A. Casanueva

Statistical downscaling of climate impact indices: testing the direct approach.

Climate Impact Indices (CIIs) are being increasingly used in different socioeconomic sectors to transfer information about climate change impacts to stakeholders. Typically, CIIs comprise into a single index several weather variables —such as temperature, wind speed, precipitation and humidity— which are relevant for a particular problem of interest. Moreover, most of the CIIs require daily (or monthly) physical coherence among these variables for their proper calculation. This constraints the number of statistical downscaling techniques suitable for a component-wise approach to this problem. We test the suitability of the alternative “direct” downscaling approach in which the downscaling method is applied directly to the CII, thus circumventing the multi-variable problem and allowing the use of a wider range of downscaling methods. For illustrative purposes, we consider two popular CIIs —the Fire Weather Index (FWI) and the Physiological Equivalent Temperature (PET), used in the wildfire and tourism sectors, respectively— and compare the performance of the two approaches using the analog method, a simple and popular method providing inter-variable dependence. The results obtained with ‘perfect’ reanalysis predictors are comparable for both approaches, although smaller accuracy is obtained in general with the direct approach. Moreover, similar climate change ‘deltas’ are obtained with both approaches when applied to an illustrative future global projection using the ECHAM5 model. Overall, there is a trade-off between performance and simplicity which needs to be balanced for each particular application.

Towards a fair comparison of statistical and dynamical downscaling in the framework of the EURO-CORDEX initiative

Both statistical and dynamical downscaling methods are well established techniques to bridge the gap between the coarse information produced by global circulation models and the regional-to-local scales required by the climate change Impacts, Adaptation, and Vulnerability (IAV) communities. A number of studies have analyzed the relative merits of each technique by inter-comparing their performance in reproducing the observed climate, as given by a number of climatic indices (e.g. mean values, percentiles, spells). However, in this paper we stress that fair comparisons should be based on indices that are not affected by the calibration towards the observed climate used for some of the methods. We focus on precipitation (over continental Spain) and consider the output of eight Regional Climate Models (RCMs) from the EURO-CORDEX initiative at 0.44∘ resolution and five Statistical Downscaling Methods (SDMs) —analog resampling, weather typing and generalized linear models— trained using the Spain044 observational gridded dataset on exactly the same RCM grid. The performance of these models is inter-compared in terms of several standard indices —mean precipitation, 90th percentile on wet days, maximum precipitation amount and maximum number of consecutive dry days— taking into account the parameters involved in the SDM training phase. It is shown, that not only the directly affected indices should be carefully analyzed, but also those indirectly influenced (e.g. percentile-based indices for precipitation) which are more difficult to identify. We also analyze how simple transformations (e.g. linear scaling) could be applied to the outputs of the uncalibrated methods in order to put SDMs and RCMs on equal footing, and thus perform a fairer comparison.

Improved compact microstrip low pass filter with novel distributions of complementary split ring resonators (CSRRs)

In this contribution, the coupling characteristics of three novel coupling structures for double CSRRs are applied. Firstly the concept of complementary split ring resonators (CSRRs) is utilized to improve the selectivity of a microwave low pass filter (LPF). To this end, a step-impedance low-pass filter (SILPF) is first optimized and then built. The proposed filters consist of an asymmetrical microstrip step discontinuity circuit with harmonic suppression and CSRRs to improve sharp rejection. Moreover, different coupling structures can cause different frequency responses, especially the stopband characteristics. In order to improve the optimized SILPF, a novel compact low pass filter using single and a pair of double CSRRs is proposed. Properties of these configurations are discussed, and two manufactured prototypes have been successfully tested. The results show the usefulness and validity of the new structures with high rejection capabilities.

Modal Analysis of Discontinuities in Planar Transmission Lines: using Orthogonality as the Criterion for Selecting Modes

The technique of modal analysis has been used together with the spectral domain approach (SDA) to analyze single and cascaded step discontinuities in planar transmission lines, particularly in boxed microstrip and finlines. These kinds of discontinuities appear frequently in MICs and MMICs. Convergence was studied as a function of the number of modes (propagating, evanescent and complex modes) in order to determine the scattering matrix parameters and represent each component of the fundamental mode on each side of the discontinuity. This study showed that these sets of modes may be non-orthogonal and, consequently, a selection of modes based on orthogonality is made. Finline and microstrip discontinuities have been studied with this criterion. It is possible to obtain good convergence and satisfactory behavior of the components of the fields if the number of modes used is sufficient and if they form a complete set.

An innovative fast powerful method for tackling electromagnetic eigenvalue problems for multistrip transmission lines

A full-wave electromagnetic technique is developed for the rapid and accurate calculation of dispersion characteristics in multiconductor and multilayer planar transmission lines. The proposed method is based on the Mrozowski and Przybyszewski algorithms. This powerful method calculates an approximate value of propagation constant at a desired frequency based on more accurate computations of the field distribution and propagation constant at a few selected frequency points. Comparison with previously accurate published data and numerical tests are first performed to confirm the accuracy of our procedure. Numerical results for several configurations are presented.

Study of a Low-Pass Filter in Microstrip Line Applying Modal Analysis in the Spectral Domain

An abrupt change in microstrip linewidth, commonly called a microstrip impedance step, is a discontinuity that appears frequently in MMICs, such as, stepped impedance transformers and matching networks for example. Therefore, the accurate description of these step-discontinuties is important for the computer-aided design of conventional and monolithic MICs. In this work we have studied the set of modes that appears in a boxed microstrip in order to apply modal analysis in the spectral domain to the study of simple and cascaded step discontinuities. In order to check its precision, our method has been applied to a nine section low-pass filter, made up of a cascade of microstrip step discontinuities. Several filters have been designed, built and tested at different frequencies. We have compared these designs with Touchstone and shown that at low frequencies both methods give similar results, but when the frequency is higher, the Touchstone results are farther from the experimental results than the design obtained with the modal analysis method.

Direct and component-wise bias correction of multi-variate climate indices: the percentile adjustment function diagnostic tool

The use and development of bias correction (BC) methods has grown fast in recent years, due to the increased demand of unbiased projections by many sectoral climate change impact applications. Case studies are frequently based on multi-variate climate indices (CIs) combining two or more essential climate variables that are frequently individually corrected prior to CI calculation. This poses the question of whether the BC method modifies the inter-variable dependencies and eventually the climate change signal. The direct bias correction of the multi-variate CI stands as a usual alternative, since it preserves the physical and temporal coherence among the primary variables as represented in the dynamical model output, at the expense of incorporating the individual biases on the CI with an effect difficult to foresee, particularly in the case of complex CIs bearing in their formulation non-linear relationships between components. Such is the case of the Fire Weather Index (FWI), a meteorological fire danger indicator frequently used in forest fire prevention and research. In the present work, we test the suitability of the direct BC approach on FWI as a representative multi-variate CI, assessing its performance in present climate conditions and its effect on the climate change signal when applied to future projections. Moreover, the results are compared with the common approach of correcting the input variables separately. To this aim, we apply the widely used empirical quantile mapping method (QM), adjusting the 99 empirical percentiles. The analysis of the percentile adjustment function (PAF) provides insight into the effect of the QM on the climate change signal. Although both approaches present similar results in the present climate, the direct correction introduces a greater modification of the original change signal. These results warn against the blind use of QM, even in the case of essential climate variables or uni-variate CIs.

A New Low-Pass Filter in Asymmetrical Finline Topology Using Split-Ring Resonators

A variation of the quasi-static equivalent circuit model formulation of miniaturized magnetic resonant structures -i.e., split-ring resonator (SRR)- is presented. The validity of this model is verified by means of an analytical model that uses a new, simple and accurate analytical design formula for the SRRs inductance, full-wave simulations and measurements. These structures are inserted on the opposite side of a compact low-pass filter (LPF) in asymmetrical finline consisting of several notches alternating with a number of single-ridge finline sections. A soft transition from metal waveguide to finline is guaranteed by tapering the finline slot employing a numerically adjusted expression. Finally, experimental results of the filter are presented in order to demonstrate the feasibility of the proposed structure.

New architectures for planar filters using split-ring resonators

An improved technique is outlined to design filters in planar configurations. The new procedure is applied to enhance the performance of some filters in planar configuration. This paper illustrates that complementary split-ring resonators (CSRRs), electrically coupled to a microstrip transmission line and split-ring resonators (SRRs) magnetically coupled to a finline structure can be applied to improve the design of such filters. For this propose, classical variants of millimeter wave filters have been analyzed. These components include microstrip low-pass filters, finline bandpass/bandstop filters and antipodal finline bandstop filters. The properties of these configurations are discussed; the experimental data are in good agreement with the simulations. The results show the usefulness and validity of the new structures as it is possible to achieve a very low insertion loss and very sharp transition bands with high rejection capabilities.

A Two-Port WR75 Waveguide Turnstile Gyromagnetic Switch

The two-port reflection gyromagnetic waveguide switch described in this paper consists of a 90° Faraday rotator in a re-entrant or an inverted re-entrant turnstile geometry in the E-plane at the junction of two H-plane rectangular waveguides. It adjustment is a two-step eigenvalue problem. One adjustment fixes the electrical length of the circular Faraday rotator waveguide and produces a passband in its frequency response and the other fixes its gyrotropy and produces a stopband there. This paper also includes the separate synthesis of the passband condition in a WR75 waveguide at a frequency of 13.25 GHz using two different processes. The switch has two passband conditions at the design frequency, each of which is verified experimentally The stopband is separately established experimentally by magnetizing the gyromagnetic resonator.