Teleconnections between Ethiopian summer rainfall and sea surface temperature: part II. Seasonal forecasting   总被引：1，自引：0，他引：1  

G. T. Diro  D. I. F. Grimes  E. Black 《Climate Dynamics》2011,37(1-2):121-131

A seasonal forecasting system that is capable of skilfully predicting rainfall totals on a regional scale would be of great value to Ethiopia. Here, we describe how a statistical model can exploit the teleconnections described in part 1 of this pair of papers to develop such a system. We show that, in most cases, the predictors selected objectively by the statistical model can be interpreted in the light of physical teleconnections with Ethiopian rainfall, and discuss why, in some cases, unexpected regions are chosen as predictors. We show that the forecast has skill in all parts of Ethiopia, and argue that this method could provide the basis of an operational seasonal forecasting system for Ethiopia.  相似文献   

Teleconnections between Ethiopian summer rainfall and sea surface temperature: part I��observation and modelling     

G. T. Diro  D. I. F. Grimes  E. Black 《Climate Dynamics》2011,37(1-2):103-119

In this study, the oceanic regions that are associated with anomalous Ethiopian summer rains were identified and the teleconnection mechanisms that give rise to these associations have been investigated. Because of the complexities of rainfall climate in the horn of Africa, Ethiopia has been subdivided into six homogeneous rainfall zones and the influence of SST anomalies was analysed separately for each zone. The investigation made use of composite analysis and modelling experiments. Two sets of composites of atmospheric fields were generated, one based on excess/deficit rainfall anomalies and the other based on warm/cold SST anomalies in specific oceanic regions. The aim of the composite analysis was to determine the link between SST and rainfall in terms of large scale features. The modelling experiments were intended to explore the causality of these linkage. The results show that the equatorial Pacific, the midlatitude northwest Pacific and the Gulf of Guinea all exert an influence on the summer rainfall in various part of the country. The results demonstrate that different mechanisms linked to sea surface temperature control variations in rainfall in different parts of Ethiopia. This has important consequences for seasonal forecasting models which are based on statistical correlations between SST and seasonal rainfall totals. It is clear that such statistical models should take account of the local variations in teleconnections.  相似文献   

Rock lead isotopes in northeast Queensland     

L. P. Black  J. R. Richards 《Australian Journal of Earth Sciences》2013,60(3):321-330

U‐Pb and Th‐Pb studies of rocks from an extensive Palaeozoic volcano‐plutonic province in northeast Queensland support conclusions derived from a previous Rb‐Sr study. The data oppose an earlier hypothesis, that two widespread and fundamentally different magma types are present. Interpretation of the lead data, however, must be treated with some caution since uranium movement apparently begins at a very early stage of weathering; X‐ray fluorescence data are displayed in a manner which suggests a simple rejection criterion.  相似文献   

Rb‐Sr systematics of the Coolgarra Batholith,North Queensland     

C. Johnston  L. P. Black 《Australian Journal of Earth Sciences》2013,60(3):309-324

The Coolgarra Batholith in north‐east Queensland is composed of the Go Sam and Nettle granite suites which were emplaced approximately 314 Ma ago. Initial ⁸⁷Sr/⁸⁶Sr ratios of the Nettle Suite appear to be marginally above 0.710, a value characteristic of a wide range of Late Palaeozoic felsic igneous rocks in the region. This suite appears to have been derived from an extensive isotopically homogeneous crustal source distinct from rocks which crop out in the Palaeozoic Hodgkinson Basin or Precambrian Georgetown Inlier. Higher and more variable initial ⁸⁷Sr/⁸⁶Sr ratios (0.727–0.744) of the Go Sam Suite are attributed to a combination of magmatic and hydrothermal processes. Isotopic data, thus, cannot be used to constrain the nature of the Go Sam source rocks. Tungsten (with or without tin) mineralization is associated with the Nettle Suite plutons, with which it shares a common age, whereas the Go Sam Suite is characterized by prominent tin mineralization. One tin occurrence is the same age as, or only slightly younger than, the Nettle Suite tungsten (with or without tin) mineralization. Another tin deposit yields an age of 301 Ma, suggesting the presence of a significantly younger granite at depth.  相似文献   

Dating of Neoproterozoic and Cambrian orogenies in Tasmania*     

N. J. Turner  L. P. Black  M. Kamperman 《Australian Journal of Earth Sciences》2013,60(5):789-806

A coherent set of timing constraints is produced for Tasmania's Proterozoic and Cambrian geology when only mineral ages are considered and whole‐rock ages excluded. The oldest recognised event is the formation of sedimentary deposits which contain detrital zircons that indirectly indicate a depositional age younger than 1180 Ma. Partial melts of these sedimentary rocks were incorporated in Neoproterozoic, Devonian and probably Cambrian felsic magmas. Neoproterozoic granite on King Island has an age of 760 ± 12 Ma and is part of a high‐level intrusive episode that accompanied the Wickham Orogeny, an event with regionally varied strain that is represented in northwestern Tasmania by a low‐angle unconformity, by altered granitoid with a magmatic age of 777 ± 7 Ma, and by the thick turbidite pile of the Burnie and Oonah Formations with its syndepositional intrusions of Cooee Dolerite. The late Neoproterozoic was relatively quiet tectonically but by early in the Middle Cambrian a crustal collision which marked the early phase of the Tyennan Orogeny brought about high‐level emplacement of ultramafic‐bearing allochthons and deep‐seated metamorphism of quartzose sedimentary and basaltic rocks. The ultramafic allochthons carried tonalite that had crystallised only shortly before at 510 ± 6 Ma, while the deep‐seated metamorphism produced eclogite at 502 ± 8 Ma. By middle Middle Cambrian times the metamorphic rocks had been uplifted and they experienced repeated uplift during the period of Mt Read volcanism and onward to the close of the Tyennan Orogeny in the Early Ordovician, an overall period of some 20 million years from the early Middle Cambrian. Regionally varied strain was again a feature during the Tyennan Orogeny, with the Smithton area in northwestern Tasmania and King Island occupying relatively undeformed cratonic positions.  相似文献   

Secondary uranium mineralization in southern Finland and its relationship to recent glacial events     

David Read  Stuart Black  Tracy Buckby  Karl-Heinz Hellmuth  Nuria Marcos  Marja Siitari-Kauppi 《Global and Planetary Change》2008,60(3-4):235-249

Uranium series dating has been carried out on secondary uranyl silicate minerals formed during sub-glacial and post-glacial weathering of Proterozoic uraninite ores in south west Finland. The samples were obtained from two sites adjacent to the Salpauselkä III ice marginal formation and cover a range of depths, from the surface to more than 60 m. Measured ages fall into three distinct groups, 70–100 ka, 28–36 ka and < 2500 yr. The youngest set is associated with surface exposures and the crystals display clear evidence of re-working. The most likely trigger for uranium release at depths below the surface weathering zone is intrusion of oxidising glacial melt water. The latter is often characterised by very high discharge rates along channels, which close once the overpressure generated at the ice margin is released. There is excellent correspondence between the two Finnish sites and published data for similar deposits over a large area of southern and central Sweden. None of the seventy samples analysed gave a U–Th age between 40 and 70 ka; a second hiatus is apparent at 20 ka, coinciding with the Last Glacial Maximum. Thus, the process responsible for uranyl silicate formation was halted for significant periods, owing to a change in geochemical conditions or the hydrogeological regime. These data support the presence of interstadial conditions during the Early and Middle Weichselian since in the absence of major climatic perturbations the uranium phases at depth are stable. When viewed in conjunction with proxy data from mammoth remains it would appear that the region was ice-free prior to the Last Glacial Maximum.  相似文献   

Assessing Tower Flux Footprint Climatology and Scaling Between Remotely Sensed and Eddy Covariance Measurements   总被引：2，自引：1，他引：1  

Baozhang?Chen  T.?Andrew?Black  Nicholas?C.?Coops  Thomas?Hilker  J.?A.? Trofymow  Kai?Morgenstern 《Boundary-Layer Meteorology》2009,130(2):137-167

We describe pragmatic and reliable methods to examine the influence of patch-scale heterogeneities on the uncertainty in long-term eddy-covariance (EC) carbon flux data and to scale between the carbon flux estimates derived from land surface optical remote sensing and directly derived from EC flux measurements on the basis of the assessment of footprint climatology. Three different aged Douglas-fir stands with EC flux towers located on Vancouver Island and part of the Fluxnet Canada Research Network were selected. Monthly, annual and interannual footprint climatologies, unweighted or weighted by carbon fluxes, were produced by a simple model based on an analytical solution of the Eulerian advection-diffusion equation. The dimensions and orientation of the flux footprint depended on the height of the measurement, surface roughness length, wind speed and direction, and atmospheric stability. The weighted footprint climatology varied with the different carbon flux components and was asymmetrically distributed around the tower, and its size and spatial structure significantly varied monthly, seasonally and inter-annually. Gross primary productivity (GPP) maps at 10-m resolution were produced using a tower-mounted multi-angular spectroradiometer, combined with the canopy structural information derived from airborne laser scanning (Lidar) data. The horizontal arrays of footprint climatology were superimposed on the 10-m-resolution GPP maps. Monthly and annual uncertainties in EC flux caused by variations in footprint climatology of the 59-year-old Douglas-fir stand were estimated to be approximately 15–20% based on a comparison of GPP estimates derived from EC and remote sensing measurements, and on sensor location bias analysis. The footprint-variation-induced uncertainty in long-term EC flux measurements was mainly dependent on the site spatial heterogeneity. The bias in carbon flux estimates using spatially-explicit ecological models or tower-based remote sensing at finer scales can be estimated by comparing the footprint-weighted and EC-derived flux estimates. This bias is useful for model parameter optimizing. The optimization of parameters in remote-sensing algorithms or ecosystem models using satellite data will, in turn, increase the accuracy in the upscaled regional carbon flux estimation.  相似文献   

A conceptual framework for multi-regional climate change assessments for international market systems with long-term investments     

Julie A. Winkler  Suzanne Thornsbury  Marco Artavia  Frank-M. Chmielewski  Dieter Kirschke  Sangjun Lee  Malgorzata Liszewska  Scott Loveridge  Pang-Ning Tan  Sharon Zhong  Jeffrey A. Andresen  J. Roy Black  Robert Kurlus  Denys Nizalov  Nicole Olynk  Zbigniew Ustrnul  Costanza Zavalloni  Jeanne M. Bisanz  Géza Bujdosó  Lesley Fusina  Yvonne Henniges  Peter Hilsendegen  Katarzyna Lar  Lukasz Malarzewski  Thordis Moeller  Roman Murmylo  Tadeusz Niedzwiedz  Olena Nizalova  Haryono Prawiranata  Nikki Rothwell  Jenni van Ravensway  Harald von Witzke  Mollie Woods 《Climatic change》2010,103(3-4):445-470

A conceptual framework for climate change assessments of international market systems that involve long-term investments is proposed. The framework is a hybrid of dynamic and static modeling. Dynamic modeling is used for those system components for which temporally continuous modeling is possible, while fixed time slices are used for other system components where it can be assumed that underlying assumptions are held constant within the time slices but allowed to vary between slices. An important component of the framework is the assessment of the “metauncertainty” arising from the structural uncertainties of a linked sequence of climate, production, trade and decision-making models. The impetus for proposing the framework is the paucity of industry-wide assessments for market systems with multiple production regions and long-term capital investments that are vulnerable to climate variations and change, especially climate extremes. The proposed framework is pragmatic, eschewing the ideal for the tractable. Even so, numerous implementation challenges are expected, which are illustrated using an example industry. The conceptual framework is offered as a starting point for further discussions of strategies and approaches for climate change impact, vulnerability and adaptation assessments for international market systems.  相似文献   

Effects of Roll Vortices on Turbulent Fluxes in the Hurricane Boundary Layer   总被引：1，自引：0，他引：1  

Jun A. Zhang  Kristina B. Katsaros  Peter G. Black  Susanne Lehner  Jeffrey R. French  William M. Drennan 《Boundary-Layer Meteorology》2008,128(2):173-189

Boundary-layer secondary circulations or ‘roll vortices’ can have a significant influence on the turbulent exchange of momentum, sensible heat and moisture throughout the hurricane boundary layer. In this study, analyses of data from a WP-3D aircraft of the National Oceanic and Atmospheric Administration (NOAA) are presented. As part of the Coupled Boundary Layer Air-Sea Transfer (CBLAST)-hurricane experiment sponsored through the Office of Naval Research and NOAA’s annual hurricane research program, flights were conducted to investigate energy exchange across the air–sea interface. We present the first in-situ aircraft-based observations of rolls in the hurricane boundary layer and investigate their influence on energy and momentum exchange. The rolls detected in Hurricane Isidore (year 2002) have a characteristic wavelength of about 900 m, in good agreement with analyses of data from a synthetic aperture radar image captured by the Canadian Space Agency’s RADARSAT satellite in the same storm. Our analyses of the airborne data suggest that roll vortices may be a significant factor modulating the air–sea momentum exchange.  相似文献   

Sediment facies and pathways of sand transport about a large deep water headland,Cape Rodney,New Zealand     

Terry M. Hume  John W. Oldman  Kerry P. Black 《新西兰海洋与淡水研究杂志》2013,47(4):695-717

Cape Rodney is a large headland that protrudes 3–4 km into deep water in the Hauraki Gulf and separates the Mangawhai‐Pakiri and Omaha littoral cells. Detailed swath mapping of seabed sediments around Cape Rodney was carried out using by side‐scan sonar and ground‐truthed by SCUBA, grab sampling, and video. Despite the barrier imposed by the headland two pathways of sand transport around the headland, separated by the topographic high of Leigh Reef, have been identified. One lies close to the headland, where sand from the beach and nearshore of the Mangawhai‐Pakiri embayment is driven by waves and currents along a 500‐m‐wide pathway in c. 20–25 m depth around the headland to the vicinity of Leigh Harbour. The other lies in 50 m water‐depth seawards of Leigh Reef. Here fine sand, sourced from the nearshore of the Mangawhai‐Pakiri embayment and driven offshore from the tip of the headland, is transported back and forth by tidal currents in 50 m water depth on the floor of the Jellicoe Channel. The sand bodies along both these pathways are thin and so sand leakage from the Mangawhai‐Pakiri embayment is thought to be small. Transport at these depths is dependent on both tide and wave generated currents and episodic occurring during storm events. The sediment facies associated with little sand transport about a headland in deep water is one of thin and discontinuous and patchy sand cover between rocky areas and over coarser megarippled substrate. Ocean swell, tidally driven phase eddies that spin up on both sides of the headland, and bathymetry all play a role in shaping those facies.  相似文献