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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.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Pioneer 8 traversal of the geomagnetic tail at 1600 R(E)

The Pioneer 8 spacecraft (launched on December 13, 1967) first crossed the geomagnetic tail at a downstream distance of 500-800 R(E) as it left the earth-moon system, and during a two-week period centered on January 23, 1968, the magnetometer, plasma probe and plasma wave instrument all detected specific tail-related phenomena. In April and May of 1985, Pioneer 8 traversed the expected position of the earth's tail once again, at an average downstream distance of 1650 R(E). This report contains a summary of the 1985 Pioneer 8 measurements, and a brief discussion of the limited information available on solar wind variations and terrestrial magnetic activity indicators.

Scarf, Frederick L.↗
NASA NTRS1988

Empirical global model of upper thermosphere winds based on atmosphere and dynamics explorer satellite data

Thermospheric wind data obtained from the Atmosphere Explorer E and Dynamics Explorer 2 satellites have been used to generate an empirical wind model for the upper thermosphere, analogous to the MSIS model for temperature and density, using a limited set of vector spherical harmonics. The model is limited to above approximately 220 km where the data coverage is best and wind variations with height are reduced by viscosity. The data base is not adequate to detect solar cycle (F10.7) effects at this time but does include magnetic activity effects. Mid- and low-latitude data are reproduced quite well by the model and compare favorably with published ground-based results. The polar vortices are present, but not to full detail.

Hedin, A. E.↗
NASA NTRS1989

Disturbances in the Arizona Monsoon

Numerical modeling simulations of tropical squall lines were begun to determine the role of large scale terrain features over Arizona and Mexico in their initiation and propagation. Installation was completed for a short-base, high resolution lightning location and detection network in and around Tucson. Data from a Doppler wind profiler is being analyzed to determine the role of large scale heating over the inter-mountain plateau region in governing local diurnal wind variations and possible relationships to the monsoon flow. The portable solar photometer for determining high temporal resolution values of the local precipitable water vapor was completed and calibrated. The assembly is nearly completed for a multi-channel microwave passive radiometer to determine local temperature and water vapor profiles.

Gall, Robert↗
NASA NTRS1989

Simultaneous observations of neutral winds and electric fields at spaced locations in the dawn auroral oval

Results are presented on simultaneous observations of neutral winds and electric fields at spaced locations in the dawn auroral oval, carried out during a chemical release experiment on March 21, 1987. The observed plasma drifts and electron densities indicated the presence of a significant coupling between plasma and neutrals at the altitude of the F region but little coupling in the lower E region. The wind variations in the height range between 95 and 130 km were suggestive of the variations and amplitudes expected if the flow was dominated by the semidiurnal tide. However, a comparison of the flow with the model developed by Forbes (1982) showed that the phase differs by 4-5 hours from the predictions. Moreover, the measured divergence and vorticity in the flow are much larger than those predicted by the model, indicating that higher-order modes than those treated by Forbes may contribute significantly to the high-latitude thermospheric flow.

Larsen, M. F.↗
NASA NTRS1989

IUE observations of variability in the WN6 star HD 192163

Results are presented of a study of 77 high-resolution IUE spectra of the WN6 star HD 192163, for which new IUE observations obtained over 48 hrs in 1987 were combined with data drawn from the IUE archive, covering various epochs over the 1978-1987 period. The 1987 series of 48 spectra were found to exhibit significant variability over a period of 24 hrs in the N IV 1718-A, C IV 1550-A, and He II 1640-A P Cygni profiles. The possible causes of these variabilities are considered in terms of binary-induced changes due to a compact companion and intrinsic stellar wind variations.

Saint-Louis, N.↗
NASA NTRS1990

Vertical structure and characteristics of 23-60 day (zonal) oscillations over the tropical latitudes during the winter months of 1986 - Results of equatorial wave campaign-II

Results are presented of the equatorial wave campaign-II, a meteorological rocket study which was part of the Indian Middle Atmosphere Program. The equatorial wave campaign-II was conducted from Shar, India (13.7 deg N, 80.2 deg E) from January 15-February 28, 1986. By means of high altitude balloon and the RH-200 meteorological rocket, winds were measured from ground level up to 60 km altitude once each day during the 45-day period. The oscillation frequencies of the deviations in the east-west component of the winds from their mean at each 1-km height interval are obtained by the maximum entropy method. The phases and amplitudes of these frequencies are determined by use of the least squares method on the wind variation time series. Enhanced wave activity is shown to take place in the troposphere and lower mesosphere. The tropospheric waves observed suggest themselves to be Rossby waves of extratropical origin penetrating to tropical latitudes. The observed stratospheric/mesospheric waves appear to emanate from a source around the stratopause.

Raghavarao, R.↗
NASA NTRS1993

Zonal mean winds in the equatorial mesosphere and lower thermosphere observed by the High Resolution Doppler Imager

This paper presents analyses of mesospheric and lower thermospheric zonal mean winds observed by the High Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite (UARS). Monthly averages of the equatorial zonal mean zonal winds are presented for January 1992 through June 1993. Equatorial zonal winds in the 70-90 km region are dominated by a semiannual oscillation (SAO), ranging from 30 m/s (westerly) to -100 m/s (easterly). At high latitudes the zonal wind variations are predominantly annual. Above 90 km, the low-latitude flow is easterly at all times, punctuated by a small semiannual variation. This behavior may be related to the deposition of momentum by the diurnal tides.

Lieberman, R. S.↗
NASA NTRS1995

Modulated mountain waves

The theory of mountain waves is usually discussed for the case of a steady background wind. Here, the consequences of a superimposed diurnal (or other periodic) background wind variation are considered in outline. They are found to be sufficiently complicated as to warrant avoidance in detailed case studies. They include, however, the production of freely propagating waves and may be of interest on that account for other purposes.

Hines, Colin O.↗
NASA NTRS1997

A Well-Calibrated Ocean Algorithm for Special Sensor Microwave/Imager

I describe an algorithm for retrieving geophysical parameters over the ocean from special sensor microwave/imager (SSM/I) observations. This algorithm is based on a model for the brightness temperature T(sub B) of the ocean and intervening atmosphere. The retrieved parameters are the near-surface wind speed W, the columnar water vapor V, the columnar cloud liquid water L, and the line-of-sight wind W(sub LS). I restrict my analysis to ocean scenes free of rain, and when the algorithm detects rain, the retrievals are discarded. The model and algorithm are precisely calibrated using a very large in situ database containing 37,650 SSM/I overpasses of buoys and 35,108 overpasses of radiosonde sites. A detailed error analysis indicates that the T(sub B) model rms accuracy is between 0.5 and 1 K and that the rms retrieval accuracies for wind, vapor, and cloud are 0.9 m/s, 1.2 mm, and 0.025 mm, respectively. The error in specifying the cloud temperature will introduce an additional 10% error in the cloud water retrieval. The spatial resolution for these accuracies is 50 km. The systematic errors in the retrievals are smaller than the rms errors, being about 0.3 m/s, 0.6 mm, and 0.005 mm for W, V, and L, respectively. The one exception is the systematic error in wind speed of -1.0 m/s that occurs for observations within +/-20 deg of upwind. The inclusion of the line-of-sight wind W(sub LS) in the retrieval significantly reduces the error in wind speed due to wind direction variations. The wind error for upwind observations is reduced from -3.0 to -1.0 m/s. Finally, I find a small signal in the 19-GHz, horizontal polarization (h(sub pol) T(sub B) residual DeltaT(sub BH) that is related to the effective air pressure of the water vapor profile. This information may be of some use in specifying the vertical distribution of water vapor.

Wentz, Frank J.↗
NASA NTRS1999

The Importance of Meteorological Measurement for the Scientific Study of the Mesosphere

The rocket-borne falling sphere technique has been providing temperature and wind measurements to 90 km. For example, the High Resolution Doppler Imager (HRDI) experiment on the Upper Atmosphere Research Satellite (UARS) and during the GUARA Campaign. The measurement of temperature and wind using the falling sphere method is well known, but will be briefly reviewed. The vertical resolution of the data is examined at different geographical locations and seasons. Time/height sections characterizing the temperature and wind structure will be presented for low (Alcantara, Brazil), middle (Wallops Island and Barking Sands, Hawaii), and high latitudes (ARR and ESRANGE). We address radar quality required, data smoothing, and expected measurement accuracy. Special emphasis will be given to the data gathered during the GUARA campaign, especially small- and large-scale motions including transports of momentum and heat. In the GUARA campaign, the combined Use of small meteorological payloads to measure large scale temperature and wind variations coupled with measurements of small scale turbulence from the larger rockets provided clear cut evidence of gravity wave breaking in the 85 to 90 km region.

Schmidlin, F. J.↗
NASA NTRS1999

The Importance of Meteorological Measurements for the Scientific Study of the Mesosphere

The rocket-borne falling sphere technique has been providing temperature and wind measurements to 90 km. For example, the HRDI experiment on the Upper Atmosphere Research Satellite (UARS) and during the GUARA Campaign. The measurement of temperature and wind using the falling sphere method is well known, but will be briefly reviewed. The vertical resolution of the data is examined at different geographical locations and seasons. Time/height sections characterizing the temperature and wind structure will be presented for low (Alcantara, Brazil), middle (Wallops Island and Barking Sands, Hawaii), and high latitudes (ARR and ESRANGE). We address radar quality required, data smoothing, and expected measurement accuracy. Special emphasis will be given to the data gathered during the GUARA campaign, especially small- and large-scale motions including transports of momentum and heat. In the GUARA campaign, the combined use of small meteorological payloads to measure large scale temperature and wind variations coupled with measurements of small scale turbulence from the larger rockets provided clear cut evidence of gravity wave breaking in the 85 to 90 km region.

Schmidlin, F. J.↗
NASA NTRS2016

Applying Required Navigation Performance Concept for Traffic Management of Small Unmanned Aircraft Systems

In anticipation of a rapid increase in the number of civil Unmanned Aircraft System(UAS) operations, NASA is researching prototype technologies for a UAS Traffic Management (UTM) system that will investigate airspace integration requirements for enabling safe, efficient low-altitude operations. One aspect a UTM system must consider is the correlation between UAS operations (such as vehicles, operation areas and durations), UAS performance requirements, and the risk to people and property in the operational area. This paper investigates the potential application of the International Civil Aviation Organizations (ICAO) Required Navigation Performance (RNP) concept to relate operational risk with trajectory conformance requirements. The approach is to first define a method to quantify operational risk and then define the RNP level requirement as a function of the operational risk. Greater operational risk corresponds to more accurate RNP level, or smaller tolerable Total System Error (TSE). Data from 19 small UAS flights are used to develop and validate a formula that defines this relationship. An approach to assessing UAS-RNP conformance capability using vehicle modeling and wind field simulation is developed to investigate how this formula may be applied in a future UTM system. The results indicate the modeled vehicles flight path is robust to the simulated wind variation, and it can meet RNP level requirements calculated by the formula. The results also indicate how vehicle-modeling fidelity may be improved to adequately verify assessed RNP level.

required navigation performance↗
NASA NTRS2023

The Complexity of the Day-Side X-Line During Southward Interplanetary Magnetic Field

High-resolution global magnetohydrodynamics (MHD) simulations include both meso- and global-scale processes occurring at the magnetopause, which interact to determine the time-dependent orientation of the day-side x-line (DXL). This study demonstrates that the global orientation of the DXL in GAMERA global MHD simulations varies on a time scale of minutes during steady southward interplanetary magnetic field conditions. This behavior manifests in observational data when reconnection outflows indicate that the direction to the x-line is opposite to the prediction from a steady-state model of the reconnection location. Because steady-state models of the DXL do not capture dynamics that are independent of solar wind variations, particularly surface waves and flux transfer events, they represent a time-averaged state of the system.

Brandon Burkholder↗
NASA NTRS1993

Latitudinal Variation of Solar Wind Speed and Mass Flux in the Acceleration Region of the Solar Wind during Solar Minimum Inferred from Spectral Broadening measurements

In this paper, we use an aggregate of S-band 2.3 GHz (13 cm) spectral broadening observations conducted during solar minimum conditions by the Mariner 4, Pioneer 10, Mariner 10, Helios 1 & 2 and Viking spacecraft to infer the first measurements of the latitudinal variation of solar wind speed and mass flux in the acceleration region of the solar wind at 3-8 R(sub o).

latitudinal variation of solar wind mass flux in a↗
NASA NTRS1982

Radial variation of the solar wind speed between 1 and 15 AU

Pioneer 10 and 11 solar wind speeds measured between 1.4 and 15.2 AU are compared with those of IMP 6, 7, and 8 measured at 1 AU for 90-day intervals centered on six solar radial alignments between 1973 and 1978. The time profile of the solar wind speed undergoes change as the distance from the sun increases, which is due to interaction of adjacent solar wind streams. Speed variations are smaller at greater radial distance and both the highest and lowest speeds disappear as radial distance increases. For periods with extremely high speed solar wind streams, the mean solar wind speed decreases as the distance from the sun increases, which must be due to the disappearance of the highest speeds of the streams with increasing distance. It is concluded that at distances from the sun greater than 30-40 AU, the solar wind behavior may closely resemble that of a radially expanding constant speed plasma.

Collard, H. R.↗
NASA NTRS1995

Large-scale variations of solar wind elemental composition and charge states with heliospheric latitude

The Solar Wind Ion Composition Spectrometer (SWICS) onboard Ulysses allows determination of the elemental composition of the solar wind and the charge states of all major solar wind ion species. Ulysses left the ecliptic plane in early 1992, crossed the Sun's south polar region in late 1994 and made a fast approach back towards the ecliptic in the first half of 1995. Data from this period were investigated for long-term variations in the solar wind composition. At midlatitudes Ulysses encountered periodically the fast solar wind stream emerging from the south coronal hole. As a consequence, dramatic variations in the charge-states arise, between high charge-states dominating in the current sheet solar wind and low charge states in the coronal hole stream. However, the initial analysis indicates that from midlatitudes onwards, with Ulysses permanently immersed in the coronal hole stream, the charge state and elemental abundance ratios of the major solar wind ion species stayed essentially constant. This implies that the temperature profile in the coronal hole at solar wind source altitudes exhibit no variation with solar latitude. It confirms that the south coronal hole is essentially unstructured down to scale lengths of several degrees in solar latitude.

Woch, J.↗
NASA NTRS1993

Magnetospheric response to solar wind dynamic pressure variations: Interaction of interplanetary tangential discontinuities with the bow shock

Some magnetic impulse events observed in the polar region are related to vortices associated with plasma convection in the ionosphere. Recent analyses of satellite and ground data suggest that the interaction of solar wind dynamic pressure pulses and the magnetosphere may lead to the formation of velocity vortices in the magnetopause boundary layer region. This can in turn lead to the presence of vortices in the polar ionosphere. However, before reaching the Earth's magnetopause, these interplanetary pressure pulses must interact with and pass through the bow shock. A variation of the solar wind dynamic pressure may be associated with shocks, magnetic holes, or tangential discontinuities (TDs) in the interplanetary medium. We study the interaction of interplanetary TDs with the Earth's bow shock (BS) using both theoretical analysis and MHD computer simulations. It is found that as a result of the collision between a TD and the BS, the jump in the solar wind dynamic pressure associated with the TD is significantly modified, the bow shock moves, and a new fast shock or fast rarefaction wave, which propagates in the downstream direction, is excited. Our theoretical analysis shows that the change in the plasma density across the interplanetary TD plays the most important role in the collision process. In the case with an enhanced dynamic pressure behind the interplanetary TD, the bow shock is intensified in strength and moves in the earthward direction. The dynamic pressure jump associated with the transmitted TD is generally reduced from the value before the interaction. A fast compressional shock is excited ahead of the transmitted TD and propagates toward the Earth's magnetosphere. For the case in which the dynamic pressure is reduced behind the interplanetary TD, the pressure jump across the transmitted TD is substantially weakened, the bow shock moves in the sunward direction, and a rarefaction wave which propagates downstream is excited. We also simulate and discuss the interaction of a pair of tangential discontinuities, which may correspond to a magnetic hole, with the BS.

Wu, Bor-Han↗
NASA NTRS1982

The dynamics of the Venus ionosphere. II - The effects of the time scale of the solar wind dynamic pressure variations

The effects on the upper dayside Venus ionosphere of a slow increase in solar wind dynamic pressure are simulated numerically with a one-dimensional (spherically symmetric) Lagrangian hydrodynamical code. The simulation is started with an extended ionosphere in pressure equilibrium with the solar wind at the ionopause. The pressure at the ionopause is gradually increased to five times the initial pressure with rise times of 5, 15, and 30 min. It is found that, for rise times greater than about 10 min, the compression of the ionopause is nearly adiabatic, with the ionopause moving downward at velocities of approximately 1-2 km/sec until it reaches a maximally compressed state, at which time the motion reverses. For short rise times the compression produces a shock wave similar to that occurring in the case of a sudden increase in pressure. The global implications of these processes are discussed within the context of Pioneer Venus observations and future theoretical work on this problem is outlined.

Stein, R. F.↗