Joan Bech

The Sensitivity of Single Polarization Weather Radar Beam Blockage Correction to Variability in the Vertical Refractivity Gradient

Radars operating in complex orographic areas usually suffer from partial or total beam blockage by surrounding targets at their lowest elevation scans. The need for radar quantitative precipitation estimates in such environments led to the development of beam blockage corrections. This paper aims at evaluating the performance of beam blockage corrections under different electromagnetic propagation conditions with particular interest in anaprop situations. Three years of radiosonde data collected at Barcelona, Spain, a typical Mediterranean coastal site, are used to characterize the behavior of the vertical refractivity gradient near a weather radar. Three different targets surrounding the radar have been chosen and used to evaluate the different beam shielding simulated under different propagation conditions. A simple interception function between the radar beam and the topography is proposed and used for the different targets and propagation conditions considered. Results show that beam blockage correction is generally robust, with departures of 1 dB from the standard propagation conditions correction less than 10% of the time. However, as the presence of extreme anaprop cases would lead to higher differences, the monitoring of the propagation conditions is suggested as a criteria to be considered, among others such as the analysis of the echo structure, as a quality control of the radar quantitative precipitation estimate.

Modeling Raindrop Size Distribution and Z(R) Relations in the Western Mediterranean Area

This study shows the results of the modeling of drop size distributions (DSD) observed during a 2-yr study in Barcelona. Thirty-second individual sample collections of drop sizes and velocities were measured with an optical disdrometer and grouped into different classes according to their rain rate. Using the moments method, the entire experimental dataset was fitted to three standard distribution functions: exponential, gamma, and lognormal. Relationships were found between rain rate R and other moments of the DSD, such as optical attenuation S, liquid water content W, and reflectivity Z. Although gamma distribution generally reproduced experimental measurements more accurately, the Z(R) relationship, which is particularly relevant in radar meteorology, yielded the best results when calculated from fitted exponential distribution.

Plants from Mine Spoils in the South American Area as Potential Sources of Germplasm for Phytoremediation Technologies

The selection of adequate plant species is a prerequisite for cleaning-up contaminated soils by means of phytoextraction which is a time and cost-effective technology. Here first results of the screening of plant species from three different mining areas in South America are reported: A copper mine in Peru (Mina Turmalina), a silver mine in Ecuador (Mina San Bartolome) and a copper mine in Chile (Mina El Teniente). The accumulation of heavy metals and As in shoots as a function of extractable metal concentrations in the soils was analyzed in field samples. The different plant species collected on the severely polluted soils exhibited large differences in shoot accumulation of heavy metals and As. Among the grass species (Poaceae), the highest shoot As concentrations were found in Paspalum sp. (> 1.000 μg/g) and Eriochloa ramosa (460 μg/g) from the Cu mine in Peru, and in Holcus lanatus and Pennisetum clandestinum (> 200 μg/g) from the silver mine in Ecuador. Paspalum racemosum also accumulated considerable concentrations of Cu and Zn. The species from the genus Bidens (Asteraceae) were able not only to accumulate high shoot As concentrations (> 1000 μg/g in B. cynapiifolia from Peru), but also considerable amounts of Pb (B. humilis from Chile). The highest Cu shoot concentrations were found in Mullinum spinosum (870 μg/g) and in B.cynapiifolia (620 μg/g). The shoot accumulation of Zn was highest in Baccharis amdatensis (> 1900 μg/g) and in Rumex crispus (1300 μg/g) from the silver mine in Ecuador. The potential usefulness of these species for phytoremediation technologies is discussed.

Weather radar anaprop conditions at a mediterranean coastal site

Abstract Many weather radars are affected by some type of anomalous propagation (AP) with a wide variety of frequency and intensity. Some geographical areas have been described to be particularly prone to AP. Even in some sites, AP is not statistically abnormal at all but dominant. Severe AP cases have been reported in coastal areas affected by strong temperature inversions and humidity contrasts such as the Baltic Sea, the Indic Ocean or the Mediterranean. In this paper we present average and extreme propagation conditions in the coastal area of Barcelona (NE Spain) calculated using three years of radiosonde data. Occurrence of different propagation conditions is discussed and related to local prevailing circulations such as the sea breeze with particular interest in the nearby Vallirana weather radar. The effect of some extreme ducting episodes seems to be remarkable in beam blocking correction procedures leading to wrong precipitation estimates when anaprop and rainfall occur at the same time. The use of radiosonde and mesoscale NWP data to derive operationally propagation conditions jointly with other existing techniques based in the analysis of radar data is overviewed.

Baseline Concentrations of Potentially Toxic Elements in Natural Surface Soils in Torrelles (Spain)

The objective of this article is to establish baseline concentrations of Ba, Cr, Cu, Ni, Pb, Sr, V, and Zn (aqua regia-extractable) in natural surface soils of the Torrelles Municipal District and to investigate the relationships between these elements and soil properties and between the element concentrations themselves. Upper baseline concentrations of these elements were (mg kg −1): Ba 272.6, Cr 40.8, Cu 31.0, Ni 29.9, Pb 68.1, Sr 83.0, V 49.7, and Zn 132.7; most corresponded with the values reported in the literature. Correlation analysis showed that total Fe and Al have the strongest relationships with trace elements.

How Robust Are Trends in the Brewer–Dobson Circulation Derived from Observed Stratospheric Temperatures?

AbstractMost global circulation models and climate–chemistry models forced with increasing greenhouse gases predict a strengthening of the Brewer–Dobson circulation (BDC) in the twenty-first century, and some of them claim that such strengthening has already begun at the end of the twentieth century. However, observational evidence for such a trend remains inconclusive. The goal of this paper is to examine the evidence for observed trends in the stratospheric overturning circulation using a suite of currently available observational stratospheric temperature data. Trends are examined as “departures” from the global mean temperature, since such trends reflect the effects of dynamics and spatially inhomogeneous radiative forcing and are to first order independent of the direct radiative effects of increasing well-mixed greenhouse gas concentrations.The primary conclusion of the study is that temperature observations do not reveal statistically significant trends in the Brewer–Dobson circulation over the per...

Evaluation of atmospheric anomalous propagation conditions: an application for weather radars

Several meteorological conditions are known to cause anomalous propagation (AP) of microwave radiation. The effect of AP in weather radar measurements my be important as spurious echoes from distant ground targets may appear as precipitation leading to wrong rainfall estimations. AP may also affect dramatically the quality of clear air radar observations. In this study, more than one hundred radiosonde ascents are examined to evaluate the occurrence of AP at the coastal site of Barcelona (Spain). Temperature and humidity profiles are used to calculate refractivity gradients and to estimate the existence of ducting layers. Ducts represent the worst case of super refraction and within them microwaves travel trapped like in a waveguide. To detect thin AP features a vertical resolution higher than that given by standard operational radiosonde data is desirable. For this reason, radiosonde data recorded every 10 s have been used. Results are compared against standard operational radiosonde analysis revealing a significantly higher number of AP layers. The output of a mesoscale numerical weather prediction model is also used to derive refractivity gradients. The ability of the model to simulate the propagation conditions is overviewed in order to assess the feasibility of an operational diagnostic AP product.

Quality Control of Antenna Alignment and Receiver Calibration Using the Sun: Adaptation to Midrange Weather Radar Observations at Low Elevation Angles

A quality control method for combined online monitoring of weather radar antenna pointing biases and receivercalibrationusingsolarsignalsdetectedbyanoperationalradarisadaptedforapplicationtomidrange radar data (80‐150km). As the original method was developed using long-range data, additional criteria based on robust statistical estimators are imposed in the sun signature detection and selection process, allowing to discard observations biased by ground clutter or precipitation and to remove very influential outliers. The validity ranges of the physical model describing the solar interferences detected by the scanning radar antenna are explicitly defined and an equation for estimation of the effective scanning width in reception is provided in a thorough theoretical derivation. The method proposed reveals its sensitivity to changes in the antenna pointing accuracy and receiver calibration when applied to operational data obtained with three C-band radars during one year. A comparative study on the goodness of fit between a three- and a five-parameter model highlights the effect on the stability and accuracy of the antenna and receiver parameters retrieved for each radar system, considering the dissimilar information content of the observations collected by each radar. The performance of the proposed methodology under the effects of the presence of ground clutter and radio local area network interferences is discussed in the results presented.

Effects of Anomalous Propagation Conditions on Weather Radar Observations

The effect of atmospheric propagation on radar observations is an important topic both for radar application developers and end-users of radar products, particularly of weather radar systems. An excellent review of this subject is given by Patterson (2008), and most general books about weather radars have a chapter on the topic –see for example Battan (1973), Collier (1996), Doviak and Zrnic (2006), Rinehart (2001) or Sauvageot (1991).

Observed Changes in Daily Precipitation Extremes at Annual Timescale Over the Eastern Mediterranean During 1961–2012

The Eastern Mediterranean is one of the most prominent hot spots of climate change in the world and extreme climatic phenomena in this region such as drought or extreme rainfall events are expected to become more frequent and intense. In this study climate extreme indices recommended by the joint World Meteorological Organization Expert Team on Climate Change Detection and Indices are calculated for daily precipitation data in 70 weather stations during 1961–2012. Observed trends and changes in daily precipitation extremes over the EM basin were analysed using the RClimDex package, which was developed by the Climate Research Branch of the Meteorological Service of Canada. Extreme and heavy precipitation events showed globally a statistically significant decrease in the Eastern Mediterranean and, in the southern parts, a significant decrease in total precipitation. The overall analysis of extreme precipitation indices reveals that decreasing trends are generally more frequent than increasing trends. We found statistically significant decreasing trends (reaching 74% of stations for extremely wet days) and increasing trends (reaching 36% of stations for number of very heavy precipitation days). Finally, most of the extreme precipitation indices have a statistically significant positive correlation with annual precipitation, particularly the number of heavy and very heavy precipitation days.