Forcing mechanisms of a heavy precipitation event in the southeastern Adriatic area

The aim of this study was to identify the main mesoscale features and mechanisms responsible for the generation of an extreme precipitation event as a contribution to improving the modelling of processes that produce HPEs. The event occurred during the morning hours on 22 November 2010 over the Dubrovnik coast in Croatia and the hinterland mountain range of the southern Dinaric Alps and caused severe flash floods and landslides and consequent interruption of traffic and electricity supply as well as other infrastructural damage. The analysis is geographically focused on the southern portion of the eastern Adriatic region, which is prone to relatively frequent heavy precipitation events that occur mostly in autumn. This area is one of the rainiest in Europe with expected annual amounts of precipitation greater than 5,000 mm in the mountainous hinterland. The mechanisms responsible for the formation of convection were analysed using synop measurements, satellite data and numerical experiments performed with the WRF model, which was set up at the convection-permitting resolution in the innermost domain. Satellite data were used to identify the precipitation systems and to estimate the intensity of the precipitation during the period of interest. The development of the precipitation system was connected to a strong large-scale ascent over the southern Italy and southern Adriatic due to the advection of warm air and cyclonic vorticity advection, which increases with height. The numerical simulations highlighted the essential role of a southerly low-level jet stream in the transport of warm and moist air towards the affected area. The convergence of two branches of low-level marine air favoured convection triggered over the coast and sea. Furthermore, numerical sensitivity experiments suggested that the orography of the Dinaric Alps plays an essential role in the precipitation maximum over the mountainous hinterland, but also that the orography was not the crucial factor in the heavy precipitation near Dubrovnik. This study highlights the need for a dense network of observations, especially radar measurements, to validate the simulated mechanisms and improve numerical forecasts via data assimilation.     

Effect of glacier loading/deloading on volcanism: postglacial volcanic production rate of the Dyngjufjöll area,central Iceland

Tephrochronological dating of postglacial volcanism in the Dyngjufjöll volcanic complex, a major spreading center in the Icelandic Rift Zone, indicates a high production rate in the millennia following deglaciation as compared to the present low productivity. The visible and implied evidence indicates that lava production in the period 10 000–4500 bp was at least 20 to 30 times higher than that in the period after 2900 bp but the results are biased towards lower values for lava volumes during the earlier age periods since multiple lava layers are buried beneath younger flows. The higher production rate during the earlier period coincides with the disappearance of glaciers of the last glaciation. Decreasing lithostatic pressure as the glacier melts and vigorous crustal movements caused by rapid isostatic rebound may trigger intense volcanism until a new pressure equilibrium has been established.     

Phytoplankton life cycle transformations lead to species-specific effects on sediment processes in the Baltic Sea

In order to study the sediment response to different addition of organic matter, we added cultures of the dinoflagellates Scrippsiella hangoei and Woloszynskia halophila and the diatom Pauliella taeniata to aquaria containing natural sediment. The biomass added was 1550–3260 mg C m⁻², and in the control, no biomass was added (n=3). Oxygen profiles at the sediment–water interface and inorganic nutrients in the near bottom water were determined once a week. In the additions of P. taeniata and W. halophila the sediment quickly became anoxic, and subsequently there was a flux of >1 mmol PO₄³⁻ m⁻² d⁻¹ out of the sediment in these treatments. The majority of the released P came from P stored in the sediment and not from the organic phosphorus added. The result was very different for the S. hangoei addition. This species underwent a life cycle change to form temporary cysts. During this process there was a net uptake of nutrients. After the formation of cysts the concentration of inorganic nutrient was similar to that of the control. Cysts generally survive for long periods in the sediment (months to years) before germinating, but can also be permanently buried in the sediment. The novel idea presented here is that the phytoplankton composition may directly affect sediment processes such as oxygen consumption and phosphorus release, through species-specific life cycle changes and yields of resting stages produced prior to sedimentation. This can be an important aspect of nutrient cycling in eutrophic waters, like the Baltic Sea, where there is large year-to-year difference in the amount of resting stages settling at the sea floor, mainly due to differences in abundance of diatoms and dinoflagellates during the spring bloom. If yields of resting stages change, e.g. due to changes in the phytoplankton community, it may lead to alterations in the biogeochemical cycling of nutrients.     

Reservoir description using dynamic parameterisation selection with a combined stochastic and gradient search

There is a correspondence between flow in a reservoir and large scale permeability trends. This correspondence can be derived by constraining reservoir models using observed production data. One of the challenges in deriving the permeability distribution of a field using production data involves determination of the scale of resolution of the permeability. The Adaptive Multiscale Estimation (AME) seeks to overcome the problems related to choosing the resolution of the permeability field by a dynamic parameterisation selection. The standard AME uses a gradient algorithm in solving several optimisation problems with increasing permeability resolution. This paper presents a hybrid algorithm which combines a gradient search and a stochastic algorithm to improve the robustness of the dynamic parameterisation selection. At low dimension, we use the stochastic algorithm to generate several optimised models. We use information from all these produced models to find new optimal refinements, and start out new optimisations with several unequally suggested parameterisations. At higher dimensions we change to a gradient-type optimiser, where the initial solution is chosen from the ensemble of models suggested by the stochastic algorithm. The selection is based on a predefined criterion. We demonstrate the robustness of the hybrid algorithm on sample synthetic cases, which most of them were considered insolvable using the standard AME algorithm.     

X-ray, Lyα and Hα emission from simulated disk galaxies

The X-ray properties of the haloes of disk galaxies formed in fully cosmological, hydro/gravity simulations are discussed. The results are found to be consistent with observational X-ray detections and upper limits. Disk galaxy haloes are predicted to be about an order of magnitude brighter at z ∼ 1 than at z=0. The Lyα and Hα surface brightness of an edge-on, Milky Way like model galaxy has been determined. The emission is found to be quite extended, with a scale height of about 600 pc, neglecting dust corrections. This revised version was published online in August 2006 with corrections to the Cover Date.     

Understanding the statistical properties of the percent model affinity index can improve biomonitoring related decision making

The percent model affinity (PMA) index is used to measure the similarity of two probability profiles representing, for example, an ideal profile (i.e. reference condition) and a monitored profile (i.e. possibly impacted condition). The goal of this work is to study the effects of sample size, evenness, true value of the index and number of classes on the statistical properties of the estimator of the PMA index. We derive and extend previous formulas of the expectation and variance of the estimator for estimated monitored profile and fixed reference profile. Using the obtained extension, we find that the estimator is asymptotically unbiased, converging faster when the profiles differ. When both profiles are estimated, we calculate the expectation using transformation rules for expectation and in addition derive the formula for the estimator’s variance. Since the computation of the probabilities in the variance formula is slow, we study the behavior of the variance with simulation experiments and assess whether it could be approximated with the variance for the fixed reference profile. Finally, we provide a set of recommendations for the users of the PMA index to avoid the most common caveats of the index.     

Fine‐scale diet of the Australian sea lion (Neophoca cinerea) using DNA‐based analysis of faeces

We applied DNA‐based faecal analysis to determine the diet of female Australian sea lions (n = 12) from two breeding colonies in South Australia. DNA dietary components of fish and cephalopods were amplified using the polymerase chain reaction and mitochondrial DNA primers targeting the short (~100 base pair) section of the 16S gene region. Prey diversity was determined by sequencing ~50 amplicons generated from clone libraries developed for each individual. Faecal DNA was also combined and cloned from multiple individuals at each colony and fish diversity determined. Diets varied between individuals and sites. Overall, DNA analysis identified a broad diversity of prey comprising 23 fish and five cephalopod taxa, including many species not previously described as prey of the Australian sea lion. Labridae (wrasse), Monacanthidae (leatherjackets) and Mullidae (goat fish) were important fish prey taxa. Commonly identified cephalopods were Octopodidae (octopus), Loliginidae (calamary squid) and Sepiidae (cuttlefish). Comparisons of fish prey diversity determined by pooling faecal DNA from several samples provided a reasonable but incomplete resemblance (55–71%) to the total fish diversity identified across individual diets at each site. Interpretation of diet based on the recovery of prey hard‐parts identified one cephalopod beak (Octopus sp.) and one fish otolith (Parapriacanthus elongatus). The present study highlights the value of DNA‐based analyses and their capabilities to enhance information of trophic interactions.     

Comparing long term sediment records to current biological quality element data - Implications for bioassessment and management of a eutrophic lake

Defining reference conditions for lakes situated in areas of human settlement and agriculture is rarely straightforward, and is especially difficult within easily eroding and nutrient rich watersheds. We used diatoms, cyanobaterial akinetes, remains of green algae and chironomid head capsules from sediment samples of Lake Kirmanjärvi, Finland, to assess its deviation from the initial ecological status. These site-specific records of change were compared to current type-specific ecological status assessment. All paleolimnological data indicated deviation from natural conditions and mirrored the current, monitoring-based assessment of “moderate” ecological lake status. However, the sediment data showed that the lake should be re-typified as a naturally eutrophic lake. Sediment records as well as current monitoring data indicated temporary improvement in water quality in response to extensive fish manipulation. Our results suggest that paleolimnological records can be used to derive site-specific reference conditions and that extensive restoration efforts can result in gradual, observable improvements of water quality and ecological status.