Crossing Filaments

Solar filaments show the position of large-scale polarity-inversion lines and are used for the reconstruction of large-scale solar magnetic field structure on the basis of Hα synoptic charts for the periods that magnetographic measurements are not available. Sometimes crossing filaments are seen in Hα filtergrams. We analyze daily Hα filtergrams from the archive of Big Bear Solar Observatory for the period of 1999 – 2003 to find crossing and interacting filaments. A number of examples are presented and filament patterns are compared with photospheric magnetic field distributions. We have found that all crossing filaments reveal quadrupolar magnetic configurations of the photospheric field and presume the presence of null points in the corona.     

Mapping the thickness of sediments in the Ljubljana Moor basin (Slovenia) using microtremors

The Ljubljana Moor basin is characterized by moderate bedrock topography and thicknesses of Quaternary lacustrine and fluvial sediments ranging from 0 to 200 m. More than 65 boreholes which reached the bedrock were drilled in the area, but their distribution in the basin is very uneven and some data from the boreholes uncertain. There are also no data on S-velocity distribution within the basin, but seismic refraction measurements pointed out a rather uniform increase of P-velocity with depth, great impedance contrast with the bedrock and relatively small lateral velocity variations. The microtremor horizontal-to-vertical spectral ratio (HVSR) method was therefore applied as a complementary tool to seismic refraction survey to map the thickness of sediments. First, microtremors were measured at the locations of boreholes which reached the bedrock and the resonance frequencies determined. The inverse power relationship between the resonance frequency and the thickness of sediments was then determined from 53 data pairs. The quality of the correlation is moderate due to possible heterogeneities in sediments and possible 3D effects in some minor areas, but the obtained parameters correspond well to the values obtained in six other European basins. Secondly, a 16 km-long discontinuous seismic refraction profile was measured across the whole basin, leaving uncovered some larger segments where active seismic measurements were not possible. Microtremors were then measured at 64 locations along the same profile, using 250 m point spacing, without leaving any gaps. The frequency–thickness relationship was used to invert resonance frequencies to depths. These were first validated using the results of the seismic refraction survey, which showed good agreement, and finally used for interpolation in the segments of missing refraction data to obtain a continuous depth profile of the bedrock. The study has shown that the microtremor method can be used as a complementary tool for mapping the thickness of unconsolidated sediments also in areas characterized by moderate bedrock topography. As the input data are always to some extent uncertain, it is important to have a sufficiently large number of borehole data to establish a frequency–thickness relationship, as well as some additional independent geophysical information for its validation.     

Position-domain integrity risk-based ambiguity validation for the integer bootstrap estimator

Integrity monitoring for ambiguity resolution is of significance for utilizing the high-precision carrier phase differential positioning for safety–critical navigational applications. The integer bootstrap estimator can provide an analytical probability density function, which enables the precise evaluation of the integrity risk for ambiguity validation. In order to monitor the effect of unknown ambiguity bias on the integer bootstrap estimator, the position-domain integrity risk of the integer bootstrapped baseline is evaluated under the complete failure modes by using the worst-case protection principle. Furthermore, a partial ambiguity resolution method is developed in order to satisfy the predefined integrity risk requirement. Static and kinematic experiments are carried out to test the proposed method by comparing with the traditional ratio test method and the protection level-based method. The static experimental result has shown that the proposed method can achieve a significant global availability improvement by 51% at most. The kinematic result reveals that the proposed method obtains the best balance between the positioning accuracy and the continuity performance.     

The extension of the parametrization of the radio source coordinates in geodetic VLBI and its impact on the time series analysis

The radio sources within the most recent celestial reference frame (CRF) catalog ICRF2 are represented by a single, time-invariant coordinate pair. The datum sources were chosen mainly according to certain statistical properties of their position time series. Yet, such statistics are not applicable unconditionally, and also ambiguous. However, ignoring systematics in the source positions of the datum sources inevitably leads to a degradation of the quality of the frame and, therefore, also of the derived quantities such as the Earth orientation parameters. One possible approach to overcome these deficiencies is to extend the parametrization of the source positions, similarly to what is done for the station positions. We decided to use the multivariate adaptive regression splines algorithm to parametrize the source coordinates. It allows a great deal of automation, by combining recursive partitioning and spline fitting in an optimal way. The algorithm finds the ideal knot positions for the splines and, thus, the best number of polynomial pieces to fit the data autonomously. With that we can correct the ICRF2 a priori coordinates for our analysis and eliminate the systematics in the position estimates. This allows us to introduce also special handling sources into the datum definition, leading to on average 30 % more sources in the datum. We find that not only the CPO can be improved by more than 10 % due to the improved geometry, but also the station positions, especially in the early years of VLBI, can benefit greatly.     

Estimating areal production of intertidal microphytobenthos based on spatio-temporal community dynamics and laboratory measurements

In situ Microphytobenthic community dynamics were combined with laboratory measurement of predominant species by fluorescence methods to estimate the areal primary production. Field investigation of community dynamics of microphytobenthos (MPB) was conducted from August 2006 to August 2007 in intertidal flats of the Nakdong River estuary, Korea. MPB Biomass varied between 0.47 and 16.58 μg cm^?3 in the surface 1 cm sediment, with two dominant diatom species, Amphora coffeaeformis and Navicula sp., occupying average 77.2 ± 14.9% of total number of MPB cells. The biomass was higher in the slightly muddy sand sites than that in the sand site, and showed different pattern of seasonal variation. The profile of vertical distribution of biomass was an exponential decrease trend with depth in sediments. The biomass proportions in the uppermost 3 mm were 57.6% and 37.8% with and without the presence of biofilm, respectively. The two dominant species were cultured in laboratory, and their photosynthetic parameters, rETR_max (relative maximum electron transport rate), α (light utilization coefficient) and E _k (light saturation parameter) were derived from rETR (relative ETR)-irradiance curves by Imaging- PAM (pulse amplitude modulated) fluorometry. The rETR-irradiance curves showed no significant difference of photosynthetic activities between the two species. The areal potential production ranged from 0.74 to 2.22 g C m^?2 d^?1.     

Devonian ichnofossils from the Farakah Muth section of the Pin Valley,Spiti Himalaya

The Muth Formation is one of the most characteristic marker horizon traced throughout the northwestern Himalaya. The present studies were carried out in the Farakah Muth (Pin Valley) section of Spiti Basin. The formation uniformly consists of quartzarenite with a high textural and compositional maturity. The development of carbonate beds in the upper part of the Muth Formation separates it conformably from the overlying Lipak Formation. A variety of traces were observed throughout the succession, includes: Metaichna, Planolites, Skolithos, vertical and horizontal burrows. The presence of ichnofossils in the Muth Formation of the Farakah section indicates subtidal settings having soft sandy substrate, whereas, the gradual maturity of the quartz grains from base to top indicates deposition under high energy condition.     

Pollution characteristics of alluvial groundwater from springs and bore wells in semi-urban informal settlements of Douala,Cameroon, Western Africa

Alluvial groundwater from springs and bore wells, used as the major source of water for drinking and other domestic purposes in the semi-urban informal settlements of Douala, Cameroon, has been studied. Six representative springs, four bore wells and two hand dug wells, situated in the Phanerozoic basin were selected, from which a total of 72 water samples were analyzed for chemical characteristics and indicators of bacterial contamination. The results showed anthropogenic pollution, evident from high concentrations of organic (up to 94.3 mg NO₃/l nitrate) fecal coliform and fecal streptococcus detected in the springs and bore wells (with values of 2,311 and 1,500 cfu/100 ml, respectively). The pH ranged from 3.4–6.5, which is lower than the guidelines for drinking water. Groundwater samples from background upstream inland natural areas W1 and W2 had low electrical conductivity (54.2 and 74.8 μs/cm, respectively) and major ions, which increased downstream in the valleys, peaking in the more densely settled areas. An acceptable concentration of solutes was observed for the bore wells except for a single sample from B4. The bore-well sample B4 registered the highest microbial content (2,130 cfu/100 ml) and nitrate level(26 mg/l), which could be due to the bottom of this well lying just at or close to the zone of mixing between sewage and groundwater. The absence of a direct correlation between nitrate and fecal matter suggests multiple sources of contamination. The shallow alluvial aquifer consists of unconsolidated deposits of gravel, sand, silt and clay. The springs, therefore, receive direct recharge from the ground surface with limited contaminant attenuation, which leads to water quality deterioration, especially during the rainy season. This shows the urgent need to put basic service infrastructures in place. The local population should be sensitized to the importance of chlorinating and boiling drinking water to prevent health hazards.     

Change of multifractal thermal characteristics in the western Philippine sea upper layer during internal wave-soliton propagation

The upper layer (above 140 m depth) temperature in the western Philippine Sea near Taiwan was sampled using a coastal monitoring buoy (CMB) with 15 attached thermistors during July 28–August 7, 2005. The data were collected every 10 min at 1, 3, 5, 10, 15, and 20 m using the CMB sensors, and every 15 sec at 15 different depths between 25 m and 140 m. Internal waves and solitons were identified from the time-depth plot of the temperature field. Without the internal waves and solitons, the power spectra, structure functions, and singular measures (representing the intermittency) of temperature field satisfy the power law with multi-scale characteristics at all depths. The internal waves do not change the basic characteristics of the multifractal structure. However, the internal solitons change the power exponent of the power spectra drastically, especially in the low wave number domain; they also break down the power law of the structure function and increase the intermittency parameter. The physical mechanisms causing these different effects need to be explored further.     

Influence of Environmental Factors on Spawning of the American Horseshoe Crab (<Emphasis Type="Italic">Limulus polyphemus</Emphasis>) in the Great Bay Estuary,New Hampshire,USA

The Great Bay Estuary, New Hampshire, USA is near the northern distribution limit of the American horseshoe crab (Limulus polyphemus). This estuary has few ideal beaches for spawning, yet it supports a modest population of horseshoe crabs. There is no organized monitoring program in the Great Bay Estuary, so it is unclear when and where spawning occurs. In this 2-year study (May through June, 2012 and 2013), >5,000 adult horseshoe crabs were counted at four sites in the estuary. The greatest densities of horseshoe crabs were observed at Great Bay sites in the upper, warmer reaches of the estuary. Peaks of spawning activity were not strongly correlated with the times of the new or full moons, and similar numbers of horseshoe crabs were observed mating during daytime and nighttime high tides. While many environmental factors are likely to influence the temporal and spatial patterns of spawning in this estuary, temperature appears to have the most profound impact.     

Seasonal variations of the surface currents in the Tsushima Strait

Seasonal variations of the surface currents in the Tsushima Strait were investigated by analyzing the monthly mean surface currents measured with HF radar. Several new features of the surface currents have been found. One notable feature is the large, complicated seasonal variation in the current structure in the eastern channel of the strait. For example, in the southeastern and northwestern regions of the channel, southwestward countercurrents are found in summer while southeastward acrossshore currents are found in autumn and winter. The wind-driven flow (Ekman flow) as well as surface geostrophic currents are responsible for these complicated variations of the surface currents. To quantify each variation of the flow and current, the wind-driven flow was calculated from the monthly wind (more precisely, the friction velocity) using the monthly speed factor and deflection angle estimated in our previous study, and the surface geostrophic currents were then estimated by subtracting the wind-driven flow from the measured surface currents. It was found that the acrossshore currents are the wind-driven flow, and that the surface geostrophic currents flow almost in the along-shore direction, indicating the validity of the decomposition of the surface velocity into the wind-driven flow and the geostrophic currents using the speed factor and deflection angle. A real-vector empirical orthogonal function (EOF) analysis of the surface geostrophic currents shows a pair of eddies in the lee of Tsushima and Iki Islands as the first mode, which indicates that the southwestward countercurrents in the eastern channel are formed primarily by the incoming Tsushima Warm Current.