Numerical study of mean flow patterns in the South China Sea and the Luzon Strait

Previous investigations have suggested that wind stress curl, the balance of influx- and outflux-induced upwelling, as well as a positive vorticity source fed from the left flank of the Kuroshio are all possible mechanisms that contribute to a persistent cyclonic gyre in the South China Sea (SCS). Studies have also suggested that the loop current that forms from the Kuroshio intrusion in the Luzon Strait, similar to the Loop Current in the Gulf of Mexico (GOM), has rarely been observed in the northern SCS. In this research, an idealized numerical model driven by annual mean wind stress was adopted to investigate the relative importance of dynamic processes that control the mean flow pattern of Kuroshio in the Luzon Strait and regulate circulation in the SCS. An analysis of results drawn from numerical experiments suggests that the three mechanisms are of approximately equal importance in the formation of the persistent cyclonic gyre in the northern SCS. Unlike the Gulf Stream which enters the Gulf of Mexico through the Yucatan Channel, the two topographic ridges that align nearly meridionally in the Luzon Strait keep the Kuroshio flowing roughly northward without distinct intrusion into the SCS. Unsurprisingly, an anticyclonic loop current similar to the Gulf Stream pathway in the GOM was barely observed in the northern SCS.     

International Heliophysical Year 2007: A Report from the UN/NASA Workshop Bangalore, India, 27 November–1 December 2006

The IHY Secretariat and the United Nations Basic Space Science Initiative (UNBSSI) assist scientists and engineers from all over the world in participating in the International Heliophysical Year (IHY) 2007. A major thrust of IHY/UNBSSI is to deploy arrays of small, inexpensive instruments such as magnetometers, radio telescopes, GPS receivers, all-sky cameras, etc. around the world to allow global measurements of ionospheric and heliospheric phenomena. The small instrument programme is envisioned as a partnership between instrument providers and instrument hosts in developing nations. The IHY/UNBSSI can facilitate the deployment of several of these networks world-wide. Existing data bases and relevant software tools will be identified to promote space science activities in developing nations. Extensive data on space science have been accumulated by a number of space missions. Similarly, long-term data bases are available from ground-based observations. These data can be utilized in ways different from originally intended for understanding the heliophysical processes. This paper provides a comprehensive overview of IHY/UNBSSI, its achievements, future plans, and outreach to the 192 Member States of the United Nations as recorded in the UN/NASA workshop in India.     

Weather observations on Whistler Mountain during five storms

A greater understanding of precipitation formation processes over complex terrain near the west coast of British Colombia will contribute to many relevant applications, such as climate studies, local hydrology, transportation, and winter sport competition. The phase of precipitation is difficult to determine because of the warm and moist weather conditions experienced during the wintertime in coastal mountain ranges. The goal of this study is to investigate the wide range of meteorological conditions that generated precipitation on Whistler Mountain from 4–12 March 2010 during the SNOW-V10 field campaign. During this time period, five different storms were documented in detail and were associated with noticeably different meteorological conditions in the vicinity of Whistler Mountain. New measurement techniques, along with the SNOW-V10 instrumentation, were used to obtain in situ observations during precipitation events along the Whistler mountainside. The results demonstrate a high variability of weather conditions ranging from the synoptic-scale to the macro-scale. These weather events were associated with a variation of precipitation along the mountainside, such as events associated with snow, snow pellets, and rain. Only two events associated with a rain–snow transition along the mountainside were observed, even though above-freezing temperatures along the mountainside were recorded 90 % of the time. On a smaller scale, these events were also associated with a high variability of snowflake types that were observed simultaneously near the top of Whistler Mountain. Overall, these detailed observations demonstrate the importance of understanding small-scale processes to improve observational techniques, short-term weather prediction, and longer-term climate projections over mountainous regions.     

Mid-Mountain Clouds at Whistler During the Vancouver 2010 Winter Olympics and Paralympics

A comprehensive study of mid-mountain clouds and their impacts on the Vancouver 2010 Winter Olympics and Paralympics is presented. Mid-mountain clouds were frequently present on the Whistler alpine venue, as identified in an extensive archive of webcam images over a 45-day period from February 5 to March 21, 2010. These clouds posed serious forecast challenges and had significant impacts on some Olympic and Paralympic alpine skiing competitions. Under fair weather conditions, a diurnal upslope (anabatic) flow can work in concert with a diurnal temperature inversion aloft to produce a localized phenomenon known as “Harvey’s Cloud” at Whistler. Two detailed case studies in this paper suggest that mid-mountain clouds can also develop in the area as a result of a moist valley flow interacting with a downslope flow descending from the mountaintop. A southerly inflow through the Sea-to-Sky corridor can be channeled by the local topography into a westerly upslope flow toward Whistler Mountain, resulting in orographic clouds on the alpine venue. Under favorable circumstances, these clouds are trapped to the mid-mountain zone by the leeward subsidence of an elevated southerly flow. The presence of the downslope subsidence was manifested by a distinguished dry layer observed on the top of the mid-mountain clouds in both cases. It is the subsidence-induced adiabatic warming that imposes a strong buoyant suppression to trap the mid-mountain cloud. On the other hand, the subsidence-induced dry layer has the potential to trigger evaporative instability to periodically breakup the mid-mountain cloud.     

Beta Gyres in Global Analysis Fields

A three-component decomposition is applied to global analysis data to show the existence of a beta gyre, which causes Tropical Cyclone (TC) to drift from a large-scale environmental steering current. Analyses from the Global Data Assimilation and Prediction System (GDAPS) of the Korea Meteorological Adminis-tration (KMA), the Global Forecast System (GFS) of NCEP, and the Navy Operational Global Atmospheric Prediction System (NOGAPS) are used in this study. The structure of the beta gyre obtained in our anal...     

Performance evaluation of active wireline heave compensation systems in marine well logging environments

The basic functionality and performance of a new Schlumberger active wireline heave compensation system on the JOIDES Resolution was evaluated during the sea trial and a 3-year period of the IODP Phase II operations. A suite of software programs was developed to enable real-time monitoring of the dynamics of logging tools, and assess the efficiency of wireline heave compensation during downhole operations. The evaluation of the system effectiveness was performed under normal logging conditions as well as during stationary tests. Logging data were analyzed for their overall quality and repeatability, and to assess the reliability of high-resolution data such as formation microscanner (FMS) electrical images. This revealed that the system reduces 65–80 % of displacement or 88–98 % variance of downhole tool motion in stationary mode under heave conditions of ±0.2–1.5 m and water depths of 300–4,500 m in open holes. Under similar water/heave conditions, the compensator system reduces tool displacement by 50–60 %, or 75–84 % variance in downhole tool motion during normal logging operations. Such compensation efficiency (CE) is comparable to previous compensation systems, but using advanced and upgradeable technologies, and provides 50–85 % heave motion and heave variance attenuation. Moreover, logging down/up at low speeds (300–600 m/h) reduces the system’s CE values by 15–20 %, and logging down at higher speeds (1,000–1,200 m/h) eliminates CE values by 55–65 %. Considering the high quality of the logging data collected, it is concluded that the new system can provide an improved level of compensation over previous systems. Also, if practically feasible, future integration of downhole cable dynamics as an input feedback into the current system could further improve its compensation efficiency during logging operations.     

In situ U-Pb, O and Hf isotopic compositions of zircon and olivine from Eoarchaean rocks, West Greenland: New insights to making old crust

The sources and petrogenetic processes that generated some of the Earth’s oldest continental crust have been more tightly constrained via an integrated, in situ (U-Pb, O and Hf) isotopic approach. The minerals analysed were representative zircon from four Eoarchaean TTG tonalites and two felsic volcanic rocks, and olivine from one harzburgite/dunite of the Itsaq Gneiss Complex (IGC), southern West Greenland. The samples were carefully chosen from localities with least migmatisation, metasomatism and strain. Zircon was thoroughly characterized prior to analysis using cathodoluminescence, scanning electron, reflected and transmitted light imaging. The zircon from all but one sample showed only minor post-magmatic recrystallisation. ²⁰⁷Pb/²⁰⁶Pb dating of oscillatory-zoned zircon using SHRIMP RG (n = 142) indicates derivation of the felsic igneous rocks from different batches of magma at 3.88, 3.85, 3.81, 3.80 and 3.69 Ga.Analyses of ¹⁸O/¹⁶O compositions of olivine from a harzburgite/dunite (n = 8) using SHRIMP II in multi-collector mode, indicate that the oxygen isotopic composition of this sample of Eoarchaean mantle (δ¹⁸O_Ol = 6.0 ± 0.4‰) was slightly enriched in ¹⁸O, but not significantly different from that of the modern mantle. Zircon δ¹⁸O measurements from the six felsic rocks (n = 93) record mean or weighted mean compositions ranging from 4.9 ± 0.7‰ to 5.1 ± 0.4‰, with recrystallised domains showing no indication of oxygen isotopic exchange during younger tectonothermal events. δ¹⁸O_Zr compositions indicate that the primary magmas were largely in equilibrium with the mantle or mantle-derived melts generated at similar high temperatures, while calculated tonalite δ¹⁸O_WR compositions (6.7-6.9‰) resemble those of modern adakites.LA-MC-ICPMS zircon ¹⁷⁶Hf/¹⁷⁷Hf analyses were obtained from six samples (n = 122). Five samples record weighted mean initial ε_Hf compositions ranging from to 0.5 ± 0.6 to −0.1 ± 0.7 (calculated using λ¹⁷⁶Lu = 1.867 × 10⁻¹¹ yr⁻¹), while one sample records a composition of 1.3 ± 0.7, indicating the magmas were generated from a reservoir with a time averaged, near chondritic Lu/Hf. The derivation of TTG magmas from a chondritic Lu/Hf source implies either that there was not voluminous continental crustal growth nor major mantle differentiation leading to Lu/Hf fractionation during the Hadean or Eoarchaean, or alternatively that rapid recycling of an early formed crust allowed the early mantle to maintain a chondritic Lu/Hf.Previous studies have demonstrated that ancient TTG rocks were mostly produced by dehydration melting of mafic rocks within the stability field of garnet, probably in flatly-subducted or buried oceanic crust. The oxygen isotopic signatures measured here at high spatial resolution allow the source materials to be better defined. Melting of a mixed mafic source consisting of ∼80% unaltered gabbro (δ¹⁸O_WR = 5.5‰) with ∼20% hydrothermally altered gabbro/basalt (δ¹⁸O_WR = 4.0‰) would produce tonalite magmas within the average compositional range observed. ¹⁸O-enriched components such as altered shallow basaltic oceanic crust and pelagic or continental sediments were not present in the sources of these TTG melts. The absence of high ¹⁸O signatures may indicate either the rarity of low temperature altered sediments, or their effective removal from the down-going slab.     

Baseline and distribution of organic pollutants and heavy metals in tidal creek sediments after Hurricane Sandy in the Meadowlands of New Jersey

The relatively low cost of lands along with a privileged location near an urban center attracted industry to the Meadowlands of New Jersey and the absence of regulations resulted in vast amounts of industrial waste emitted into the air and dumped to nearby estuaries and marshlands. Hurricane Sandy created an unprecedented sea surge that overtopped berms and tide gates and extensively flooded approximately 22.8 km² of a low lying basin that includes Berry’s Creek, a tributary to the Hackensack River and well known for its legacy of high levels of contamination. The sea surge connected Berry’s Creek with eastern creeks that flow into the Hackensack River for several tidal cycles. The objectives of this study were to establish a baseline for organic pollutants and heavy metals post Superstorm Sandy, determine whether contaminants from highly contaminated areas moved to the eastern creeks during the surge and measure contaminant gradients around tide gates. Cadmium, mercury and chromium were the most abundant contaminants in sediments, and pollutants responsible for the highest ecological risk were Hg and polychlorinated biphenyls (PCBs). Concentrations of PCBs were higher in the western creeks and contrary to metals did not show concentration gradients from either side of tide gates. Massive export of contaminants from western to eastern creeks due to the surge was not apparent. The abundance of heavy metals in the vicinity of tide gates shows that they play a role in their distribution across the estuary.