A long-term comparison of wind and tide measurements in the upper mesosphere recorded with an imaging Doppler interferometer and SuperDARN radar at Halley, Antarctica

International audienceData from a co-located imaging Doppler interferometer and SuperDARN radar recorded since 1996 have been analysed in a consistent manner to determine daily mean winds and tides in the upper mesosphere. By comparing only days when both techniques were recording good quality data it is shown that the SuperDARN radar winds and tides correlate best with the IDI height bin 90?95 km. On timescales of one hour the winds derived from each technique correlate poorly, whereas the daily mean winds are in much better agreement suggesting that the two radars are sensitive to different parts of the gravity wave spectrum. Regression analysis reveals that the observed SuperDARN daily mean meridional wind strength is approximately 65% that recorded by the IDI while the zonal winds are of similar magnitude, in good quantitative agreement with previous studies which have shown contamination to SuperDARN-derived winds due to the significant back lobe of the radar radiation pattern. Climatologically the two techniques observe similar monthly mean winds with the SuperDARN meridional winds suppressed compared to the IDI which tends to record winds more poleward and eastward than those derived by the SuperDARN radar during the summer months, and to be slightly more equatorward during the winter. The 12-h tidal amplitude and phase in both the zonal and meridional components derived from both techniques are in excellent agreement, whereas the 24-h tides are seen much more strongly in the SuperDARN radar, especially in wintertime, with poor phase agreement. Long term comparison of the two techniques reveals a tendency for the IDI meridional winds to be more poleward during solar maximum especially during summer time; an effect which is not reproduced in the meridional winds derived from the SuperDARN radar. These results are discussed in the context of previous studies to independently determine the veracity of each technique

Excitation of remarkably nondispersive surface plasmons on a nondiffracting, dual-pitch metal grating

Copyright © 2002 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 80 (2002) and may be found at http://link.aip.org/link/?APPLAB/80/2410/1A nondiffracting metallic lamellar grating formed from three equally spaced grooves per repeat period, with one being slightly shallower than the other two is examined at microwave frequencies. When filled with a slightly lossy dielectric, this structure supports a remarkably nondispersive surface plasmon polariton mode, which exhibits strong selective absorption of incident power. Measured reflectivities show excellent agreement with the results predicted by a rigorous coupled wave theory

Coupling of near-grazing microwave photons to surface plasmon polaritons via a dielectric grating

Copyright © 2000 by the American Physical SocietyA dielectric grating on top of a planar metal substrate is shown to couple near-grazing microwave photons to surface plasmon polaritons (SPPs). It is shown that when the grating grooves are oriented such that they are parallel to the plane of incidence (φ=90°), coupling to SPPs with both s- and p-polarized photons is possible at three different energies. It is demonstrated that one mode is coupled via p-polarized radiation and the other two modes are both coupled via s-polarized radiation. A multilayer, multishape differential grating theory allows the identities of each of the modes to be confirmed by modeling the electromagnetic fields above the metal substrate. In addition, a comparison between the experimentally derived reflectivity scans and the theoretical model is made.Defence Evaluation and Research Agency (DERA), Farnboroug

The coupling of microwave radiation to surface plasmon polaritons and guided modes via dielectric gratings

Copyright © 2000 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Applied Physics 87 (2000) and may be found at http://link.aip.org/link/?JAPIAU/87/2677/1It is shown that an absorbing dielectric layer, sinusoidally modulated in height, on top of a planar metal substrate, may be used to provide coupling between both s- and p-polarized incident microwave photons and surface plasmon polaritons, which propagate along the metal–dielectric interface. The study is carried out using paraffin wax as the dielectric material on an aluminum-alloy plate and the wax is sufficiently thick such that it may also support a guided mode. Energy reradiated from these excited modes into diffracted orders is recorded by monitoring the specular beam reflectivity as a function of wavelength (7.5<λ0<11.3 mm) and azimuthal angle of incidence (0°<φ<90°). The azimuthal-angle-dependent reflectivity scans are fitted using a multilayer, multishape differential formalism to model conical diffraction with a single set of parameters describing the grating profile, and the permittivity and thickness of the wax layer

Gratingless enhanced microwave transmission through a subwavelength aperture in a thick metal plate

Copyright © 2002 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 81 (2002) and may be found at http://link.aip.org/link/?APPLAB/81/4661/1Remarkably enhanced transmission of microwave radiation through a single subwavelength slit in a thick metallic substrate surrounded by just a pair of parallel deep and narrow grooves is recorded. By also patterning the output face of the metal slab with two grooves there is strong exit beam confinement. There are no gratings in this structure and, hence, the transmission mechanism is not related to the conventional grating coupling of surface plasmons on the upper and lower surfaces of the substrate. Instead, the slit and the four grooves are all resonant, which is the essence of the functioning of the arrangement. The enhancement is due to the collective excitation of the Fabry–Pérot mode in the slit and the cavity modes in the grooves. A finite-element modeling code is used to optimize the response of the structure, and to investigate the electromagnetic fields in the vicinity of the substrate

Spatial transformations: from fundamentals to applications

We acknowledge the financial support of the Engineering and Physical Sciences Research Council (EPSRC), via the programme grant ‘The Quest for Ultimate Electromagnetics using Spatial Transformations (QUEST)’, grant no. EP/I034548/1

Massively sub-wavelength guiding of electromagnetic waves

Open Access journalRecently a new form of ultra-thin flexible waveguide consisting of a conducting comb-like structure with a thickness of the order of 1/600(th) of the operating wavelength was presented. However, whilst the thickness of the guide was massively sub-wavelength, the remaining dimensions (the height and period of the comb) were much longer. In this paper we propose, and experimentally verify, that a modified guiding geometry consisting of a chain of ultra-thin conducting spirals allows guiding of electromagnetic waves with wavelengths that are many times (40+) longer than any characteristic dimension of the guide, enabling super-sub-wavelength guiding and localisation of electromagnetic energy.Engineering and Physical Sciences Research Council (EPSRC

Atmospheric effects of radiation belt precipitation over Antarctica

第3回極域科学シンポジウム　横断セッション「中層大気・熱圏」 11月26日（月） 国立極地研究所 ２階大会議