South Station Research Articles

TEC measurements and modelling over Southern Africa during magnetic storms; a comparative analysis

This paper presents the results from a study designed to investigate the ability of a newly developed neural network (NN) based model to follow total electron content (TEC) dynamics over the Southern African region. The investigation is carried out by comparing results from the NN model with actual TEC data derived from Global Positioning System (GPS) observations and TEC values predicted by the International Reference Ionosphere (IRI-2007) model during magnetic storm periods over Southern Africa. The magnetic storm conditions chosen for the study presented in this paper occurred during the periods 16–21 April 2002, 1–6 October 2002, and 28 October–01 November 2003. A total of six South African GPS stations were used for the validation of the two models during these periods. A statistical analysis of the comparison between the actual TEC behaviour and that predicted by the two models is shown. In addition, ionosonde measurements from the South African Louisvale (28.5°S, 21.2°E) station, located close to one of the validation GPS stations used, are also considered during the Halloween storm period of 28–31 October 2003. The generalisation of TEC behaviour by the NN model is demonstrated by producing predicted TEC maps during magnetic storm periods over South Africa. Presented results demonstrate the ability of NNs in predicting TEC variability over South Africa during magnetically disturbed conditions, and highlight areas for improvement.

PERFORMANCE OF SOME NEW CITRUS VARIETIES UNDER SOUTH EL-TAHRIER DISTRICT CONDITIONS

The performance of two lemon cultivars namely Feminello and Eureka lemon (Citrus limon (L.) Brum.f), four orange cultivars namely navel orange (Navelina, Navelate, Newhall and Washington navel orange (Citrus sinensis L. Osbeck)) and four mandarin cultivars namely seedless mandarin, thorny Clementine, thornless Clementine and Balady mandarin (Citrus reticulata Blanco), respectively were done at South El Tahrir research station, Beheira Gov. during 2006/2007 and 2007/2008 under similar cultural practices. Preliminary observations under the prevailing conditions indicated that Feminello lemon, Newhall navel orange, Washington navel orange and both thornless and thorny Clementine were excellent with an average 7.46, 6.87, 6.45 and 6.58 ton/fed, respectively whereas Navelina, Navelate and Balady and seedless mandarin occupied the second position. However, the vegetative growth of the promising varieties was directly proportional to root horizontal and vertical extension.

Application of coal fly ash to circumneutral mine waters for the removal of sulphates as gypsum and ettringite

South African power stations generate large amounts of highly alkaline fly ash (FA). This waste product has a serious impact on the environment. Acid mine drainage (AMD) is another environmental problem associated with mining. AMD has high heavy metal content in addition to high sulphate concentrations. Several studies have shown that 80–90% of sulphates can be removed when FA is co-disposed with AMD rich in Fe and Al. In South Africa, sources of contaminated mine waters, unlike AMD have circumneutral pH and much lower concentrations of Fe and Al, but rich in Ca and Mg. Treatment of such waters with FA resulted in no significant removal of sulphates when treated to pH less than 10. Subsequent treatment of circumneutral mine water to pH greater than 11 resulted in more than 60% sulphate removal. Treatment of circumneutral mine water to pH greater than 11 with FA followed by seeding with gypsum crystals and the addition of amorphous Al(OH) 3 resulted in removal of sulphate to levels below the Department of Water Affairs and Forestry (DWAF) water quality effluent limit (500 ppm).

Simulation of storm surge, wave, and coastal inundation in the Northeastern Gulf of Mexico region during Hurricane Ivan in 2004

Hurricane-induced storm surge, waves, and coastal inundation in the northeastern Gulf of Mexico region during Hurricane Ivan in 2004 are simulated using a fine grid coastal surge model CH3D (Curvilinear-grid Hydrodynamics in 3D) coupled to a coastal wave model SWAN, with open boundary conditions provided by a basin-scale surge model ADCIRC (Advanced CIRCulation) and a basin-scale wave model WW3 (WaveWatch-III). The H∗wind, a reanalysis 10-m wind produced by the NOAA/AOML Hurricane Research Division (HRD), and a relatively simple analytical wind model are used, incorporating the effect of land dissipation on hurricane wind. Detailed comparison shows good agreement between the simulated and measured wind, waves, surge, and high water marks. Coastal storm surge along the coast is around 2–3 m, while peak surge on the order of 3.5 m is found near Pensacola, which is slightly to the east of the landfall location on Dauphin Island. Wind waves reach 20 m at the Mobile South station (National Data Buoy Center buoy 42040) on the shelf and 2 m inside the Pensacola/Escambia Bay. Model results show that wave-induced surge (total surge subtracted by the meteorologically-induced surge due to wind and pressure) accounts for 20–30% of the peak surge, while errors of the simulated surge and waves are generally within 10% of measured data. The extent of the simulated inundation region is increased when the effects of waves are included. Surge elevations simulated by the 3D model are generally up to 15% higher than that by the 2D model, and the effects of waves are more pronounced in the 3D results. The 3D model results inside the Pensacola/Escambia Bay show significant vertical variation in the horizontal currents. While the estuary has little impact on the surge elevation along the open coastal water, surge at the head of Escambia Bay is more than 50% higher than that at the open coast with 1.5 h delay.

Effect of Traffic Rate and Type on Soil Compaction in Sandy South Georgia Soils

Soil compaction is one of the largest problems faced by modern mechanized agricultural and forestry operations. This makes research in the area of soil compaction critical. This study was undertaken to see how different types and levels of traffic have influenced soil compaction in sandy soils at the Valdosta State University Lake Louise field station south of Valdosta, GA. Four different traffic patterns were investigated in this study. The first area has relatively high vehicular traffic, the second more moderate vehicular traffic, and the third area a relatively low level of vehicle traffic. The fourth area has experienced foot, horse, and ATV traffic, but full sized vehicles like cars and vans have not been used in the area. To study compaction, soil cores of known volume were taken at the soil surface and at 30-cm depths. These cores were taken both in the trafficked area (road, trail) and alongside the trafficked area at three locations for each treatment. Average soil bulk density values for the trafficked and untrafficked areas were statistically compared to determine the effects of traffic patterns on soil compaction. Results indicate that soils were more compacted along trafficked areas than in the corresponding untrafficked areas with the exception of the fourth area, which had experienced the lightest traffic load.

A Terrestrial Reference Frame (TRF), coordinates and velocities for South American stations: contributions to Central Andes geodynamics

Abstract. Satellite positioning systems allow the fixing of the location of a point on the Earth's surface with very good precision and accuracy. To do this, however, it is necessary to determine the point coordinates taking account the reference system and the movements that affect them because of tectonic plate movements. These reference systems are materialized by a significant number of continuous measurement stations in South America. In SIRGAS (Sistema de Referencia Geocéntrico para las Américas), there are four Analysis Centers that process the data collected from satellites of the Global Navigation Satellite Systems (GNSS), with the primary purpose to maintain the international terrestrial reference frame through calculation of the coordinates and velocities of the continuous GNSS stations of the SIRGAS-CON Network. In this work, we demonstrate the quality of the solutions from CIMA, one of the SIRGAS official processing centers operating in Mendoza, Argentina, in comparison with other South American processing centers. The importance of precise calculations of coordinates and velocities in a global frame is also shown. Finally, we give estimations of velocities from stations located within deformation zones in the Central Andes.

Heavy daily-rainfall characteristics over the Gauteng Province

Daily rainfall over the Gauteng Province, South Africa, was analysed for the summer months of October to March using 32-yr (1977 to 2009) daily rainfall data from about 70 South African Weather Service stations. The monthly and seasonal variation of heavy rainfall occurrences was also analysed. Three 24-h heavy rainfall classes are defined considering the area-average rainfall. A significant rainfall event is defined when the average rainfall exceeds 10 mm, a heavy rainfall event when the average rainfall exceeds 15 mm and a very heavy rainfall event when the average rainfall exceeds 25 mm. January months have the highest monthly average rainfall as well as the highest number of heavy and very heavy rainfall days. The month with the second-highest number of heavy and very heavy rainfall days is February followed by March and October. December has the second-highest monthly average rainfall and the most days with rain. However, it is also the month with the lowest number of heavy and very heavy rainfall days. The highest 24-h rainfall recorded at a single station during the 32-yr period was 300 mm in December 2006. However, rainfall exceeding 115 mm at a single rainfall station in the Gauteng Province is very rare and does not occur every year. January months receive these events more than any other month but this only transpires in approximately a third of years. The central and north-western parts of the Province experience the most events where the rainfall at a single station surpasses 75 and 115 mm. With regard to seasonal rainfall, the 1995/96 summer rainfall season had the highest seasonal rainfall during this 32-yr period followed by the 1999/2000 season. The 1995/96 season had above normal rainfall in both early and late summer but the 1999/2000 season was dry in early summer and very wet in late summer. Significantly high seasonal rainfall is associated with above-normal rainfall in late summer.

Comparison between observed ionospheric foF2 and IRI-2001 predictions over periods of severe geomagnetic activities at Grahamstown, South Africa

The observed ionospheric F2 critical frequency ( foF2) values over a South Africa mid-latitude station, Grahamstown, (geographic coordinates: 33.3°S, 26.5°E), were analysed and compared with International Reference Ionosphere (IRI) model, using the CCIR (Comite´ Consultatif International des Radio communications) and URSI (Union Radio-Scientifique Internationale) coefficients, during four geomagnetically disturbed days in the year 2000. These days are April 5, May 23, August 10 and September 15. The data were analysed for five days around the storm day. Comparisons between the IRI-2001 predicted foF2 values, using both CCIR and URSI coefficients and the observed values are shown with their root-mean-square error (RMSE) and the relative deviation module mean (rdmm) for the various storm periods. The CCIR option performed more accurately than the URSI option. In general, the model generates good results when compared with observed foF2 values during geomagnetic storms, although some improvements are still necessary to be implemented in order to obtain better predictions.

<strong>Polychaete fauna in the vicinity of bluefin tuna sea-cages in Ensenada, Baja California, Mexico</strong>

This paper describes the polychaete fauna in Salsipuedes Bay, Baja California. Sea-cage farming results in a rain of organic matter onto the underlying benthos. There is growing concern over the effects of tuna sea-cages on the local sediment chemistry and benthic communities. Eighteen stations were sampled with a Van Veen grab (0.1 m2) from the oceanographic vessel Francisco de Ulloa in March 2003 and October 2004. Redox potential in 2003 ranged between ‑113 and ‑200 mV, while in 2004 it ranged between ‑110 and ‑302 mV. Organic carbon concentrations varied between 0.20% and 2.53 %, lowest values were located in the southern part of the bay; highest concentrations were found at stations 18–22 situated in the northern section, west of the tuna pens. Organic N varied between 0.02% and0.12%, highest concentrations (0.07–0.12%) were located at stations 16–21 in the northern section of the bay; stations situated at the south and near the coast presented the lowest N concentrations (0.02–0.04%). A total of 9,291 organisms belonging to seven phyla were collected: Polychaeta, Mollusca, Crustacea, Echinodermata, Cnidaria, Sipuncula, and Bryozoa. Polychaetes accounted for 62% of all invertebrate macrofauna, with 5,765 specimens representing 34 families and 146 species. The best represented families in 2003 and 2004 were Paraonidae, Cirratulidae, Spionidae, Capitellidae, Syllidae, Nephtyidae, Lumbrineridae, and Glyceridae. Polychaetes were dominant at almost all sampling stations. Families with the highest species richness were Paraonidae (14 spp.), Spionidae (11 spp.), Onuphidae (11 spp.), Maldanidae (10 spp.), Syllidae (9 spp.), Cirratulidae and Ampharetidae with 7 species each. Among the most abundant species were Aphelochaeta multifilis, Mediomastus ambiseta, Prionospio steenstrupi Spiophanes bombyx, Apoprionospio pygmaea, Paraonella sp., Monticellina sp., Aricidea (Allia) ramosa, Spiophanes bombyx, Spiophanes duplex, and Levinsenia gracilis. The dominant trophic group was deposit-feeders, followed by carnivores. In 2003 Shannon index varied between 2.26 and 3.40 bits/ind.; the highest diversity values were found in the southern section of Salsipuedes Bay. In 2004 diversity fluctuated between 2.31and 3.35; the highest values were found at three stations in the northern section south of the tuna pens. Stress-predictability modeling characterized 85% of stations in 2003 and 78% in 2004 as presenting favorable and stable conditions, the rest were considered moderately disturbed. Non-metric multidimensional scaling (MDS) separated stations depending on the distance to the tuna pens. Our results indicate that Salsipuedes Bay is still a favorable environment for polychaetes. Apparently local circulation has at least partially dispersed the excess organic matter.

Copepod feeding study in the upper layer of the tropical South China Sea

The South China Sea (SCS) is the world’s largest marginal sea being notable for vertical mixing at various scales resulting in a sequence of chemical and biological dynamics in surface waters. We investigated the ingestion, gut content, evacuation and clearance rates of copepods collected from six stations (including a South East Asia Time Series station) along a transect line in the tropical of a SCS cruise during September 27, 1999 to October 2, 1999. The goal of the present study was to understand the feeding ecology of copepods in the upper water layers (0–5 m) of the northern SCS during autumn. We measured the gut pigment contents of 33 copepod species by the gut fluorescence method. The gut chlorophyll a values of most small size copepods ( 2 mm) had significantly higher values than medium sized copepods (1–2 mm) and smaller sized copepods. The present study shows that the performance of feeding on phytoplankton was variable in different sized copepod groups, suggesting that copepods obtained in the tropical area of the southeastern Taiwan Strait might be opportunistic feeders.

Is the north side of the Strait of Gibraltar more diverse than the south side? A case study using the intertidal peracarids (Crustacea: Malacostraca) associated to the seaweedCorallina elongata

The objectives of this study were to describe the peracaridean fauna associated to the algaeCorallina elongatafrom the Strait of Gibraltar, and explore possible biodiversity and biogeographical patterns of variation along the north–south and Atlantic–Mediterranean axes across the Strait of Gibraltar. Twenty-five stations were selected along the north and south coasts of the Strait to cover the broadest possible range of human pressure and environmental conditions, including both natural rocky shores and artificial breakwaters. The algaCorallina elongatawas selected as substrate, and the peracaridean crustaceans were identified to species level and classified in geographical distribution groups. Univariate and multivariate analyses were conducted to explore and confirm patterns of variation. Forty peracarid species were collected, most of them with an Atlantic–Mediterranean distribution (67%) with only the gammaridParhyale eburnea, being an endemic Mediterranean species. The most common species collected during the present study were the gammaridsHyale stebbingi, Jassa marmorata, Stenothoe monoculoidesandAmpithoespp., the caprellidsCaprella grandimanaandC. penantis, the isopodIschyromene lacazeiand the tanaidTanais dulongi. The number of species per station and the diversity index were significantly higher in the stations located along the north side of the Strait of Gibraltar. However, the two-way ANOVA discarded differences between north and south due to the type of substrate (natural versus artificial) and degree of human pressure. Based on peracaridean assemblages, the Strait of Gibraltar behaves as a whole and homogeneous region, with a very similar faunal composition in all stations and there is not a clear gradient of species substitution from the Mediterranean to the Atlantic stations. Provided that we selected the same substrate in all stations, and that statistical analyses revealed that differences between north and south stations were not due to environmental factors such as anthropogenic stress or type of substrate, we should look to historical biogeographical reasons to explain the higher diversity in the north side of the Strait of Gibraltar.

Leaching characteristics of selected South African fly ashes: Effect of pH on the release of major and trace species

Fly ash samples from two South African coal-fired power stations were subjected to different leaching tests under alkaline and acidic conditions in an attempt to assess the effect of pH on the leachability of species from the fly ashes and also assess the potential impact of the fly ashes disposal on groundwater and the receiving environment. To achieve this, German Standard leaching (DIN-S4) and Acid Neutralization Capacity (ANC) tests were employed. Mineralogical characterization of the fresh fly ashes revealed mullite and quartz as the major mineral phases with minor peaks of CaO and calcite. Chemical characterization by X-ray fluorescence (XRF) spectrometry revealed that the two fly ashes are similar, and consist of SiO2, Al2O3, Fe2O3 and CaO as the main components with Cr, Co, Ni, Cu, Zn, V and Pb as minor components. Ca, Mg, Na, K and SO4 were significantly leached into solution under the two leaching conditions with the total amounts in ANC leachates higher than that of DIN-S4. This indicates that a large fraction of the soluble salts in unweathered fly ash are easily leached. These species represents the fraction that can be flushed off initially from the surface of ash particles on contacting the ash with water. Al and Si were only observed in the leachates of the ANC test. Results obtained from the total acid-digestion and DIN-S4 leaching test indicated some toxic elements in the fly ashes are not easily solubilized. The amounts of toxic trace elements such as As, Se, Cd, Cr and Pb leached out of the fly ashes when in contact with de-mineralized water (DIN-S4 test) were low and below the Target Water Quality Range (TWQR) of South Africa. This is explained by their low concentrations in the fly ashes and their solubility dependence on the pH of the leaching solution. However the amounts of some minor elements such as B, Mn, Fe, As and Se leached out at lower pH ranging between 10 to 4 (ANC test) were slightly higher than the TWQR, an indication that the pH of the leaching solution plays a significant role on the leaching of species in fly ash. The high concentrations of the toxic elements released from the fly ashes at lower pH gives an indication that the disposal of the fly ash could have adverse effects on the receiving environment if the pH of the solution contacting the ashes is not properly monitored. The study indicated that on contact with water in a disposal scenario fly ash will release high amounts of soluble species.

Daily Rainfall Variability over Northeastern Argentina in the La Plata River Basin

We did a brief description of the climatic behavior and after this we analyzed the temporal variation in the total number of days a year with rainfall and the number of days a year with rainfall above the 100 mm threshold at the rain gauging stations in northeastern Argentina south of the La Plata River basin. The results show an increase both in the frequency of daily rainfall, especially during the winter season, and the frequency of days with heavy rainfall starting in the early 1970s. The increase in frequency of occurrence is more significant in the case of heavy rainfall. The annual maximum rainfall was calculated for periods of 1, 3, 5, 7, and 10 consecutive days at regional rain gauging stations for the respective historical periods, and the rain intensity-duration-return period curves (IDT) were determined on a frequency analysis. The IDT curves were compared with rainfall intensity-duration data of critical storms occurring in the last decades. We noticed that the rain intensities of critical storms (mostly convective) widely exceeded the intensities given by the 100-year IDT curves, particularly for short durations. The increase in both the frequency of heavy rainfall occurrence and rain intensity from the 1970s onward shows an increase in frequency and intensity of the meso-scale convective systems in the region resulting from climatic change. These systems tend to produce rainfall of very high intensity that is spatially concentrated and which generally produces significant floods in the local rivers.

Russia Wharf Tunnelling Project

AbstractThe Silver Line Phase II in Boston, USA, (Logan Airport to South Station) includes the crossing of the Russia Wharf, a 100 year old, three building complex, each seven stories high. The first use of ground freezing and NATM in the US enabled these office buildings to stay fully operational and minimized the impacts on the tenants and these old structures while tunnelling underneath. Mitigation of settlements included temporary and permanent underpinning, raising and lowering of building columns and facades and the use of ground freezing which also created stable face conditions for the NATM mining operation only a few feet below surface.

A modified analytical method for the shipboard determination of nanomolar concentrations of orthophosphate in seawater

A method for the determination of nanomolar concentrations of orthophosphate in oligotrophic seawater developed by Liang et al. (2007) has been modified to make it fully feasible for shipboard application and for faster sample throughput with minimized sample volume. The technique is based on the flow injection method with solid phase extraction on a Sep-Pak C18 cartridge and colorimetric detector. The Schlieren effect was minimized by rinsing the cartridge sequentially with 5 mL water and 2 mL 95% ethanol solution. With three micro pumps in parallel, savings of up to 80% in amount of reagents and 25% volume of seawater samples could be achieved in comparison to the previous method. Variation of stopped flow time and sample loading time gave 3 different standard curves, which corresponded to 3 linear ranges within 3.4 and 515 nM. The modified method permits the analysis of samples over a wide range of concentrations, and has been successfully applied to shipboard determination of trace orthophosphate in more than 200 seawater samples during a one-month cruise in the South China Sea. For seawater at concentrations of 20.6, 82.5, 206.2 nM orthophosphate, the relative standard deviations (RSD) (n = 6), determined daily for 6 days on board ship were 4.45%, 4.73% and 6.75%, respectively. Five seawater samples collected in the Station SEATS (South East Asia Time Series Station at 18°N, 116°E) were analyzed using the present method both on board and in a land-based laboratory, as well as with the magnesium hydroxide-induced coprecipitation (MAGIC) method, and showed no significant difference according to the statistical t-test.

Gas station south of Memphis, Desoto County, Mississippi, 2006

Gas station south of Memphis, Desoto County, Mississippi, 2006

A model for freeze–thaw cycling of the South Pole Station exterior sheathing

An infrared survey [Phetteplace, G. 2006. An Infrared Survey of the South Pole Station Modernization Project, Final Project Report to National Science Foundation, US Army Cold Regions Research and Engineering Laboratory, Hanover, NH.] of the new South Pole Elevated Station revealed evidence of excessive air exfiltration in some locations. Despite the relatively low indoor humidity normal in the South Pole Station, typically less than 10% relative humidity (RH), there was concern that excessive exfiltration could result in moisture accumulation within the building walls. While the accumulation and freezing of moisture at any point in the wall section could be problematic, what was felt to be of greater concern was the potential for repeated freeze-thaw cycling near the exterior oriented strand board (OSB) sheathing due to the significant diurnal temperature cycling of the siding during the Antarctic summers. The intense solar radiation conditions on vertical surfaces at the low Antarctic summer sun angles results in very high solar fluxes, and surface temperatures can rise well above freezing even in ambient temperatures that are -20 °C or lower. Typical building energy analysis methods are not suited to analysis of this problem for a variety of reasons. Thus we constructed a finite difference heat transfer model of the wall section with a full compliment of realistic boundary conditions for the South Pole application. The base case of the planned wall section and various potential retrofits were evaluated with the model using actual weather data for six summer seasons. The results show that under the worse case summer season the base case wall section would see approximately 44 freeze-thaw cycles. That number would be reduced to only 12 with the addition of either 25 mm of extruded polystyrene foam insulation, or 19 mm of plywood and 13 mm of the same insulation. Over a 25 year period these same additions to the exterior of the building would reduce the number of freeze-thaw cycles by over a factor of six.

Different Planctomycetes diversity patterns in latitudinal surface seawater of the open sea and in sediment

The 16S rRNA gene approach was applied to investigate the diversity of Planctomycetes in latitudinal surface seawater of the Western Pacific Ocean. The results revealed that the Pirellula-Rhodopirellula-Blastopirellula clade dominated the Planctomycetes community at all surface seawater sites while the minority genera Gemmata and Planctomyces were only found at sites H5 and H2 respectively. Although the clone frequency of the PRB clade seemed stable (between 83.3% and 94.1%) for all surface seawater sites, the retrieved Pirellula-Rhodopirellula-Blastopirellula clade presented unexpected diversity. Interestingly, low latitude seawater appeared to have higher diversity than mid-latitudes. integral-LIBSHUFF software analysis revealed significantly different diversity patterns between in latitudinal surface seawater and in the sediment of South China Sea station M2896. Our data suggested that different hydrological and geographic features contributed to the shift of Planctomycetes diversity in marine environments. This is, to our knowledge, the first systematic assessment of Planctomycetes in latitudinal surface seawater of the open sea and the first comparison of diversity pattern between surface seawater and sediments and has broadened our understanding of Planctomycetes diversity in marine environments.

The GEOSAT electrical propulsion subsystem based on the KM-45 HET

India's low power GEOSAT communication satellite to be launched in 2008 will be using electrical propulsion system as an experimental payload augmenting the chemical propulsion system. India's low power communication typically can provide 700W of power in the beginning of life. Hence, a power and mass optimized electrical propulsion system (EPS) is designed to provide inclination and eccentricity control during North South Station keeping operations. The EPS is based on four 350W rated Hall effect thrusters (HET) designed, developed and qualified as per the required standards of GEOSAT mission. This paper presents the overview of the Electrical Propulsion System and its elements along with the results of the qualification tests and intended flight operations.

Busting down the door: The role of sisters in Muslim community radio in South Africa

abstract Community participation is a fundamental element of community radio and therefore one of its most important licence criteria. Many South African community radio stations are faith-based. However, existing research on community participation in such radio stations is based mainly on Christian stations, while the focus of this study is on a Muslim station. This article considers the participation of women at Radio Al-Ansaar in Durban, South Africa. It investigates how and to what extent community radio is used as a tool to advance the empowerment of Muslim sisters and examines the representation of women at board and operational level. It also questions if the radio station enables free participation among women across all portfolios, or if there exists a glass ceiling preventing women's participation. The paper outlines some of the successes, challenges and obstacles faced by the sisters of Al-Ansaar.