Application of the gravimetric method for a world geodetic system

It is desirable to unify the various unconnected geodetic systems of the world into a common earth-centered world datum. This can be achieved by gravimetric means. The gravimetric deflection components have been determined at a certain number of stations in different areas. Utilizing the differences between the gravimetric and astro-geodetic deflection components, the reduction of the major geodetic datums into a common world geodetic system has been accomplished. Geophysical Studies Section Aeronautical Chart and Information Center Presented at the Twelfth General Assembly of the International Union of Geodesy and Geophysics Helsinki, Finland     

Extreme fractionation of 234U238U and 230Th234U in spring waters,sediments, and fossils at the Pomme de Terre Valley,southwestern Missouri

Isotopic fractionation as great as 1600% exists between ²³⁴U and ²³⁸U in spring waters, sediments, and fossils in the Pomme de Terre Valley, southwestern Missouri. The activity ratios of ${}^{234}\text{U}{}^{238}\text{U}$ in five springs range from 7.2 to 16 in water which has been discharged for at least the past 30,000 years. The anomalies in ${}^{234}\text{U}{}^{238}\text{U}$ ratio in deep water have potential usefulness in hydrologic investigations in southern Missouri. Clayey units overlying the spring bog sediments of Trolinger Spring are enriched in ²³⁰Th relative to their parent ²³⁴U by as much as 720%. The results indicate that both preferential displacement via alpha recoil ejection and the preferential emplacement via recoiling and physical entrapment are significant processes that are occurring in the geologic environment.     

Clark lake microbursts: On a lower limit to type III burst brightness temperatures

Further observations of solar microbursts by the Clark Lake radioheliograph are reported. The microbursts have properties consistent with weak type III bursts, with the implication that type III's can have brightness temperatures as low as 10⁶ K. We explore the importance of this result. A single model to explain the stronger type III bursts and the weaker microbursts is sought. We show that none of the models for stabilizing the strongest type III electron streams can explain the observed microbursts: these models have threshold levels of Langmuir waves which imply emission (due to spontaneous scattering off ions) with brightness temperatures in excess of those observed. It appears that either some vital physics is still missing from models for type III bursts, or that microbursts should have properties significantly different from those of type III bursts. In the latter case further observations should allow important tests of type III models.     

Estimating limiting age for pleistocene erosional surfaces in central Montana by uranium-series dating of associated travertines

Travertine deposits overlie the highest Number 2 surfaces in central Montana and clasts of travertine occur in gravels on lower Number 2 surfaces. Dating these travertine deposits may provide limits on the ages of surfaces that record intervals of extensive erosion during Pleistocene time. Analysis of three travertine samples from the southeast side of The Park yield an average uranium-thorium age of 73 000 ±+M 7 000 years. Another sample from the west side of The Park is 320 000 (+ 160 000, ? 70 000) years old. These results indicate that travertine deposits may have formed at several intervals. The surface beneath The Park travertine is older than about 320 000 years. Number 2 pediment gravels that contain travertine downslope from the oldest dated sample may be younger than about 320 000 years.     

Dusky dolphin movement patterns: short-term effects of tourism

Cetacean-oriented tourism has experienced rapid growth in the last two decades, accompanied by increasing concerns about the effects of tourism on target species. Here, we used shore-based observations of dusky dolphin (Lagenorhynchus obscurus) groups near Kaikoura, New Zealand, and generalised additive models to quantify changes in group speed, reorientation and linearity relative to natural and anthropogenic factors. Summer months were characterised by slower speeds and more changes in direction than winter months. Group speeds were higher at the beginning and end of the day, with slower speeds at midday. Speeds were slower when vessels were present, and dolphin groups changed direction more often when aircraft circled overhead. Effects were positively correlated with number of vessels present within 300 m. Short-term changes have potential to lead to long-term impacts, and further acoustic and energetic studies are proposed to elucidate whether these effects are likely to reduce individual fitness.     

Observing the reconnection region in a transequatorial loop system

A vertical current sheet is a crucial element in many flare/coronal mass ejection (CME) models. For the first time, Liu et al. reported a vertical current sheet directly imaged during the flare rising phase with the EUV Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). As a follow-up study, here we present the comprehensive analysis and detailed physical interpretation of the observation. The current sheet formed due to the gradual rise of a transequatorial loop system. As the l...     

Deep Solar Activity Minimum 2007 – 2009: Solar Wind Properties and Major Effects on the Terrestrial Magnetosphere

We discuss the temporal variations and frequency distributions of solar wind and interplanetary magnetic field parameters during the solar minimum of 2007?–?2009 from measurements returned by the IMPACT and PLASTIC instruments on STEREO-A. We find that the density and total field strength were significantly weaker than in the previous minimum. The Alfvén Mach number was higher than typical. This reflects the weakness of magnetohydrodynamic (MHD) forces, and has a direct effect on the solar wind–magnetosphere interactions. We then discuss two major aspects that this weak solar activity had on the magnetosphere, using data from Wind and ground-based observations: i) the dayside contribution to the cross-polar cap potential (CPCP), and ii) the shapes of the magnetopause and bow shock. For i) we find a low interplanetary electric field of 1.3±0.9 mV?m^?1 and a CPCP of 37.3±20.2 kV. The auroral activity is closely correlated to the prevalent stream–stream interactions. We suggest that the Alfvén wave trains in the fast streams and Kelvin–Helmholtz instability were the predominant agents mediating the transfer of solar wind momentum and energy to the magnetosphere during this three-year period. For ii) we determine 328 magnetopause and 271 bow shock crossings made by Geotail, Cluster 1, and the THEMIS B and C spacecraft during a three-month interval when the daily averages of the magnetic and kinetic energy densities attained their lowest value during the three years under survey. We use the same numerical approach as in Fairfield’s (J. Geophys. Res. 76, 7600, 1971) empirical model and compare our findings with three magnetopause models. The stand-off distance of the subsolar magnetopause and bow shock were 11.8 R _E and 14.35 R _E, respectively. When comparing with Fairfield’s (1971) classic result, we find that the subsolar magnetosheath is thinner by ～1 R _E. This is mainly due to the low dynamic pressure which results in a sunward shift of the magnetopause. The magnetopause is more flared than in Fairfield’s model. By contrast the bow shock is less flared, and the latter is the result of weaker MHD forces.

     

Propagation of electrons emitting weak type III bursts in coronal streamers

We report the observations of weak type III bursts at 73.8, 57.5, 50.0, and 38.5 MHz from Clark Lake Radio Observatory on four days and discuss their characteristics. In addition to Clark Lake data, the magnetogram and sunspot/active region data and the coronal streamer data obtained by HAO's Coronagraph/Polarimeter aboard SMM satellite are used to study the location of the burst sources with respect to the coronal streamers emanating from active regions. It is shown that the bursts occur within or close to the edge of dense coronal streamers implying that the coronal streamers contain open magnetic field lines along which the electrons generating the bursts propagate. The positional analysis of the bursts is used to estimate the variation of coronal electron density with radial distance.On leave from the Indian Institute of Astrophysics, Kodaikanal, India.     

Use of 234U and 238U isotopes to evaluate contamination of near-surface groundwater with uranium-mill effluent: a case study in south-central Colorado, U.S.A.

The ²³⁴U/²³⁸U alpha activity ratio (AR) was determined in 47 samples of variably uraniferous groundwater from the vicinity of a uranium mill near Cañon City, Colorado. The results illustrate that uranium isotopes can be used to determine the distribution of uranium contamination in groundwater and to indicate processes such as mixing and chemical precipitation that affect uranium concentrations. Highly to moderately contaminated groundwater samples collected from the mill site and land immediately downgradient from the mill site contain more than 100?μg/l of dissolved uranium and typically have AR values in the narrow range of 1.0–1.06. Other samples from the shallow alluvial aquifer farther downgradient from the mill contain 10–100?μg/l uranium and plot along a broad trend of increasing AR (1.06–1.46) with decreasing uranium concentration. The results are consistent with mixing of liquid mill waste (AR≈1.0) with alluvial groundwater of small, but variable, uranium concentrations and AR of 1.3–1.5. In the alluvial aquifer, the spatial distribution of wells with AR values less than 1.3 is consistent with previous estimates of the probable distribution of contamination, based on water chemistry and hydrology. Wells more distant from the area of probable contamination have AR values that are consistently greater than 1.3 and are indicative of little or no contamination. The methodology of this study can be extended usefully to similar sites of uranium mining, milling, or processing provided that local geohydrologic settings promote uranium mobility and that introduced uranium contamination is isotopically distinct from that of local groundwater.     

A Quartz-bearing Orthopyroxene-rich Websterite Xenolith from the Pannonian Basin, Western Hungary: Evidence for Release of Quartz-saturated Melts from a Subducted Slab

An unusual quartz-bearing orthopyroxene-rich websterite xenolithhas been found in an alkali basaltic tuff at Szigliget, Bakony–BalatonHighland Volcanic Field (BBHVF), western Hungary. Ortho- andclinopyroxenes are enriched in light rare earth elements (LREE),middle REE and Ni, and depleted in Nb, Ta, Sr and Ti comparedwith ortho- and clinopyroxenes occurring in either peridotiteor lower crustal granulite xenoliths from the BBHVF. Both ortho-and clinopyroxenes in the xenolith contain primary and secondarysilicate melt inclusions, and needle-shaped or rounded quartzinclusions. The melt inclusions are rich in SiO₂ and alkalisand poor in MgO, FeO and CaO. They are strongly enriched inLREE and large ion lithophile elements, and display negativeNb, Ta and Sr anomalies, and slightly positive Pb anomalies.The xenolith is interpreted to represent a fragment of an orthopyroxene-richbody that crystallized in the upper mantle from a hybrid meltthat formed by interaction of mantle peridotite with a quartz-saturatedsilicate melt that was released from a subducted oceanic slab.Although the exact composition of the slab melt cannot be determined,model calculations on major and trace elements suggest involvementof a metasedimentary component. KEY WORDS: quartz; mantle; silicate melt inclusion; SiO₂-rich melt; subduction; Carpathian-Pannonian Region