Results from the Covered Catchment Experiment at Gårdsjön, Sweden, after ten years of clean precipitation treatment

The Covered Catchment Experiment at Gordsjon is a large scale forest ecosystem manipulation, where acid precipitation was intercepted by a 7000 m(2) plastic roof and replaced by 'clean precipitation' sprinkled below the roof for ten years between 1991 and 2001. The treatment resulted in a strong positive response of runoff quality. The runoff sulphate, inorganic aluminium and base cations decreased, while there was a strong increase in runoff ANC and a moderate increase in pH. The runoff continued to improve over the whole duration of the experiment. The achieved quality was, however, after ten years still considerably worse than estimated pre-industrial runoff at the site. Stable isotopes of sulphur were analysed to study the soil sulphur cycling. At the initial years of the experiment, the desorption of SO4 from the mineral soil appeared to control the runoff SO4 concentration. However, as the experiment proceeded, there was growing evidence that net mineralisation of soil organic sulphur in the humus layer was an additional source of SO4 in runoff. This might provide a challenge to current acidification models. The experiment convincingly demonstrated on a catchment scale, that reduction in acid deposition causes an immediate improvement of surface water quality even at heavily acidified sites. The improvement of the runoff appeared to be largely a result of cation exchange processes in the soil due to decreasing concentrations of the soil solution, while any potential change in soil base saturation seemed to be less important for the runoff chemistry over the short time period of one decade. These findings should be considered when interpreting and extrapolating regional trends in surface water chemistry to the terrestrial parts of ecosystems.

Soil moisture mediates association between the winter North Atlantic Oscillation and summer growth in the Park Grass Experiment

Several aspects of terrestrial ecosystems are known to be associated with the North Atlantic Oscillation (NAO) through effects of the NAO on winter climate, but recently the winter NAO has also been shown to be correlated with the following summer climate, including drought. Since drought is a major factor determining grassland primary productivity, the hypothesis was tested that the winter NAO is associated with summer herbage growth through soil moisture availability, using data from the Park Grass Experiment at Rothamsted, UK between 1960 and 1999. The herbage growth rate, mean daily rainfall, mean daily potential evapotranspiration (PE) and the mean and maximum potential soil moisture deficit (PSMD) were calculated between the two annual cuts in early summer and autumn for the unlimed, unfertilized plots. Mean and maximum PSMD were more highly correlated than rainfall or PE with herbage growth rate. Regression analysis showed that the natural logarithm of the herbage growth rate approximately halved for a 250 mm increase in maximum PSMD over the range 50-485 mm. The maximum PSMD was moderately correlated with the preceding winter NAO, with a positive winter NAO index associated with greater maximum PSMD. A positive winter NAO index was also associated with low herbage growth rate, accounting for 22% of the interannual variation in the growth rate. It was concluded that the association between the winter NAO and summer herbage growth rate is mediated by the PSMD in summer.

An observing system simulation experiment to evaluate the scientific merit of wind and ozone measurements from the future SWIFT instrument

(from author) One of the first papers in the peer-review literature to discuss an OSSE to evaluate future wind observations in the stratosphere. Provides key evidence to justify the construction of the SWIFT instrument (currently planned to be built by the Canadian Space Agency for launch on ~ 2010).

Aerosol Direct Radiative Impact Experiment (ADRIEX) overview

The Aerosol Direct Radiative Experiment (ADRIEX) took place over the Adriatic and Black Seas during August and September 2004 with the aim of characterizing anthropogenic aerosol in these regions in terms of its physical and optical properties and establishing its impact on radiative balance. Eight successful flights of the UK BAE-146 Facility for Atmospheric Airborne Measurements were completed together with surface-based lidar and AERONET measurements, in conjunction with satellite overpasses. This paper outlines the motivation for the campaign, the methodology and instruments used, describes the synoptic situation and provides an overview of the key results. ADRIEX successfully measured a range of aerosol conditions across the northern Adriatic, Po Valley and Black Sea. Generally two layers of aerosol were found in the vertical: in the flights over the Black Sea and the Po Valley these showed differences in chemical and microphysical properties, whilst over the Adriatic the layers were often more similar. Nitrate aerosol was found to be important in the Po Valley region. The use of new instruments to measure the aerosol chemistry and mixing state and to use this information in determining optical properties is demonstrated. These results are described in much more detail in the subsequent papers of this special issue.

Overview of observations from the RADAGAST experiment in Niamey, Niger: 2. Radiative fluxes and divergences

Broadband shortwave and longwave radiative fluxes observed both at the surface and from space during the Radiative Atmospheric Divergence using ARM Mobile Facility, GERB data and AMMA Stations (RADAGAST) experiment in Niamey, Niger, in 2006 are presented. The surface fluxes were measured by the Atmospheric Radiation Measurement (ARM) Program Mobile Facility (AMF) at Niamey airport, while the fluxes at the top of the atmosphere (TOA) are from the Geostationary Earth Radiation Budget (GERB) instrument on the Meteosat-8 satellite. The data are analyzed as daily averages, in order to minimize sampling differences between the surface and top of atmosphere instruments, while retaining the synoptic and seasonal changes that are the main focus of this study. A cloud mask is used to identify days with cloud versus those with predominantly clear skies. The influence of temperature, water vapor, aerosols, and clouds is investigated. Aerosols are ubiquitous throughout the year and have a significant impact on both the shortwave and longwave fluxes. The large and systematic seasonal changes in temperature and column integrated water vapor (CWV) through the dry and wet seasons are found to exert strong influences on the longwave fluxes. These influences are often in opposition to each other, because the highest temperatures occur at the end of the dry season when the CWV is lowest, while in the wet season the lowest temperatures are associated with the highest values of CWV. Apart from aerosols, the shortwave fluxes are also affected by clouds and by the seasonal changes in CWV. The fluxes are combined to provide estimates of the divergence of radiation across the atmosphere throughout 2006. The longwave divergence shows a relatively small variation through the year, because of a partial compensation between the seasonal variations in the outgoing longwave radiation (OLR) and surface net longwave radiation. A simple model of the greenhouse effect is used to interpret this result in terms of the dependence of the normalized greenhouse effect at the TOA and of the effective emissivity of the atmosphere at the surface on the CWV. It is shown that, as the CWV increases, the atmosphere loses longwave energy to the surface with about the same increasing efficiency with which it traps the OLR. When combined with the changes in temperature, this maintains the atmospheric longwave divergence within the narrow range that is observed. The shortwave divergence is mainly determined by the CWV and aerosol loadings and the effect of clouds is much smaller than on the component fluxes.

Results from the CERN pilot CLOUD experiment

During a 4-week run in October–November 2006, a pilot experiment was performed at the CERN Proton Synchrotron in preparation for the Cosmics Leaving OUtdoor Droplets (CLOUD) experiment, whose aim is to study the possible influence of cosmic rays on clouds. The purpose of the pilot experiment was firstly to carry out exploratory measurements of the effect of ionising particle radiation on aerosol formation from trace H2SO4 vapour and secondly to provide technical input for the CLOUD design. A total of 44 nucleation bursts were produced and recorded, with formation rates of particles above the 3 nm detection threshold of between 0.1 and 100 cm−3 s−1, and growth rates between 2 and 37 nm h−1. The corresponding H2SO4 concentrations were typically around 106 cm−3 or less. The experimentally-measured formation rates and H2SO4 concentrations are comparable to those found in the atmosphere, supporting the idea that sulphuric acid is involved in the nucleation of atmospheric aerosols. However, sulphuric acid alone is not able to explain the observed rapid growth rates, which suggests the presence of additional trace vapours in the aerosol chamber, whose identity is unknown. By analysing the charged fraction, a few of the aerosol bursts appear to have a contribution from ion-induced nucleation and ion-ion recombination to form neutral clusters. Some indications were also found for the accelerator beam timing and intensity to influence the aerosol particle formation rate at the highest experimental SO2 concentrations of 6 ppb, although none was found at lower concentrations. Overall, the exploratory measurements provide suggestive evidence for ion-induced nucleation or ion-ion recombination as sources of aerosol particles. However in order to quantify the conditions under which ion processes become significant, improvements are needed in controlling the experimental variables and in the reproducibility of the experiments. Finally, concerning technical aspects, the most important lessons for the CLOUD design include the stringent requirement of internal cleanliness of the aerosol chamber, as well as maintenance of extremely stable temperatures (variations below 0.1 _C).

Consumer willingness to pay for in-flight service and comfort levels: A choice experiment

In the competitive aviation market as a result of the emergence of low cost carriers, charter airlines have had to reconsider their approach to service provision. Specifically, the reduction in service and comfort levels offered by the low cost airlines provides charter carriers with an opportunity to differentiate their product based on the quality of the offering. To consider this strategic option we employ an on-line choice experiment to examine consumer choices with respect to the bundle of services on offer when deciding to purchase a flight, With these data we use the Bayesian methods to estimate a mixed logit specification. Our results reveal that in principle passengers are willing to pay a relatively large amount for enhanced service quality. (C) 2008 Elsevier Ltd. All rights reserved.

Response of free eggs on infective juvenile root-knot nematode Meloidogyne javanica through neem (Azadirachta indica A. Juss) amended soil

Air-dried and 3 mm pore size sieved soil was amended with neem crude formulations (leaves and cake) @ 3% w/w and a refined product, aza @ 0.05 and 0.1 w/w. Three days after treatment, 500 eggs of M. javanica held in 2 ml water were added in each dish. In another experiment, soil was amended with neem crude formulations @ 10. 5, 2.5 and 1% w/w and refined formulation aza @ 0.025, 0.05, 0.1 and 0.5% w/w. Three days after amendment 1000 plus minus 21 freshly hatched J2 held in 3 ml water were added to the amended soil. Untreated soil was kept as control. Comparison of treatments means showed that all the neem formulations caused significant reduction of hatching. Neem crude formulations were more effective in reducing hatching as compared to commercial product aza. Among the crude formulations, neem leaves were most effective in reducing hatching. In other experiment all the doses of neem crude and refined formulations differed significantly with control in reducing the mobility of juveniles. It was observed that by increasing the dose of the formulations the mobility was reduced accordingly.