The Uppsala urban meteorology project

An extensive urban meteorology project in Uppsala, Sweden, is described. The city itself is considered suitable as a kind of model city, being almost circular, having sharp urban/rural boundaries and being situated in a relatively flat area. The project incorporates numerous measurements. A main station with a 100-m mast is situated at the NE urban/rural border. Its instrumentation consists of a slow-response (profile) system and a turbulence system. The profile instrumentation is described in detail. In addition to the main station, the project comprises: measurements from two 14-m masts, one on the top of a centrally located building, the other mobile; pilot balloon ascents; tethered balloon soundings, car-borne temperature traverses etc. Some preliminary results are presented: analyses of wind profiles from the mast and three-dimensional heat island studies.     

Arctic climate change in 21st century CMIP5 simulations with EC-Earth

The Arctic climate change is analyzed in an ensemble of future projection simulations performed with the global coupled climate model EC-Earth2.3. EC-Earth simulates the twentieth century Arctic climate relatively well but the Arctic is about 2 K too cold and the sea ice thickness and extent are overestimated. In the twenty-first century, the results show a continuation and strengthening of the Arctic trends observed over the recent decades, which leads to a dramatically changed Arctic climate, especially in the high emission scenario RCP8.5. The annually averaged Arctic mean near-surface temperature increases by 12 K in RCP8.5, with largest warming in the Barents Sea region. The warming is most pronounced in winter and autumn and in the lower atmosphere. The Arctic winter temperature inversion is reduced in all scenarios and disappears in RCP8.5. The Arctic becomes ice free in September in all RCP8.5 simulations after a rapid reduction event without recovery around year 2060. Taking into account the overestimation of ice in the twentieth century, our model results indicate a likely ice-free Arctic in September around 2040. Sea ice reductions are most pronounced in the Barents Sea in all RCPs, which lead to the most dramatic changes in this region. Here, surface heat fluxes are strongly enhanced and the cloudiness is substantially decreased. The meridional heat flux into the Arctic is reduced in the atmosphere but increases in the ocean. This oceanic increase is dominated by an enhanced heat flux into the Barents Sea, which strongly contributes to the large sea ice reduction and surface-air warming in this region. Increased precipitation and river runoff lead to more freshwater input into the Arctic Ocean. However, most of the additional freshwater is stored in the Arctic Ocean while the total Arctic freshwater export only slightly increases.     

Petrology of iron-rich magmatic segregations associated with strongly peraluminous trondhjemite in the Cornucopia stock, northeastern Oregon

The Middle Cretaceous Cornucopia stock in the Blue Mountains of northeastern Oregon is a small composite intrusion consisting of hornblende biotite tonalite, biotite trondhjemite, and three cordierite two mica trondhjemite units. Unusual magnetite + biotite-rich tonalitic rocks are associated with the Crater Lake cordierite trondhjemite, the youngest of the intrusions. Oxide-rich tonalites are characterized by high Fe (~47-68 wt% total Fe as FeO), low SiO₂ (<36 wt%), and enrichments in HFSE and REE (La_(N)=361-903). Oxide-rich tonalites appear in a variety of forms, including composite dikes and sheets, in which they are associated with leucocratic tonalite. Leucotonalite is lower in SiO₂ (60-72 wt%) than Crater Lake trondhjemite, and generally has DREE contents and Eu anomalies intermediate between the oxide-rich tonalite and Crater Lake compositions. Oxide-rich tonalites crosscut, and are crosscut by, shear zones in the host trondhjemite, indicating their emplacement late in the pluton's crystallization history. Granitic dikes crosscut the composite dikes in all localities. Geochemical considerations and sedimentary-like structures, such as load casts and bedding of magnetite-rich assemblages in the composite dikes and sheets, are suggestive of crystal settling from an Fe-rich parental magma. The Fe-rich liquid parental to the oxide-rich tonalite-leucotonalite pairs formed by extensive, in-situ, plagioclase + quartz-dominated crystallization of strongly peraluminous trondhjemite. Early magnetite saturation in the trondhjemite was suppressed, either because the parental trondhjemitic magma had a lower initial total Fe content or because it had a lower ferric-ferrous ratio, possibly reflecting a lower oxygen fugacity. Accumulation of magnetite from Fe-rich residual magma is a viable mechanism for the concentration of iron, and the subsequent formation of Fe-rich rocks, in calcic siliceous intrusions. Apparently, Fe-enrichment can occur locally in calcic magmas, and is not restricted to rocks of mafic tholeiitic or anorthositic affinity.     

The use of natural analogues to assess radionuclide transport

Predicting the long-term safety and performance of a repository for intermediate- to high-level radioactive wastes requires the evaluation of various scenarios which may influence the integrity of the repository system. One such scenario, radionuclide transport, is described, and some of the geochemical processes which serve to enhance or retard transport are illustrated with examples selected from natural analogue or natural system studies. These studies, as distinct from laboratory simulations, help considerably in understanding how near- and far-field radionuclide transport mechanisms work over geological timescales (thousands to hundreds of thousands of years), more in line with the anticipated lifespan of a repository.

Processes addressed include: stability of the spent fuel UO₂ matrix; bentonite backfill as a barrier to radionuclide diffusion; retention of radionuclides by absorption on fracture minerals; transport and diffusion of radionuclides controlled by interconnected bedrock porosity; geochemical influence and behaviour of repository construction materials on radionuclide transport.     

Cloud radiative forcing of subtropical low level clouds in global models

Simulations of subtropical marine low clouds and their radiative properties by nine coupled ocean-atmosphere climate models participating in the fourth assesment report (AR4) of the intergovernmental panel on climate change (IPCC) are analyzed. Satellite observations of cloudiness and radiative fluxes at the top of the atmosphere (TOA) are utilized for comparison. The analysis is confined to the marine subtropics in an attempt to isolate low cloudiness from tropical convective systems. All analyzed models have a negative bias in the low cloud fraction (model mean bias of −15%). On the other hand, the models show an excess of cloud radiative cooling in the region (model mean excess of 13 W m⁻²). The latter bias is shown to mainly originate from too much shortwave reflection by the models clouds rather than biases in the clear-sky fluxes. These results confirm earlier studies, thus no major progress in simulating the marine subtropical clouds is noted. As a consequence of the combination of these two biases, this study suggests that all investigated models are likely to overestimate the radiative response to changes in low level subtropical cloudiness.     

Phosphorus release from coastal Baltic Sea sediments as estimated from sediment profiles

We used the decline in total phosphorus (P) concentration with depth in sediment profiles from the North-western Baltic Proper coastal zone to calculate the site-specific amount of sediment P eventually to be released to the water column: The potentially mobile P. P fractionation revealed that iron bound P dominated the potentially mobile P at sites with oxic surface sediment layers. Organic P forms were also a major constituent of the potentially mobile P pool. We determined that 1–7 g P/m² were potentially mobile at our sites, and the turnover time of this P pool was considered short, i.e., less than a decade. To determine long-term average P fluxes to and from the surface sediment layer, we first multiplied the constant and relatively low P concentration in deeper sediment layers with the sediment accumulation rate to gain the P burial rate. Then the average total P concentration in settling matter was multiplied with the sediment accumulation rate to estimate the depositional P flux at each site. The difference between the depositional and burial rates represents the long-term average release rate of sediment P and varied between 1.0 and 2.7 g P/m² yr among our sites. These rates are at the same order of magnitude as values reported from other areas of the Baltic Sea, and constitute a major source of P to the water column.     

Interferometric space missions for the search for terrestrial exoplanets: Requirements on the rejection ratio

The requirements on space missions designed to study Terrestrial exoplanets are discussed. We then investigate whether the design of such a mission, specifically the Darwin nulling interferometer, can be carried out in a simplified scenario. The key element here is accepting somewhat higher levels of stellar leakage. We establish detailed requirements resulting from the scientific rationale for the mission, and calculate detailed parameters for the stellar suppression required to achieve those requirements. We do this utilizing the Darwin input catalogue. The dominating noise source for most targets in this sample is essentially constant for all targets, while the leakage diminishes with the square of the distance. This means that the stellar leakage has an effect on the integration time only for the nearby stars, while for the more distant targets its influence decreases significantly. We assess the impact of different array configurations and nulling profiles and identify the stars for which the detection efficiency can be maximized.