Resolution dependence of tropical cyclone formation in CMIP3 and finer resolution models

Detection of tropical lows is performed in a suite of climate model simulations using objectively-determined detection thresholds that are resolution-dependent. It is found that there is some relationship between model resolution and tropical cyclone formation rate even after the resolution-dependent tropical cyclone detection threshold is applied. The relationship is investigated between model-simulated tropical cyclone formation and a climate-based tropical cyclone Genesis Potential Index (GPI). It is found that coarser-resolution models simulate the GPI better than they simulate formation of tropical cyclones directly. As a result, there appears to be little relationship from model to model between model GPI and the directly-simulated cyclone formation rate. Statistical analysis of the results shows that the main advantage of increasing model resolution is to give a considerably better pattern of cyclone formation. Finer resolution models also simulate a slightly better pattern of GPI, and for these models there is some relationship between the pattern of GPI simulated by each model and that model’s pattern of simulated tropical cyclone formation.     

Effect of wave-induced mixing on Antarctic sea ice in a high-resolution ocean model

Ocean Dynamics - In this study, we investigate how sea ice extent and thickness are affected by additional turbulent mixing from unbroken surface waves. This ‘surface wave mixing’ (SWM)...     

Temporal and Spatial Dynamics of Estuarine Shoreline Change in the Albemarle-Pamlico Estuarine System,North Carolina,USA

Many shoreline studies rely on historical change rates determined from aerial imagery decades to over 50 years apart to predict shoreline position and determine setback distances for coastal structures. These studies may not illustrate the coastal impacts of short-duration but potentially high-impact storm events. In this study, shoreline change rates (SCRs) are quantified at five different sites ranging from marsh to sediment bank shorelines around the Albemarle-Pamlico estuarine system (APES) for a series of historical (decadal to 50-year) and short-term (bimonthly) time periods as well as for individual storm events. Long-term (historical) SCRs of approximately ?0.5 ± 0.07 m year^?1 are observed, consistent with previous work along estuarine shorelines in North Carolina. Short-term SCRs are highly variable, both spatially and temporally, and ranged from 15.8 ± 7.5 to ?19.3 ± 11.5 m year^?1 at one of the study sites. The influence of wave climate on the spatial and temporal variability of short-term erosion rates is investigated using meteorological observations and coupled hydrodynamic (Delft3D) and wave (SWAN) models. The models are applied to simulate hourly variability in the surface waves and water levels. The results indicate that in the fetch-limited APES, wind direction strongly influences the wave climate at the study sites. The wave height also has an influence on short-term SCRs as determined from the wave simulations for individual meteorological events, but no statistical correlation is found for wave height and SCRs over the long term. Despite the significantly higher rates of shoreline erosion over short time periods and from individual events like hurricanes, the cumulative impact over long time periods is low. Therefore, while the short-term response of these shorelines to episodic forcing should be taken into account in management plans, the long-term trends commonly used in ocean shoreline management can also be used to determine erosion setbacks on estuarine shorelines.     

Rare earth element patterns of rocks from the centre 3 igneous complex,Ardnamurchan, Argyllshire

Systematic, differences in absolute abundancies and distribution patterns of rare earth elements are shown to exist for the main rock types of the third and final phase of the Tertiary igneous complex of Ardnamurchan. Published partition coefficients of the rare earth elements between crystals and host magmas of extrusive rocks have been used, together with modes of the Ardnamurchan rocks, to estimate the rare earth element patterns of the parent magmas. The results confirm that the basic rocks formed by crystal fractionation but that continued crystal fractionation from a single parent magma could not have formed the intermediate rocks.     

Mid-infrared source multiplicity within hot molecular cores traced by methanol masers

We present high resolution, mid-infrared (MIR) images towards three hot molecular cores signposted by methanol maser emission: G173.49+2.42 (S231, S233IR), G188.95+0.89 (S252, AFGL-5180) and G192.60−0.05 (S255IR). Each of the cores was targeted with Michelle on Gemini North using five filters from 7.9 to 18.5 μm. We find each contains both large regions of extended emission and multiple, luminous point sources which, from their extremely red colours ( F _18.5/ F _7.9≥ 3), appear to be embedded young stellar objects. The closest angular separations of the point sources in the three regions are 0.79, 1.00 and 3.33 arcsec corresponding to linear separations of 1700, 1800 and 6000 au, respectively. The methanol maser emission is found closest to the brightest MIR point source (within the assumed 1-arcsec pointing accuracy). Mass and luminosity estimates for the sources range from 3 to  22 M_⊙  and from 50 to 40 000  L_⊙  , respectively. Assuming the MIR sources are embedded objects and the observed gas mass provides the bulk of the reservoir from which the stars formed, it is difficult to generate the observed distributions for the most massive cluster members from the gas in the cores using a standard form of the initial mass function.     

Thermal metamorphism of primitive meteorites—XL The enstatite meteorites: origin and evolution of a parent body

We report neutron activation data for Ag, As, Bi, Cd, Co, Cs, Cu, Ga, In, Rb, Se, Te, Tl and Zn in samples of Abee heated at temperatures of 1000–1400°C in a low-pressure environment (initially ~ 10^?5 atm H₂) and in 9 enstatite achondrites (aubrites) and the silicate portion of the unique stony-iron, Mt Egerton. Trace element losses in heated Abee progress with temperature, the lowest retention being 2.4 × 10^?6 of initial contents. These data indicate trace element loss above 1000°C via diffusion-controlled processes having apparent activation energies of 8–55 kcal/mol ; only Co exhibits a significantly higher energy. These trace element data and those for aubrites, Mt Egerton and E4–6 chondrites, and mineralogic and isotopic evidence link all enstatite meteorites to a common parent body. Volatile, mobile elements vary inversely with cobalt content in aubrites and Mt Egerton but directly in E4–6 chondrites; this is inconsistent with all genetic models positing fractionation of such elements during nebular condensation and accretion. However, the data are consistent with the idea that aubrites and Mt. Egerton reflect fractional crystallization of a magma produced from enstatite chondrite-like parent material (probably E6) and late introduction of chalcophiles and mobile elements transported by FeS-Fe eutectic from an E4–6 region experiencing open-system metamorphism. As suggested earlier, the only primary process that affected enstatite meteorites involved fractionation of non-volatile lithophiles from sulfides and metal during condensation and accretion of chondritic parent material from the nebula. If, as seems likely, volatile/mobile elements reflect secondary processes, they can only be used to establish alteration conditions within the enstatite parent body and not to estimate temperatures during primary nebular condensation and accretion.     

The Cwm Llwyd Outlier,Carmarthenshire, South‐West Wales – Britain's deepest karstic subsidence or Variscan pull‐apart structure?

The Cwm Llwyd Outlier of Namurian Middle Shales in the central part of the Black Mountain escarpment of South Wales is an unusual structure. It occupies a topographic depression located more than 2 km from the main outcrop of the Middle Shales and has a stratigraphic discordance with its wall‐rocks of more than 300 m. Previous interpretations advocating a karstic origin imply that this is the deepest known subsidence in Great Britain. However, although the outlier lies among some of the finest epikarst landforms in the country, several factors indicate that the subsidence was not caused by a karstic mechanism. These include the amount of stratigraphic displacement in contrast to the depth of available vertical space in the putative host Carboniferous Limestone, the relatively simple form of the outlier, and the absence of brecciation, marginal solution residues and associated palaeoendokarst features in the adjacent wall‐rocks. The outlier is re‐interpreted here as the product of faulting which occurred during a Variscan strike‐slip or transpressive tectonic regime, producing local sinistral transtension that may have been re‐activated in the Palaeogene period. Remapping the outlier at a scale of 1:2 500 indicates that the present structure is related principally to a left‐stepping offset between the Cwm Llwyd and Llwyn Celyn faults. Analogies are drawn with the Cainozoic pull‐apart structures in Southwest England. Near‐surface reddening and kaolinization of the beds probably represent pre‐Pleistocene weathering. Copyright © 2006 John Wiley & Sons, Ltd.