRAM results are also provided.

H L Justh↗
NASA NTRS2003

Mars Global Reference Atmospheric Model (Mars-GRAM) and Database for Mission Design

Mars Global Reference Atmospheric Model (Mars-GRAM 2001) is an engineering-level Mars atmosphere model widely used for many Mars mission applications. From 0-80 km, it is based on NASA Ames Mars General Circulation Model, while above 80 km it is based on Mars Thermospheric General Circulation Model. Mars-GRAM 2001 and MGCM use surface topography from Mars Global Surveyor Mars Orbiting Laser Altimeter. Validation studies are described comparing Mars-GRAM with Mars Global Surveyor Radio Science and Thermal Emission Spectrometer data. RS data from 2480 profiles were used, covering latitudes 75 deg S to 72 deg N, surface to approximately 40 km, for seasons ranging from areocentric longitude of Sun (Ls) = 70-160 deg and 265-310 deg. RS data spanned a range of local times, mostly 0-9 hours and 18-24 hours. For interests in aerocapture and precision landing, comparisons concentrated on atmospheric density. At a fixed height of 20 km, RS density varied by about a factor of 2.5 over ranges of latitudes and Ls values observed. Evaluated at matching positions and times, these figures show average RSMars-GRAM density ratios were generally 1+/-)0.05, except at heights above approximately 25 km and latitudes above approximately 50 deg N. Average standard deviation of RSMars-GRAM density ratio was 6%. TES data were used covering surface to approximately 40 km, over more than a full Mars year (February, 1999 - June, 2001, just before start of a Mars global dust storm). Depending on season, TES data covered latitudes 85 deg S to 85 deg N. Most TES data were concentrated near local times 2 hours and 14 hours. Observed average TES/Mars-GRAM density ratios were generally 1+/-0.05, except at high altitudes (15-30 km, depending on season) and high latitudes (greater than 45 deg N), or at most altitudes in the southern hemisphere at Ls approximately 90 and 180 deg. Compared to TES averages for a given latitude and season, TES data had average density standard deviation about the mean of approximately 2.5% for all data, or approximately 1-4%, depending on time of day and dust optical depth. Average standard deviation of TES/Mars-GRAM density ratio was 8.9% for local time 2 hours and 7.1% for local time 14 hours. Thus standard deviation of observed TES/Mars-GRAM density ratio, evaluated at matching positions and times, is about three times the standard deviation of TES data about the TES mean value at a given position and season.

Justus, C. G.↗
NASA NTRS1981

Reference model atmosphere calculation - The Sunspot sunspot model

A composite temperature-density model of sunspots is developed from the results of five previous modeling attempts. The model is designed to describe the region extending from the deepest photospheric layers up through the chromosphere-corona transition region. Photospheric, chromospheric, and transition region temperature distributions proposed by other authors are employed to quantity the phenomena out to 2280 km. Additional calculations yield the various line profiles, the internal properties of the region above the sunspot including the chromospheric net radiative cooling rates, and the radiative flux as a function of depth in the photosphere. Observations of the hydrogen ion flux is used to account for the net cooling in the temperature minimum region. Furthermore, the integrated radiative flux is found to be constant with depth in the photosphere.

Avrett, E. H.↗
NASA NTRS1993

Global Reference Atmosphere Model (GRAM)

4D model provides atmospheric parameter values either automatically at positions along linear path or along any set of connected positions specified by user. Based on actual data, GRAM provides thermal wind shear for monthly mean winds, percent deviation from standard atmosphere, mean vertical wind, and perturbation data for each position.

Johnson, D. L.↗
NASA NTRS1993

Model atmospheres - Tool for identifying interstellar features

Model atmosphere parameters are derived for 14 early A stars with rotation velocities, from optical spectra, in excess of 80 km/s. The models are compared with IUE observations of the stars in regions where interstellar lines are expected. In general, with the assumption of solar abundances, excellent fits are obtained in regions longward of 2580 A, and accurate interstellar equivalent widths can be derived using models to establish the continuum. The fits are poorer at shorter wavelengths, particularly at 2026-2062 A, where the stellar model parameters seem inadequate. Features indicating mass flows are evident in stars with known infrared excesses. In gamma TrA, variability in the Mg II lines is seen over the 5-year interval of these data, and also over timescales as short as 26 days. The present technique should be useful in systematic studies of episodic mass flows in A stars and for stellar abundance studies, as well as interstellar features.

Frisch, P. C.↗
NASA NTRS2019

Mars Global Reference Atmospheric Model (Mars-GRAM) Upgrades

The inability to test planetary spacecraft in the flight environment prior to a mission requires engineers to rely on ground-based testing and models of the vehicle and expected environments. One of the most widely used engineering models of the Martian atmosphere is the Mars Global Reference Atmospheric Model (Mars-GRAM) developed and maintained by the NASA Marshall Space Flight Center (MSFC). The NASA Science Mission Directorate (SMD) has provided funding support to upgrade the planetary GRAMs in Fiscal Year 2018 and 2019. This poster summarizes the upgrades that have been made to Mars-GRAM, the release status of Mars-GRAM, the new GRAMs that are under development, and future Mars-GRAM upgrade plans.

Justh, H. L.↗
NASA NTRS2024

Replicating the Hadley Cell Edge and Subtropical Jet Latitude Disconnect in Idealized Atmospheric Models

Recent work has shown that variability in the subtropical jet's (STJ) latitude, ϕSTJ, is not coupled to that of the Hadley cell (HC) edge, ϕHC, but the robustness of this disconnect has not been examined in detail. Here, we use meteorological reanalysis products, comprehensive climate models, and an idealized atmospheric model to determine the necessary processes for a disconnect between ϕHC and ϕSTJ in the Northern Hemisphere's December–January–February season. We find that a decoupling can occur in a dry general circulation model, indicating that large-scale dynamical processes are sufficient to reproduce the metrics' relationship. It is therefore not reliant on explicit variability in the zonal structure, convection, or radiation. Rather, the disconnect requires a sufficiently realistic climatological basic state. Further, we confirm that the robust disconnect between ϕSTJ and ϕHC across the model hierarchy reveals their differing sensitivities to midlatitude eddy momentum fluxes; ϕHC is consistently coupled to the latitude of maximum eddy momentum flux, but ϕSTJ is not.

Molly E. Menzel↗
NASA NTRS1992

An interpretation of the spectral properties of hot hydrogen-rich white dwarfs with stratified H/He model atmospheres

A grid of stratified H/He model atmospheres applicable to the interpretation of the spectral properties of hot H-rich white dwarfs (WDs) is computed. Samples of hot DA WDs observed with Exosat and Einstein are analyzed using the models. Six out of six objects with T(eff) = 35,000 K or less do not show a EUV/soft X-ray flux deficiency and therefore can be understood solely in terms of pure hydrogen atmospheres. A majority of DA WDs hotter than this value do show a flux deficiency and thus require the presence of some absorbers in their atmospheres. It is shown that the Exosat broadband photometry of Feige 24 and G191 B2B cannot be explained in terms of stratified atmospheres. Absorption by heavy elements is certainly responsible for the required EUV/soft X-ray opacity source in these cases. However, the Exosat data are consistent with the hypothesis of stratified atmospheres in the four remaining objects.

Vennes, Stephane↗
NASA NTRS1988

The GISS global climate-middle atmosphere model. I - Model structure and climatology

A coupled global climate/middle atmosphere model (GCMAM) is developed by extending the Hansen et al. (1983) GISS global climate model to include the middle atmosphere up to 85 km. The model includes numerical solutions of the primitive equations, calculations of the radiative and surface fluxes, and a complete hydrologic cycle with convective and cloud-cover parameterizations. In addition, a parameterized gravity wave drag cycle is incorporated, in which gravity-wave momentum fluxes due to flow over topography, wind shear, and convection are calculated at each grid box, using theoretical relationships between the grid-scale variables and expected source strengths. The results of the GCMAM demonstrate that the model produces a reasonable simulation of the stratosphere. It is shown that the improvements over the previous version were achieved largely through the incorporation of the parameterized gravity wave drag.

Rind, D.↗
NASA NTRS2017

Treatment of Overlapping Gaseous Absorption with the Correlated-k Method in Hot Jupiter and Brown Dwarf Atmosphere Models

The correlated-k method is frequently used to speed up radiation calculations in both one-dimensional and three-dimensional atmosphere models. An inherent difficulty with this method is how to treat overlapping absorption, i.e. absorption by more than one gas in a given spectral region. We have evaluated the applicability of three different methods in hot Jupiter and brown dwarf atmosphere models, all of which have been previously applied within models in the literature: (i) Random overlap, both with and without resorting and rebinning, (ii) equivalent extinction and (iii) pre-mixing of opacities, where (i) and (ii) combine k-coefficients for different gases to obtain k-coefficients for a mixture of gases, while (iii) calculates k-coefficients for a given mixture from the corresponding mixed line-by-line opacities. We find that the random overlap method is the most accurate and flexible of these treatments, and is fast enough to be used in one-dimensional models with resorting and rebinning. In three-dimensional models such as GCMs it is too slow, however, and equivalent extinction can provide a speed-up of at least a factor of three with only a minor loss of accuracy while at the same time retaining the flexibility gained by combining k-coefficients computed for each gas individually. Pre-mixed opacities are significantly less flexible, and we also find that particular care must be taken when using this method in order to to adequately resolve steep variations in composition at important chemical equilibrium boundaries. We use the random overlap method with resorting and rebinning in our one-dimensional atmosphere model and equivalent extinction in our GCM, which allows us to e.g. consistently treat the feedback of non-equilibrium chemistry on the total opacity and therefore the calculated P-T profiles in our models.

atmospheres↗
NASA NTRS1972

Four-dimensional world-wide atmospheric models (surface to 25 km altitude)

Four-dimensional atmospheric models previously developed for use as input to atmospheric attenuation models are evaluated to determine where refinements are warranted. The models are refined where appropriate. A computerized technique is developed that has the unique capability of extracting mean monthly and daily variance profiles of moisture, temperature, density and pressure at 1 km intervals to the height of 25 km for any location on the globe. This capability could be very useful to planners of remote sensing of earth resources missions in that the profiles may be used as input to the attenuation models that predict the expected degradation of the sensor data. Recommendations are given for procedures to use the four-dimensional models in computer mission simulations and for the approach to combining the information provided by the 4-D models with that given by the global models.

Spiegler, D. B.↗
NASA NTRSDate not supplied

Global Reference Atmospheric Model (GRAM) Suite Overview and Current Status

• Engineering-oriented atmospheric models that estimate mean values and statistical variations of atmospheric properties for numerous planetary destinations • Currently available for Earth, Mars, Venus, Titan, Neptune, Uranus, and Jupiter • Outputs include atmospheric density, temperature, pressure, chemical composition, radiative fluxes (for Mars-GRAM), and wind components along a user-defined path – Includes seasonal, diurnal, geographic, and altitude variations • Widely used by the engineering community because of their ability to create realistic atmospheric dispersions • Can be integrated into high fidelity flight dynamic simulations of launch, entry, descent and landing (EDL), aerobraking and aerocapture • Optional trajectory input file consisting of time, height, latitude, and longitude can be used to provide the GRAM trajectory path • Optional auxiliary profile consisting of height, latitude, longitude, temperature, pressure, density, eastward wind, and northward wind may be used to replace model data in the GRAMs • Not a forecast model

atmospheric models↗
NASA NTRS1990

Extensive middle atmosphere (20-120 KM) modification in the Global Reference Atmospheric Model (GRAM-90)

The Global Reference Atmospheric Model (GRAM) is currently available in the 'GRAM-88' version (Justus, et al., 1986; 1988), which includes relatively minor upgrades and changes from the 'MOD-3' version (Justus, et al., 1980). Currently a project is underway to use large amounts of data, mostly collected under the Middle Atmosphere Program (MAP) to produce a major upgrade of the program planned for release as the GRAM-90 version. The new data and program revisions will particularly affect the 25-90 km height range. Sources of data and preliminary results are described here in the form of cross-sectional plots.

Justus, C. G.↗
NASA NTRSDate not supplied

Comparison and Analysis of the Venus Global Reference Atmospheric Model

The goal of this research was to analyze the Venus Global Reference Atmospheric Model (Venus-GRAM) and determine how accurately the model is following its primary source data from the Venus International Reference Atmosphere (VIRA). A comparative analysis between Venus-GRAM and the Venus Climate Database (VCD) was also conducted. The VCD is an atmospheric model developed by the Laboratoire de Météorologie Dynamique (LMD) for both scientific and engineering purposes. The purpose of this work is to ensure the most up-to-date data is being used to prepare for future probe and aerocapture missions.

Libby Cutler↗
NASA NTRS1975

A grid of model atmospheres for metal-deficient giant stars. I

A grid of flux-constant model atmospheres for stars with effective temperatures between 3750 and 6000 K, log g between 0.75 and 3.0, and (A/H) between -3.0 and 0.0 has been constructed. The line absorption is approximated by opacity distribution functions. Metal lines and molecular lines, including those from the infrared bands of CO and CN, are taken into account. The variation of the structure of the models with metal abundance and microturbulence parameter is found to be quite regular and not very drastic. The surface cooling produced by CO is important for all the models with a maximum temperature of 5000 K, while CN mainly causes a backwarming effect but is not very important for solar CNO abundances. The effects of convection, estimated by using the mixing-length approximation, are important only for the coldest models. The models compare very well with models from overlapping regions of other grids. A solar model consistent with the grid models is found to agree satisfactorily with empirical solar model atmospheres. The careful use of scaled solar models for stars with (A/H) approximately equal to zero is justified.

Gustafsson, B.↗
NASA NTRS2005

Atmospheric Models for Mars Aerocapture

level Mars atmospheric model. Applications include systems design, performance analysis, and operations planning for aerobraking, entry descent and landing, and aerocapture. Typical Mars aerocapture periapsis altitudes (for systems with rigid- aeroshell heat shields) are about 50 km. This altitude is above the 0-40 km height range covered by Mars Global Surveyor Thermal Emission Spectrometer (TES) nadir observations. Recently, TES limb sounding data have been made available, spanning more than two Mars years (more than 200,000 data profiles) with altitude coverage up to about 60 km, well within the height range of interest for aerocapture. Results are presented comparing Mars-GRAM atmospheric density with densities from TES nadir and limb sounding observations. A new Mars-GRAM feature is described which allows individual TES nadir or limb profiles to be extracted from the large TES databases, and to be used as an optional replacement for standard Mars-GRAM background (climatology) conditions. For Monte-Carlo applications such as aerocapture guidance and control studies, Mars-GRAM perturbations are available using these TES profile background conditions.

Justus, C. G.↗
NASA NTRS1969

Model atmospheres of late-type stars.

Model atmospheres of late type stars with solar abundances, effective temperatures between 2000-4000 K and gravities corresponding to dwarf, giant and supergiant stars

Auman, J. R., Jr.↗