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

Diffraction by a truncated planar array of dipoles: a Wiener-Hopf approach

This is the final version. Available on open access from Elsevier via the DOI in this recordWe present a rigorous solution to the problem of scattering of a semi-infinite planar array of dipoles, i.e., infinite in one direction and semi-infinite in the other direction, thus presenting an edge truncation, when illuminated by a plane wave. Such an arrangement represents the canonical problem to investigate the di raction occurring at the edge-truncation of a planar array. By applying the Wiener-Hopf technique to the Z-transformed system of equations derived from the electric field integral equation, we provide rigorous close form expressions for the dipoles’ currents. We find that such currents are represented as the superposition of the infinite array solution plus a perturbation, which comprises both edge di raction and bound surface waves excited by the edge truncation. Furthermore, we provide an analytical approximation for the double-infinite sum involved in the calculation which drastically reduces the computational e ort of this approach and also provides physically-meaningful asymptotics for the di racted currents.Engineering and Physical Sciences Research Council (EPSRC

Wiener-Hopf analysis of the scattering by a two dimensional periodic semi-infinite array of dipoles

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordWe present a rigorous solution of the scattering of plane waves by a truncated planar array of dipoles which is infinite and periodic in one direction and semi-infinite in the orthogonal direction, thus presenting an edge truncation. By applying the Wiener-Hopf technique to the Z-transformed system of equations derived from the electric field integral equation, the contributions to the current on the dipoles due to the scattering by the edge of the array and the excitation of surface waves are obtained rigorously.Engineering and Physical Sciences Research Council (EPSRC

Theoretical and experimental exploration of finite sample size effects on the propagation of surface waves supported by slot arrays (article)

This is the final version of the article. Available from American Physical Society via the DOI in this record.The dataset associated with this article is in ORE at: http://hdl.handle.net/10871/28223The propagation of surface waves supported by a finite array of slots perforated on a zero thickness perfect electrically conducting screen is studied both experimentally and theoretically. To generate numerical results, the integral equation satisfied by the electric field in the slots is efficiently solved by means of Galerkin’s method, treating the metal as perfectly conducting. The finite size of the array along the direction of propagation creates a family of states of higher momentum and lower amplitude than the single mode for the corresponding infinite array. These modes are spaced in momentum with a periodicity inversely proportional to the length of the array. In addition, the finite width in the transverse direction produces a set of higher frequency modes due to this additional quantization. Both effects arising from finite sample length and width are explained by the theoretical model and validated experimentallyThe authors wish to acknowledge financial support from the Engineering and Physical Sciences Research Council (EPSRC) of the United Kingdom, via the EPSRC Centre for Doctoral Training in Metamaterials (Grant No. EP/L015331/1). R.R.B. and F.M. acknowledge financial support from the Spanish MINECO (Grant No. TEC2013-41913-P) and the Spanish Junta de Andalucía (Grant No. P12-TIC-1435)

Theoretical and experimental exploration of finite sample size effects on the propagation of surface waves supported by slot arrays (article)

This is the final version of the article. Available from American Physical Society via the DOI in this record.The dataset associated with this article is in ORE at: http://hdl.handle.net/10871/28223The propagation of surface waves supported by a finite array of slots perforated on a zero thickness perfect electrically conducting screen is studied both experimentally and theoretically. To generate numerical results, the integral equation satisfied by the electric field in the slots is efficiently solved by means of Galerkin’s method, treating the metal as perfectly conducting. The finite size of the array along the direction of propagation creates a family of states of higher momentum and lower amplitude than the single mode for the corresponding infinite array. These modes are spaced in momentum with a periodicity inversely proportional to the length of the array. In addition, the finite width in the transverse direction produces a set of higher frequency modes due to this additional quantization. Both effects arising from finite sample length and width are explained by the theoretical model and validated experimentallyThe authors wish to acknowledge financial support from the Engineering and Physical Sciences Research Council (EPSRC) of the United Kingdom, via the EPSRC Centre for Doctoral Training in Metamaterials (Grant No. EP/L015331/1). R.R.B. and F.M. acknowledge financial support from the Spanish MINECO (Grant No. TEC2013-41913-P) and the Spanish Junta de Andalucía (Grant No. P12-TIC-1435)

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

On the extraordinary optical transmission in parallel plate waveguides for non-TEM modes

This is the final version of the article. Available from Optical Society of America via the DOI in this record.Extraordinary transmission has been recently measured in a parallel plate waveguide (PPWG) through a metal strip with a patterned 1-D periodic array of circular holes, the metal strip being embedded inside the PPWG. Wood’s anomaly and the extraordinary transmission peak (EOT) were detected for transverse electric (TE) mode excitation at frequencies higher than those found for TEM mode excitation. In this paper we provide an explanation for this frequency shift by decomposing the problem of a TE mode impinging on the 1-D array of holes into two problems of plane waves impinging obliquely on 2-D periodic arrays of holes. By then solving the integral equation for the electric field on the surface of the holes, the origin of the frequency shift is proved both mathematically and physically in terms of the symmetries present in the system.Engineering and Physical Sciences Research Council (EPSRC) (EP/L015331/1) and “Junta de Andalucía” (P12-TIC-1435)

Remarkable transmission of microwaves through a wall of long metallic bricks

Copyright © 2001 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 79 (2001) and may be found at http://link.aip.org/link/?APPLAB/79/2844/1The transmitted intensity of a microwave beam through a thick continuous metal wall will be effectively zero due to the almost complete exclusion of the electric field from the metal. However, it is shown here that by removing less than 20% of the wall material to produce a regular array of bricks, up to 90% of the radiation is transmitted, despite the gaps between the bricks being less than 5% of the incident wavelength. This result is attributed to the excitation of a set of resonant waves along the cavity length through the coupling together of surface–plasmon modes across its width

Extraordinary transmission and radiation from finite by infinite arrays of slots

This is the author accepted manuscript. The final version is available from IEEE via the DOI in this recordIn this communication an efficient Method of Moments (MoM) code is used for the analysis of the extraordinary transmission (EOT) through a periodic array of rectangular slots in a conducting screen, in the case where the number of slots is finite in one direction and infinite in the orthogonal direction. The slots can be arbitrarily rotated within the periodic unit cell. Once the magnetic current density on the slots is obtained by means of MoM, both the transmission coefficient and the far field radiated by the array of slots are computed. The onset of EOT turns out to be strongly dependent on the orientation of the slots with respect to the direction in which the array is infinite. If the slots are perpendicular to this direction, EOT appears for a single infinite chain of slots. However, tens of parallel chains of slots are required to reproduce the EOT response when the slots are aligned along the parallel chains direction. The obtained radiation patterns show the excitation of grating lobes as the number of slots grows in the direction where the arrays are finite.Engineering and Physical Sciences Research Council (EPSRC)Junta de AndaluciaSpanish Ministry of Economy, Industry and Competitivenes