Noise source level density due to surf. I. Monterey Bay, CA

Ambient noise measurements made in Monterey Bay, CA, in 1981 were reduced by estimations of wave-breaking noise and the residual noise was combined with modeled transmission loss (TL) to estimate the spectral source level of surf-generated noise. A Hamilton geoacoustic model of the coastal environment was derived and used in a finite-element parabolic equation propagation-loss model to obtain TL values. Estimates of both the continuous, or local, and discrete components of wave-breaking noise intensity were subtracted from the total measured noise field to determine the contribution due to surf only. Surf breaking on a uniform 12.5-km linear section of beach near Ft. Ord was found to be the dominant source of surf-generated noise. Estimated noise source level densities for heavy surf at Ft. Ord beach varied from 138 dB ref. 1 μPa Hz^-1/2 m at 1 m from the source at 50 Hz to 107 dB at 1 kHz, with a slope of about -5 dB per octave. Although these results must be considered as preliminary, since they are based on a small number of measurements, they may he useful for prediction of ambient noise in other littoral regions     

THE CORRELATION BETWEEN SUNSPOT AND CORONAL HOLE CYCLES AND A FORECAST OF THE MAXIMUM OF SUNSPOT CYCLE 23

We have shown in previous papers that a close relationship exists between the evolution of polar coronal hole area, estimated from K-coronameter observations, and the Wolf sunspot number, with a time lag of about half a solar cycle. In this paper we study the same relationship, but with the total coronal hole area at the base of the corona as obtained from a potential field model of the coronal magnetic field, which provides a more complete series of about three solar cycles. We confirm the relationship for the two last cycles and find that the forward time shift in the coronal hole area for the best correlation with sunspot number is almost the same for cycles 21 and 22, and this shift is also the time between peaks in both series. We use this result to make an early prediction of the time and size of the sunspot maximum for solar cycle 23, and find that this should occur early in 2001 and have a magnitude of about 190, similar to that of the two previous sunspot cycles.     

Limits on the 2.2-μm contrast ratio of the close-orbiting planet HD 189733b

We obtained 238 spectra of the close-orbiting extrasolar giant planet HD 189733b with resolution   R ∼ 15 000  during one night of observations with the Near-Infrared High-Resolution Spectrograph (NIRSPEC), at the Keck II Telescope. We have searched for planetary absorption signatures in the  2.0–2.4 μm  region where H₂O and CO are expected to be the dominant atmospheric opacities. We employ a phase-dependent orbital model and tomographic techniques to search for the planetary absorption signatures in the combined stellar and planetary spectra. Because potential absorption signatures are hidden in the noise of each single exposure, we use a model list of lines to apply a spectral deconvolution. The resulting mean profile possesses a signal-to-noise ratio (S/N) that is 20 times greater than that found in individual lines. Our spectral time series thus yields spectral signatures with a mean S/N = 2720. We are unable to detect a planetary signature at a contrast ratio of  log₁₀( F _p/ F _*) =−3.40  , with 63.8 per cent confidence. Our findings are not consistent with model predictions which nevertheless give a good fit to mid-infrared observations of HD 189733b. The 1σ result is a factor of 1.7 times less than the predicted 2.185-μm planet/star flux ratio of  log₁₀( F _p/ F _*) ∼−3.16  .     

A piecewise exponential model for seismic well-logging data

Conventional methods of analyzing sonic log data do not always yield accurate information on each velocity segment of a well. It is shown here that the velocity-depth parameters and the sections of approximately constant velocity may be more precisely defined by using an exponential spline to model the data.     

Non-linear compton and inverse compton effect

A charged particle of arbitrary initial motion and position is subjected to an intense circularly polarized electromagnetic wave. The electromagnetic radiation which results is calculated exactly and the results are expressed in terms of the power observed per unit bandwidth per unit solid angle.Several special cases are considered in order to demonstrate the range of possibilities which this type of interaction may have in astrophisics and numerical examples are given for the Crab pulsar.     

Core 14220 and the lateral continuity of soils at Apollo 14 Station G

Three soil samples at Apollo 14 Station G could potentially be used for stratigraphic correlation. Recently dissected core 14220, and core 14230 are 4 m apart and form the east leg of a triangle with an apex 7m to the west that contains trench samples 14145, 14156 and 14149, from top to bottom. Core 14220 penetrated approximately as deeply as the trench and showed a similar lithologic succession. At the base of both sections is a basalt-rich soil, overlain by a series of units that contain distinctive clasts of light soil and pebble-sized glass fragments. Fine-grained dark soil rich in vesicular glass is at the surface in both sections. The succession of similar soil types suggests that the trench correlates with 14220; but poor sample recovery makes thickness comparisons uncertain. Core 14230 appears to closely correlate with the middle of core 14220. The second layer from the top of 14220 and the top of 14230 are fine-grained with an unusually high percentage of light-matrix breccia, and the next stratum down in both cores is coarser and rich in light annealed-matrix breccia. The principal lithologic types that do not match, successionally, from core to core, are zones rich in vesicular glass and soil breccia. Such rock types are of regolith origin and probably represent patchy and discontinuous deposits.     

Formation of the prelunar accretion disk

According to the single-impact hypothesis for forming the Moon, the angular momentum needed for the present Earth-Moon system can be imparted to the proto-Earth by a collision with a body having one-tenth of the mass or more. The collision must vaporize a large amount of rock which must stay in the form of vapor after expanding in density by a factor of several, so that pressure gradients can accelerate significant amounts of the matter into orbital motion about the proto-Earth. A successful theory must put considerably more than a lunar mass into orbit, having considerably more angular momentum than is needed to assemble a lunar mass in orbit at 3 Earth radii. Such a collision has been simulated by a particular form of a particle-in-cell representation of hydrodynamics and 78 cases have been run representing variations in a variety of parameters. A significant fraction of the cases were successful in creating a satisfactory prelunar accretion disk. A fairly common characteristic of these cases was the presence of an excess velocity in the collision (above that of a parabolic orbit), implying that the projectile involved in the collision existed in an Earth-crossing orbit of significant ellipticity. A majority of the mass of the prelunar accretion disk is contributed by the projectile.