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NASA NTRS1990

Heating of ion conics in the cusp/cleft

Ion conic distributions are often observed in the cusp/cleft region of the dayside magnetosphere. These ions can be heated by resonant interaction with broadband low-frequency (near the ion gyrofrequency) waves. Data from one cusp/cleft crossing of the polar orbiting DE-1 satellite is studied in detail. Observed cool O(+) distributions and observed wave intensities are used as input to a Monte Carlo simulation. The theoretically obtained hot O(+) distributions are in good agreement with the corresponding observed distributions. This resonant heating by broadband low-frequency waves is important for the outflow of ionospheric ions into the magnetosphere.

Andre, Mats↗

NASA NTRS1991

The behavior of wave 2 in the Southern Hemisphere stratosphere during late winter and early spring

The behavior of wave 2 in the Southern Hemisphere (SH) winter and early spring stratosphere has been examined in detail using 10 years of NMC data. Wave 2 is characterized by a broad meridional structure peaking between 55 and 65 S, and regular eastward propagation, with periods ranging from 5 to 40 days. The range of maximum geopotential height amplitudes is from 600 to 1000 m for a year. Consideration is also given to the relationship of wave 2 to other features of stratospheric circulation, Eliassen-Palm fluxes, and synoptic maps. The results obtained show that the zonal mean state of the SH stratosphere frequently satisfies conditions for instability. It is concluded that both instability of zonally symmetric and asymmetric states, and nonlinear interactions between wave 1 and wave 2 are of importance for determining the behavior of wave 2 in the SH winter and spring stratosphere.

Manney, G. L.↗

NASA NTRS1992

Numerical simulations of convectively generated stratospheric gravity waves

A 2D model of a mesoscale convective flow is used to simulate the excitation and vertical propagation of gravity waves. Data obtained show that, in the absence of storm-relative mean winds in the stratosphere, the primary mode of excitation of gravity waves is by mechanical forcing owing to oscillatory updrafts. The stratospheric response consists of waves whose periods match the primary periods of the forcing. Due to the tendency of the oscillating updrafts to propagate toward the rear of the storm, gravity wave propagation is limited primarily to the rearward direction. Results suggest that squall-line-generated gravity waves arise from mechanical forcing rather than thermal effects.

Fovell, R.↗

NASA NTRS1993

A comprehensive analysis of electron conical distributions from multi-satellite databases

This report consists of a copy of a paper that has been submitted to the 'Journal of Geophysical Research', entitled 'DE 1 and Viking Observations Associated With Electron Conical Distributions,' and an abstract of another paper (included as an appendix to the report) that is about to be submitted to the same journal entitled 'Perpendicular Electron Heating by Absorption of Auroral Kilometric Radiation.' A bibliography of other papers that have been published as a result of this project follows. The purpose of this project was to use the DE 1 and Viking particle and wave data to better understand the source mechanism of electron conical distributions. We have shown that electron conics are often associated with upper hybrid waves in the nightside auroral region. We have also shown that electron conics are observed near auroral kilometric radiation (AKR) source regions and may be the result of perpendicular heating due to waves. We have completed a statistical study of electron conics observed by DE-l and Viking. The study shows the occurrence frequency and location of electron conical distributions; there are some differences between the results of DE and Viking perhaps due to different regions sampled.

Menietti, J. Douglas↗

NASA NTRS1980

Optical image and laser slope meter intercomparisons of high-frequency waves

Spectral analyses of optical images of the ocean surface, obtained by a digital video system, are presented and compared with wave data measured simultaneously by the JPL Waverider-mounted laser slope meter. The image analyses, which incorporate several new ideas, provide two-dimensional wave number spectra of slope, covering wavelengths from 10 cm to 10 m. These slope spectra are converted to wave height spectra by a new technique which includes the effects of sky radiance gradients. Space-time spectra are also presented for waves whose frequencies are less than 2 Hz. The JPL slope frequency spectra are compared with image wave number spectra which have been converted to frequency spectra by use of the gravity wave dispersion relation. Results of comparisons between the frequency spectra obtained from the two different measurements show reasonable agreement for frequencies less than 3 Hz.

Lubard, S. C.↗

NASA NTRS1990

The plasma wave signature of a 'magnetic hole' in the vicinity of the magnetopause

Wave spectral measurements in the region of the September 4, 1984 magnetic hole obtained with the plasma wave instrumentation aboard the AMPTE IRM spacecraft are presented. The instrument is briefly described. The full wave data is given and possible reasons for the typical form of the spectra inside the hole are discussed. Relevant observations are presented and different wave modes and their possible origins are discussed. A summary is given with a discussion of ideas about the origin and formation of holes.

Treumann, R. A.↗

NASA NTRS1991

The stratospheric 4-day wave in NMC data

The observed characteristics of the 4-day eastward-moving wave 1 in the Southern Hemisphere polar winter stratosphere are surveyed using ten years of National Meteorological Center (NMC) geopotential height data. The 4-day wave is shown to be an ubiquitous feature in the Southern Hemisphere polar winter stratosphere and is usually prominent during July and August. Growth of the 4-day wave is characterized by two types of structures. Some episodes exhibit NW to SE phase tilts and a single high-latitude maximum. Others show NE to SW phase tilts during growth and a high-latitude maximum out of phase with a secondary lower-latitude maximum. Stability analyses show that all characteristics of the first type of episode are consistent with barotropic instability of the stratospheric polar night jet. Analyses of climatological fields suggest that characteristics of the second type of episode may be consistent with barotropic instability of the double-peaked mesospheric jet.

Manney, Gloria L.↗

NASA NTRS1997

First Test of Stochastic Growth Theory for Langmuir Waves in Earth's Foreshock

This paper presents the first test of whether stochastic growth theory (SGT) can explain the detailed characteristics of Langmuir-like waves in Earth's foreshock. A period with unusually constant solar wind magnetic field is analyzed. The observed distributions P(logE) of wave fields E for two intervals with relatively constant spacecraft location (DIFF) are shown to agree well with the fundamental prediction of SGT, that P(logE) is Gaussian in log E. This stochastic growth can be accounted for semi-quantitatively in terms of standard foreshock beam parameters and a model developed for interplanetary type III bursts. Averaged over the entire period with large variations in DIFF, the P(logE) distribution is a power-law with index approximately -1; this is interpreted in terms of convolution of intrinsic, spatially varying P(logE) distributions with a probability function describing ISEE's residence time at a given DIFF. Wave data from this interval thus provide good observational evidence that SGT can sometimes explain the clumping, burstiness, persistence, and highly variable fields of the foreshock Langmuir-like waves.

Cairns, Iver H.↗

NASA NTRS1978

Ocean waves

Ocean wave data can be obtained from such active microwave probe techniques as monostatic HF and VHF, bistatic HF, HF synthetic aperture radar, altimeters, satellite and airborne synthetic aperture radar, carrier wave or pulsed dual-frequency radars, and coastal surveillance radar. Approaches to texture analysis of ocean wave imagery are discussed, with attention given to transform techniques or spatial frequency analysis, and the analysis of second-order gray level statistics. In addition, recommendations are made for further work on the modulation of short gravity waves by longer waves as a function of wind speed and wave direction, and the derivation of transfer functions for the ocean response of dual-frequency radars.

Bartsch, N.↗

NASA NTRS1981

The Seasat commercial demonstration program

The background and development of the Seasat commercial demonstration program are reviewed and the Seasat spacecraft and its sensors (altimeter, wind field scatterometer, synthetic aperture radar, and scanning multichannel microwave radiometer) are described. The satellite data distribution system allows for selected sets of data, reformatted or tailored to specific needs and geographical regions, to be available to commercial users. Products include sea level and upper atmospheric pressure, sea surface temperature, marine winds, significant wave heights, primary wave direction and period, and spectral wave data. The results of a set of retrospective case studies performed for the commercial demonstration program are described. These are in areas of application such as marine weather and ocean condition forecasting, offshore resource exploration and development, commercial fishing, and marine transportation.

Mccandless, S. W.↗

NASA NTRS1980

Synthetic aperture radar imaging of ocean waves - Comparison with wave measurements

Synthetic aperture radar images of ocean waves were obtained in conjunction with reference wave data near Marineland, Florida, December 14, 1975. Each of the various types of measurements were processed into a form that allowed direct comparisons with the others. Maxima of radar spectra occurred at the same frequencies as the maxima of reference wave height spectra. In a comparison of a radar spectrum with observed spectra of wave height, wave orbital velocity, and surface slope the high-frequency portion of the radar spectrum lay near and between the wave height and the orbital velocity spectra but differed significantly from the surface slope spectrum. The radar-derived mean directions and model-fitted directional spreads of wave energy were close to the values from a directional wave buoy and indicated the accuracy of radar measurements of wave direction. However, a directional plot of a radar spectrum near shore at the frequency of the maximum showed a sharper peak than such a plot of a fitted spectrum derived from reference data.

Mcleish, W.↗

NASA NTRS1984

Strong electron heat flux modes in Jupiter's foreshock

Analysis of Voyager plasma wave data from the Jovian foreshock has revealed the existence of a new oscillation with center frequency below fp and typically lying above the upper limit Doppler shift frequency for ion acoustic waves. The properties of these waves are consistent with modes generated by a strong electron heat flux in an unmagnetized plasma. Such modes become unstable when the effective drift velocity exceeds n(cold)/(hot) exp 1/2 times the thermal speed of the hot component. The occasional simultaneous appearance of more than one frequency band is a possible indication of multiple magnetic connection with the shock.

Moses, S. L.↗

NASA NTRS2007

Consistency of Post-Newtonian Waveforms with Numerical Relativity

General relativity predicts the gravitational radiation signatures of mergers of compact binaries,such as coalescing binary black hole systems. Derivations of waveform predictions for such systems are required for optimal scientific analysis of observational gravitational wave data, and have so far been achieved primarily with the aid of the post-Newtonian (PN) approximation. The quaIity of this treatment is unclear, however, for the important late inspiral portion. We derive late-inspiral wave forms via a complementary approach, direct numerical simulation of Einstein's equations, which has recently matured sufficiently for such applications. We compare waveform phasing from simulations covering the last approximately 14 cycles of gravitational radiation from an equal-mass binary system of nonspinning black holes with corresponding 3PN and 3.5PN waveforms. We find phasing agreement consistent with internal error estimates based in either approach, at the level of one radian over approximately 10 cycles. The result suggests that PN waveforms for this system are effective roughly until the system reaches its last stable orbit just prior to the final merger.

Baker, John G.↗

NASA NTRS1995

Investigation of plasma instabilities in the polar cusp

This technical paper describes the occurrence of magnetosonic waves in the dayside and nightside polar magnetosphere and the roles that these waves can play in the heating of ions in the ionosphere. Plasma waves near the auroral kilometric radiation (AKR) source regions is studied, using wave data obtained from both the Galileo and DE-1. During the Galileo encounter with the Earth in 1992, very intense auroral kilometric radiation was observed. The high spectral resolution obtained by the wide-band receiver of the plasma wave instrument on board the spacecraft often show distinctive, dispersive, arc-like features each extending over a period of several seconds. Similar features were also observed by De-1. These features may be due to an intrinsic velocity and/or to a source simulation by different wave modes. A reply to the comment by Orlowski and Russell on the earlier paper 'Electron Beam Excitation of Upstream Waves in the Whistler Frequency Mode Frequency Range' is also included.

Wong, H. K.↗

NASA NTRS1990

Follow-on cable coupling lightning test. Volume 3: Appendixes E and F

The following subject areas are covered: (1) Follow-on cable coupling lightning test swept continuous wave data plots, and (2) USBI cable coupling responses, EMA final test report (Lightning test results for the modified systems tunnel bonding on the Space Shuttle Solid Rocket Booster: tabulation of cable responses to threat level lightning testing; demonstration of linear extrapolation of swept continuous wave testing to NASA lightning specification).

Source record↗

NASA NTRS1998

Long-Term Global Morphology of Gravity Wave Activity Using UARS Data

This is the first quarter's report on research to extract global gravity-wave data from satellite data and to model those observations synoptically. Preliminary analysis of global maps of extracted middle atmospheric temperature variance from the CRISTA instrument is presented, which appear to contain gravity-wave information. Corresponding simulations of global gravity-wave and mountain-wave activity during this mission period are described using global ray-tracing and mountain-wave models, and interesting similarities among simulated data and CRISTA data are noted. Climatological simulations of mesospheric gravity-wave activity using the HWM-03 wind-temperature climatology are also reported, for comparison with UARS MLS data. Preparatory work on modeling of gravity wave observations from space-based platforms and subsequent interpretation of the MLS gravity-wave product are also described. Preliminary interpretation and relation to the research objectives are provided, and further action for the next quarter's research is recommended.

Eckermann, Stephen D.↗

NASA NTRS1983

Narrowband electromagnetic emissions from Jupiter's magnetosphere

Recent studies of wideband plasma wave data from Voyagers 1 and 2 have revealed the existence of narrowband radio emissions escaping from Jupiter's magnetosphere in the frequency range 1-12 kHz. These narrowband emissions are very similar to narrowband emissions previously discovered near earth and Saturn, and are believed to be produced by mode conversion from locally generated upper hybrid resonance waves at odd half-integral harmonics of the electron cyclotron frequency. This mode conversion process is believed to be one of the basic mechanisms for generating planetary radio emissions.

Gurnett, D. A.↗

NASA NTRS1978

The problem of low energy particle measurements in the magnetosphere

The accurate measurement of low energy (less than 100 eV) particle properties in the magnetosphere has been difficult, partly because of the low density of such particles, but more particularly because of spacecraft interference effects. Some early examples of how these phenomena have affected particle measurements on an OGO spacecraft are presented. Data obtained with the UCSD particle detectors on ATS-6 are then presented showing how some of these difficulties have been partially overcome. Future measurements of low energy particles in the magnetosphere can be improved by: (1) improving the low energy resolution of detectors; (2) building electrostatically clean spacecraft; (3) controlling spacecraft potential; and (4) using auxiliary measurements, particularly wave data.

Whipple, E. C., Jr.↗