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Observations of semidiurnal surface currents in the Kauai Channel, Hawaii, are interpreted in the light of the interaction of internal tides with energetic surface-intensified mesoscale currents. The impacts on internal tide propagation of a cyclone of 55-km diameter and ∼100-m vertical decay scale, as well as of vorticity waves of ∼100-km wavelength and 100–200-m vertical decay scales, are investigated using 3D ray tracing. The Doppler-shifted intrinsic frequency is assumed to satisfy the classic hydrostatic internal wave dispersion relation, using the local buoyancy frequency associated with the background currents through thermal-wind or gradient-wind balance. The M2 internal tide rays with initial horizontal wavelength of 50 km and vertical wavelength of O(1000 m) are propagated from possible generation locations at critical topographic slopes through idealized mesoscale currents approximating the observed currents. Despite the lack of scale separation between the internal waves and background state, which is required by the ray-tracing approximation, the results are qualitatively consistent with observations: the cyclone causes the energy of internal tide rays propagating through its core to increase near the surface (up to a factor of 15), with surfacing time delayed by up to 5 h (∼150° phase lag), and the vorticity waves enhance or reduce the energy near the surface, depending on their phase. These examples illustrate the fact that, even close to their generation location, semidiurnal internal tides can become incoherent with astronomical forcing because of the presence of mesoscale variability. Internal tide energy is mainly affected by refraction through the inhomogeneous buoyancy frequency field, with Doppler shifting playing a secondary but not negligible role, inducing energy transfers between the internal tides and background currents. Furthermore, the vertical wavelength can be reduced by a factor of 6 near the surface in the presence of the cyclone, which, combined with the energy amplification, leads to increased vertical shear within the internal tide rays, with implications for internal wave-induced mixing in the ocean. [ABSTRACT FROM AUTHOR]

The accuracy of most widely used empirical models are investigated using the spectrally accelerated forward-backward (FBSA) method as a benchmark solution. First, FBSA results are obtained for propagation over large scale terrain profiles and compared with measurements to assess the accuracy of FBSA. Then, accuracy of some International Telecommunication Union (ITU) and Federal Communications Commission (FCC) propagation models are investigated. It has been observed that, for rural areas, the prediction of the most recent ITU recommended propagation model (Rec. 1546) deviates much more than older models do. [ABSTRACT FROM AUTHOR]

Analyzes the behavior of a multiple element radio antenna system in an indoor environment based on the measurements taken in the Lucent Bell Labs building in Crawford Hill, New Jersey. Effect of antenna polarization on the capacity of a multiple element system in an indoor environment; Propagation characteristics of the horizontally versus the vertically polarized electric fields; Capacity measurements for constant transmitted power.

The rapid displacement of the ocean floor during large ocean earthquakes or volcanic eruptions causes the propagation of tsunami waves on the surface of the ocean, and consequently internal gravity waves (IGWs) in the atmosphere. IGWs pierce through the troposphere and into the ionospheric layer. In addition to transferring energy to the ionosphere, they cause significant variations in ionospheric parameters, so they have considerable effects on the propagation of radio waves through this dispersive medium. In this study, double-frequency measurements of the Global Positioning System (GPS) and ionosonde data were used to determine the ionospheric disturbances and irregularities in response to the tsunami induced by the 2011 Tohoku earthquake. The critical frequency of the F2 layer (foF2) data obtained from the ionosonde data also showed clear disturbances that were consistent with the GPS observations. IGWs and tsunami waves have similar propagation properties, and IGWs were detected about 25 min faster than tsunami waves in GPS ground stations at the United States west coast, located about 7900 km away from the tsunami's epicenter. As IGWs have a high vertical propagation velocity, and propagate obliquely into the atmosphere, IGWs can also be used for tsunami early warning. To further investigate the spatial variation in ionospheric electron density (IED), ionospheric profiles from FORMOSAT-3/COSMIC (F3/C) satellites were investigated for both reference and observation periods. During the tsunami, the reduction in IED started from 200 km and continued up to 272 km altitude. The minimum observed reduction was 2.68 × 105 el/cm3, which has happened at 222 km altitude. The IED increased up to 767 km altitude continuously, such that the maximum increase was 3.77 × 105 el/cm3 at 355 km altitude. [ABSTRACT FROM AUTHOR]

Describes the development of a vertical-plane-launch (VPL) technique for approximating a full three-dimensional (3-D) site-specific ray trace to predict radio wave propagation effects in cities. Comparison of the predictions of the VPL technique with measurements for Rosslyn, Virginia; Improvement showed by the VPL method.

Information about the 2006 Antennas and Propagation Society Symposium in the U.S. is presented. The conference has been joint with the American Electromagnetics meeting. The joint meetings draw a larger group together to interact. The papers and research about antennas and propagation were reviewed and presented at the conference.

Cites the various propagation handbooks released by the NASA Propagation program. Propagation effects of satellite system design based on 10-100 gigahertz; Propagation effects based on frequencies below 10 gigahertz by Warren L. Flock; Handbook of propagation effects for vehicular and mobile satellite systems by Julius Goldhirsh and Wolfhard J. Vogel.

Discusses the meaning of NAPEX. Origin of the terminology from the National Aeronautics Space Administration Propagation Experimenters; Application of the term to meetings conducted by communication engineers in the field of electromagnetics.

The article provides information about the articles published within the issue May 2006 of "IEEE Transactions on Antennas and Propagation," in the U.S. The current issue highlights current and emerging research in the terahertz (THz) and optical antenna fields, as well as applications of this technology. It consist of invited and contributed papers on novel antenna structures and systems operating in the THz and optical regimes.