13-month climatology of the aerosol hygroscopicity at the free tropospheric site Jungfraujoch (3580 m a.s.l.)

A hygroscopicity tandem differential mobility analyzer (HTDMA) was operated at the high-alpine site Jungfraujoch in order to characterize the hygroscopic diameter growth factors of the free tropospheric Aitken and accumulation mode aerosol. More than ~5000 h of valid data were collected for the dry diameters <i>D</i><sub>0</sub> = 35, 50, 75, 110, 165, and 265 nm during the 13-month measurement period from 1 May 2008 through 31 May 2009. No distinct seasonal variability of the hygroscopic properties was observed. Annual mean hygroscopic diameter growth factors (<i>D</i>/<i>D</i><sub>0</sub>) at 90% relative humidity were found to be 1.34, 1.43, and 1.46 for <i>D</i><sub>0</sub> = 50, 110, and 265 nm, respectively. This size dependence can largely be attributed to the Kelvin effect because corresponding values of the hygroscopicity parameter κ are nearly independent of size. The mean hygroscopicity of the Aitken and accumulation mode aerosol at the free tropospheric site Jungfraujoch was found to be κ≈0.24 with little variability throughout the year. <br><br> The impact of Saharan dust events, a frequent phenomenon at the Jungfraujoch, on aerosol hygroscopicity was shown to be negligible for <i>D</i><sub>0</sub><265 nm. Thermally driven injections of planetary boundary layer (PBL) air, particularly observed in the early afternoon of summer days with convective anticyclonic weather conditions, lead to a decrease of aerosol hygroscopicity. However, the effect of PBL influence is not seen in the annual mean hygroscopicity data because the effect is small and those conditions (weather class, season and time of day) with PBL influence are relatively rare. <br><br> Aerosol hygroscopicity was found to be virtually independent of synoptic wind direction during advective weather situations, i.e. when horizontal motion of the atmosphere dominates over thermally driven convection. This indicates that the hygroscopic behavior of the aerosol observed at the Jungfraujoch can be considered representative of the lower free troposphere on at least a regional if not continental scale

Chemical and physical influences on aerosol activation in liquid clouds: a study based on observations from the Jungfraujoch, Switzerland

A simple statistical model to predict the number of aerosols which activate to form cloud droplets in warm clouds has been established, based on regression analysis of data from four summertime Cloud and Aerosol Characterisation Experiments (CLACE) at the high-altitude site Jungfraujoch (JFJ). It is shown that 79 % of the observed variance in droplet numbers can be represented by a model accounting only for the number of potential cloud condensation nuclei (defined as number of particles larger than 80 nm in diameter), while the mean errors in the model representation may be reduced by the addition of further explanatory variables, such as the mixing ratios of O3, CO, and the height of the measurements above cloud base. The statistical model has a similar ability to represent the observed droplet numbers in each of the individual years, as well as for the two predominant local wind directions at the JFJ (northwest and southeast). Given the central European location of the JFJ, with air masses in summer being representative of the free troposphere with regular boundary layer in-mixing via convection, we expect that this statistical model is generally applicable to warm clouds under conditions where droplet formation is aerosol limited (i.e. at relatively high updraught velocities and/or relatively low aerosol number concentrations). A comparison between the statistical model and an established microphysical parametrization shows good agreement between the two and supports the conclusion that cloud droplet formation at the JFJ is predominantly controlled by the number concentration of aerosol particles

Registration of the Chickpea Germplasm PHREC-Ca-Comp. #1 with Enhanced Resistance to Ascochyta Blight

The chickpea or garbanzo bean (Cicer arietinum L.) germplasm PHREC-Ca-Comp. #1 (Reg. No. GP-282, PI 659664) was developed by the former Alternative Crops Breeding Program at the University of Nebraska Agricultural Research Division and was released in 2010. It was bred specifically for adaptation to growing conditions in Nebraska and for enhanced resistance to Ascochyta blight, a major disease of chickpea caused by Ascochyta rabiei (Pass.) Labr. PHREC-Ca- Comp. #1 is a composite of PI 315797, PI 343014, PI 379217, PI 471915, PI 598080, and W6 17256. The composite was developed in the fall of 2002 and was evaluated in six irrigated and four dryland environments at Scottsbluff, Sidney, and Alliance, NE, from 2004 to 2009. Across irrigated environments, PHREC-Ca-Comp. #1 had the lowest severity rating for Ascochyta blight and a higher yield under both irrigated and dryland conditions than ‘Sierra’, ‘Dwelley’, ‘Dylan’, and ‘Troy’. PHREC-Ca-Comp. #1 is a small, round, cream-colored kabuli-type chickpea. It exhibits an upright, indeterminate growth habit. Plants average 66 cm in height and have excellent resistance to lodging. PHREC-Ca-Comp. #1 has a fern leaf structure and white flowers and blooms 44 d after planting. It is a midseason bean, maturing 116 d after planting. Although its seed size does not meet commercial standards, PHREC-Ca-Comp. #1 has value in breeding programs as a source of resistance to Ascochyta blight and because of its high yield potential

Spin-Electron-Phonon Excitation in Re-based Half-Metallic Double Perovskites

A remarkable hardening (~ 30 cm-1) of the normal mode of vibration associated with the symmetric stretching of the oxygen octahedra for the Ba2FeReO6 and Sr2CrReO6 double perovskites is observed below the corresponding magnetic ordering temperatures. The very large magnitude of this effect and its absence for the anti-symmetric stretching mode provide evidence against a conventional spin-phonon coupling mechanism. Our observations are consistent with a collective excitation formed by the combination of the vibrational mode with oscillations of local Fe or Cr 3d and Re 5d occupations and spin magnitudes.Comment: 12 pages, 4 figure

Effect of magnetic order on the superfluid response of single-crystal ErNi2_{2}B2_{2}C: A penetration depth study

We report measurements of the in-plane magnetic penetration depth $\Delta \lambda$(T) in single crystals of ErNi$_{2}$B$_{2}$C down to $\sim$0.1 K using a tunnel-diode based, self-inductive technique at 21 MHz. We observe four features: (1) a slight dip in $\Delta \lambda$(T) at the N$\acute{e}$el temperature $T_{N}$ = 6.0 K, (2) a peak at $T_{WFM}$ = 2.3 K, where a weak ferromagnetic component sets in, (3) another maximum at 0.45 K, and (4) a final broad drop down to 0.1 K. Converting to superfluid density $\rho_{s}$, we see that the antiferromagnetic order at 6 K only slightly depresses superconductivity. We seek to explain some of the above features in the context of antiferromagnetic superconductors, where competition between the antiferromagnetic molecular field and spin fluctuation scattering determines increased or decreased pairbreaking. Superfluid density data show only a slight decrease in pair density in the vicinity of the 2.3 K feature, thus supporting other evidences against bulk ferromagnetism in this temperature range.Comment: 15 pages, 5 figure

Effects of relative humidity on aerosol light scattering in the Arctic

Aerosol particles experience hygroscopic growth in the ambient atmosphere. Their optical properties – especially the aerosol light scattering – are therefore strongly dependent on the ambient relative humidity (RH). In-situ light scattering measurements of long-term observations are usually performed under dry conditions (RH>30–40%). The knowledge of this RH effect is of eminent importance for climate forcing calculations or for the comparison of remote sensing with in-situ measurements. This study combines measurements and model calculations to describe the RH effect on aerosol light scattering for the first time for aerosol particles present in summer and fall in the high Arctic. For this purpose, a field campaign was carried out from July to October 2008 at the Zeppelin station in Ny-Ålesund, Svalbard. The aerosol light scattering coefficient σ<sub>sp</sub>(λ) was measured at three distinct wavelengths (λ=450, 550, and 700 nm) at dry and at various, predefined RH conditions between 20% and 95% with a recently developed humidified nephelometer (WetNeph) and with a second nephelometer measuring at dry conditions with an average RH<10% (DryNeph). In addition, the aerosol size distribution and the aerosol absorption coefficient were measured. The scattering enhancement factor <i>f</i>(RH, λ) is the key parameter to describe the RH effect on σ<sub>sp</sub>(λ) and is defined as the RH dependent σ<sub>sp</sub>(RH, λ) divided by the corresponding dry σ<sub>sp</sub>(RH<sub>dry</sub>, λ). During our campaign the average <i>f</i>(RH=85%, λ=550 nm) was 3.24±0.63 (mean ± standard deviation), and no clear wavelength dependence of <i>f</i>(RH, λ) was observed. This means that the ambient scattering coefficients at RH=85% were on average about three times higher than the dry measured in-situ scattering coefficients. The RH dependency of the recorded <i>f</i>(RH, λ) can be well described by an empirical one-parameter equation. We used a simplified method to retrieve an apparent hygroscopic growth factor <i>g</i>(RH), defined as the aerosol particle diameter at a certain RH divided by the dry diameter, using the WetNeph, the DryNeph, the aerosol size distribution measurements and Mie theory. With this approach we found, on average, <i>g</i>(RH=85%) values to be 1.61±0.12 (mean±standard deviation). No clear seasonal shift of <i>f</i>(RH, λ) was observed during the 3-month period, while aerosol properties (size and chemical composition) clearly changed with time. While the beginning of the campaign was mainly characterized by smaller and less hygroscopic particles, the end was dominated by larger and more hygroscopic particles. This suggests that compensating effects of hygroscopicity and size determined the temporal stability of <i>f</i>(RH, λ). During sea salt influenced periods, distinct deliquescence transitions were observed. At the end we present a method on how to transfer the dry in-situ measured aerosol scattering coefficients to ambient values for the aerosol measured during summer and fall at this location

Saharan dust events at the Jungfraujoch: detection by wavelength dependence of the single scattering albedo and analysis of the events during the years 2001 and 2002

International audienceScattering and absorption coefficients have been measured continuously at several wavelengths since March 2001 at the high altitude site Jungfraujoch (3580 m a.s.l.). From these data, the wavelength dependences of the Ångström exponent and particularly of the single scattering albedo are determined. While the exponent of the single scattering albedo is usually positive, it becomes negative during Saharan dust events (SDE) due to the greater size of the mineral aerosols and to their different chemical composition. This change in the sign of the single scattering exponent turns out to be a simple means for detecting Saharan dust events. The occurrence of SDE detected by this new method was largely confirmed by visual inspection of filter colors and by studying long-range back-trajectories. An examination of SDE over a 22 months period shows that SDE are more frequent during the March?June period as well as during October and November. The trajectory analysis indicated a mean traveling time of 96.5 h with the most important source countries situated in the northern and north-western part of the Saharan desert. Most of the SDE do not lead to a detectable increase of the 48 h total suspended particulate matter (TSP) at the Jungfraujoch. During Saharan dust events, the average contribution of this dust to hourly TSP at the JFJ is 16 ?g/m3, which corresponds to an annual mean of 0.8 ?g/m3 or 24% of TSP

Measured and predicted aerosol light scattering enhancement factors at the high alpine site Jungfraujoch

Ambient relative humidity (RH) determines the water content of atmospheric aerosol particles and thus has an important influence on the amount of visible light scattered by particles. The RH dependence of the particle light scattering coefficient (σ<sub>sp</sub>) is therefore an important variable for climate forcing calculations. We used a humidification system for a nephelometer which allows for the measurement of σ<sub>sp</sub> at a defined RH in the range of 20–95%. In this paper we present measurements of light scattering enhancement factors <i>f</i>(RH)=σ<sub>sp</sub>(RH)/σ<sub>sp</sub>(dry) from a 1-month campaign (May 2008) at the high alpine site Jungfraujoch (3580 m a.s.l.), Switzerland. Measurements at the Jungfraujoch are representative for the lower free troposphere above Central Europe. For this aerosol type hardly any information about the <i>f</i>(RH) is available so far. At this site, <i>f</i>(RH=85%) varied between 1.2 and 3.3. Measured <i>f</i>(RH) agreed well with <i>f</i>(RH) calculated with Mie theory using measurements of the size distribution, chemical composition and hygroscopic diameter growth factors as input. Good <i>f</i>(RH) predictions at RH<85% were also obtained with a simplified model, which uses the Ångström exponent of σ<sub>sp</sub>(dry) as input. RH influences further intensive optical aerosol properties. The backscatter fraction decreased by about 30% from 0.128 to 0.089, and the single scattering albedo increased on average by 0.05 at 85% RH compared to dry conditions. These changes in σ<sub>sp</sub>, backscatter fraction and single scattering albedo have a distinct impact on the radiative forcing of the Jungfraujoch aerosol

The Ice Selective Inlet: a novel technique for exclusive extraction of pristine ice crystals in mixed-phase clouds

Climate predictions are affected by high uncertainties partially due to an insufficient knowledge of aerosol-cloud interactions. One of the poorly understood processes is formation of mixed-phase clouds (MPCs) via heterogeneous ice nucleation. Field measurements of the atmospheric ice phase in MPCs are challenging due to the presence of supercooled liquid droplets. The Ice Selective Inlet (ISI), presented in this paper, is a novel inlet designed to selectively sample pristine ice crystals in mixed-phase clouds and extract the ice residual particles contained within the crystals for physical and chemical characterisation. Using a modular setup composed of a cyclone impactor, droplet evaporation unit and pumped counterflow virtual impactor (PCVI), the ISI segregates particles based on their inertia and phase, exclusively extracting small ice particles between 5 and 20 μm in diameter. The setup also includes optical particle spectrometers for analysis of the number size distribution and shape of the sampled hydrometeors. The novelty of the ISI is a droplet evaporation unit, which separates liquid droplets and ice crystals in the airborne state, thus avoiding physical impaction of the hydrometeors and limiting potential artifacts. The design and validation of the droplet evaporation unit is based on modelling studies of droplet evaporation rates and computational fluid dynamics simulations of gas and particle flows through the unit. Prior to deployment in the field, an inter-comparison of the WELAS optical particle size spectrometers and a characterisation of the transmission efficiency of the PCVI was conducted in the laboratory. The ISI was subsequently deployed during the Cloud and Aerosol Characterisation Experiment (CLACE) 2013 – an extensive international field campaign encompassing comprehensive measurements of cloud microphysics, as well as bulk aerosol, ice residual and ice nuclei properties. The campaign provided an important opportunity for a proof of concept of the inlet design. In this work we present the setup of the ISI, including the modelling and laboratory characterisation of its components, as well as a case study demonstrating the ISI performance in the field during CLACE 2013

Effects of Field Peas in Beef Finishing Diets

Feeding field peas was compared to using corn in beef finishing diets. Diets containing field peas at 0%, 20%, 40%, and 59% replacement of corn in ration DM were fed to 129 steers. Dry matter intake increased from the 0% to 40% diets, but decreased when 59% peas replaced corn compared to 40%. No significant differences in ADG and G:F were observed. Field peas can replace 59% of the corn DM in beef finishing diet with no significant differences in animal gain or feed efficiency