Annual and interannual variation in boreal forest aerosol particle number and volume concentration and their connection to particle formation

We investigated size-resolved submicrometre aerosol particle number and volume concentration time series as well as aerosol dynamic parameters derived from Differential Mobility Particle Sizer (DMPS) measurements at five background stations in the Nordic boreal forest area. The stations in question were Aspvreten, Hyytiälä and Utö in southern Finland and Sweden, and Värriö and Pallas in the Finnish Lapland. The objective of our investigation was to identify and quantify annual and interannual variation observable in the time series. We found that the total number and mass concentrations were much lower at the Lapland stations than at the southern stations and that the total particle number was strongly correlated to particle formation event frequency. The annual total number concentration followed the annual distribution of particle formation events at the southern stations but much less clearly at the Lapland stations. The volume concentration was highest during summer, in line with higher condensation growth rates; this is in line with the assumption that a large part of the particle volume is produced by oxidized plant emissions. The decrease of sulphate emissions in Europe was not visible in our data set. Aerosol dynamic parameters such as condensation sink, condensation sink diameter and the power law exponent linking coagulation losses and condensation sink are presented to characterize the submicron Nordic background aerosol.     

Chlorine partitioning in the stratosphere based on in situ measurements

Balloon‐borne cryogenic air sampler experiments have been conducted from a tropical (Hyderabad, 17.5°N) and a midlatitude (GAP, southern France, 44°N) station since 1987 in the altitude range of about 8‐35 km. Air samples are analysed at the Max Planck Institute for Aeronomy (MPAE) and Physical Research Laboratory (PRL) using various gas chromatographic techniques to obtain the vertical distributions of several halogenated source gases and long‐lived dynamical tracers. These observations are used to determine the stratospheric partitioning of the chlorine species into their organic and inorganic forms for the altitude range of 20 to 35 km. Distributions of inorganic chlorine indicate increase in their abundances with altitude, latitude and time. Mixing ratio correlations of organic and inorganic chlorine with N₂O have been obtained which also suggest that the rate of increase in inorganic halogens component in the stratosphere is larger than the increase rate of total organic halogen. This supports previous assessments that halogen‐induced ozone depletion will continue to be observed for a few more years, despite the decrease of halocarbon loading into the stratosphere since 1994.     

The Late Quaternary sedimentary record in Scoresby Sund, East Greenland

Until recently, little was known about the Quaternary marine sedimentary record in East Greenland. Geophysical and geological investigations in Scoresby Sund were undertaken to characterize the nature and chronology of this record. Seismic records show that almost 70% of the outer fjord system is covered by about 10 m of unlithified sediments, making direct correlation with the Quaternary records on land and the adjacent continental margin difficult. These acoustically unstratified sediments are scoured by icebergs above 550 m water depth. Almost 90% of core material is massive diamicton of Holocene age, deposited mainly from iceberg rafting and turbid meltwater. Sedimentation rates are 0.1 -0.3 m 1000 yr-¹. Thicker accumulations of unlithified Quaternary sediments in Scoresby Sund occur as sediment ridges and in two other major depocentres. A low sediment ridge runs across the mouth of Scoresby Sund, and is interpreted as an end moraine of Late Weichselian Flakkerhuk stadial age. The very restricted sediment thickness suggests that grounded ice filled the fjord during the Flakkerhuk and an ice shelf was not present. High inputs of ice rafted debris to the continental margin at about 18 000 BP indicate this as a probable age for the moraine. During the Allerød Interstadial, ice probably retreated from the outer fjord system, since massive diamictons similar to those of Holocene age are present at the base of most cores. A major depocentre of acoustically stratified sediments at the head of Hall Bredning is interpreted to represent ice proximal deposits from a glacier margin extending across the fjord. It is adjacent to dated moraines on land and is inferred to be of Milne Land stadial age (about 10 000 BP). A similar age is interpreted for acoustically laminated sediments and a moraine at the entrance of Vikingebugt, on the south side of Scoresby Sund. Dated kame terraces in the inner fjord system indicate that ice retreated to its present position 6–7000 years ago.     

Thermobarometry of phengite-bearing eclogites in the Dabie Mountains of central China

Pressure–temperature conditions for formation of the peak metamorphic mineral assemblages in phengite-bearing eclogites from Dabieshan have been assessed through a consideration of Fe²⁺–Mg²⁺ partitioning between garnet–omphacite and garnet–phengite pairs and of the reaction equilibrium celadonite+pyrope+grossular=muscovite+diopside, which incorporates an evaluation of the extent of the strongly pressure-dependent inverse Tschermak's molecule substitution in the phengites. For the latter equilibrium, the calibration and recommended activity–composition models indicated by 45 ) have been employed and importantly yield results consistent with petrographic evidence for the stability at peak conditions of coesite in certain samples and quartz in others. Confirmation that in some phengite-eclogite samples peak silicate mineral assemblages have equilibrated at confining pressures sufficient for the stability of coesite (and in some cases even diamond) rather negates previous suggestions that coesite may have been stabilized in only very localized, possibly just intracrystalline, domains. Inherent difficulties in the evaluation of peak metamorphic temperatures from Fe²⁺–Mg²⁺ partitioning between mineral phases, due to uncertainties over Fe³⁺/Fe²⁺ ratios in the minerals (especially omphacites), and to re-equilibration during extensive retrograde overprinting in some samples, are also assessed and discussed. Our results indicate the existence in south-central Dabieshan of phengite eclogites with markedly different equilibration conditions within two structurally distinct tectonometamorphic terranes. Thus our data do not support earlier contentions that south-central Dabieshan comprises a structurally coherent continental-crust terrane with a regional P–T gradient signalling previous deepest-level subduction in the north. Instead, we recognize the Central Dabie ultra-high-pressure (coesite eclogite-bearing) terrane to be structurally overlain by a Southern Dabie high-pressure (quartz eclogite-bearing) terrane at a major southerly dipping shear zone along which late orogenic extensional collapse appears to have eliminated at least 20 km of crustal section.     

Decision makers' perspectives on European geographic information policy issues

The proposals for a European policy framework for Geographic Information (GI) recently put forward by Directorate General XIII raise three sets of issues about measures required to facilitate the dissemination of GI in the European Union: (1)'hot topics' such as privacy and the legal protection of databases that apply to information generally; (2) GI issues such as reference data and metadata services that may require action by the European Commission; and (3) perceived barriers to the development of a European GI market. This paper examines the views of 20 experts responsible for the provision and management of GI in key organizations throughout Europe. A Delphi-style strategy was used to identify the relative importance of the issues raised by the proposals and to ascertain the level of agreement as to the importance of these issues between the experts. The results show that issues relating to copyright, the protection of intellectual property rights, data quality, and data access policies were ranked highly by most of the respondents. A lack of awareness, education, and training (as opposed to the lack of public domain data and metadata services) were viewed as the main barriers to the deveiopment of the GI market in Europe.     

ON TURBULENCE CLOSURE CONSTANTS FOR ATMOSPHERIC BOUNDARY-LAYER MODELLING: NEUTRAL STRATIFICATION

Constant sets for several turbulence closure models,based on data for the atmospheric boundary layer, areproposed. They differ from those currently used inengineering situations but are self-consistent andtuned to represent atmospheric boundary-layerturbulence. The proposed constant sets are tested in a simple,one-dimensional, neutrally-stratified planetaryboundary-layer flow over a horizontally homogeneousand aerodynamically rough flat surface. Comparisons ofmodel results with similarity theory and large-eddysimulation show promise for improving boundary-layerpredictions.