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The passage of graviational waves changes the arm lengths between corners of the LISA spacecraft formation. These changes are detected interferometrically and recorded as phase measurements. The time series are reduced to reveal several signal types.
A method of extracting sea height information from Synthetic Aperture Radar (SAR) complex data was studied. A fundamental SAR ocean imaging model for gravity waves showed that information about the long wave is present in the SAR complex data, especially its phase. Phase demodulation algorithm followed by linear regression and filtering was employed. Only the latter two steps incorporated a priori information that might be available. A relatively simplified simulation indicated that the finite bandwidth of the SAR system imposed the apparently most serious limitation. A preliminary application to SEASAT-SAR complex imagery was encouraging. Information about the long wave, if incorporated into a more sophisticated phase demodulation structure, i.e., at an earlier point in the algorithm, could conceivably mitigate this bandwidth limitation.
Previously collected data on atmospheric pressure, density, temperature and winds between 25 and 200 km from sources including Meteorological Rocket Network data, ROBIN falling sphere data, grenade release and pitot tube data, meteor winds, chemical release winds, satellite data, and others were analyzed by a daily difference method and results on the distribution statistics, magnitude, and spatial structure of gravity wave and planetary wave atmospheric variations are presented. Time structure of the gravity wave variations were determined by the analysis of residuals from harmonic analysis of time series data. Planetary wave contributions in the 25-85 km range were discovered and found to have significant height and latitudinal variation. Long period planetary waves, and seasonal variations were also computed by harmonic analysis. Revised height variations of the gravity wave contributions in the 25 to 85 km height range were computed. An engineering method and design values for gravity wave magnitudes and wave lengths are given to be used for such tasks as evaluating the effects on the dynamical heating, stability and control of spacecraft such as the space shuttle vehicle in launch or reentry trajectories.
Annual simulations of Mars' atmosphere have been conducted with the NASA Ames Mars General Circulation Model (MGCM) using the newly-acquired MOLA topography data. The data is provided at 1 x 1 deg resolution, and is used by the MGCM at 7.5 x 9 deg resolution. The vertical domain in the simulations reported here extends to around 80 km. Simulated stationary wave activity is examined in each hemisphere as a function of season (at every 30 deg of Ls), dust loading (dust visible opacities of 0.3, 1, and 3), and topography (comparing results with MOLA vs. Smith-Zuber topography). Additional information is contained in the original extended abstract.
Features and applications of the Shuttle tethered satellite system (TSS) are outlined. The TSS would be mounted on a normal cargo pallet and used to deploy or retrieve payloads weighing up to 500 kg from the Orbiter by reeling in or unreeling a tether line extended along the gravity gradient vertical. Attaching a conducting wire to the tether would permit electrodynamic measurements of space plasma. An initial mission under development is to deploy an instruments package 20 km above the Orbiter with a conducting wire tether, thereby obtaining data on low frequency hydromagnetic waves generated by tether passage through the space plasma. An aerodynamics package could also be lowered to 130 km, where measurements can be made with magnetometers for geoscience data, atmospheric composition, and cosmic dust can be collected. Details of engineering assignments for the TSS divided up between NASA and the Italian National Research Council are discussed.
This volume (2), which consists of two parts (A and B), of the Plasma Diagnostics Package (PDP) Final Science Report contains a summary of all of the data reduction and scientific analyses which were performed using PDP data obtained on STS-51F as a part of the Spacelab 2 (SL-2) payload. This work was performed during the period of launch, July 29, l985, through June 30, l988. During this period the primary data reduction effort consisted of processing summary plots of the data received by 12 of the 14 instruments located on the PDP and submitting these data to the National Space Science Data Center (NSSDC). The scientific analyses during the performance period consisted of follow-up studies of shuttle orbiter environment and orbiter/ionosphere interactions and various plasma particle and wave studies which dealt with data taken when the PDP was on the Remote Manipulator System (RMS) arm and when the PDP was in free flight. Of particular interest during the RMS operations and free flight were the orbiter wake studies and joint studies of beam/plasma interactions with the SL-2 Fast Pulse Electron Generator (FPEG) of the Vehicle Charging and Potential Investigation (VCAP). Internal reports, published papers and presentations which involve PDP/SL-2 data are listed in Sections 3 and 4. A PDP/SL-2 scientific results meeting was held at the University of Iowa on June 10, l986. This meeting was attended by most of the PDP and VCAP investigators and provided a forum for discussing and comparing the various results, particularly with regard to the PDP free flight.
Major elements of an experiment called the Infrared Sensing Aeroheating Flight Experiment are discussed. The primary experiment goal is to provide reentry global temperature images from infrared measurements to define the characteristics of hypersonic boundary-layer transition during flight. Specifically, the experiment is to identify, monitor, and quantify hypersonic boundary layer windward surface transition of the X-33 vehicle during flight. In addition, the flight data will serve as a calibration and validation of current boundary layer transition prediction techniques, provide benchmark laminar, transitional, and fully turbulent global aeroheating data in order to validate existing wind tunnel and computational results, and to advance aeroheating technology. Shuttle Orbiter data from STS-96 used to validate the data acquisition and data reduction to global temperatures, in order to mitigate the experiment risks prior to the maiden flight of the X-33, is discussed. STS-96 reentry mid-wave (3-5 Pm) infrared data were collected at the Ballistic Missile Defense Organization/Innovative Sciences and Technology Experimentation Facility site at NASA-Kennedy Space Center and subsequently mapped into global temperature contours using ground calibrations only. A series of image mapping techniques have been developed in order to compare each frame of infrared data with thermocouple data collected during the flight. Comparisons of the ground calibrated global temperature images with the corresponding thermocouple data are discussed. The differences are shown to be generally less than about 5%, which is comparable to the expected accuracy of both types of aeroheating measurements.
Extreme events, especially heat waves, have seemingly become more frequent and intense in the past decades worldwide, likely associated with global warming. This study uses the extreme detection indices product derived from the NASA Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) data to address whether heat waves have become more intense and frequent in North America in the past 40 years. We also examine in-depth the recent heat wave in June 2023 in Canada and the associated drought and wildfire events and compare them with previous years. We use additional data products in this study for cross-validation, including surface temperature from Phase 2 of the North American Land Data Assimilation System (NLDAS 2.0) and Atmospheric Infrared Sounder (AIRS) version 7, with a shorter data latency, only a few days. In addition, we will demonstrate how to efficiently conduct long-term time-series data analysis, which involves a large volume of data, using data services developed at NASA GES DISC, such as Giovanni, datarod, and Thematic Real-time Environmental Distributed Data Services (THREDDS) Data Server (TDS). These services can be used to visualize and explore extreme events, and to download only the data that is of interest.
Wave-like perturbations have been observed in the nightside neutral density data acquired for He, N, O, N2 and CO2 by the Pioneer Venus Orbiter Neutral Mass Spectrometer (ONMS) during entry in late 1992. The data cover an altitude range of 133-200 km from 0.5-4.5 hours local solar time and occur at medium solar activity (F(sub 10.7) = 120) The perturbations, with an effective wavelength along the orbit of about 100 to 600 km, have similar amplitudes for the various species and helium is out of phase with respect to the heavier mass species. The measurements are comparable to those observed in 1978-80 at solar maximum activity (F(sub 10.7) = 200) above 145 km. Between 133 and 160 km the rms amplitudes grow with altitude at a rate of about (1.6, 2.1, 2.7, 4.4) x 10(exp -3)/ km for N, O, N2, and CO2 respectively. The average rms amplitudes above 145 km of 0.08 for N and O and 0.1 for N2 are comparable in magnitude to those observed in the earlier 1978-80 data of 0.06, 0.08 and 0.095 respectively. CO2 is an exception for which the entry value is 0.17 compared to 0.09 earlier. By combining the two overlapping data sets there is a suggestion that the CO2 amplitudes grow in value with altitude up to about 140-170 km and then decrease in amplitude. Like the earlier data, the entry data are consistent with the interpretation that the neutral density perturbations are due to gravity waves propagating upward from the lower thermosphere. Earlier data sampled a higher altitude region where dissipation is important in limiting and ultimately reversing the growth of gravity waves while the lower altitude entry data probed the region where growth of these waves can be observed.
Examples of propagating electromagnetic Alfven/ion cyclotron waves in plasma particle and magnetic field data observed by the ATS-6 geostationary satellite are discussed. These waves were viewed mainly near the afternoon and dusk regions of the earth's magnetosphere with normalized frequencies in the 0.05 to 0.5 range. Two wave events were analyzed: both appeared coincidentally with the encounter of cool plasma populations which joined the hot populations already present. An electromagnetic ion cyclotron instability was proposed as the wave generation mechanism; this theory was tested by evaluating the linear growth integrals under the measured anisotropic hot ion distribution.
The directional spectrum of a fully arisen, about 3 m sea as measured by an experimental airborne radar, the NASA K(u)-band radar ocean wave spectrometer (ROWS), is compared to reference pitch-roll buoy data and to the classical SWOP (stereo wave observations project) spectrum for fully developed conditions. The ROWS spectrum, inferred indirectly from backscattered power measurements at 5-km altitude, is shown to be in excellent agreement with the buoy spectrum. Specifically, excellent agreement is found between the two nondirectional height spectra, and mean wave directions and directional spreads as functions of frequency. A comparison of the ROWS and SWOP spectra shows the two spectra to be very similar, in detailed shape as well as in terms of the gross spreading characteristics. Both spectra are seen to exhibit bimodal structures which accord with the Phillips' (1958) resonance mechanism. This observation is thus seen to support Phillips' contention that the SWOP modes were indeed resonance modes, not statistical artifacts.
Controlled laboratory experiments have been conducted to study the kinematics of wave-current interactions. The results confirm the conservation of waves under the steady state condition. The data also show that the kinematic effect of the current on waves can be treated as a simple Doppler shift. After the Doppler correction, the kinematics of the waves (either breaking or nonbreaking) follow the linear theory very well.
Ultraviolet albedo contrasts in the Venus atmosphere are probably large-scale atmospheric waves propagating slowly with respect to the rapid cloud-top zonal winds. Using a simple theoretical model and profiles of mean wind and thermal structure based on Pioneer Venus data, planetary-scale gravity waves with phase velocities matching the speeds of the UV markings are found. An upward-propagating wave, and waves trapped at cloud levels are proposed as candidates to explain the observed UV features.
Data from the Atmosphere Explorer-C satellite clearly exhibit wavelike variations in neutral composition, ion density, and electron temperature, which appear to be a general feature of the atmosphere. The neutral constituents do not exhibit uniform wave characteristics since the density variations of argon are approximately twice those of molecular nitrogen and helium structure has about one-half the amplitude of the N2 variation. The waves evident in the ion density are nearly in phase with the heavy neutrals, while the electron-temperature variations are predominantly out of phase with those in the ion density. A simple model is suggested to explain the neutral composition results, wherein the enhancements in the major gas densities are in phase with the vertical component of the perturbation velocity of the gas. The vertical velocity modifies the composition by transporting parcels of air to higher or lower regions where the composition is different. The phase relationship between density and velocity implies phase velocities (assuming that these are gravitational waves) of the order of 500 meters per sec.
Density fluctuations obtained along seven Space Shuttle reentry tracks are used to examine the horizontal structure and the vertical distribution of density variance in the mesosphere and lower thermosphere. The tracks lie primarily over open ocean at middle and low latitudes and represent the only measurements of horizontal atmospheric structure at these heights available to date. The density fluctuations are interpreted in terms of gravity-wave motions and reveal significant density (and velocity) variance at horizontal scales ranging from about 10 to 1000 km. Fluctuation amplitudes are used to infer corresponding velocity perturbations and characteristic vertical scales and frequencies of the wave spectrum. Results suggest that the mean velocity variance is smaller over the Pacific ocean than over major land masses, and that the variance increases with height in a manner consistent with that expected in the present of wave saturation processes.
Details of the method used to measure the stress wave factor are described. Frequency spectra of the stress waves are analyzed in order to clarify the nature of the wave phenomena involved. The stress wave factor was measured with simple contact probes requiring only one-side access to a part. This is beneficial in nondestructive evaluations because the waves can run parallel to fiber directions and thus measure material properties in directions assumed by actual loads. The technique can be applied where conventional through transmission techniques are impractical or where more quantitative data are required. The stress wave factor was measured for a series of graphite/polyimide composite panels, and results obtained are compared with through transmission immersion ultrasonic scans.
When galaxies merge, the supermassive black holes in their centers may form binaries and emit low-frequency gravitational radiation in the process. In this paper, we consider the galaxy 3C 66B, which was used as the target of the first multimessenger search for gravitational waves. Due to the observed periodicities present in the photometric and astrometric data of the source, it has been theorized to contain a supermassive black hole binary. Its apparent 1.05-year orbital period would place the gravitational-wave emission directly in the pulsar timing band. Since the first pulsar timing array study of 3C 66B, revised models of the source have been published, and timing array sensitivities and techniques have improved dramatically. With these advances, we further constrain the chirp mass of the potential supermassive black hole binary in 3C 66B to less than (1.65±0.02)×109Me using data from the NANOGrav 11-year data set. This upper limit provides a factor of 1.6 improvement over previous limits and a factor of 4.3 over the first search done. Nevertheless, the most recent orbital model for the source is still consistent with our limit from pulsar timing array data. In addition, we are able to quantify the improvement made by the inclusion of source properties gleaned from electromagnetic data over “blind” pulsar timing array searches. With these methods, it is apparent that it is not necessary to obtain exact a priori knowledge of the period of a binary to gain meaningful astrophysical inferences.
The observation is discussed of a train of hydromagnetic waves with a period of about 150 sec seen at synchronous orbit by the ATS 6 spacecraft on June 27, 1974. The critical observation is a phase shift of 90 deg between east-west oscillations of the particle flow and the east-west component of magnetic field oscillations. This phase shift alone suggests a standing rather than a propagating hydromagnetic wave. Careful processing of the particle data makes it possible to determine the drift velocity and hence the electric field of the wave. The wave electric field together with the time-varying magnetic field reveals an oscillating Poynting vector with zero mean component aligned with the ambient magnetic field and nonzero azimuthal (westward) component.