Study of vertical structure of aerosol optical properties with sun photometers and ceilometer during the MACRON campaign in 2007

This paper presents the measurements of a vertical structure of aerosol optical properties performed during the MACRON (Maritime Aerosol, Clouds and Radiation Observation in Norway) campaign, which took place in July and August 2007 at ALOMAR observatory on Andøya island (69.279°N, 16.009°E, elevation 380 m a.s.l.). The mean value of the aerosol optical thickness (AOT) at 500 nm during campaign was 0.12. Significant increase of the AOT above longtime mean value was observed on 7 and 8 August 2007 when the AOT exceeded 0.4 at 500 nm. Analyses of back trajectories show the aerosol transported from over Africa and Central Europe. The aerosol extinction coefficient obtained from the synergy of ceilometer and sun photometer observations reached 0.05–0.08 km^?1 (at 1064 nm) in the dust layer. The single scattering albedo at the ALOMAR observatory decreased during the dust episode to 0.93–0.94, which indicates some absorptive aerosols in the lower PBL.     

Diversity and conservation status of large branchiopods (Crustacea) in ponds of western Poland

A survey on temporary ponds has been conducted in search for large branchiopod crustaceans (Anostraca, Notostraca, Spinicaudata and Laevicaudata) in Wielkopolska province (western Poland). 728 pools have been studied and large branchiopods have been found in 221 of them. Seven species have been recorded, including three anostracans: Branchipus schaefferi, Chirocephalus shadini and Eubranchipus grubii; two notostracans: Lepidurus apus and Triops cancriformis; one spinicaudatan, Cyzicus tetracerus and one laevicaudatan, Lynceus brachyurus. According to the analysis of co-occurrence, the species form three groups, differing in habitat preferences and conservation status. The number of species shows that the diversity of globally threatened large branchiopods is still relatively high in the region. On the other hand, their conservation status is highly diverse and in most species unfavourable. Distribution of all species is highly clustered: large branchiopods have been generally found in 33 UTM squares (10 × 10 km) of 96 squares studied. However, only two species, i.e. E. grubii and L. apus occurred in more than five such squares and could be assessed as moderately widespread. Most water bodies inhabited by large branchiopods occur in groups forming patches of suitable habitats which are dispersed among prevailing seemingly unsuitable areas. Sustaining the existence of large metapopulations seems, therefore, to be essential for conservation of branchiopod species diversity. Field observations also bring some examples of human activities unintentionally supporting the branchiopod conservation.     

Mobility of lowland stream Trichoptera under experimental habitat and flow conditions

The species-specific mobility of six species of lowland stream Trichoptera was studied in flume experiments with different habitats and current flows. The test species were selected according to their occurrence along the environmental gradient from more natural towards highly disturbed sandy, lowland streams of the North-West European plain. Two groups of species were distinguished, three species occurring more frequently towards the natural end versus three occurring more frequently towards the disturbed end of the stream disturbance gradient. Experiments were conducted in a temperature and light controlled environment in indoor, re-circulating, man-made stream channels with four replicate gutters each. The bottom of each gutter held ten trays filled with five selected habitat materials (two trays each), which provided refugia and food. Three flow treatments with constant current velocities of 10, 30, or 50 cm/s were applied. Movements were scored based on visual observations of the position of each individual at fixed time points. The first day after release, individuals moved around very actively; this ‘release effect’ was removed from further analyses. The trichopteran species occurring near the more natural end of the disturbance gradient exhibited significantly less mobility (on average 10-15% of individuals actively moved around) than the species from the more disturbed end of the gradient (on average 30-40% of individuals actively moved around). The first group of trichopteran species also spent significantly longer times in the leaves habitat compared to the other three species, which moved more or less independent of habitat. With increasing current velocity, all test species moved more frequently, particularly the species from the more disturbed end of the gradient. This could indicate behavior to avoid dislodgement. The mobility of all species exceeded the mobility needed to use habitat resources of food and shelter, both present in excess. Therefore, short-term movement could also be (partly) a random behavior. Overall, the more tolerant species from the disturbed end of the gradient showed more mobility and flexibility than the species occurring under more or less natural stream conditions. This was consistent with the hypothesis that mobility is an adaptation of tolerant, ubiquitous species. Mobility is an adaptation of r-strategists.     

The effect of glaciation on the intensity of seismic ground motion

Seismicity is known to contribute to landscape denudation through its role in earthquake‐triggered slope failure; but little is known about how the intensity of seismic ground motions, and therefore triggering of slope failures, may change through time. Topography influences the intensity of seismic shaking – generally steep slopes amplify shaking more than flatter slopes – and because glacial erosion typically steepens and enlarges slopes, glaciation may increase the intensity of seismic shaking of some landforms. However, the effect of this may be limited until after glaciers retreat because valley ice or ice‐caps may damp seismic ground motions. Two‐dimensional numerical models (FLAC 6.0) were used to explore how edifice shape, rock stiffness and various levels of ice inundation affect edifice shaking intensity. The modelling confirmed that earthquake shaking is enhanced with steeper topography and at ridge crests but it showed for the first time that total inundation by ice may reduce shaking intensity at hill crests to about 20–50% of that experienced when no ice is present. The effect is diminished to about 80–95% if glacier ice level reduces to half of the mountain slope height. In general, ice cover reduced shaking most for the steepest‐sided edifices, for wave frequencies higher than 3 Hz, and when ice was thickest and the rock had shear stiffness well in excess of the stiffness of ice. If rock stiffness is low and shear‐wave velocity is similar to that of ice, the presence of ice may amplify the shaking of rock protruding above the ice surface. The modelling supports the idea that topographic amplification of earthquake shaking increases as a result of glacial erosion and deglaciation. It is possible that the effect of this is sufficient to have influenced the distribution of post‐glacial slope failures in glaciated seismically active areas. Copyright © 2012 John Wiley & Sons, Ltd.     

Seismic records of late Pleistocene aridity in Lake Tanganyika,tropical East Africa

New intermediate-resolution, normal-incidence seismic reflection profiles from Lake Tanganyika’s central basin capture dramatic evidence of base-level change during two intervals of the late Pleistocene. Four seismically-defined stratigraphic sequences (A–D) tied to radiocarbon-dated sediment cores provide a chronology for fluctuating environmental conditions along the Kalya Platform. Stacked, oblique clinoforms in Sequence C are interpreted as prograding siliciclastic deltas deposited during a major regression that shifted the paleo-lake shore ∼21 km towards the west prior to ∼106 ka. The topset-to-foreset transitions in these deltas suggest lake level was reduced by ∼435 m during the period of deposition. Mounded reflections in the overlying sequence are interpreted as the backstepping remnants of the delta system, deposited during the termination of the lowstand and the onset of transgressive conditions in the basin. The youngest depositional sequence reflects the onset of profundal sedimentation during the lake level highstand. High amplitude reflections and deeply incised channels suggest a short-lived desiccation event that reduced lake level by ∼260 m, interpreted as a product of Last Glacial Maximum (32–14 ka) aridity. Paleobathymetric maps constructed for the two interpreted regressions reveal that despite the positive lake-floor topography created by the Kavala Island Ridge Accommodation Zone, Lake Tanganyika remained a large, mostly connected water body throughout the late Pleistocene. The results of this analysis further imply that Lake Tanganyika is the most drought resistant water body in the East African tropics, and may have acted as a refuge for local and migrating fauna during periods of prolonged aridity.     

First Imaging of Coronal Mass Ejections in the Heliosphere Viewed from Outside the Sun – Earth Line

We show for the first time images of solar coronal mass ejections (CMEs) viewed using the Heliospheric Imager (HI) instrument aboard the NASA STEREO spacecraft. The HI instruments are wide-angle imaging systems designed to detect CMEs in the heliosphere, in particular, for the first time, observing the propagation of such events along the Sun – Earth line, that is, those directed towards Earth. At the time of writing the STEREO spacecraft are still close to the Earth and the full advantage of the HI dual-imaging has yet to be realised. However, even these early results show that despite severe technical challenges in their design and implementation, the HI instruments can successfully detect CMEs in the heliosphere, and this is an extremely important milestone for CME research. For the principal event being analysed here we demonstrate an ability to track a CME from the corona to over 40 degrees. The time – altitude history shows a constant speed of ascent over at least the first 50 solar radii and some evidence for deceleration at distances of over 20 degrees. Comparisons of associated coronagraph data and the HI images show that the basic structure of the CME remains clearly intact as it propagates from the corona into the heliosphere. Extracting the CME signal requires a consideration of the F-coronal intensity distribution, which can be identified from the HI data. Thus we present the preliminary results on this measured F-coronal intensity and compare these to the modelled F-corona of Koutchmy and Lamy (IAU Colloq. 85, 63, 1985). This analysis demonstrates that CME material some two orders of magnitude weaker than the F-corona can be detected; a specific example at 40 solar radii revealed CME intensities as low as 1.7×10⁻¹⁴ of the solar brightness. These observations herald a new era in CME research as we extend our capability for tracking, in particular, Earth-directed CMEs into the heliosphere.     

The rectilinear three-body problem

The rectilinear equal-mass and unequal-mass three-body problems are considered. The first part of the paper is a review that covers the following items: regularization of the equations of motion, integrable cases, triple collisions and their vicinities, escapes, periodic orbits and their stability, chaos and regularity of motions. The second part contains the results of our numerical simulations in this problem. A classification of orbits in correspondence with the following evolution scenarios is suggested: ejections, escapes, conditional escapes (long ejections), periodic orbits, quasi-stable long-lived systems in the vicinity of stable periodic orbits, and triple collisions. Homothetic solutions ending by triple collisions and their dependence on initial parameters are found. We study how the ejection length changes in response to the variation of the triple approach parameters. Regions of initial conditions are outlined in which escapes occur after a definite number of triple approaches or a definite time. In the vicinity of a stable Schubart periodic orbit, we reveal a region of initial parameters that corresponds to trajectories with finite motions. The regular and chaotic structure of the manifold of orbits is mostly defined by this periodic orbit. We have studied the phase space structure via Poincaré sections. Using these sections and symbolic dynamics, we study the fine structure of the region of initial conditions, in particular the chaotic scattering region.     

Modelling the time course of shade,temperature, and wood recovery in streams with riparian forest restoration

Action is increasingly being taken in New Zealand and elsewhere to restore ecological function to streams through planting of riparian zones. We used simulation modelling to explore the relative performance of three strategies to restore the riparian zone of a pastoral stream to native forest by: (1) passive regeneration; (2) planting then abandonment of a Pinus radiata plantation; and (3) active restoration by planting selected native trees. We linked the forest model LINKNZ with a shade and temperature model (sWAIORA), and a wood model (OSU_STREAMWOOD) to simulate recovery trajectories for key forest stream attributes in hypothetical streams (1.3–14.0 m channel width) in the central North Island, New Zealand. Both active restoration strategies outperformed passive regeneration in shade, temperature and stream wood volume for most of the simulation time (800 years). Although the abandoned pine plantation provided greatest shade initially (<100 years), active native planting provided the greatest benefits overall. In general, recovery of stream shade (and temperature) is expected within decades, is accelerated by deliberate planting, and is fastest in small streams in which thermal stress from sunlight exposure is greatest. However, full recovery of stream and riparian function may take centuries, being dependent on large trees providing wood to structure the channel.     

Baseflow water chemistry in New Zealand rivers 1. Characterisation

In late summer to autumn 1987, 96 rivers throughout New Zealand were sampled in baseflow (< median flow) conditions, usually on three separate occasions. A wide range of water quality determinands were analysed to characterise water quality comprehensively at lower than median flows. River waters in New Zealand range widely in composition, particularly plant nutrients, but tend to be more dilute than world average freshwater (WAFW) because run‐off (specific yield) of water is generally high. Sodium and calcium are the most important cations in New Zealand rivers which can be described as “calcium‐sodium bicarbonate waters”, whereas WAFW is calcium bicarbonate water. Almost all river sites met existing guidelines and standards for drinking water, ecological protection, and freshwater fisheries.