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NASA NTRS1991

The Upper Atmosphere Research Satellite (UARS) - An overview

UARS is designed to provide the most extensive data base ever obtained on the coupled energy input, chemistry, and dynamics of the earth's upper atmosphere to increase enormously the current understanding of the upper atmosphere and to improve assessments of the depletion of stratospheric ozone caused by human activities. The UARS mission, observatory, and investigations are described. The UARS experimental investigations consist of energy input experiments, chemical species and temperature experiments, and dynamics experiments. Two instruments measure solar UV energy input while another measures energetic particle energy input and associated X-radiation emission from the atmosphere. Four instruments address chemical concentrations, and two make direct measurements of upper atmosphere winds.

Mcneal, Robert J.↗

NASA NTRS2008

What Might We Learn About Magnetospheric Substorms at the Earth from the MESSENGER Measurements at Mercury?

Satellite observations at the Earth, supported by theory and modeling, have established a close connection between the episodes of intense magnetospheric convection termed substorms and the occurrence of magnetic reconnection. Magnetic reconnection at the dayside magnetopause results in strong energy input to the magnetosphere. This energy can either be stored or used immediately to power the magnetospheric convection that produces the phenomena that collectively define the 'substorm.' However, many aspects of magnetic reconnection and the dynamic response of the coupled solar wind - magnetosphere - ionosphere system at the Earth during substorms remain poorly understood. For example, the rate of magnetic reconnection is thought to be proportional to the local Alfven speed, but the limited range of changes in this solar wind parameter at 1 AU have made it difficult to detect its influence over energy input to the Earth's magnetosphere. In addition, the electrical conductance of the ionosphere and how it changes in response to auroral charged particle precipitation are hypothesized to play a critical role in the development of substorms, but the nature of this electrodynamic interaction remain difficult to deduce from Earth observations alone. The amount of energy the terrestrial magnetosphere can store in its tail, the duration of the storage, and the trigger(s) for its dissipation are all thought to be determined by not only the microphysics of the cross-tail current layer, but also the properties of the coupled magnetosphere - ionosphere system. Again, the separation of microphysics effects from system response has proved very difficult using measurements taken only at the Earth. If MESSENGER'S charged particle and magnetic field measurements confirm the occurrence of terrestrial-style substorms in Mercury's miniature magnetosphere, then it may be possible to determine how magnetospheric convection, field-aligned currents, charged particle acceleration, reconnection, and tail energy storage are influenced by the intense magnetic reconnection expected to be associated with solar wind conditions at 0.3 - 0.5 AU from the Sun and the simplified electrodynamic feed-back anticipated for a planet lacking an ionosphere. MESSENGER observations from its 14 January 2008 Mercury flyby relevant to the occurrence of magnetic reconnection and substorms at Mercury will be discussed.

Slavin, James A.↗

NASA NTRS1988

Supernovae and supernova remnants

The basic features and astrophysics of supernovae of types Ia, Ib, and II and of SNRs are discussed, summarizing the results of recent ground-based and space observations obtained at different wavelengths. Typical data are presented in graphs and sample images, and consideration is given to their implications for shock heating by the initial explosion, radioactive energy input, circumstellar interaction, and pulsar energy input. SNRs described include Tycho's remnant, Kepler's remnant, the Cyg loop, Pup A, the Crab Nebula, the Vela and Crab pulsars, and 0540-69.3 in the LMC. The need for high-spatial-resolution IR and X-ray spectra of these objects is indicated.

Chevalier, Roger A.↗

NASA NTRS1995

Star formation activity in spiral galaxy disks and the properties of radio halos: Observational evidence for a direct dependence

In this article we address observationally the questions: how does star formation (SF) in the disks of galaxies lead to the creation of radio halos, and what minimum energy input into the interstellar medium (ISM) is needed to facilitate this? For the investigation we use a sample of five edge-on galaxies exhibiting radio continuum emmission in their halos and enhanced SF spread over large parts of their disks. In a detailed study of the two galaxies in our sample for which we have the best data, NGC 891 and NGC 4631, we show that the radio halos cut off abruptly at galactocentric radii smaller than those of the underlying thin radio disks. Our most important result is that the halo cutoffs are spatially coincident with the radii where the SF activity in the underlying disks drops sharply. The difference in radius of the emission distributions tracing ongoing SF in the disks (IRAS 50 micrometers, H alpha) versus that of the nonthermal radio continuum thin disks (tracing the distribution of cosmic-ray (CR) electrons) is typically a few kpc. This difference in extent is caused by CR diffusion. We have measured the CR diffusion coefficients in the thin disks of both NGC 891 and NGC 4631. For radial diffusion of CR electrons within the galactic disks the values are D(sub r) = 1.1-2.5 x 10 (exp 29) sq cm/s (NGC 4631) and D(sub r) = 1.2 x 10(exp 29) sq cm/s (NGC 891). For motions in the z-direction in areas within the thin disks where no outflows occur, we derive a firm upper limit of D(sub z) less than or equal to 0.2 x 10(exp 28) sq cm/s for NGC 891. The value for NGC 4631 is D(sub z = 1.4 x 10 (exp 28) sq cm/s. The other three galaxies in our sample, NGC 3044, NGC 4666, and NGC 5775 show (at the sensitivity of our data) less extended, more filamentary radio halos. Isolates spurs or filaments of nonthermal radio continuum emission in their halos are traced only above the most actively star-forming regions in the disks. This, in conjuction with the results obtained for NGC 891 and NGC 4631, suggests a direct connection between the shapes and radial extents of radio halos of normal galaxies and the level and the spatial distribution of the current SF in their disks. The existence of filamentary structures implies that expansion and convection of CR-heated plasma plays an important role even at low z-distances above the plane. Based on radio data we derive the disk-averaged mean energy input rates into the ISM due to supernova explosions per unit surface area in nine galaxies, including the ones in our sample. We find a clear trend in the sense that the galaxies with the highest mean energy input rates in the underlying disks have the most extended and pervasisve radio halos. Below a certain threshohld, outflows are inhibited. As a lower limit for this threshhold we derive an energy input rate of approximately 10 (exp -4) erg/s sq cm. The fact that radio halo emission is found only above the most luminous giant H 2 regions in late-type 'normal' galaxies (of type Sbc or later) indicates that only these are capable of initiating disk-halo interactions by locally exceeding the threshold. The distribution of the local outflows determines the overall shapes of the CR halos and leads to the observed filamentary structures.

Dahlem, Michael↗

NASA NTRS1997

Comparisons of Solar Wind Coupling Parameters with Auroral Energy Deposition Rates

Measurement of the global rate of energy deposition in the ionosphere via auroral particle precipitation is one of the primary goals of the Polar UVI program and is an important component of the ISTP program. The instantaneous rate of energy deposition for the entire month of January 1997 has been calculated by applying models to the UVI images and is presented by Fillingim et al. In this session. A number of parameters that predict the rate of coupling of solar wind energy into the magnetosphere have been proposed in the last few decades. Some of these parameters, such as the epsilon parameter of Perrault and Akasofu, depend on the instantaneous values in the solar wind. Other parameters depend on the integrated values of solar wind parameters, especially IMF Bz, e.g. applied flux which predicts the net transfer of magnetic flux to the tail. While these parameters have often been used successfully with substorm studies, their validity in terms of global energy input has not yet been ascertained, largely because data such as that supplied by the ISTP program was lacking. We have calculated these and other energy coupling parameters for January 1997 using solar wind data provided by WIND and other solar wind monitors. The rates of energy input predicted by these parameters are compared to those measured through UVI data and correlations are sought. Whether these parameters are better at providing an instantaneous rate of energy input or an average input over some time period is addressed. We also study if either type of parameter may provide better correlations if a time delay is introduced; if so, this time delay may provide a characteristic time for energy transport in the coupled solar wind-magnetosphere-ionosphere system.

Elsen, R.↗

NASA NTRS1987

Theory of transition-layer emission measures and coronae

The basic equations describing the energy equilibria, the conductive heat flux, and the temperature stratifications for stellar transition layers and coronae with 'open' field lines are summarized. The temperature dependence of the emission measures for lines originating in different temperature regions of the transition zone is determined. It is found that the stellar transition regions consist of two basically different parts: the lower part where mechnical energy input is balanced by the radiative losses, and the upper part where the mechanical energy input is balanced by the divergence of the conductive flux and radiative losses. In the lower part, the temperature stratification is determined by an equilibrium between mechanical flux input and radiative energy losses. The coronal temperatures increase with increasing mechanical flux and damping length in the upper transition zone.

Bohm-Vitense, Erika↗

NASA NTRS1998

Comparison of Energy Deposition in the Auroral Oval and Cap Regions for Cases Where Transpolar Structures Exist

For several cases where the full auroral zone is imaged and transpolar structures exist, we compare the total energy input to the auroral oval with the total energy input in the polar cap. This comparison is made for cases where auroral intensification near local midnight is and is not observed. Temporal evolution of the energy balance between the energy deposited in the oval and polar cap can be used to understand the mechanism that triggers substorms.

Spann, J. F., Jr.↗

NASA NTRS1990

MHD study of temporal and spatial evolution of simulated interplanetary shocks in the ecliptic plane within 1 AU

The present parametric study of interplanetary shock propagation to 1 AU uses a two- and-one-half-dimensional MHD time-dependent model whose input conditions encompass initial shock velocity, driving-pulse duration, and pulse width at the near-sun position of 18 solar radii. It is found that, for input pulses with modest angular width and temporal duration, the propagation of the resulting interplanetary fast-forward shock waves primarily depends on the net input energy. While the properties of the reverse shocks are also a function of input energy, they depend on the specific values of the input pulse shock velocity, width, and duration.

Smith, Zdenka↗

NASA NTRS1980

Coronal heating by stochastic magnetic pumping

Recent observational data cast serious doubt on the widely held view that the Sun's corona is heated by traveling waves (acoustic or magnetohydrodynamic). It is proposed that the energy responsible for heating the corona is derived from the free energy of the coronal magnetic field derived from motion of the 'feet' of magnetic field lines in the photosphere. Stochastic motion of the feet of magnetic field lines leads, on the average, to a linear increase of magnetic free energy with time. This rate of energy input is calculated for a simple model of a single thin flux tube. The model appears to agree well with observational data if the magnetic flux originates in small regions of high magnetic field strength. On combining this energy input with estimates of energy loss by radiation and of energy redistribution by thermal conduction, we obtain scaling laws for density and temperature in terms of length and coronal magnetic field strength.

Sturrock, P. A.↗

NASA NTRS1988

On the energy crisis in the Io plasma torus

Recent calculations of the energy balance of the Io plasma torus show that the observed UV and EUV radiation cannot be maintained solely via energy input by the ion pickup mechanism. Current theoretical models of the torus must be modified to include non-local energy input. It is argued that the required energy may be supplied by inward diffusion of energetic heavy ions with energies less than about 20 keV.

Smith, Robert A.↗

NASA NTRS1981

Coronal heating by stochastic magnetic pumping

Recent observational data cast serious doubt on the widely held view that the sun's corona is heated by traveling waves (acoustic or magnetohydrodynamic). It is here proposed that the energy responsible for heating the corona is derived from the free energy of the coronal magnetic field derived from motion of the 'feet' of magnetic field lines in the photosphere. Stochastic motion of the feet of magnetic field lines leads, on the average, to a linear increase of magnetic free energy with time. This rate of energy input is calculated for a simple model of a single thin flux tube. The model appears to agree well with observational data if the magnetic flux originates in small regions of high magnetic field strength as proposed by Tarbell et al. (1979). On combining this energy input with estimates of energy loss by radiation and of energy redistribution by thermal conduction, scaling laws are obtained for density and temperature in terms of length and coronal magnetic field strength.

Sturrock, P. A.↗

NASA NTRS1991

Numerical simulations of flares on M dwarf stars. I - Hydrodynamics and coronal X-ray emission

Flare-loop models are utilized to simulate the time evolution and physical characteristics of stellar X-ray flares by varying the values of flare-energy input and loop parameters. The hydrodynamic evolution is studied in terms of changes in the parameters of the mass, energy, and momentum equations within an area bounded by the chromosphere and the corona. The zone supports a magnetically confined loop for which processes are described including the expansion of heated coronal gas, chromospheric evaporation, and plasma compression at loop footpoints. The intensities, time profiles, and average coronal temperatures of X-ray flares are derived from the simulations and compared to observational evidence. Because the amount of evaporated material does not vary linearly with flare-energy input, large loops are required to produce the energy measured from stellar flares.

Cheng, Chung-Chieh↗

NASA NTRS1990

Earth observing satellite: Understanding the Earth as a system

There is now a plan for global studies which include two very large efforts. One is the International Geosphere/Biosphere Program (IGBP) sponsored by the International Council of Scientific Unions. The other initiative is Mission to Planet Earth, an unbrella program for doing three kinds of space missions. The major one is the Earth Observation Satellite (EOS). EOS is large polar orbiting satellites with heavy payloads. Two will be placed in orbit by NASA, one by the Japanese and one or two by ESA. The overall mission measurement objectives of EOS are summarized: (1) the global distribution of energy input to and energy output from the Earth; (2) the structure, state variables, composition, and dynamics of the atmosphere from the ground to the mesopause; (3) the physical and biological structure, state, composition, and dynamics of the land surface, including terrestrial and inland water ecosystems; (4) the rates, important sources and sinks, and key components and processes of the Earth's biogeochemical cycles; (5) the circulation, surface temperature, wind stress, sea state, and the biological activity of the oceans; (6) the extent, type, state, elevation, roughness, and dynamics of glaciers, ice sheets, snow and sea ice, and the liquid equivalent of snow in the global cryosphere; (7) the global rates, amounts, and distribution of precipitation; and (8) the dynamic motions of the Earth (geophysics) as a whole, including both rotational dynamics and the kinematic motions of the tectonic plates.

Soffen, Gerald↗

NASA NTRS1992

Phase change energy storage for solar dynamic power systems

This paper presents the results of a transient computer simulation that was developed to study phase change energy storage techniques for Space Station Freedom (SSF) solar dynamic (SD) power systems. Such SD systems may be used in future growth SSF configurations. Two solar dynamic options are considered in this paper: Brayton and Rankine. Model elements consist of a single node receiver and concentrator, and takes into account overall heat engine efficiency and power distribution characteristics. The simulation not only computes the energy stored in the receiver phase change material (PCM), but also the amount of the PCM required for various combinations of load demands and power system mission constraints. For a solar dynamic power system in low earth orbit, the amount of stored PCM energy is calculated by balancing the solar energy input and the energy consumed by the loads corrected by an overall system efficiency. The model assumes an average 75 kW SD power system load profile which is connected to user loads via dedicated power distribution channels. The model then calculates the stored energy in the receiver and subsequently estimates the quantity of PCM necessary to meet peaking and contingency requirements. The model can also be used to conduct trade studies on the performance of SD power systems using different storage materials.

Chiaramonte, F. P.↗

NASA NTRS1980

'GAIM' - Gas-addition, impedance-matched arc driver

A conceptual view for a GAIM energy/driver system to maximize shock-tube performance through efficient interfacing of the energy source with the gas dynamics of the arc driver is presented. Electrical and arc-chamber requirements are evaluated utilizing two new computer codes. One code calculates the shock wave generated for a selected time rate and magnitude of arc-energy input; the other computes the values of external circuit elements required to produce the selected energy input, with the driver represented as the load element of the electrical discharge circuit. Results indicate that the energy-storage capability and the driver arrangement needed to produce the highest shock Mach number can be achieved by means of driver gas addition and by impedance matching (GAIM). Design criteria are presented for arc energy requirements necessary to produce given shock-wave speeds. Shock velocities as high as the 70 km/sec required for simulating Jovian entry now seem possible in shock-tube operation. Practical implementation of a GAIM system is discussed.

Dannenberg, R. E.↗

NASA NTRS2011

MAVEN - Mars Atmosphere and Volatile EvolutioN Mission

NASA's MAVEN mission (to be launched in late 2013) is the first mission to Mars devoted to sampling all of the upper atmosphere neutral and plasma environments, including the well-mixed atmosphere, the exosphere, ionosphere, outer magnetosphere and near-Mars solar wind. It will fill in some measurement gaps remaining from the successful Mars Global Surveyor and the on-going Mars Express missions. The primary science objectives of MAVEN are: 1. Provide a comprehensive picture of the present state of the upper atmosphere and ionosphere of Mars; 2. Understand the processes controlling the present state; and 3. Determine how loss of volatiles to outer space in the present epoch varies with changing solar condition - EUY, solar wind and interplanetary magnetic field measurements will provide the varying solar energy inputs into the system. Knowing how these processes respond to the Sun's energy inputs in the current epoch will provide a framework for projecting atmospheric processes back in time to profile MARS' atmospheric evolution and to explore "where the water went", A description will be given of the science objectives, the instruments, and the current status of the project, emphasizing the value of having collaborations between the MAVEN project and the Mars upper atmosphere science community.

Grebowsky, Joseph M.↗

NASA NTRS2015

On the Thermal Anomaly of Lake Untersee

Reported here is the outcome from a student internship undertaken with Dr. Chris McKay at the NASA Ames Research Center. The project for this internship focuses on Lake Untersee, an Earth analog for icy moons. The anoxic hole of Lake Untersee has a thermal bump that was first observed by Wand et al., 1997 and has been confirmed several times (Wand et al., 2006; Andersen 2011). The expected thermal profile of the hole is linear from 0 C at the thermocline to approximately 4 C, the ground temperature in Antarctica, at the bottom. Instead, there is an increase from 0 C near the thermocline to 5 C which is maintained for 7 m, then a linear profile to approximately 4 C near the bottom. Thermal modeling was conducted to quantify the energy input required to maintain the bump. The results revealed 2 sources. Chemical reactions and radiative energy were analyzed as possible explanation. The chemical analysis revealed a peak in Chlorophyll a at the same depth as the shallower source and several interesting reactions with maximum rates at the same location as the lower depth source. However, the energy released from these reactions was orders of magnitude smaller than required source. The radiation analysis revealed a profile with two peaks in similar locations to the sources and a total energy input within a factor of 1.5 of the required sources. The conclusion from this work is that photosynthesis and the chemical reactions support microbial life in the water column which in turn acts as an opacity to convert radiative energy into thermal energy. Recommendations for future work are aimed at quantifying the quantity and types of microbes present in the water column. Beyond the work of the project, two field trips are described and a discussion on benefits to the student of the internship is given.

Earth analog for icy moons↗

NASA NTRS1988

SN 1987A - Out on the tail

The expected light curve of Supernova 1987A is calculated for the next 10 yr based solely upon energy input from radioactive decay of Co-56 and Co-57. During the third year, energy input from Co-57 begins to dominate. How the bolometric (ultraviolet-optical-infrared) light curve deviates from that given by 100 percent deposition of the gamma-rays is a measure of the mixing that has gone on in the supernova. Current measurements favor a mixed model. The radioactive light curve decreases beneath 10 to the 39th ergs/s at an age of about 900 days, by which time the neutron star remnant should have made its presence known.

Pinto, Philip A.↗